Absorbent materials

Abstract

The invention provides absorbent articles which are formed from or which incorporate a cellulose / alginate-containing material, wherein said material comprises cellulose fibres and alginate from a brown seaweed, and wherein said material is obtained by a process comprising at least the following steps: (i) providing a brown seaweed, or part thereof; (ii) dividing the brown seaweed, or part thereof, into a plurality of portions; (iii) washing the plurality of portions with water whereby to remove water-soluble components and recovering the residual wet residue; (iv) converting at least a portion of calcium alginate present in said residual wet residue into a water-soluble alginate whereby to provide a residue containing cellulose fibres and water-soluble alginate; and (v) de-watering said residue containing cellulose fibres and water-soluble alginate whereby to provide said absorbent cellulose / alginate-containing material as a dry residue.

Description

[0001] Absorbent Materials

[0002] Field of the invention

[0003] The present invention relates to absorbent materials and to absorbent products which incorporate or are formed from such materials. It further relates to methods for the production of such materials and to their use as absorbents in applications that require the absorption and retention of aqueous fluids.

[0004] More specifically, the invention relates to absorbent materials produced from brown seaweed and to products, such as consumer articles, made from such materials. The absorbent materials comprise cellulose fibres and alginate in water-soluble form and are capable of the uptake and retention of water and other aqueous fluids, in particular saline solution.

[0005] Advantageously, the absorbent materials are obtained from a renewable resource and can thus be produced sustainably. They are also biodegradable. Such materials may therefore provide an alternative to traditional superabsorbent polymers such as sodium polyacrylate which is made from non-renewable resources and is not classified as biodegradable.

[0006] Background of the invention

[0007] Absorbent materials are capable of imbibing and holding onto aqueous fluids and may absorb many times their own weight in water or other aqueous fluids, for example saline solution. Such materials are used in a wide range of applications, for example to absorb and retain bodily fluids and exudates in absorbent textile materials, for liquid or moisture absorption in food packaging, and as water retention agents in agriculture and horticulture.

[0008] Cellulose-based materials have long been used for the absorption of water and other aqueous fluids. These include fluff pulps which are generally based on Kraft pulping and optimised for high bulk and absorbency. Kraft fibres, produced by chemical pulping of wood chips, are capable of absorbing between 5 and 10 times their mass of water. The pores left behind by the breakdown and dissolution of the lignin during pulping and bleaching gives rise to extensive porosity which allows the materials to take up liquids via capillary action. However, Kraft fibres suffer from a key deficiency in that the wet Kraft fibres have low retention capacity, especially when pressure is applied. In recent decades, this has led to the increased use of superabsorbent polymer (SAP) materials (also known as “hydrogels”), such as sodium polyacrylate. Such materials have reported absorbency levels in the hundreds of grams of water per gram of SAP and are able to provide significant resistance to the release of fluid on compression. Hydrogels that can accommodate more water than 10 g / g are commonly referred to as “superabsorbents”. The ability of SAP materials to swell and restrain liquids to a remarkable extent has led to their widespread use in disposable diapers and in related products, such as other sanitary hygiene products.

[0009] Hybrid products combining cellulosic fibres with SAPs are well known. Within such products, the cellulosic fibres (i.e. the fluff pulp) are used primarily to provide structure (i.e. integrity) and wicking. Although these fibres can accommodate some liquid, most of the absorption capacity of such products is attributed to the inclusion of SAPs such as sodium polyacrylate.

[0010] The absorbency characteristics of both cellulose-based materials and SAPs can be affected by the nature of the aqueous fluid to be absorbed. There is often a strong contrast between the amount of pure water taken up by such absorbents vs. the corresponding amount of saline solution. Industry standards require that SAPs are tested for their free swelling capacity when exposed to 0.9% NaCI. This is representative of their functionality in the presence of bodily fluids that they may be expected to absorb when in use, such as in diapers and other incontinence products. Although SAPs can absorb many thousand times their own weight in pure water, the presence of electrolytes such as sodium chloride severely restricts their absorption capacity.

[0011] The most widely used SAP products, such as sodium polyacrylate, are not readily biodegradable. This prevents any waste disposable articles that contain SAPs from degrading and can lead to the accumulation of products, such as disposable diapers, in landfill. SAP materials are also derived from non-renewable resources including petroleum-derived acrylamide and acrylic acid monomers. By contrast, the renewable and biodegradable nature of cellulose is well known.

[0012] There thus remains a need for alternative absorbent materials. In particular there is a need for such materials that are not only biodegradable and which can be produced sustainably from renewable resources, but which can absorb and retain bodily fluids containing electrolytes such as NaCI.

[0013] Summary of the invention

[0014] The inventors now propose that brown seaweed can be processed to produce a range of materials that contain both cellulose and water-soluble alginate (referred to herein as “cellulose I alginate-containing materials”) and which are capable of the absorption and retention of water and other aqueous fluids. Advantageously, such materials are produced without the production of any waste seaweed residue and they are biodegradable. The extent of re-hydration and retention capacity of such materials is unexpected, particularly in the presence of electrolytes such as sodium chloride. This makes the materials suitable for use in a wide range of potential applications that require the uptake and retention of fluids, such as in the production of personal hygiene products.

[0015] Brown seaweed is a source of commercially useful products for use in a variety of applications, for example in the food, cosmetics and pharmaceutical industries, as well as in agriculture and in animal feed. To obtain such products, it is generally necessary to process the seaweed and, in many cases, to extract the products. This is the case for alginate which is a polysaccharide that can be extracted from brown seaweed. The polysaccharides in brown seaweed differ considerably from those found in terrestrial plants. Alginate is the main structural component of the cell wall of the kelp Laminaria hyperborea and is present at high concentrations in the main stem (the “stipe”). Cellulose is present in lower amounts. Whereas cellulose found in terrestrial plants, for example in wood, contains significant amounts of lignin and hemi-cellulose that must be chemically removed before it can be used in several of its applications, the cellulose obtained from seaweed does not contain either lignin or hemi-cellulose. “Alginate” is a term generally used in the industry to refer to alginic acid and any derivative of alginic acid, such as the salts of alginic acid. Alginates are made up of linear chains formed from two monomers, namely p-D-mannuronic acid (M) and a-L-guluronic acid (G) residues. The M and G monomers are covalently linked to form a linear copolymer. There are three types of segments in the linear structure: M blocks which consist of continuous M units, G blocks which consist of continuous G units, and MG blocks which contain heterogeneous or alternating M and G units. Alginate is present in the cell walls of brown seaweeds in the form of insoluble salts of alginic acid with multi-valent cations, such as calcium or aluminium. Mainly it is present as the calcium salt of alginic acid. Potassium and sodium salts may also be present. Sodium alginates are water-soluble polymers which give highly viscous solutions. In the presence of multi-valent cations, such as calcium, sodium alginate has the ability to form a gel. Divalent cations such as calcium ions bind G-blocks of aligned alginate chains giving rise to cross-linking between separate alginate chains or within the same alginate chain. This process gives rise to a gel-network.

[0016] Alginates are conventionally extracted from brown seaweed as the soluble sodium salt. Conversion of insoluble calcium alginate into soluble sodium alginate renders the alginate “extractable”. The method of extraction impacts the chemical and mechanical properties of the alginate and determines its use. The properties of the alginate, for example its viscosity when dissolved in water or the strength of the gel obtained on the addition of calcium salts, are determined by its molecular weight, the arrangement of the M and G residues in the polymer chains, and the overall M / G ratio of the alginate chain. In the presence of Ca2+ions, for example, the G- blocks form ionic complexes to generate a cross-linked structure known as the “egg-box model” which is responsible for strong gel formation. The proportion of the M, G and MG blocks determines the physical properties of alginates. Alginates with high G have higher gelling properties, whereas those with high M are preferred for use as viscosity modifiers as they do not form strong gels in the presence of multi-valent cations. Alginates with low G / M ratios provide elastic gels, whereas those with high G / M ratios generate brittle gels. The G / M ratio can be altered by chemical or enzymatic modification of the alginate.

[0017] The native alginate present in brown seaweed has a high molecular weight and contains multi-valent cations, both of which render it insoluble. Extraction of alginate generally requires a multi-stage process which involves treatment in acid solution, typically hydrochloric or sulphuric acid, to convert the native alginate to alginic acid followed by treatment with sodium carbonate to convert the insoluble alginic acid to soluble sodium alginate. Treatment with sodium hydroxide at high pH (typically pH 11 or higher) and heat may also be required to facilitate hydrolysis of the alginate chains to reduce their molecular weight to the point where they become soluble. The result of the process is a viscous fluid which requires ‘thinning’ (e.g. by dilution in water) to allow separation of the soluble alginate from the remaining seaweed residue. The dissolved alginate is then recovered from the aqueous solution, for example by adding acid to precipitate alginic acid, by adding a calcium salt to precipitate calcium alginate (from any alginate fragments that contain G-blocks), or by adding an anti-solvent such as ethanol.

[0018] In the commercial production of alginate, sodium carbonate is added to the seaweed material to reach a pH of at least 10, typically higher (e.g. a pH in the range of 10-12). The basic pH leads to the formation of water-soluble sodium alginate which is then separated from the alkaline-insoluble residue and further processed to recover the alginate. Once the alginate has been extracted, an insoluble seaweed residue remains. This is generated in large quantities when alginate is extracted on an industrial scale and contains insoluble cellulose and other polysaccharides, in addition to some remaining (i.e. non-extracted) alginate. Once any remaining alginate has been removed by hydrolysis (e.g. by treatment of the seaweed residue with 5% sodium hydroxide at 80°C), this residue may be further processed to isolate the cellulose. However, this process is energy intensive and may not always be commercially viable. The seaweed residue remaining after any industrial alginate extraction process is thus generally considered to be of low commercial value and is treated as a waste material which is disposed of without attempting recovery of the cellulose.

[0019] The absorbent materials herein described are obtained from brown seaweed and contain cellulose fibres and alginate. The presence of cellulose imparts structural integrity to the materials. Importantly, the alginate is “functionalised” by conversion of the native insoluble form into a water-soluble form, such as sodium alginate, but is not intentionally extracted from the seaweed matrix. At least a proportion of the alginate is retained in the material but in water-soluble form. Although not wishing to be bound by theory, the presence of water-soluble alginate is thought to allow the cellulose fibres, once dried, to take up and bind an aqueous liquid via osmosis without the need for any further functionalisation of the cellulose, such as micro- or nano-fibrillation, which is generally required to enable pure cellulose fibres obtained from seaweed (i.e. from which all native alginate has been removed) to re-swell by capillary uptake of a liquid, once the cellulose has been dried. Appropriate selection of the type of brown seaweed and the part (or parts) of the seaweed used in the alginate conversion process influences the composition (e.g. G-content, M- content and M / G ratio) of the soluble alginate remaining in the seaweed residue and thus the absorption and retention properties of the final material. For example, alginate present in the stipe of Laminaria hyperborea is higher in G-content, whereas that obtained from the leaf (the “blade”) is lower in G-content (typically the leaf contains 50:50 M:G). A range of cellulose I alginate-containing materials are thus provided in which their ability to absorb and retain fluids can be tailored according to need.

[0020] The ability of the cellulose I alginate-containing materials to re-swell on contact with an aqueous liquid and to retain the liquid makes them suitable for use in a wide range of applications in which the uptake of free liquid is desirable. Such applications are described herein and include, but are not limited to, wound dressings (to absorb wound exudate), baby diapers (nappies), feminine hygiene products (sanitary pads, tampons, etc.), incontinence pads, and packaging materials for foods such as fresh or frozen meat or fish, and fruit.

[0021] As evidenced herein, unlike sodium polyacrylate, the materials do not show a loss in performance in the presence of a 0.9% NaCI solution. This makes them particularly suitable for use as absorbent materials for bodily fluids. Results obtained by the inventors and reported herein also show that the materials perform better than expected when dispersed in a fibrous carrier matrix such as Kraft cellulose pulp (“fluff pulp”) to provide composite materials, i.e. the properties of the composite materials are greater than the expected additive effect of the individual components. The free swelling capacity and retention capacity of such composite materials also significantly outperforms that of a similar composite material which includes sodium polyacrylate. Results documented herein also show that a further improvement in fluid uptake and retention of the composite materials can be achieved by impregnation of the fibrous carrier matrix with a water-soluble calcium salt such as calcium lactate.

[0022] Detailed description of the invention

[0023] The invention generally relates to absorbent cellulose I alginate-containing materials obtained from brown seaweed. As used herein, the term “absorbent” means capable of imbibing and holding onto an aqueous fluid. In some aspects, the invention relates to superabsorbent cellulose I alginate-containing materials obtained from brown seaweed. The term “superabsorbent”, as used herein, refers to an absorbent material that can absorb more water than 10 g / g.

[0024] The materials are produced by a process in which at least a proportion of the native insoluble alginate in brown seaweed (either in the whole seaweed or part of the seaweed) is converted into a water-soluble form and is retained in the seaweed matrix. This contrasts with a conventional alginate production process in which the alginate, following conversion to a water-soluble form, is then extracted and recovered. The cellulose I alginate-containing materials herein described comprise cellulose fibres and water-soluble alginate and are obtained, obtainable, or directly obtained by any of the processes as herein described. For use as absorbents, such materials are generally provided in dry particulate form.

[0025] Based on their absorbent properties, the materials herein described find use in the production of absorbent products. Such products are generally referred to herein as “absorbent articles”. The term “article” is used herein to define an object which has a given shape, surface or design which determines its function.

[0026] In one aspect, the invention thus provides an absorbent article comprising an absorbent cellulose I alginate-containing material, wherein said material comprises cellulose fibres and alginate from a brown seaweed, and wherein said material is obtained by a process comprising at least the following steps:

[0027] (i) providing a brown seaweed, or part thereof;

[0028] (ii) dividing the brown seaweed, or part thereof, into a plurality of portions;

[0029] (iii) washing the plurality of portions with water whereby to remove water- soluble components and recovering the residual wet residue; (iv) converting at least a portion of calcium alginate present in said residual wet residue into a water-soluble alginate whereby to provide a residue containing cellulose fibres and water-soluble alginate; and

[0030] (v) de-watering said residue containing cellulose fibres and water-soluble alginate whereby to provide said absorbent cellulose I alginate-containing material as a dry residue.

[0031] As used herein, the term “dry residue” refers to a residue having a water content of less than about 20 wt.%, preferably less than about 15 wt.% (based on the total weight of the dry residue). In some embodiments, the dry residue will have a water content of from 1 wt.% to 20 wt.%, preferably from 5 wt.% to 15 wt.%, more preferably from 10 to 12 wt.%, for example about 10 wt.%. Water content may be determined by any method known in the art, for example the method described herein in the examples.

[0032] The absorbent article may be formed from the absorbent cellulose I alginate- containing material or it may incorporate the absorbent cellulose I alginate- containing material.

[0033] In one embodiment, the absorbent article has a structure which serves to retain the absorbent material. The absorbent cellulose I alginate-containing material may, for example, be dispersed, embedded or otherwise attached to the structure to form the article.

[0034] In one embodiment, the absorbent article is formed from the absorbent material. In this embodiment, the absorbent cellulose I alginate-containing material may be formed, shaped or moulded to form the article.

[0035] In one embodiment, the absorbent article is a consumer article which in use is intended to absorb and retain an aqueous fluid, for example water or a bodily fluid. In one embodiment, the absorbent article will be a disposable absorbent article. By “disposable” it will be understood that the article is intended to be single use.

[0036] As a result of the process used in its production, the absorbent cellulose I alginate- containing material will be provided in particulate form. Depending on its intended use, the particle size of the material may be adjusted. In some embodiments, the process for production of the absorbent material may additionally comprise further processing of the dry residue to reduce its particle size. The need for any further reduction in particle size, or the extent of any such reduction, will depend on the intended end use of the absorbent material and the extent of size reduction that has already been carried out to produce the plurality of portions in step (ii) of the process. Methods suitable for reducing the particle size of the dry residue are well known in the art and can readily be selected, but include milling and / or grinding, for example.

[0037] The process herein described may be performed in respect of any brown seaweed, or any part (or parts) thereof, that contains native insoluble alginate.

[0038] As used herein, and unless otherwise specified, the term “alginate” is broadly used to refer not only to alginic acid salts (which may be referred to in the art as “alginates”), but to any other derivative of alginic acid and alginic acid itself. As noted herein, alginic acid is a polysaccharide consisting of blocks of (1 -4)-linked - D-mannuronate (M), a-L-guluronate (G), and blocks having an alternating structure (MG). Any reference herein to “native insoluble alginate” is intended to refer to alginate in its naturally occurring form, in particular calcium alginate. Where reference is made to a “soluble alginate”, it will be understood that this refers to a soluble form, for example the soluble sodium form. It may, however, also refer to any other mono-ion form that is soluble such as potassium alginate or ammonium alginate. As will be understood, any reference herein to a “soluble alginate” refers to an alginate that is soluble in water. An “insoluble alginate” will be understood to refer to an alginate that is insoluble in water, such as an insoluble salt of alginic acid with a multi-valent cation, such as calcium or aluminium. Typically, the native insoluble alginate will comprise calcium alginate. Examples of soluble alginates include sodium alginate, potassium alginate and ammonium alginate. Typically, the soluble alginate will be sodium alginate. Any “soluble” form of alginate that is not intimately entangled or inter-twined with cellulose may also be referred to herein as “extractable alginate”, i.e. it can be extracted from the seaweed by direct solubilisation. Examples of brown seaweeds (i.e. Phaeophyceae) that contain alginate and which may be employed in the process herein described include, but are not limited to, those selected from the group consisting of Laminaria spp., Fucales spp., Ascophyllum spp., Durvillaea spp., Ecklonia spp., Lessonia spp., Macrocystis spp., Sargassum spp., and Saccharina spp.

[0039] Examples of particular species of brown seaweed that find use in the invention include, but are not limited to, Laminaria hyperborea, Laminaria digitata, Lessonia trabeculata, Lessonia flavicans, Lessonia brasiliensis, Lessonia nigrescens Saccharina latissima, Saccharina japonica and Fucus serratus.

[0040] Laminaria spp. are particularly suitable, such as Laminaria hyperborea and Laminaria digitata, in particular Laminaria hyperborea.

[0041] The process described herein may be carried out in respect of fresh, frozen or dried brown seaweed or any part thereof that contains alginate. By “fresh”, it is intended that the seaweed or part thereof has not dehydrated to any appreciable extent following harvest. Alternatively, following commercial harvesting, the seaweed or any part (or parts) thereof may be dried. For example, it may be air dried at ambient temperature or at an elevated temperature. Following drying, it may be shredded or flaked to produce a material which can be stored prior to processing as herein described. Any dried seaweed material may be re-hydrated prior to subjecting it to a process as herein described. Alternatively, contact with water in the washing step may be used for the purpose of re-hydration.

[0042] Brown seaweed typically comprise three distinct morphological parts or sections: the leaf (also known as the “frond” or “blade”), the stipe (a ‘stem-like’ structure), and the haptera (a ‘root-like’ structure which anchors the seaweed to the ocean floor and which is also sometimes referred to as the “holdfast”). These parts are different in terms of their physical properties and chemical composition. Harvesting methods involve cutting of the stipe close to the holdfast. Following harvesting, the leaf and stipe will typically be separated from one another to form the different “parts”. Whilst the process herein described may be performed in respect of the whole seaweed (i.e. the stipe and leaf), typically it will be carried out in respect of one or more separated parts. Alginate is located in the structural tissues of the stipe of brown seaweed, for example in the stipe of Laminaria hyperborea. In one embodiment, the process will be performed on the stipe of the seaweed. The seaweed part which is used in the process of the invention may therefore comprise substantially only the stipe. Use of the stipe of Laminaria hyperborea is particularly preferred. Alternatively, the process may be performed on the leaf of the seaweed, or on part of the leaf.

[0043] Where part of the leaf is used, this will generally be the thickest part taken from the base of the leaf. Use of the leaf, or any part of the leaf, of Laminaria hyperborea is preferred. Alternatively, the process may be performed in respect of the whole seaweed, for example a combination of both the stipe and the leaf. As described herein, selection of the appropriate part (or parts) of the seaweed for use in the process can influence the properties of the material that is obtained.

[0044] Epiphytes are organisms that grow on the surface of brown seaweed in the marine environment. These include other species of algae, bacteria, fungi, sponges, bryozoans, ascidians, protozoa, crustaceans, molluscs and other sessile organisms. It may be beneficial for these to be removed (or substantially removed) prior to use of the seaweed, or any part of the seaweed, in the process as herein described. Where it is desirable to remove epiphytes from the surface of the seaweed or part thereof, any conventional method may be used. For example, these may be removed by high pressure water washing. In some embodiments, however, the epiphytes need not be removed. The seaweed, or part thereof, which is used in the process may therefore carry epiphytes on its surface.

[0045] The stipe of the seaweed may be selected for use in the process of the invention due to its higher alginate content and / or the higher G-content of the alginate. The stipe may be substantially cylindrical and comprises three distinctive regions defined based on their radial distance from the centre axis of the stipe. The radially inner portion comprises a core region of the stipe referred to as the “inner core”; the radially intermediate portion surrounding the core comprises a tissue region referred to as the “outer core”; and the radially outermost portion comprises a protective surface layer which may be referred to as the “outer layer”. This outer layer may also be referred to as the “bark”, “peel” or “skin” of the stipe. The stipe may be processed to remove some or all of its outer surface layer prior to processing as herein described. However, in one embodiment, it need not be removed. For example, stipe which has not been subjected to any chemical or physical process to remove the outermost surface layer, i.e. in which the outer layer remains substantially “intact”, may be used in the process. Such a stipe may be referred to as “unpeeled” stipe. In one set of embodiments, therefore, the seaweed for use in the process may be whole seaweed (i.e. stipe and leaf) in which the stipe retains the outer surface layer, or stipe which has been separated from the leaf but which still retains the outer surface layer. In one set of embodiments, the unpeeled stipe of Laminaria hyperborea may be used.

[0046] The process herein described may also be carried out in respect of a stipe from which the outermost layer has been substantially removed, i.e. “peeled” stipe. In an embodiment, the process may therefore comprise the step of removal of an outwardly facing surface layer from the stipe or sections of stipe which contains unwanted pigments such as polyphenols. The outwardly facing surface layer for removal will comprise at least the epidermis layer and may additionally comprise the meristoderm layer. Typically, the outwardly facing surface layer that is removed will include at least the epidermis and meristoderm layers. Removal of the surface layer may be carried out using any method known in the art. For example, it may be removed by a chemical stripping process or by a mechanical method. Mechanical methods include peeling, abrasion or scraping. These may be done manually (i.e. by hand) but more typically will be carried out using an automated machine such as a peeling and / or abrading machine known in the art for peeling and / or abrading vegetables. Suitable peeling methods are described in WO 2015 / 067971 , the entire contents of which are incorporated herein by reference. The thickness of the outwardly facing surface layer of the stipe to be removed will be dependent on the type, age and thickness (i.e. diameter) of the macroalgae but can readily be determined by those skilled in the art in order to ensure that substantially all of the pigment-bearing outer layer has been removed. The outwardly facing surface layer of the stipe that is removed may have a thickness of at least 0.5 mm, preferably at least 1.5 mm. For example, it may have a thickness in the range of from 0.5 mm to 2.5 mm. Prior to processing the seaweed, or part thereof, to convert at least a proportion of its native insoluble alginate content into a soluble alginate, the seaweed, or part thereof, will be reduced in size in order to increase its surface area and thus improve the efficiency of the washing and conversion process. This is step (ii) of the process as herein described. The method used to divide the seaweed, or part thereof, into a plurality of portions, for example a plurality of stipe or leaf portions, is not of particular importance and any known method may be used to reduce the size of the material. For example, the seaweed or part thereof (e.g. the stipe or the leaf) may be divided by any combination of cutting, chopping, blending, and milling. If appropriate, it may be cut into smaller sections (for example, by cutting or chopping) prior to blending or milling. This may be useful to aid in handling of the material during any subsequent step of blending or milling.

[0047] In one embodiment, in step (ii), the seaweed or part thereof may be divided into a plurality of portions by cutting or chopping. Cutting or chopping may be appropriate to reduce the size of the seaweed, or part thereof, into smaller portions. For example, the stipe may be cut into lengths of from 5 to 100 mm, for example 5 to 10 mm.

[0048] The cut portions of the seaweed or part thereof may be passed directly to the washing stage of the process. In this case, further size reduction of the material may be performed during the washing step, for example by wet milling or blending. Alternatively, the cut portions may be further reduced in size prior to washing. In one embodiment, in step (ii), the seaweed or part thereof may thus be divided into a plurality of portions by cutting followed by milling. Milling may be carried out using any conventional milling machine known in the art. If desired, milling may involve more than one milling stage involving the use of progressively finer screens to provide the desired particle size. Milled portions may have a particle size ranging from 0.1 mm to 10 mm, preferably from 1 mm to 5 mm, e.g. from 1 mm to 2 mm.

[0049] In step (iii) of the process herein described, the plurality of seaweed portions (e.g. the stipe and / or leaf portions) are subjected to water washing in order to remove water-soluble components (such as unwanted salts and other low molecular weight components) prior to carrying out alginate conversion. Washing of the plurality of seaweed portions is carried out by contacting the portions of seaweed with water. Deionised or demineralised water may be used for this purpose, but it is generally preferred that potable water (containing calcium ions) or seawater is used in order to reduce the loss of any low molecular weight “G” bearing alginate from the material.

[0050] Water washing may be carried out by adding the plurality of seaweed portions, for example dried or wet flakes, to water, stirring and allowing to stand. In some embodiments, the seaweed portions may be further reduced in size during water washing, for example by methods such as blending or wet milling. Washing may be carried out in a continuous or batch-wise process. Multiple water washing steps may be conducted in which water is removed from the solid-liquid mass at the end of each washing step, the solid seaweed residue is collected and transferred to the next washing stage.

[0051] The temperature of the water used for washing and duration of washing may readily be selected by those skilled in the art and will take account of the type of seaweed, whether the seaweed portions are obtained from the whole seaweed, or from the stipe or leaf, the number of washing steps, etc. Lower temperatures and / or shorter treatment times are generally preferred to reduce the energy requirements of the process and may be appropriate for washing of stipe portions, for example. Where any leaf portions are present, for example when processing the seaweed as a whole or the separated leaf, a higher washing temperature will generally be required to effectively remove the fucoidan.

[0052] For stipe, the water washing step may conveniently be conducted at ambient temperature, i.e. at 18 to 25°C. The duration of water washing may range from 10 to 60 minutes, for example it may be about 30 minutes.

[0053] In the case of leaf (or whole seaweed where leaf parts are present), the water washing step may conveniently be conducted at a temperature in the range of 30 to 70°C, preferably 50 to 70°C, for example about 60°C. The duration of water washing may range from 10 to 60 minutes, for example it may from 30 to 60 minutes, for example about 30 minutes. Hot water washing will generally be followed by a cold water wash, for example by washing of the material at ambient temperature, i.e. at 18 to 25°C. The duration of any cold water wash may range from 10 to 60 minutes, for example it may be about 30 minutes and may be repeated as required.

[0054] Washing may be carried out until the conductivity of the water which is removed is sufficiently reduced and indicative of the removal of a sufficient amount of unwanted salts from the material. A conductivity of less than about 200 pS may, for example, be appropriate. If necessary, multiple washing steps may be performed.

[0055] In one embodiment, the wash solution removed from the solid-liquid mass at the end of each washing step may be collected and processed to recover one or more water-soluble components. For example, one or more of fucoidan, laminarin and mannitol may be recovered. Methods for the recovery of such substances are well known in the art and include, but are not limited to, ultrafiltration and spray-drying. Typically, recovery might be performed by carrying out ultrafiltration followed by spray-drying.

[0056] Following the washing step (or final washing step), the material may be processed to remove excess water from the residual solids prior to further processing as described herein to convert the native alginate into a soluble form. Excess water will typically be removed by mechanical methods such as centrifugation. A horizontal centrifuge may, for example, be used.

[0057] Prior to conversion of at least a portion of the native insoluble alginate into soluble form (step (iii)), the seaweed or part thereof may be subjected to certain pretreatments, such as methods to adjust the M / G ratio of the alginate. For example, it may be subjected to a pre-treatment capable of enriching the G-content of the material (i.e. increasing the G / M ratio). Acid treatment at elevated temperature may, for example, be performed to hydrolyse the “M” blocks and thereby enrich the G-content of the alginate. Such treatment is particularly suitable in the case of leaf alginate, for example, which is lower in G-content than alginate present in the stipe. Other known methods that may be employed to hydrolyse the “M” blocks include enzymatic treatment, for example using lyase enzymes. Suitable methods for enhancing the G-content of alginate include those described in EP 0 980 391 , the entire contents of which are incorporated herein by reference. For example, C5 epimerases may be used to convert “M” blocks to “G” blocks. The processes herein described are intended to provide a cellulose I alginate- containing material in which alginate is retained or substantially retained within the seaweed matrix, i.e. it is not intended that it is extracted and recovered.

[0058] Accordingly, any additional processing steps that may adversely disrupt the alginate chains should be minimised, or avoided. Such processing steps include high temperature treatments, especially where these may be carried out for long periods.

[0059] Any high temperature treatment or pre-treatment that could disrupt the alginate chains should be minimised. For example, any treatment of the seaweed with a super-heated solvent (e.g. super-heated water) should be avoided, or at least minimised. As used herein, the term “super-heated solvent” refers to a solvent, for example water, an alcohol, or a mixture thereof, heated to a temperature above its normal boiling point at atmospheric pressure but below the critical temperature at a pressure sufficient to maintain the liquid state. “Super-heated water” is water which is in a liquid state under pressure and at a temperature above its boiling point but below its critical temperature, i.e. between 100 and 374°C.

[0060] Other treatments that would disrupt the alginate should also be avoided, such as exposure of the material to microwaves during processing. In one embodiment, the processes herein described thus exclude any step involving exposure of any of the following materials to microwaves: the seaweed, or part thereof, any of the intermediate products produced during the process, and the final seaweed residue containing cellulose and alginate.

[0061] Known methods for the conversion of native alginate in seaweed into a water- soluble form may be used in the process herein described whereby to convert at least a portion of calcium alginate present in the residual wet residue into a water- soluble alginate. This is step (iv) of the process. The aim is to convert the insoluble native alginate present in the seaweed material into a water-soluble form, at least a portion of which will be retained in the solid residue when this is de-watered to form the final material. No active step of extraction of alginate to separate this from the seaweed residue will, however, be performed. Various methods may be employed to convert the native insoluble alginate into a water-soluble alginate (e.g. sodium alginate) and to recover a residue containing cellulose fibres and water-soluble alginate. As herein described, the intention of the production process is to retain at least some of the converted (i.e. solubilised) alginate in the final seaweed residue since this contributes to the desired absorbent properties of the material. In preferred embodiments of the process, the intention is to retain as much of the converted (i.e. solubilised) alginate as possible though, in practice it will be appreciated that some (possibly low) amount of alginate may be lost. The degree of loss of any alginate will depend on factors such as the type of brown seaweed, the part (or parts) of the seaweed employed, the processing steps used to treat the seaweed and perform the alginate conversion and recovery of the dry residue in step (v). Steps (iv) and (v) of the process can be adjusted to minimise loss of the solubilised alginate from the seaweed residue, for example using the types of methods herein described.

[0062] Step (iv) of the process involves converting at least a proportion of the native calcium alginate present in the residual solids in the washed solid fraction (i.e. the “residual wet residue”) into a water-soluble alginate. In one embodiment, this step of the process will be performed in a way which minimises the loss of alginate, once solubilised, from the seaweed matrix. Methods suitable for minimising the loss of soluble alginate from the seaweed matrix are illustrated in the examples but these are not intended to be limiting on the scope of the invention and other methods may also be employed. At any stage in this step of the process in which the metal ions of the alginate have been exchanged by protons and it is thus in the form of alginic acid, it will be insoluble and thus non-extractable. At any pH below or equivalent to the pKa of alginic acid (i.e. at or lower than pH 4.6), the alginate will remain insoluble. In order to minimise the loss of alginate when it is converted to a soluble form (e.g. to sodium alginate), the addition of any fluid to achieve this conversion should preferably be carried out in such a way that the overall amount of fluid which contacts the seaweed particles is kept to a minimum, i.e. the minimum amount required to achieve the conversion.

[0063] As observed in the results provided herein, an unintentional loss in alginate from the seaweed material during the conversion process can still provide a cellulose I alginate-containing material having desirable fluid uptake and retention capabilities. Provided that the seaweed matrix retains at least a proportion of alginate in solubilised form, the inventors have found that this can still provide useful absorbent materials.

[0064] As described herein, the process is intended to convert the native alginate in the seaweed matrix into a water-soluble form. In a preferred set of embodiments, the intention is to maximise retention of this water-soluble form of the alginate in the final seaweed residue. Preferably, the process herein described thus does not involve the extraction and recovery of alginate from the brown seaweed.

[0065] The loss of dry matter from the brown seaweed is an indication of the amount of alginate that is lost from the seaweed matrix during the process herein described. The “loss of dry matter” is the difference in the dry matter content of the washed seaweed material (i.e. following removal of salts and other water-soluble components in accordance with step (iii) of the process as herein described) and the dry matter content of the seaweed residue after processing (i.e. following completion of step (v) of the process as herein described). In some embodiments, the loss of dry matter may be up to about 75%. In other embodiments, the loss of dry matter will be less than about 60%, less than about 50%, or less than about 40%. In other embodiments, the loss of dry matter will be less than about 30%, for example less than about 25%, or less than about 15%. In other embodiments, the loss of dry matter will be less than about 10%, for example less than about 5%, less than about 4%, less than about 3%, less than about 2% or less than about 1%.

[0066] The following methods are illustrative of step (iv) of the process and are not intended to be limiting on the scope of the invention.

[0067] In one embodiment, step (iv) may be performed by a process involving acid cation exchange followed by treatment with an alkali whereby to convert the calcium alginate into a water-soluble form. This step may thus comprise an acid cation exchange step in which the residual wet residue of the seaweed, or part thereof, is contacted with an aqueous solution of a mineral acid whereby to effect exchange of the native calcium ions in the seaweed matrix with hydrogen ions to form alginic acid. Following recovery of the resulting solid fraction, this is then contacted with an alkali whereby to convert the alginic acid into a water-soluble alginate (e.g. to sodium, potassium or ammonium alginate). Acidification of the seaweed may also have the advantage of removing salts and other non-target compounds such as polyphenols and other polysaccharides such as fucoidans and laminarins.

[0068] Thus, in one embodiment, an initial metal cation exchange step is employed in step (iv) to convert the insoluble alginate to alginic acid by exchanging metal cations with protons. This is carried out by the addition of a mineral acid which is added to reduce the overall pH of the residual wet residue, for example to a pH in the range of about 1.5 to about 2, e.g. to about 1.7 to about 1.9. Suitable mineral acids include hydrochloric acid and / or sulphuric acid. Conveniently, the mineral acid will be hydrochloric acid. The material can be left to stand in the presence of the mineral acid for up to 60 mins, for example up to 30 mins, for example up to approximately 15 minutes. During contact with the mineral acid, the mixture may be agitated (e.g. stirred).

[0069] Following mineral acid treatment, the process will then typically comprise the step of separating the resulting mixture into a solution phase and residual solids. For example, the material may be drained through a filter or transferred to a centrifuge to remove the acid water. The filtrate or the liquid phase from the centrifuge, which is a mineral acid solution, may be collected and if desired can be used in a subsequent metal cation exchange step, thereby improving process efficiency. The obtained solid fraction may be washed with water in one or more washing steps to remove excess mineral acid. The water for use in this part of the process will typically be deionised water in order to avoid the re-introduction of calcium ions. Washing with water is effective to increase the pH of the material, e.g. to a pH in the range of from about 3 to about 5, preferably about 3 to about 4, e.g. about 3.5 to 4, and may be repeated as required. After the washing step (or final washing step), the material is drained or centrifuged to remove as much free water as possible.

[0070] At this point, the native alginate will be present in an insoluble form, i.e. primarily in the form of alginic acid. Calcium alginate residues may also still be present. The next step of the process involves conversion of the insoluble alginate salts and / or alginic acid present in the seaweed to the soluble form (e.g. the soluble sodium form). The step of conversion will typically comprise contacting the seaweed residue with an alkali whereby to produce solubilised alginate. The alkali may be employed in solid or solution form, but typically may be used in the form of an alkaline solution. Where it is used in the form of a solution this will generally be a saturated solution.

[0071] Typically, the alkaline solution for use in the conversion process may be selected from sodium hydroxide, potassium hydroxide, ammonium hydroxide and sodium carbonate. Conveniently, it may comprise carbonate ions, for example it may be a sodium carbonate solution. For example, the step of conversion of the alginate into water-soluble form will comprise the use of sodium carbonate and / or sodium hydroxide, preferably sodium carbonate (e.g. a saturated sodium carbonate solution). The alkaline solution, for example sodium carbonate, may be employed at a suitable concentration. Preferably, it will be used at a concentration of about 10 to 15%.

[0072] Contact with the alkaline solution may comprise soaking of the solid fraction in the alkaline solution or it may involve mixing, e.g. high shear mixing, with the alkaline solution. Soaking or mixing may be carried out for a period of about 2 minutes to about 24 hours, for example 30 minutes to 24 hours, for example 30 to 45 minutes. During contact, the pH will increase and may be in range from about 6 to about 10, preferably from about 6 to 8, more preferably from about 6 to 7. Preferably the alkaline solution is added to effectively neutralise the solid fraction, for example to adjust its pH to within the range of 6 to 7, preferably 6.5 to 6.7. If necessary, additional alkaline solution can be added as required. Reaction temperature and reaction time can readily be varied. For example, the reaction temperature may be in the range from 30 to 80°C, from 40 to 70°C, or from 50 to 60°C. Conveniently, the reaction may be carried out at ambient temperature (18 to 25°C).

[0073] Other methods known in the art for the extraction of alginate from brown seaweed also find use in the production of the absorbent materials herein described to the extent that these involve the step of conversion of the native alginate to a water- soluble form. Such methods include those involving pre-treatment of the seaweed prior to conversion of the native alginate into a water-soluble form. One such method involves exposing the portions of seaweed to a weak organic acid, such as citric acid, followed by cation exchange with a mineral acid. Treatment with a weak organic acid is effective to reduce the native alginate molecular weight and decolourise the material. Thereafter, the decolourised material is subjected to treatment with a mineral acid whereby to exchange the metal ions present in the alginate structure (e.g. calcium) with hydrogen ions in order to facilitate the conversion to a soluble form of alginate. This organic acid pre-treatment process is disclosed in WO 2023 / 281262, the entire contents of which are incorporated herein by reference.

[0074] In one embodiment, step (iv) of the process herein described may thus comprise the following steps: contacting the residual wet residue with an aqueous solution of a weak organic acid; recovering the resulting solid fraction; contacting the resulting solid fraction with an aqueous solution of a mineral acid whereby to effect exchange of native calcium ions with hydrogen ions to produce alginic acid; recovering the resulting solid fraction; and contacting the solid fraction with an alkali whereby to convert the alginic acid to a water-soluble form of alginate.

[0075] As used herein, the term “organic acid” denotes an organic compound which has acidic properties. Organic acids for use in the invention may possess one or more acid groups and include any of the acids disclosed in WO 2023 / 281262. Preferred for use in the invention are any of the following acids: lactic acid, malic acid, tartaric acid, citric acid, ascorbic acid, and glycolic acid. Of these, lactic acid (E270), malic acid (E296), tartaric acid (E334), citric acid (E330), and ascorbic acid (E300) have E-numbers and are generally preferred. Particularly preferred for use in the invention are malic, citric and ascorbic acids. The use of citric acid is especially preferred.

[0076] The precise conditions for any organic acid treatment, such as the concentration of the acid, temperature and duration of treatment, etc. can readily be selected by those skilled in the art. As described in WO 2023 / 281262, by varying the organic acid treatment conditions, the nature of the solubilised alginate can be suitably adjusted. For example, the duration of exposure of the seaweed material to the organic acid, its concentration, and the temperature of the organic acid treatment have an impact on the molecular weight of the alginate. This, in turn, intrinsically influences the viscosity of the alginate when dissolved in solution. Longer treatment times and / or higher temperatures are effective to reduce the molecular weight and viscosity of the alginate, for example. The use of higher concentrations of the organic acid also reduces the molecular weight (and thus viscosity) of the alginate. Advantageously, the conditions of the organic acid pre-treatment can be adjusted to provide a water-soluble alginate having desired functional properties.

[0077] Typically, the organic acid may be employed in the form of an aqueous solution having a concentration of from 0.1 to 10.0 % w / v, from 0.25 to 5.0 % w / v, from 0.75 to 2.5 % w / v, from 1.0 to 2.0 % w / v, or from 1.0 to 1.5 % w / v, preferably about 1 % w / v. The temperature of the organic acid treatment may be selected depending on the desired molecular weight (and thus viscosity) of the converted alginate.

[0078] Generally, temperatures up to about 100°C may be employed. However, lower temperatures are generally preferred in order to reduce the overall energy requirement of the process. The use of lower temperatures may also provide a greater degree of control over the organic acid pre-treatment step (and thus its impact on the properties of the converted alginate). Temperatures in the range from 10 to 100°C, preferably 10 to 50°C, more preferably 15 to 30°C, e.g. 20 to 25°C, may be employed. Advantageously, however, this step of the process will be conducted at ambient temperature, for example in the range from 18 to 25°C. As will be understood, ambient temperature does not require any additional heating.

[0079] Higher temperatures for the organic acid treatment may be appropriate where a lower molecular weight (and thus lower viscosity) of the converted alginate is desirable and may be selected accordingly. Where higher temperatures are used, these may be in the range from 60 to 100°C, for example from 65 to 100°C, from 70 to 100°C, from 80 to 100°C, from 90 to 100°C, or from 95 to 99°C.

[0080] Duration of the organic acid treatment may be appropriately selected by those skilled in the art. For example, the timing of treatment may range from a few minutes to several hours. As will be understood, the duration for the treatment will be influenced by the selected concentration of the organic acid and the temperature employed in this step of the method. If a low concentration of organic acid is employed, the duration of treatment may for example extend to several days or even weeks. Typically, however, organic acid treatment may be carried out for up to 2 hours, for example up to 1.5 hours, e.g. up to 1 hour. Treatment may be carried out for shorter times, e.g. less than an hour, particularly in cases where elevated temperatures and / or higher concentrations of organic acid are employed. For example, treatment times may be as low as 2 minutes, or as low as 5 minutes. Treatment times may, for example, range from 2 to 60 minutes, or from 5 to 50 minutes, or from 10 to 40 minutes, or from 20 to 30 minutes.

[0081] Selection of the temperature and duration of the organic acid pre-treatment step of the method should take account of the concentration of the organic acid solution that is employed. When using higher concentrations of the organic acid, for example, shorter treatment times and / or lower temperatures may be appropriate in order to provide the desired degree of control in producing a converted alginate having the required functional properties.

[0082] In one embodiment, step (iv) may be performed by “salt conversion” using a sodium chloride solution to provide an excess of sodium ions which exchange with calcium ions in the native alginate. This step may comprise: contacting the residual wet residue with a sodium chloride solution; separating the resulting solid fraction; and washing the solid fraction with propanol. The sodium chloride solution may be employed in any suitable concentration, for example at a concentration in the range of about 5 to about 20%, e.g. about 10%. This solution is contacted with the residual wet residue in an amount to ensure the presence of an excess of sodium ions. For example, it may be added to the seaweed residue in a ratio of at least 1 :1 , for example about 2:1 (solution : solid). The resulting mixture may be left to soak or it may be stirred. Soaking or mixing may be carried out for a period of about 2 minutes to about 24 hours, for example 30 minutes to 24 hours, for example 30 minutes to 1 hour. The temperature during soaking or mixing may be in the range from 20 to 40°C, preferably from 20 to 25°C. Typically, this step may be conducted at ambient temperature (18 to 25°C). Following treatment with sodium chloride, the resulting mixture is separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove sodium chloride solution. The obtained solid fraction is washed with propanol to remove any excess sodium chloride, but not sodium alginate. The use of a 50% propanol solution is preferred. The presence of water is required for the sodium chloride to dissolve out whilst the presence of propanol precipitates the alginate. Washing may involve contacting the solid fraction with propanol and mixing, for example for a period of up to 30 minutes, for example about 10 minutes. Typically this washing step is performed at ambient temperature (18 to 25°C). Following propanol washing, the solid and liquid phases are separated, for example by filtration and / or centrifugation to recover the solid fraction. If appropriate, the step of washing with propanol may be repeated one or more times.

[0083] In one embodiment, step (iv) may be performed by “sodium citrate conversion” in which the residual wet residue is contacted with a sodium citrate solution. The sodium citrate solution may be employed in any suitable concentration, for example at a concentration in the range of about 0.5 to about 3%, e.g. about 1%. This solution is contacted with the residual wet residue in an amount to ensure the presence of an excess of citrate ions which chelate calcium ions present in the native alginate. For example, the sodium citrate solution may be added to the seaweed residue in a ratio of at least 1 :1 , for example about 2:1 (sodium citrate solution : solid). The resulting mixture may be left to soak or it may be stirred. Soaking or mixing may be carried out for a period of about 2 minutes to about 24 hours, for example 30 minutes to 24 hours, for example 30 minutes to 1 hour. The temperature during soaking or mixing may be in the range from 20 to 40°C, preferably from 20 to 25°C. Typically, this step may be conducted at ambient temperature (18 to 25°C). Following treatment with sodium citrate, the resulting mixture is then buffered to a pH in the range of from about 6 to about 10, preferably from about 6 to about 7, for example about 6.6 to 6.7. Agents which may be used to adjust the pH include sodium-based alkali agents and sodium hypochlorite. Examples of suitable sodium-based alkali agents that may be used include, but are not limited to, sodium carbonate and sodium hydroxide and mixtures thereof. Preferably the sodium-based alkali agent is sodium carbonate.

[0084] Following adjustment of the pH, the resulting mixture is then separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove excess solution. The obtained solid fraction may be washed with water, for example with deionised water, followed by filtration and / or centrifugation to recover the solid fraction. Suitable washing temperatures may readily be selected but may, for example, be in the range from 20 to 40°C, preferably washing may be conducted at ambient temperature (18 to 25°C). If appropriate, the step of water washing may be repeated one or more times.

[0085] In one embodiment, step (iv) may be performed by contacting the residual wet residue with a solution containing sodium chloride and citric acid. This step may comprise: contacting the residual wet residue with a solution containing sodium chloride and citric acid; separating the resulting solid fraction; and contacting the solid fraction with an sodium-based alkali whereby the adjust the pH to about 6 to 7. The sodium chloride may be employed in any suitable concentration, for example at a concentration in the range of about 1% to about 5%, e.g. about 2%. The citric acid may be employed in any suitable concentration, for example at a concentration in the range of about 1% to about 10%, e.g. about 5%.

[0086] The solution containing sodium chloride and citric acid is contacted with the residual wet residue in an amount to ensure the presence of an excess of sodium and citrate ions. For example, it may be added to the wet seaweed residue in a ratio of at least 1 :1 , for example about 2:1 (solution : solid). The resulting mixture may be left to soak or it may be stirred. Soaking or mixing may be carried out for a period of about 2 minutes to about 24 hours, for example 30 minutes to 24 hours, for example 30 minutes to 1 hour. The temperature during soaking or mixing may be in the range from 20 to 40°C, preferably from 20 to 25°C. Typically, this step may be conducted at ambient temperature (18 to 25°C). The resulting mixture is then separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove excess solution. The obtained solid fraction is then buffered to a pH in the range of from about 6 to about 7, for example about 6.6 to 6.7, by the addition of a sodium-based alkali.

[0087] Examples of suitable sodium-based alkali agents include sodium carbonate and sodium hydroxide. The resulting mixture is then separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove excess solution. The obtained solid fraction may be washed with water, for example with deionised water, followed by filtration and / or centrifugation to recover the solid fraction. Suitable washing temperatures may readily be selected but may, for example, be in the range from 20 to 40°C, preferably 20 to 25°C. Typically, washing may be conducted at ambient temperature (18 to 25°C). If appropriate, the step of water washing may be repeated one or more times.

[0088] In another embodiment, step (iv) may be performed using a sodium-based bleaching agent to provide an excess of sodium ions which exchange with calcium ions in the native alginate. This step may comprise contacting the residual wet residue with a bleaching agent which contains sodium ions.

[0089] Examples of suitable bleaching agents include, but are not limited to, sodium hypochlorite. The bleaching agent may be employed in any suitable concentration, for example at a concentration in the range of about 1% to about 5%, e.g. about 1%. Typically, a solution of the bleaching agent is contacted with the residual wet residue in an amount to ensure the presence of an excess of sodium ions. For example, it may be added to the seaweed residue in a ratio of at least 1 :1 , for example about 2:1 (solution : solid). The resulting mixture may be left to soak or it may be stirred. Soaking or mixing may be carried out for a period of about 2 minutes to about 24 hours, for example 30 minutes to 24 hours, for example 30 minutes to 1 hour. The temperature during soaking or mixing may be in the range from 20 to 40°C, preferably from 20 to 25°C. Typically, this step may be conducted at ambient temperature (18 to 25°C).

[0090] Following treatment with the bleaching agent, the resulting mixture is separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove the bleaching solution. The obtained solid fraction may be washed with water, for example with deionised water, followed by filtration and / or centrifugation to recover the solid fraction. Suitable washing temperatures may readily be selected but may, for example, be in the range from 20 to 30°C, preferably washing may be conducted at ambient temperature (18 to 25°C). If appropriate, the step of water washing may be repeated one or more times.

[0091] In one embodiment, step (iv) may be performed by contacting the residual wet residue with a solution containing a sodium salt of ethylenediaminetetraacetic acid (EDTA); separating the resulting solid fraction; and contacting the solid fraction with a sodium-based alkali whereby to increase the pH to about 6 to 7. The sodium EDTA solution may be employed in any suitable concentration, for example at a concentration in the range of about 3 to about 10%, e.g. about 5%. This solution is contacted with the residual wet residue in an amount to ensure the presence of an excess of EDTA ions which chelate calcium ions present in the native alginate. For example, the sodium EDTA solution may be added to the seaweed residue in a ratio of at least 1 :1, for example about 2:1 (Na EDTA solution : solid). The resulting mixture may be left to soak or it may be stirred. Soaking or mixing may be carried out for a period of about 2 minutes to about 24 hours, for example 30 minutes to 24 hours, for example 30 minutes to 1 hour. The temperature during soaking or mixing may be in the range from 20 to 40°C, preferably from 20 to 25°C. Typically, this step may be conducted at ambient temperature (18 to 25°C).

[0092] Following treatment with sodium EDTA, the resulting mixture is separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove sodium EDTA solution. Following treatment with sodium EDTA, the resulting mixture is then buffered to a pH in the range of from about 6 to about 7, for example 6.5 to 6.7 by addition of a sodium-based alkali. Examples of suitable sodium-based alkali agents that may by used include, but are not limited to, sodium carbonate and sodium hydroxide. The resulting mixture is then separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove excess solution.

[0093] In one embodiment, step (iv) may be performed by contacting the residual wet residue with a bleaching agent which contains sodium ions; separating the resulting solid fraction; contacting the solid fraction with an aqueous solution of a mineral acid whereby to adjust the pH to about 1.5 to 2, e.g. to about 1.7 to about 1.9; separating the resulting solid fraction; and contacting the solid fraction with a sodium-based alkali whereby to adjust the pH to about 6 to about 7.

[0094] Examples of suitable bleaching agents include, but are not limited to, sodium hypochlorite. The bleaching agent may be employed in any suitable concentration, for example at a concentration in the range of about 0.5 to 5%, e.g. about 1%. A solution of the bleaching agent is contacted with the residual wet residue in an amount to ensure the presence of an excess of sodium ions. For example, it may be added to the seaweed residue in a ratio of at least 1 : 1 , for example about 2:1 (solution : solid). The resulting mixture may be left to soak or it may be stirred. Soaking or mixing may be carried out for a period of about 2 minutes to about 24 hours, for example 30 minutes to 24 hours, for example 30 minutes to 1 hour. The temperature during soaking or mixing may be in the range from 20 to 40°C, preferably from 20 to 25°C. Typically, this step may be conducted at ambient temperature (18 to 25°C). Following treatment with the bleaching agent, the resulting mixture is separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove the bleaching solution. The obtained solid fraction may be washed with water, for example with deionised water, followed by filtration and / or centrifugation to recover the solid fraction. Suitable washing temperatures may readily be selected but may, for example, be in the range from 20 to 30°C. Typically, washing may be conducted at ambient temperature (18 to 25°C). If appropriate, the step of water washing may be repeated one or more times.

[0095] The resulting solid fraction is then contacted with an aqueous solution of a mineral acid to adjust the pH to about 1.5 to 2, e.g. about 1.7 to 1.9. Suitable mineral acids include hydrochloric acid and / or sulphuric acid. Conveniently, the mineral acid will be hydrochloric acid. The material can be left to stand in the presence of the mineral acid for up to 60 mins, for example up to 30 mins, for example up to approximately 15 minutes. During contact with the mineral acid, the mixture may be agitated (e.g. stirred). Following mineral acid treatment, the process will then typically comprise the step of separating the resulting mixture into a solution phase and residual solids. For example, the material may be drained through a filter or transferred to a centrifuge to remove the acid water. The obtained solid fraction may be washed with water in one or more washing steps to remove excess mineral acid. The water for use in this part of the process will typically be deionised water in order to avoid the re-introduction of calcium ions. Rinsing with water may be repeated as required. After the washing step (or final washing step), the material is drained or centrifuged to remove as much free water as possible. The resulting solid fraction is then contacted with a sodium-based alkali to adjust the pH to within a range from about 6 to about 7, preferably from about 6.5 to about 6.7. Examples of suitable sodium-based alkali agents include sodium carbonate, sodium hydroxide and mixtures thereof. Typically, the sodium-based alkali will be sodium carbonate. The resulting mixture is then separated into a solution phase and a solid fraction. For example, the material may be drained through a filter or transferred to a centrifuge to remove excess solution.

[0096] Following step (iv), the residual wet residue contains cellulose fibres in addition to water-soluble alginate, i.e. the residue is a cellulose I alginate-containing material. It may also contain additional components such as proteins and lipids. The amount of cellulose in the residue will depend on the seaweed species and the part of the seaweed used in the process. The amount of soluble alginate in the residue will depend on the conversion process employed.

[0097] In one embodiment, the residual wet residue produced following step (iv) of the process will have a pH in the range from about 4.5 to about 9, preferably from about 6 to about 7, for example from about 6.5 to 6.7.

[0098] As herein described, it is intended that the water-soluble alginate should be retained in the seaweed residue. At this point in the process, and in contrast to a conventional alginate extraction process, the solubilised alginate is not intentionally separated from the residual solids. In a conventional alginate extraction process, separation of the solubilised alginate from the residual solids may be carried out by methods such as by dilution of the residual solids with water followed by filtration and / or centrifugation. In one embodiment, such separation steps are not performed in the process herein described.

[0099] In step (v) of the process, the residual wet residue is de-watered to provide a dry residue. In some embodiments, the dry residue will have a water content of less than about 20 wt.%, preferably less than about 15 wt.% (based on the total weight of the dried residue). In some embodiments, the dry residue will have a water content of from 1 wt.% to 20 wt.%, preferably from 5 wt.% to 15 wt.%, more preferably from 10 to 12 wt.%, for example about 10 wt.%. Water content may be determined by any method known in the art, for example the method described herein in the examples.

[0100] De-watering of the residual wet residue may be carried out by any conventional method including any mechanical and / or chemical methods such as but not limited to, one or more of the following: mechanical pressing, solvent drying, spray drying, air drying, fluid bed drying, drum drying and vacuum drying. Solvent drying and / or vacuum drying is preferred.

[0101] In one embodiment, the residual wet residue is de-watered by solvent drying. Solvent drying may involve the use of an alcohol solvent such as ethanol, propan-2- ol, acetone or ether. The use of propan-2-ol is particularly preferred. The use of a solvent, such as propanol, may be beneficial in order to retain an open structure in the final material.

[0102] In certain embodiments, the seaweed residue produced in the process herein described may be processed to further adjust its physicochemical properties prior to its use as an absorbent. For example, fibrillation of the cellulose component may be desirable. Fibrillation methods are well known in the art and will generally be performed in respect of the residue before it is de-watered, i.e. whilst it remains in a wet state. If desired, therefore, fibrillation of the cellulose may be carried out to produce cellulose nanofibrils. In the preparation of nanofibrillar cellulose, cellulose fibres are disintegrated to produce fibrils having a sub-micron diameter. For example, these may have a diameter which is in the nanometer range. Disintegration methods are well known in the art and include mechanical disintegration of the cellulose material in the presence of water. Mechanical disintegration may involve grinding, crushing, or shearing of the fibrous cellulose material or any combination of these. It may be carried out using known equipment such as a fluidizer, high sheer homogenizer (e.g. a microfluidizer), grinder, etc. Disintegration may, for example, be carried out using a homogenizer in which the material is subjected to homogenization under pressure.

[0103] Following fibrillation, the resulting cellulose nanofibrils or nanofibril bundles are characterised by a high aspect ratio (i.e. length : diameter). Their length may exceed 1 pm, but their diameter is in the submicron range, i.e. less than 1 pm. Precise dimensions and size distribution of the nanofibrils or nanofibril bundles will depend on the disintegration (i.e. fibrillation) method and may vary to some extent. Typically, the diameter of the nanofibrils or nanofibril bundles will be on the nanometer scale, for example less than 20 nm. For example, their average diameter may range from 3 to 20 nm, preferably from 5 to 20 nm, e.g. from 5 to 10 nm. Typically, the average length of the nanofibrils or nanofibril bundles will be in the range from 5 to 10 pm. For example, it may be in the range from 1 to 5 pm, e.g 0.5 to 1 pm, or 0.2 to 0.5 pm.

[0104] The step of fibrillation of the seaweed residue as herein described is optional. In one set of embodiments, the process of the invention does not involve any step of nanofibrillation. In one set of embodiments, the process of the invention does not involve any step of fibrillation.

[0105] The resulting dry cellulose I alginate-containing material has the capacity to absorb and retain free liquid making it suitable for use as an absorbent material in any application where the uptake of free liquid is desired.

[0106] For use in certain applications, it may be desirable for the absorbent material to be free from colour or light in colour. A reduction in colour of the material may be achieved be appropriate selection of the starting material. For example, the use of peeled stipe from which the pigment-containing bark has been removed may be desirable. Alternatively, the use of a sodium-based bleaching agent such as sodium hypochlorite to adjust the pH during the conversion step herein described may be sufficient to provide the desired reduction in colour of the absorbent material. Alternatively, the seaweed residue may be further treated to remove or to disguise any undesired pigmentation. For example, it may be bleached or additional pigments may be added. Bleaching, or the addition of pigments to the final material, may be desirable when using unpeeled stipe or when using leaf material in the process of the invention, for example. The leaf material is more highly pigmented than the stipe.

[0107] Where bleaching is desirable, this will typically be carried out on the wet residue that is produced, i.e. prior to any drying or further processing steps. Any bleaching step may involve the use of a bleaching agent. As used herein, the term “bleaching agent” refers to a chemical agent which is capable of lightening or whitening a substrate via a chemical reaction. Typically, a bleaching agent will be one involved in a bleaching reaction which involves an oxidative or reductive process that degrades a colour pigment.

[0108] Examples of bleaching agents include, but are not limited to, any of the following: a compound comprising, or that acts as a source of, peroxide or peroxy acid, for example hydrogen peroxide, peroxide salt, peroxy acid, hydroperoxide, carbonate salt, percarbonate salt, 6-(phthalimido) peroxyhexanoic acid (PAP), peracetic acid; an oxidation catalyst, for example a mononuclear or dinuclear transition metal catalyst (for example manganese) (for example the oxidation catalyst may be selected from one or more groups selected from [(Mnlv)2(u-O)3(Me3-TACN)2]2+, [(Mnlll)2(u-O)(u-CH3COO)2(IVIe3-TACN2]2+and [MnlllMnlv(u-O)2(u-CH3COO)(Me4- DTNE)]2+and suitable salts thereof; a peroxide activator (i.e. a compound that reacts with a source of a peroxide group to provide a peroxide group), for example tetra acetyl ethylene diamine (TAED); a peroxy acid activator (i.e. a compound that reacts with a source of a peroxy acid to provide a peroxy acid group) for example tetra acetyl ethylene diamine (TAED); hypochlorite; a compound comprising, or that acts as a source of, chlorite; chlorine dioxide; a chlorite salt; and chlorine. Typical bleaching agents include hydrogen peroxide, peroxyacids, persulfates, organic peroxides and hypochlorite. Hydrogen peroxide or sodium hypochlorite is generally preferred.

[0109] An appropriate amount of any bleaching agent may readily be selected depending on the extent of lightening that is required or is desirable. The amount of bleaching agent may range from 1 to 10% by weight, preferably from 3 to 5% by weight (based on the weight of the residue). Bleaching may be carried out at a temperature in the range from 10 to 50°C, preferably from 20 to 30°C.

[0110] The step of bleaching as herein described is optional. In one set of embodiments, the process of the invention does not involve any bleaching step, i.e. the process does not involve the use of any bleaching agent. For example, the process does not involve the step of contacting any of the following materials with a bleaching agent: the seaweed, or part thereof, any of the intermediate products produced during the process, and the final seaweed residue containing cellulose and alginate. The resulting dry cellulose I alginate-containing material will be provided in particulate form, for example as a granular material. The material will include a range of particle sizes, i.e. it will be polydisperse. The precise particle size of the material may not be important but can be adjusted depending on the intended use of the material. In certain embodiments, the residue produced in the process of the invention may be further processed to reduce the particle size of the material. Size reduction may be effected by known methods such as, but not limited to, milling and / or grinding. Methods for size reduction of cellulose materials are well known in the art and include, for example, milling (e.g. ball milling or jet milling), or grinding. The particle size of the residue will depend on factors such as the method used for size reduction. Generally, the material will have an average particle size in the range from 100 to 1000 pm, preferably 200 to 700 pm, more preferably 250 to 600 pm, e.g. 250 to 500 pm. Particle size can be determined by known methods, for example by “sieve analysis” in which a sample is shaken on a stack of sieves of graduated size (largest at the top and smallest on the bottom). These are weighed empty and then at the end of the test to allow the determination of the mass (and hence %) retained at each level. Industry standards which may be followed are as follows: ISO 19.120 or ASTM 214.

[0111] In one embodiment, the resulting dry cellulose I alginate-containing material will have a free swelling capacity of from 5 to 60 g / g as measured according to the examples when using an aqueous fluid which is 0.9% NaCI dissolved in deionised water. In other embodiments, the material will have such a free swelling capacity of from 8 to 55 g / g, preferably 10 to 50 g / g, more preferably 15 to 50 g / g.

[0112] In one embodiment, the resulting dry cellulose I alginate-containing material will have a retention capacity of from 5 to 45 g / g as measured according to the examples when using an aqueous fluid which is 0.9% NaCI dissolved in deionised water. In other embodiments, the material will have such a retention capacity of from 8 to 40 g / g, preferably 10 to 40 g / g, more preferably 15 to 40 g / g.

[0113] Specific embodiments of the process of the invention are described in more detail with reference to accompanying Figs. 1 to 8. In Fig. 1 , the process involves obtaining brown seaweed (e.g. Laminaria hyperborea') having stipe and leaf portions and separating the stipe and leaf to provide seaweed parts which consist of stipe or leaf only. The stipe and leaf parts are separated by manual or automated cutting, for example using a cutting machine generally used in the art.

[0114] The stipe may be washed to remove epiphytes and then further processed intact. Following size reduction (e.g. by cutting and / or milling), the stipe portions are washed with deionised water to remove salts and other water-soluble components (for example water-soluble sugars). Following initial size reduction to approx. 1 cm (e.g. by cutting), the stipe portions are washed by soaking in deionised water to remove salts and other water-soluble components (e.g. water-soluble sugars). The particle size of the stipe portions is further reduced to approx. 2-3 mm whilst in the washing solution. Further size reduction may be achieved by known methods, such as blending or wet milling of the mixture. Following recovery of the solid fraction from the resulting mixture (e.g. by draining of the liquid), the conductivity of the separated liquid is measured to assess the extent to which salts have been removed from the seaweed. A conductivity of less than 200 pS is considered appropriate for further processing of the solid fraction. If the conductivity exceeds this value, the steps of soaking, further size reduction and water removal can be repeated. The resulting solid phase material that remains is a wet mass that contains cellulose fibres and native alginate. In Fig. 1 this is referred to as the “washed solid fraction” (also referred to herein as the “residual wet residue”). The washed solid fraction is then processed in accordance with any of the conversion processes described with reference to Figs. 2 to 6, followed by drying as described with reference to Fig. 7.

[0115] The leaf material contains alginate having a higher “M” content than that present in the stipe. This is subjected to initial size reduction to approx. 1 cm (e.g. by cutting). The leaf material is then washed by soaking in deionised water at high temperature to remove fucoidan and other water-soluble components (e.g. soluble sugars). The particle size of the leaf portions is further reduced to approx. 2-3 mm whilst in the washing solution. Further size reduction may be achieved by known methods, such as blending of the mixture. Following recovery of the solid fraction from the resulting mixture (e.g. by draining of the liquid), the leaf portions are subjected to further washing by soaking in water at ambient temperature. The solid and liquid fractions are then separated (e.g. by draining of the liquid). The conductivity of the separated liquid is measured to assess the extent to which salts have been removed from the leaf portions. A conductivity of less than 200 pS is considered appropriate for further processing of the solid fraction. If the conductivity exceeds this value, the washing steps can be repeated. The resulting solid phase material that remains is a wet mass that contains cellulose fibres and native alginate. In Fig. 1 this is referred to as the “washed solid fraction” (also referred to herein as the “residual wet residue”). The washed solid fraction is then processed in accordance with any of the conversion processes described with reference to Figs. 2 to 7, followed by drying as described with reference to Fig. 8.

[0116] Figs. 2 to 7 illustrate processes in which the washed solid fraction (the “residual wet residue”) is processed to convert the native alginate to sodium alginate.

[0117] In Fig. 2, deionised water is added to the washed solid fraction followed by the addition to mineral acid to effect cation exchange and convert the native insoluble alginate to alginic acid. Optionally, material is pre-treated with citric acid at low temperature prior to the addition of mineral acid. Following mineral acid treatment the solid fraction is recovered and washed with deionised water to remove excess mineral acid. This washing cycle may be repeated, as required. The recovered solids are then subjected to treatment with a sodium-based alkali to convert the alginic acid to sodium alginate. The sodium-based alkali is added gradually to adjust the pH to 6.5 to 6.7. Following the addition of each aliquot of sodium-based alkali, the mixture is left to stand to equilibrate and the pH is tested. If the pH is too low, an additional aliquot of sodium-based alkali is added. As the pH is brought up to the target, the fluid becomes incorporated into the mass itself and the result is a wet mass which is “sticky” but there is no (or little) fluid present. The resulting solid mass contains cellulose fibres and alginate that remains in the matrix and is present in the soluble sodium form. This solid mass is directly transferred to a suitable drying process.

[0118] In Fig. 3, a high concentration sodium chloride solution is added to the washed solid fraction to convert the native insoluble alginate to sodium alginate. Following mixing, the solid fraction is recovered. Due to the high ionic strength of the surrounding fluid, the alginate that has been converted to the soluble sodium form remains in the seaweed matrix and is not removed on draining (decantation) of the sodium chloride solution. Propan-2-ol is added to the resulting wet mass such that its concentration in the fluid surrounding the solid seaweed particles is at least 50% (e.g. between 55 and 60%). At this concentration, the sodium alginate is not soluble in the fluid and so remains in the seaweed matrix. However, the residual salt is soluble in the water present (for example, which is present in an amount of 40 to 45% of the volume of fluid). Following recovery of the residual solid, this propan-2-ol washing step may be repeated to ensure effective removal of excess sodium chloride. Propan-2-ol is added to the recovered wet mass and then drained. The result is a wet mass which is “sticky” but there is no (or little) fluid present. The resulting solid mass contains cellulose fibres and alginate that remains in the matrix and is present in the soluble sodium form. This solid mass is directly transferred to a suitable drying process.

[0119] In Fig. 4, sodium citrate or di-sodium EDTA is added to the washed solid fraction to convert the native insoluble alginate to sodium alginate. This provides a chelation exchange of calcium ions in the matrix for sodium ions. Following mixing, the pH of the mixture is buffered to a pH of 6.5 to 6.7 either by the addition of a sodium-based alkali or sodium hypochlorite. The resulting solid fraction is recovered. This solid fraction is then washed with deionised water and drained to recover the solid fraction. The resulting solid mass contains cellulose fibres and alginate that remains in the matrix and is present in the soluble sodium form. This solid mass is directly transferred to a suitable drying process. Alternatively, following the addition of di-sodium EDTA and mixing, the resulting solids are recovered. The recovered solids are then washed with deionised water and drained to recover the solid fraction. Deionised water is then added and buffered to a pH of 6.5 to 6.7 by the addition of a sodium-based alkali. Drainage of the excess liquid provides a solid fraction which contains cellulose fibres and alginate that remains in the matrix and is present in the soluble sodium form. This solid mass is directly transferred to a suitable drying process.

[0120] In Fig. 5, a solution containing sodium chloride and citric acid is added to the washed solid fraction to convert the native insoluble alginate to sodium alginate. The presence of citric acid in the surrounding fluid prevents loss of the solubilised alginate from the seaweed matrix. Alginate is not removed on draining (decantation) of the solution to recover the solid fraction. The recovered solid fraction is washed with deionised water and drained. This washing cycle may be repeated, as required. The recovered solids are then subjected to treatment with a sodium-based alkali to adjust the pH to 6.5 to 6.7. Drainage of the excess liquid provides a solid fraction which contains cellulose fibres and alginate that remains in the matrix and is present in the soluble sodium form. This solid mass is directly transferred to a suitable drying process.

[0121] In Fig. 6, a sodium hypochlorite solution is added to the washed solid fraction to convert the native insoluble alginate to sodium alginate. Following mixing, the solid fraction is recovered. This solid fraction is then washed with deionised water and drained to recover the solid fraction. This washing step may be repeated, as required. The resulting solid mass contains cellulose fibres and alginate that remains in the matrix and is present in the soluble sodium form. This solid mass is directly transferred to a suitable drying process.

[0122] In Fig. 7, a sodium hypochlorite solution is added to the washed solid fraction to convert the native insoluble alginate to sodium alginate. Following mixing, the solid fraction is recovered. This solid fraction is then washed with deionised water and drained to recover the solid fraction. The resulting solid is treated with mineral acid to adjust the pH to 1.7 to 1.9. Excess acid is drained and the resulting solid fraction is washed with deionised water. This washing step may be repeated, as required. The recovered solids are then subjected to treatment with a sodium-based alkali to adjust the pH to 6.5 to 6.7. Drainage of the excess liquid provides a solid fraction which contains cellulose fibres and alginate that remains in the matrix and is present in the soluble sodium form. This solid mass is directly transferred to a suitable drying process.

[0123] In Fig. 8, the solid wet mass produced following any of the conversion processes described in Figs. 2 to 7 is processed to form the dry residue containing cellulose and water-soluble alginate having absorbent properties. The solid wet mass is dewatered by solvent dehydration using an alcohol such as propan-2-ol as an antisolvent. Following separation of the solvent (e.g. by draining), the solid fraction is further processed to remove residual solvent, for example by centrifugation or decantation. The resulting solid material is then further dried (e.g. under vacuum at elevated temperature) to provide the final cellulose I alginate-containing material in granular form.

[0124] As a result of the methods used in their preparation, the materials herein described differ from those produced using conventional industrial processes. The invention thus further relates to the absorbent materials obtained as a result of carrying out any of the processes herein described.

[0125] In another aspect, the invention therefore provides an absorbent cellulose I alginate-containing material obtained, obtainable, or directly obtained by any process as herein described.

[0126] Specifically, the invention provides an absorbent cellulose I alginate-containing material, wherein said material comprises cellulose fibres and alginate from a brown seaweed and is obtained by a process comprising at least the following steps:

[0127] (i) providing a brown seaweed, or part thereof;

[0128] (ii) dividing the brown seaweed, or part thereof, into a plurality of portions;

[0129] (iii) washing the plurality of portions with water whereby to remove water- soluble components and recovering the residual wet residue;

[0130] (iv) converting at least a portion of calcium alginate present in said residual wet residue into a water-soluble alginate whereby to provide a residue containing cellulose fibres and water-soluble alginate; and

[0131] (v) de-watering said residue containing cellulose fibres and water-soluble alginate whereby to provide said absorbent cellulose I alginate-containing material.

[0132] In one embodiment, the absorbent cellulose I alginate-containing material is provided in dry, particulate form. In some embodiments, the material may have a water content of less than 20 wt.%, for example less than 15 wt.%. In some embodiments, the material may have a water content in the range of from 1 to 20 wt.%, from 2 to 18 wt.%, from 3 to 17 wt.%, from 4 to 16 wt.%, or from 5 to 15 wt.%, for example about 10 wt.%. The absorbent material will generally be provided in particulate form having a range of particle sizes, i.e. it will be polydisperse. Its average particle size can readily be adjusted according to the intended application. In some embodiments, the material may have an average particle size in the range of several mm, preferably from 1 to 5 mm, for example from 2 to 3 mm. In some embodiments, the material may have an average particle size in the range of from 100 to 1000 pm, or from 200 to 800 pm, or from 200 to 700 pm, or from 250 to 600 pm, e.g. from 250 to 500 pm. Particle size can be determined by known methods, such as those herein described.

[0133] In one embodiment, the absorbent cellulose I alginate-containing material will have a free swelling capacity of from 5 to 60 g / g in the presence of an aqueous fluid which is 0.9% NaCI dissolved in deionised water and as measured according to the method set out in the examples. In other embodiments, the material will have a free swelling capacity, when measured under these conditions, of from 8 to 55 g / g, preferably 10 to 50 g / g, more preferably 15 to 50 g / g.

[0134] In one embodiment, the absorbent cellulose I alginate-containing material will have a retention capacity of from 5 to 45 g / g in the presence of an aqueous fluid which is 0.9% NaCI dissolved in deionised water and as measured according to the method set out in the examples. In other embodiments, the material will have a retention capacity, when measured under these conditions, of from 8 to 40 g / g, preferably 10 to 40 g / g, more preferably 15 to 40 g / g.

[0135] As will be understood, the colour of the absorbent material will depend on the precise method used in its production. Where any bleaching agent is used in the process for conversion of the native alginate to a water-soluble form, the resulting material will be reduced in colour, i.e. it will have a reduced content of pigments. Where appropriate, an additional bleaching step may be performed in order to reduce the colour of the material if it is intended for use in any application that requires a low level of colour. In one embodiment, the absorbent cellulose I alginate-containing material herein described will be “light” in colour. In certain embodiments, the colour of the material may be described as “off-white”, “white” or even “bone white”. Due to the absorbent properties of the cellulose I alginate-containing materials herein described, these find use in a broad range of industrial applications where the ability to absorb and retain a free liquid is desired. Such applications include consumer products, medical products, as well as environmental and agricultural applications. Examples of such products are provided herein but are not intended to be limiting. The invention extends to any product which incorporates or is formed from the absorbent materials herein described.

[0136] Absorbent technology is employed in the hygiene industry for a range of products including, but not limited to, diapers for babies, children and adults (also known as “nappies”), feminine hygiene products such as sanitary pads (“sanitary napkins”) and tampons, incontinence pads, pet pads, etc.

[0137] In the medical sector, absorbent materials are employed in wound dressings, medical bandages and in disposable bed sheets, bed pads, and absorbent pads for chairs.

[0138] In the food industry, absorbent technology is employed in the form of absorbent packaging capable of absorbing moisture or fluids, such as meat or fish juices, released from any food product during transport or storage. Such packaging includes, but is not limited to, absorbent pads (also known as soaker pads), absorbent mats, absorbent liners and absorbent inter-leavers. Absorbent pads may, for example, be used in food display trays which carry fresh or frozen meats, fresh or frozen seafood (e.g. fish), or inside food punnets which carry fresh fruit, and are intended to improve the shelf-life and appearance of the food. Absorbent mats and liners may be used in crates in which fresh or frozen meat or fish is stored and / or transported. Absorbent inter-leavers may be used in the packaging of sliced meats or fish.

[0139] In the environmental and agricultural sectors, absorbent materials may find use in improving water retention in soil.

[0140] Methods for the production of absorbent products or articles which are formed from or incorporate any of the absorbent cellulose I alginate-containing materials herein described also form part of the invention. In a further aspect the invention thus provides a method of producing an absorbent article which is formed from or which incorporates an absorbent cellulose I alginate- containing material which comprises cellulose fibres and alginate from a brown seaweed, said method comprising at least the following steps:

[0141] (i) providing a brown seaweed, or part thereof;

[0142] (ii) dividing the brown seaweed, or part thereof, into a plurality of portions;

[0143] (iii) washing the plurality of portions with water whereby to remove water- soluble components and recovering the residual wet residue;

[0144] (iv) converting at least a portion of calcium alginate present in said residual wet residue into a water-soluble alginate whereby to provide a residue containing cellulose fibres and water-soluble alginate;

[0145] (v) de-watering said residue containing cellulose fibres and water-soluble alginate whereby to provide a dry residue;

[0146] (vi) optionally reducing the particle size of the dry residue; and

[0147] (vii) forming an absorbent article from the resulting absorbent cellulose I alginate-containing material or incorporating the resulting absorbent cellulose I alginate-containing material into an absorbent article.

[0148] Methods for incorporation of absorbent materials into the types of products, for example consumer articles, herein described and which are intended to be used for absorption of fluids depend on the nature of the article or product and are generally well known in the art. The level of incorporation will vary depending on the absorbency required in any given application but can be varied according to need.

[0149] In some embodiments, the absorbent cellulose I alginate-containing material herein described may be formed or shaped into an absorbent sheet, layer, pad or film.

[0150] Such products also form part of the invention.

[0151] In other embodiments, the absorbent cellulose I alginate-containing material herein described will be incorporated (e.g. dispersed or embedded) into a carrier matrix, for example a fibrous carrier matrix, to form a composite material. Such composite materials also form part of the invention. In a further aspect, the invention thus provides a composite material comprising a carrier matrix which incorporates an absorbent cellulose / alginate-containing material as herein described. The carrier matrix may be provided in the form of a sheet, layer, pad or film which may be used as such or which may be incorporated into a final product. The nature of the carrier matrix will depend on the intended use and can readily be selected based on materials generally known and used in the art. Typically, the carrier matrix will be a fibrous matrix which functions as a reservoir to hold liquid until the liquid is absorbed by the absorbent material dispersed therein. The fibrous matrix may, for example, be formed from a hydrophobic polymeric material (e.g. meltblown polyolefin fibres) and / or from cellulosic fibres (e.g. airlaid cellulosic fibres or Kraft cellulose pulp). Fibres commonly known as wood pulp fluff may, for example, form the fibrous matrix. A typical level of incorporation of the absorbent material into the fibrous carrier matrix may be at least 20 wt.%, at least 30 wt.% or at least 50 wt.%.

[0152] As evidenced in the examples, the presence of a calcium salt may further enhance the fluid uptake and retention of a carrier matrix (for example a cellulosic-based carrier) having dispersed therein an absorbent material according to the invention. In one embodiment, any of the composite materials herein described may thus additionally include a water-soluble calcium salt. Examples of suitable calcium salts include, but are not limited to calcium lactate, calcium chloride and calcium sulphate. The calcium salt may be dispersed within the carrier matrix by simple admixture of the carrier material with solid particles of the calcium salt.

[0153] Alternatively, the calcium salt may be dissolved in water and sprayed onto the carrier matrix. The level of incorporation of the calcium salt may be suitably selected by those skilled in the art. In some embodiment, the calcium salt may be present in an amount of at least 0.1 wt.%, for example at least 0.2 wt.%. In some embodiments, the calcium salt may be present in an amount of up to 15 wt.%.

[0154] In the case of a diaper, for example, the absorbent materials herein described may be used in place of known superabsorbent polymers, such as sodium polyacrylate, which are conventionally used in an absorbent core layer of the diaper to absorb and trap urine. Such core layers typically comprise a carrier matrix, such as cotton or Kraft cellulose pulp (“fluff pulp”), which provides an open matrix or channels through which urine can flow to reach the absorbent material embedded therein. An appropriate level of incorporation of the absorbent material in the carrier matrix may be at least 20 wt.%, at least 30 wt.%, at least 50 wt.%, at least 60 wt.% or at least 70 wt.%.

[0155] Any of the articles or products listed herein which incorporate an absorbent material as herein described also form part of the invention.

[0156] In one embodiment, the invention provides a diaper having an absorbent core layer which comprises a carrier matrix having dispersed therein particles of an absorbent cellulose I alginate-containing material as herein described.

[0157] In one embodiment, the invention provides an absorbent food packaging material such as a soaker pad for packaging fresh or frozen meat or fish and which is capable of absorption and retention of exudate from the meat or fish. This product may be provided in the form of a fluid-permeable envelope or sleeve which retains particles of an absorbent cellulose I alginate-containing material as herein described. Fluid-permeable materials for use in the production of soaker pads for foods are well known in the art and may be made from a range of materials including, but not limited to, poly-lactic acid (PLA).

[0158] Use of any of the cellulose I alginate-containing materials herein described as an absorbent also forms part of the invention. In a further aspect the invention thus provides the use of cellulose I alginate-containing material as an absorbent, wherein said material comprises cellulose fibres and alginate from a brown seaweed, and wherein said material is obtained by a process as herein described.

[0159] Use of any of the cellulose I alginate-containing materials herein described as a superabsorbent also forms part of the invention. In a further aspect the invention thus provides the use of cellulose I alginate-containing material as a superabsorbent, wherein said material comprises cellulose fibres and alginate from a brown seaweed, and wherein said material is obtained by a process as herein described.

[0160] The invention will be described in more detail by way of the following non-limiting Examples and the accompanying figures in which: Figure 1 is a flowchart illustrating embodiments of a process to produce a washed solid fraction (“residual wet residue”) from stipe or leaf of brown seaweed.

[0161] Figure 2 is a flowchart illustrating an embodiment of a process in which a washed solid fraction (“residual wet residue”) from stipe or leaf of brown seaweed is processed to provide a residue containing cellulose fibres and sodium alginate. Conversion of native alginate to sodium alginate is performed by acid cation exchange and treatment with a sodium-based alkali. Figure 3 is a flowchart illustrating an embodiment of a process in which a washed solid fraction (“residual wet residue”) from stipe or leaf of brown seaweed is processed to provide a residue containing cellulose fibres and sodium alginate. Conversion of native alginate to sodium alginate is performed by “salt conversion” using sodium chloride.

[0162] Figure 4 is a flowchart illustrating embodiments of a process in which a washed solid fraction (“residual wet residue”) from stipe or leaf of brown seaweed is processed to provide a residue containing cellulose fibres and sodium alginate. Conversion of native alginate to sodium alginate is performed by treatment with sodium citrate or di-sodium EDTA.

[0163] Figure 5 is a flowchart illustrating an embodiment of a process in which a washed solid fraction (“residual wet residue”) from stipe or leaf of brown seaweed is processed to provide a residue containing cellulose fibres and sodium alginate. Conversion of native alginate to sodium alginate is performed by treatment with sodium chloride and citric acid.

[0164] Figure 6 is a flowchart illustrating an embodiment of a process in which a washed solid fraction (“residual wet residue”) from stipe or leaf of brown seaweed is processed to provide a residue containing cellulose fibres and sodium alginate. Conversion of native alginate to sodium alginate is performed by treatment with sodium hypochlorite.

[0165] Figure 7 is a flowchart illustrating an embodiment of a process in which a washed solid fraction (“residual wet residue”) from stipe or leaf of brown seaweed is processed to provide a residue containing cellulose fibres and sodium alginate. Conversion of native alginate to sodium alginate is performed by treatment with sodium hypochlorite.

[0166] Figure 8 is a flowchart illustrating an embodiment of a process to produce an “absorbent cellulose / alginate-containing material” according to the invention from a residue of brown seaweed containing cellulose fibres and sodium alginate. The residue may be produced according to any of the embodiments illustrated in Figs. 2 to 7.

[0167] Figure 9 shows the free swelling capacity of absorbent cellulose I alginate- containing materials according to the invention in the presence of a 0.9% NaCI solution (0.9% NaCI dissolved in deionised water).

[0168] Figure 10 shows the retention capacity of absorbent cellulose I alginate- containing materials according to the invention in the presence of a 0.9% NaCI solution (0.9% NaCI dissolved in deionised water).

[0169] Figure 11 shows a comparison of the theoretical and measured retention capacities for the composite materials produced in Example 17 (“Pulp + Example 1”), (“Pulp + 0.43 wt.% Ca + Example 1”) and (“Pulp + 13.5 wt.% Ca + Example 1”) and for a corresponding composite material which includes sodium polyacrylate (“Polyacrylate + pulp”). Retention capacity is measured in the presence of a 0.9% NaCI solution (0.9% NaCI dissolved in deionised water).

[0170] Figure 12 shows a comparison of the theoretical and measured retention capacities for the composite materials produced in Example 18 (“Pulp + Example 11”), (“Pulp + 0.43 wt.% Ca + Example 11”) and (“Pulp + 13.5 wt.% Ca + Example 11”) and for a corresponding composite material which includes sodium polyacrylate (“Polyacrylate + pulp”). Retention capacity is measured in the presence of a 0.9% NaCI solution (0.9% NaCI dissolved in deionised water).

[0171] Examples

[0172] Materials:

[0173] Kraft cellulose pulp PW411 (“fluff pulp”).

[0174] Industry standard sodium polyacrylate (300 to 700 pm).

[0175] Laminaria hyperborea harvested near Haugesund, Norway.

[0176] Fucus serratus collected from North Landing, Flamborough, UK. Laminaria digitata collected at low tide from North Landing, Flamborough, UK. The sodium-based alkali used in all examples is a saturated solution of sodium carbonate. Measurement methods:

[0177] An analytical balance capable of weighing to 0.001 g was used and all weights were recorded to the nearest 0.01 g. The balance used was a Bonvoisin HZ5003B with a maximum capacity of 500 g.

[0178] Free Swelling

[0179] Free swelling of sample materials was determined according to the following method and calculation:

[0180] Method:

[0181] A 20 ml centrifuge tube was weighed to record its empty weight (W1). A sample of the material (0.2 to 0.5 g) was added to the tube and the weight of the tube + contents was recorded (W2). An aqueous fluid (0.9% NaCI dissolved in deionised water) was added to the sample in the tube. Once swelling started, additional fluid was added to ensure that an excess was always present. The sample was left to equilibrate for a period of 2-4 hours. Using a pipette, all excess fluid was removed from the tube. The tube + sample was reweighed and the weight recorded (W3).

[0182] Calculation:

[0183] The weight of the dry sample (W4) was calculated: W4 = (W2-W1).

[0184] The mass of fluid absorbed by the sample (W5) was calculated: W5 = (W3-W1).

[0185] The % swelling of the sample was calculated: ((W5-W4) / W5)*100.

[0186] The swelling of the sample in g / g (i.e. mass of fluid taken up by the sample based on the mass of the sample) was calculated: (W5 / W4).

[0187] Retention Capacity

[0188] The ability of the sample to retain fluid (i.e. its retention capacity) was determined according to the following method and calculation:

[0189] Method:

[0190] A 20 ml centrifuge tube was weighed to record its empty weight (W1). A sample of the material (0.2 to 0.5 g) was added to the tube and the weight of the tube + contents was recorded (W2). An aqueous fluid (0.9% NaCI dissolved in deionised water) was added to the sample in the tube. Once swelling started, additional fluid was added to ensure that an excess was always present. The sample was left to equilibrate for a period of 2-4 hours. Using a pipette, all excess fluid was removed from the tube. Additional fluid (0.9% NaCI solution or deionised water) was added, and the sample was left to equilibrate for 15 minutes. The tube containing the sample was placed in a centrifuge (Goldenwall 80-2) and centrifuged for 5 minutes at 2500 rpm (g-force 700). Using a pipette, the excess fluid was removed from the tube. The steps of adding additional fluid, centrifugation and removal of excess fluid were repeated (to complete two cycles). The tube + sample was reweighed and the weight recorded (W3).

[0191] Calculation:

[0192] The weight of the dry sample (W4) was calculated: W4 = (W2-W1).

[0193] The mass of fluid absorbed by the sample (W5) was calculated: W5 = (W3-W1). The mass retention (%) of the sample was calculated: ((W5-W4) / W5)*100.

[0194] The swelling of the sample in g / g (i.e. mass of fluid taken up and retained by the sample based on the mass of the sample) was calculated: (W5 / W4).

[0195] Dry matter content

[0196] The amount of dry matter is determined by drying a weighed amount of material at 103°C for 4 hours in a conventional oven. This test can be carried out on material at any stage of the process. This includes raw materials and finished products. The test is carried out in duplicate.

[0197] Materials:

[0198] Drying dish

[0199] Balance (4 place) Oven (1037. 2°C)

[0200] Method:

[0201] 1) Label empty aluminium weighing dish with the sample I.D. and place onto the balance. Record the empty weight (Dish).

[0202] 2) Transfer approximately 5 g of material into the drying dish and record this weight (Dish + Sample). Calculate the weight transferred (Dish + Sample - Dish) and record as (Sample) on record sheet.

[0203] 3) Place dish in oven at 103 7. 2°C and allow drying for 4 hours.

[0204] 4) After 4 hours remove the dish from the oven and allow cooling for 5 minutes. 5) Re-weigh the dish and record the dried weight (DRY).

[0205] 6) Calculate residue weight (Dry - Dish) and record on sheet (RES).

[0206] Result is expressed as solids on drying (dry matter) %: Dry matter % = (Res I Sample) x 100

[0207] Loss of dry matter - alginate yield

[0208] Alginate yield (i.e. the amount of alginate removed) can be quantified either based on the amount of alginate recovered or based on the loss of dry matter from the brown seaweed. The initial step (or steps) of washing the portions of seaweed results in the removal of salts and other water-soluble substances from the seaweed matrix. At this stage, the alginate remains in its native insoluble form and is not removed. The starting point for determining the loss of dry matter, and thus quantifying the amount of alginate extracted, is the dry matter content of the washed seaweed material. As referred to herein, the “loss of dry matter” is thus the difference in the dry matter content of the washed seaweed material (i.e. the “residual wet residue” produced following removal of salts and other water-soluble components in accordance with step (iii) of the process as herein described) and the dry matter content of the final seaweed residue (i.e. the material produced following completion of step (v) of the process as herein described).

[0209] In the processes herein described for production of the absorbent cellulose I alginate-containing materials, the intention is not to extract and recover alginate from the brown seaweed but to convert the native insoluble alginate to a soluble form and to retain at least a proportion of the soluble form of the alginate in the final material. Generally, the aim is therefore to reduce the alginate yield, i.e. the amount of alginate recovered from the seaweed. However, some unintentional loss of alginate from the seaweed matrix can occur and is acceptable. Indeed, the extent of the loss in alginate (and thus the amount of water-soluble alginate that remains in the seaweed matrix) may be tailored to adjust the absorbent properties of the final material according to need. The extent of any loss will depend on the type of brown seaweed (or part thereof) and the process conditions used to produce the cellulose / alginate-containing material.

[0210] Loss of dry matter is determined as follows: Initial dry matter content: the dry matter content of the material is determined after washing, i.e. following removal of water-soluble components, according to the method specified under “dry matter content”.

[0211] Final dry matter content: the dry matter content of the final material is determined according to the method specified under “dry matter content”.

[0212] Loss of dry matter % = (difference between initial and final dry matter content I initial dry matter content) x 100

[0213] Where ranges for loss of dry matter are recorded in any of the examples, these are based on multiple repeats performed under the same conditions. As will be appreciated, variability can arise due to the natural variability in the composition of the biomass itself (it is a non-homogeneous material). Where discrete values are recorded, these arise from a single test. In cases where the recovery of product exceeds 100% of the initial dry matter content, this may arise due to the existence of process chemical residues such as salt and sodium carbonate in the final dried product, or due to small weighing errors and experimental repeatability tolerances in the analysis methods.

[0214] Particle size

[0215] Particle size was estimated by eye, but can be determined by methods such as “sieve analysis” in which a sample is shaken on a stack of sieves of graduated size (largest at the top and smallest on the bottom). These are weighed empty and then at the end of the test to allow the determination of the mass (and hence %) retained at each level. Industry standards which may be followed in respect of the measurement of particle size of the type of materials herein described are as follows: ISO 19.120 or ASTM 214.

[0216] Example 1

[0217] Preparation of absorbent cellulose / alginate-containing material from stipe of Laminaria hyperborea

[0218] Acid cation exchange: HCI

[0219] Alginate conversion: sodium-based alkali; pH = 6.6-6.7

[0220] No alginate extraction

[0221] Propan-2-ol drying Method - Stage 1:

[0222] Frozen stipe from L. hyperborea was milled using a Ninja food processor model BN650K (800W) to produce approx. 1 cm pieces. These were then soaked for 30 minutes in deionised water at ambient temperature, while stirring using a VEVOR JJ-1 overhead stirrer, followed by blending to reduce the particle size with a Tefal “Blendforce” BL42 blender (600W) using 2 x 5 second bursts per cycle. Water was then drained from the sample to recover the solid fraction. The conductivity of the drained water was measured using a Hanna instruments model “Primo 5” conductivity meter (scale 0 to 2000 pS). The steps of soaking, blending to reduce the particle size and water removal were repeated until the water conductivity was less than 200 pS. The particle size of the resulting solid fraction was in the range of about 2-3 mm.

[0223] Method - Stage 2:

[0224] Deionised water was added to the resulting product in a ratio of 2:1 (water : solid), followed by the addition of HCI to obtain a pH of between 1.7 to 1.9 as measured using a Hanna instruments pH checker (model number HI98103). After a period of 20 minutes at ambient temperature, the acid water was drained and the solid fraction was recovered. An additional quantity of deionised water was added to the resulting solid fraction in a ratio of 2:1 (water : solid), followed by mixing for 10 minutes at ambient temperature, draining of acid water and recovering of the solid fraction. This water washing step was repeated.

[0225] The resulting product was then centrifuged for 5 minutes using a “SIA Centri 772 SEK” spin dryer (2800 rpm generating a g-force of 960) to remove as much free water as possible. The solid fraction was neutralised with a sodium-based alkali to adjust the pH to between 6.6 to 6.7, followed by drying to recover the final product. Drying was achieved by mixing the “wet” sample with propan-2-ol at a ratio of 1:1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm. Recovery after conversion from dry matter following washing: 95-105%.

[0226] Loss of dry matter: 5% or less. No loss in alginate.

[0227] The final product was a brown / green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0228] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0229] Example 2

[0230] Preparation of absorbent cellulose / alginate-containing material from stipe of Laminaria hyperborea

[0231] Citric acid pre-treatment: 1% citric acid solution; T= 20-25°C; t = 60 minutes Acid cation exchange: HCI

[0232] Alginate conversion: sodium-based alkali; pH = 6.6-6.7

[0233] No alginate extraction

[0234] Propan-2-ol drying

[0235] The method of Example 1 was repeated but with an additional citric acid pretreatment step prior to acid cation exchange. The solid fraction from Stage 1 was treated with 1% citric acid solution at ambient temperature for 60 minutes. The resulting mixture was then drained to remove excess solution and the solid fraction was recovered. This solid fraction was then subjected to the treatment set out in Example 1 to obtain the final product.

[0236] Recovery after conversion from dry matter following washing: 98-101%. Loss of dry matter: 2% or less. No loss in alginate. The final product was a pale green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0237] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0238] Example 3

[0239] Preparation of absorbent cellulose / alginate-containing material from stipe of Laminaria hyperborea

[0240] Alginate conversion: 10% NaCI; T = 20-25°C; t = 60 minutes No alginate extraction Direct vacuum drying

[0241] Method - Stage 1:

[0242] This was performed as set out in Example 1.

[0243] Method - Stage 2:

[0244] A 10% NaCI solution was added to the solid product from Stage 1 in a ratio of 2:1, followed by mixing at ambient temperature for 60 minutes using a VEVOR JJ-1 overhead stirrer. The salt solution was then drained and the solid fraction was recovered. The solid fraction was then washed with 50% propan-2-ol (to remove excess NaCI but not alginate), mixed for 10 minutes at ambient temperature and drained to recover the solid fraction. The washing step with 50% propan-2-ol was repeated. The resulting solid portion was then dried by mixing the “wet” sample with propan-2-ol at a ratio of 1 :1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then be recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approximately 500 pm.

[0245] Recovery after conversion from dry matter following washing: 105%.

[0246] Loss of dry matter: 0%. No loss in alginate.

[0247] The final product was a pale green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0248] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0249] Recovery after conversion from dry matter after washing: 105% (increase in dry matter resulting from residual excess NaCI).

[0250] Example 4

[0251] Preparation of absorbent cellulose / alginate-containing material produced from stipe of Laminaria hyperborea

[0252] Alginate conversion: 1% sodium citrate; T= 20-25°C; t = 60 minutes; followed by sodium-based alkali, pH = 6.6-6.7

[0253] No alginate extraction

[0254] Propan-2-ol drying

[0255] Method - Stage 1:

[0256] This was performed as set out in Example 1.

[0257] Method - Stage 2: A 1% sodium citrate solution was added to the solid product from Stage 1 in a ratio of 2: 1 , followed by mixing at ambient temperature for 60 minutes using a VEVOR JJ-1 overhead stirrer. The solution was then buffered to a pH of 6.6 to 6.7 with a sodium-based alkali (pH measured using a Hanna instruments pH checker, model number HI98103). The solution was then drained, and the solid fraction was recovered. The solid fraction was then washed with deionised water in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ- 1 overhead stirrer and drained to recover the solid fraction. The resulting solid portion was then dried by mixing the “wet” sample with propan-2-ol at a ratio of 1 :1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then be recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approximately 500 pm.

[0258] Recovery after conversion from dry matter following washing: 101%. Loss of dry matter: 0%. No loss in alginate.

[0259] The final product was a pale green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a loosely cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0260] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0261] Example 5

[0262] Preparation of absorbent cellulose / alginate-containing material from stipe of

[0263] Laminaria hyperborea Alginate conversion: 2% NaCI + 5% citric acid; T= 20-25°C; t = 60 minutes; followed by sodium-based alkali, pH = 6.6-6.7

[0264] No alginate extraction Propan-2-ol drying

[0265] Method - Stage 1:

[0266] This was performed as set out in Example 1.

[0267] Method - Stage 2:

[0268] A solution containing 2% NaCI and 5% citric acid was added to the solid product from Stage 1 in a ratio of 2:1, followed by mixing at ambient temperature for 60 minutes using a VEVOR JJ-1 overhead stirrer. The solution was then drained, and the solid fraction was recovered. The solid fraction was then washed by adding deionised water in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ-1 overhead stirrer and drained to recover the solid fraction. The wash process was then repeated, then drained to recover the solid fraction. Sodium-based alkali was then added to the solid fraction to achieve a pH of 6.6 to 6.7 (pH measured using a Hanna instruments pH checker, model number HI98103). The solid portion was then dried by mixing the “wet” sample with propan- 2-ol at a ratio of 1:1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0269] Recovery after conversion from dry matter following washing: 101%. Loss of dry matter: 0%. No loss in alginate.

[0270] The final product was a pale green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel. Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0271] Example 6

[0272] Preparation of absorbent cellulose / alginate-containing material from stipe of Laminaria hyperborea

[0273] Alginate conversion: 1% sodium hypochlorite; T= 20-25°C; t = 60 minutes No alginate extraction

[0274] Propan-2-ol drying

[0275] Method - Stage 1:

[0276] This was performed as set out in Example 1.

[0277] Method - Stage 2:

[0278] A 1% sodium hypochlorite bleaching solution was added to the solid product from Stage 1 in a ratio of 2:1 , followed by mixing at ambient temperature for 60 minutes using a VEVOR JJ-1 overhead stirrer. The bleaching solution was then drained, and the solid fraction was recovered. Deionised water was then added to the solid fraction in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ-1 overhead stirrer and then drained to recover the solid fraction. The solid fraction was then washed with deionised water in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ-1 overhead stirrer and drained to recover the solid fraction. The resulting solid portion was then dried by mixing the “wet” sample with propan-2-ol at a ratio of 1:1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for reuse). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm. Recovery after conversion from dry matter following washing: 75%.

[0279] Loss of dry matter: 25%. Unintentional loss of some alginate (some free alginate was found in the recovered bleaching solution).

[0280] The final product was a white granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0281] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0282] Example 7

[0283] Preparation of absorbent cellulose / alginate-containing material from stipe of Laminaria hyperborea

[0284] Alginate conversion: 5% di-sodium EDTA; T= 20-25°C; t = 60 minutes; followed by sodium-based alkali; pH = 6.6-6.7

[0285] No alginate extraction

[0286] Propan-2-ol drying

[0287] Method - Stage 1:

[0288] This was performed as set out in Example 1.

[0289] Method - Stage 2:

[0290] A 5% di-sodium EDTA solution (APC Pure, 98%) was added to the solid product from Stage 1 in a ratio of 2:1 , followed by mixing at ambient temperature for 60 minutes using a VEVOR JJ-1 overhead stirrer. The Na EDTA solution was then drained and the solid fraction was recovered. Deionised water was then added to the solid fraction in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ-1 overhead stirrer, and then drained to recover the solid fraction. The solid fraction was then washed with deionised water in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ- 1 overhead stirrer and then buffered to a pH of 6.6 to 6.7 with a sodium-based alkali (pH measured using a Hanna instruments pH checker, model number HI98103). The resulting mixture was drained to recover the solid fraction. The resulting solid portion was then dried by mixing the “wet” sample with propan-2-ol at a ratio of 1 :1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0291] Recovery after conversion from dry matter following washing: 92%.

[0292] Loss of dry matter: 8%. Unintentional loss of small amount of alginate (some free alginate found in the recovered treatment solution).

[0293] The final product was a pale green / brown granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0294] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0295] Example 8

[0296] Preparation of absorbent cellulose / alginate-containing material from stipe of Laminaria hyperborea

[0297] Alginate conversion: 1% sodium citrate; T= 20-25°C; t = 60 minutes; followed by 1% sodium hypochlorite; pH = 6.6-6.7 No alginate extraction

[0298] Propan-2-ol drying

[0299] Method - Stage 1:

[0300] This was performed as set out in Example 1.

[0301] Method - Stage 2:

[0302] A 1% sodium citrate solution was added to the solid product from Stage 1 in a ratio of 2: 1 , followed by mixing at ambient temperature for 60 minutes using a VEVOR JJ-1 overhead stirrer. The mixture was buffered to a pH of 6.6 to 6.7 with 1% sodium hypochlorite (pH measured using a Hanna instruments pH checker, model number HI98103), then drained and the solid fraction was recovered. The solid fraction was then washed with deionised water in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature and drained to recover the solid fraction.

[0303] The resulting solid portion was then dried by mixing the “wet” sample with propan-2- ol at a ratio of 1 :1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0304] Recovery after conversion from dry matter following washing: 87%.

[0305] Loss of dry matter: 13%. Unintentional loss of some alginate (some free alginate found in the recovered treatment solution).

[0306] The product was a white granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a loosely cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0307] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0308] Example 9

[0309] Preparation of absorbent cellulose / alginate-containing material from stipe of Laminaria hyperborea

[0310] Alginate conversion: 1% sodium hypochlorite; T= 20-25°C; t = 60 minutes; followed by acid cation exchange with HCI; followed by sodium-based alkali; pH = 6.6-6.7

[0311] No alginate extraction Propan-2-ol drying

[0312] Method - Stage 1:

[0313] This was performed as set out in Example 1.

[0314] Method - Stage 2:

[0315] A 1% sodium hypochlorite bleaching solution was added to the solid product from Stage 1 in a ratio of 2:1 , followed by mixing at ambient temperature for 60 minutes using a VEVOR JJ-1 overhead stirrer. The bleaching solution was then drained and the solid fraction was recovered. Deionised water was then added to the solid fraction in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ-1 overhead stirrer, then drained to recover the solid fraction. Deionised water was then added to the solid fraction in a ratio of 2:1 (water : solid), followed by HCI to adjust the pH of the mixture to between 1.7 to 1.9 and mixed using a VEVOR JJ-1 overhead stirrer (pH measured using a Hanna instruments pH checker, model number HI98103). After a period of 20 minutes, the acid water was drained and the solid fraction was recovered. Deionised water was then added to the solid fraction in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ-1 overhead stirrer, then drained to recover the solid fraction. The washing step using deionised water was then repeated. The resulting solid mass was neutralised with a sodium-based alkali to adjust the pH to a target pH of 6.6 to 6.7 as measured using a Hanna instruments pH checker, model number HI98103. The resulting solid portion was then dried by mixing the “wet” sample with propan-2-ol at a ratio of 1 :1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0316] Recovery after conversion from dry matter following washing: 64%.

[0317] Loss of dry matter: 36%. Unintentional loss of alginate (some free alginate found in the recovered bleaching solution).

[0318] The final product was a white granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0319] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0320] Example 10

[0321] Preparation of absorbent cellulose / alginate-containing material from leaf of

[0322] Laminaria hyperborea

[0323] Acid cation exchange: HCI

[0324] Alginate conversion: Sodium-based alkali; pH = 6.6-6.7

[0325] No alginate extraction

[0326] Propan-2-ol drying

[0327] Method - Stage 1:

[0328] Frozen leaf from L. hyperborea was milled using a Ninja food processor model BN650K (800W) to produce approx. 1 cm pieces. The leaf pieces were then soaked for 30 minutes in deionised water at 60°C using a 9L water heater model number MIS882. Stirring was maintained with a VEVOR JJ- 1 overhead stirrer to ensure free movement of the material. Excess water was drained and the solid fraction recovered. The recovered solid fraction was soaked for 15 minutes in deionised water at ambient temperature, excess water was drained, and the solid fraction recovered. These steps were repeated to provide two complete treatment cycles at 60°C. Following the second treatment cycle, the conductivity of the drained water was measured using a Hanna instruments model “Primo 5” conductivity meter (scale 0 to 2000 pS). The step of washing at ambient temperature and water removal were repeated until the water conductivity was less than 200 pS. The resulting solid fraction was milled to reduce the particle size of the material to between about 2-3 mm by blending to reduce the particle size with a Tefal “Blendforce” BL42 blender (600W), using 2 x 5 second bursts per cycle.

[0329] Method - Stage 2:

[0330] Deionised water was added to the resulting product in a ratio of 2:1 (water : solid), followed by the addition of HCI to obtain a pH of between 1.7 to 1.9 as measured using a Hanna instruments pH checker, model number HI98103. After a period of 20 minutes at ambient temperature, the acid water was drained, and the solid fraction was recovered. An additional quantity of deionised water was added to the resulting solid fraction in a ratio of 2:1 (water : solid), followed by mixing for 10 minutes at ambient temperature, draining of acid water and recovering of the solid fraction. This water washing step was repeated. The resulting product was then centrifuged for 5 minutes using a “SIA Centri 772 SEK” spin dryer (2800 rpm generating a g-force of 960) to remove as much free water as possible. The solid fraction was neutralised with a sodium-based alkali to adjust the pH to between 6.6 to 6.7, followed by drying to recover the final product. Drying was achieved by mixing the “wet” sample with propan-2-ol at a ratio of 1 :1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0331] Recovery after conversion from dry matter following washing: 95-105%.

[0332] Loss of dry matter: 5% or less. No loss in alginate.

[0333] The final product was a brown / green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0334] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0335] Example 11

[0336] Preparation of absorbent cellulose / alginate-containing material from leaf of Laminaria hyperborea

[0337] Citric acid pre-treatment: 1% anhydrous citric acid; T= 20-25°C; t = 60 minutes Acid cation exchange: HCI

[0338] Alginate conversion: sodium-based alkali; pH = 6.6-6.7

[0339] No alginate extraction

[0340] Propan-2-ol drying

[0341] Method - Stage 1:

[0342] This was performed as set out in Example 10.

[0343] Method - Stage 2:

[0344] The solid fraction was added to a solution containing 1% anhydrous citric acid (APC pure, BP / LISP grade 99.5 to 100.5%) in a ratio of 2:1, and stirred at ambient temperature (18 to 25°C) for 60 minutes using a VEVOR JJ-1 overhead stirrer.

[0345] After 60 minutes the acid water was drained and the solid fraction was recovered. An additional quantity of deionised water was added to the resulting solid fraction in a ratio of 2:1 (water : solid), followed by mixing for 10 minutes at ambient temperature, draining of acid water and recovering of the solid fraction. Deionised water was added to the resulting product in a ratio of 2:1 (water : solid), followed by the addition of HCI to obtain a pH of between 1.7 to 1.9 as measured using a Hanna instruments pH checker, model number HI98103. After a period of 20 minutes at ambient temperature, the acid water was drained, and the solid fraction was recovered. An additional quantity of deionised water was added to the resulting solid fraction in a ratio of 2:1 (water : solid), followed by mixing for 10 minutes at ambient temperature, draining of acid water and recovering of the solid fraction. This water washing step was repeated. The resulting product was then centrifuged for 5 minutes using a “SIA Centri 772 SEK” spin dryer (2800 rpm generating a g-force of 960) to remove as much free water as possible. The solid fraction was neutralised with a sodium-based alkali to adjust the pH to between 6.6 to 6.7, followed by drying to recover the final product. Drying was achieved by mixing the “wet” sample with propan-2-ol at a ratio of 1 :1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0346] Recovery after conversion from dry matter following washing: 95-99%. Loss of dry matter: 5% or less. No loss in alginate.

[0347] The product was a brown / green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0348] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0349] Example 12

[0350] Preparation of absorbent cellulose / alginate-containing material from leaf of Laminaria hyperborea

[0351] Alginate conversion: 1% sodium hypochlorite; T= 20-25°C; t = 60 minutes No alginate extraction

[0352] Propan-2-ol drying

[0353] Method - Stage 1:

[0354] This was performed as set out in Example 10.

[0355] Method - Stage 2:

[0356] A 1% sodium hypochlorite bleaching solution was added to the solid product from Stage 1 in a ratio of 2:1 , followed by mixing at ambient temperature for 60 minutes using a VEVOR JJ-1 overhead stirrer. The bleaching solution was then drained and the solid fraction was recovered. Deionised water was then added to the solid fraction in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ-1 overhead stirrer, then drained to recover the solid fraction.

[0357] The solid fraction was then washed with deionised water in a ratio of 2:1 (water : solid), mixed for 10 minutes at ambient temperature using a VEVOR JJ-1 overhead stirrer and drained to recover the solid fraction. The resulting solid portion was then dried by mixing the “wet” sample with propan-2-ol at a ratio of 1:1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for reuse). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0358] Recovery after conversion from dry matter following washing: 26%. Loss of dry matter: 74%. Unintentional loss of alginate (some free alginate found in the recovered bleaching solution).

[0359] The product was a brown / green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0360] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0361] Example 13

[0362] Preparation of absorbent cellulose / alginate-containing material from whole Fucus serratus

[0363] Citric acid pre-treatment: 1% anhydrous citric acid; T= 20-25°C; t = 60 minutes Acid cation exchange: HCI

[0364] Alginate conversion: sodium-based alkali; pH = 6.6-6.7

[0365] No alginate extraction

[0366] Propan-2-ol drying

[0367] Method - Stage 1:

[0368] This stage was performed as set out in Example 10.

[0369] Method - Stage 2:

[0370] The solid fraction was added to a solution containing 1% anhydrous citric acid (APC pure, BP / USP grade 99.5 to 100.5%) in a ratio of 2:1, and stirred at ambient temperature (18 to 25°C) for 60 minutes using a VEVOR JJ-1 overhead stirrer.

[0371] After 60 minutes the acid water was drained, and the solid fraction was recovered. An additional quantity of deionised water was added to the resulting solid fraction in a ratio of 2:1 (water : solid), followed by mixing for 10 minutes at ambient temperature, draining of acid water and recovering of the solid fraction. Deionised water was added to the resulting product in a ratio of 2:1 (water : solid), followed by the addition of HCI to obtain a pH of between 1.7 to 1.9 as measured using a Hanna instruments pH checker, model number HI98103. After a period of 20 minutes at ambient temperature, the acid water was drained, and the solid fraction was recovered. An additional quantity of deionised water was added to the resulting solid fraction in a ratio of 2:1 (water : solid), followed by mixing for 10 minutes at ambient temperature, draining of acid water and recovering of the solid fraction. This water washing step was repeated. The resulting product was then centrifuged for 5 minutes using a “SIA Centri 772 SEK” spin dryer (2800 rpm generating a g-force of 960) to remove as much free water as possible. The solid fraction was neutralised with a sodium-based alkali to adjust the pH to between 6.6 to 6.7, followed by drying to recover the final product. Drying was achieved by mixing the “wet” sample with propan-2-ol at a ratio of 1 :1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was then recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0372] Recovery after conversion from dry matter following washing: 98%. Loss of dry matter: 2%. No alginate loss.

[0373] The final product was a brown / green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a loosely cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0374] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained: Example 14

[0375] Preparation of absorbent cellulose / alginate-containing material from stipe of Laminaria digitata

[0376] Citric acid pre-treatment: 1% citric acid solution; T= 20-25°C; t = 60 minutes Acid cation exchange: HCI

[0377] Alginate conversion: sodium-based alkali; pH = 6.6-6.7

[0378] No alginate extraction

[0379] Propan-2-ol drying

[0380] The method of Example 1 was repeated but with an additional citric acid pretreatment step prior to acid cation exchange. The solid fraction from Stage 1 was treated with 1% citric acid solution at ambient temperature for 60 minutes. The resulting mixture was then drained to remove excess solution and the solid fraction was recovered. This solid fraction was then subjected to the treatment set out in Example 1.

[0381] Recovery after conversion from dry matter following washing: 99%.

[0382] Loss of dry matter: 1%. No alginate loss.

[0383] The final product was a brown / green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0384] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0385] Example 15

[0386] Preparation of absorbent cellulose / alginate-containing material from leaf of

[0387] Laminaria digitata Citric acid pre-treatment: 1% anhydrous citric acid; T= 20-25°C; t = 60 minutes Acid cation exchange: HCI

[0388] Alginate conversion: sodium-based alkali; pH = 6.6-6.7 No alginate extraction Propan-2-ol drying

[0389] Method - Stage 1:

[0390] This stage was performed as set out in Example 10.

[0391] Method - Stage 2:

[0392] The solid fraction was added to a solution containing 1% anhydrous citric acid (APC pure, BP / LISP grade 99.5 to 100.5%) in a ratio of 2:1, and stirred at ambient temperature (18 to 25°C) for 60 minutes using a VEVOR JJ-1 overhead stirrer. After 60 minutes the acid water was drained, and the solid fraction was recovered. An additional quantity of deionised water was added to the resulting solid fraction in a ratio of 2:1 (water : solid), followed by mixing for 10 minutes at ambient temperature, draining of acid water and recovering of the solid fraction. Deionised water was added to the resulting product in a ratio of 2:1 (water : solid), followed by the addition of HCI to obtain a pH of between 1.7 to 1.9 as measured using a Hanna instruments pH checker, model number HI98103. After a period of 20 minutes at ambient temperature, the acid water was drained, and the solid fraction was recovered. An additional quantity of deionised water was added to the resulting solid fraction in a ratio of 2:1 (water : solid), followed by mixing for 10 minutes at ambient temperature, draining of acid water and recovering of the solid fraction. This water washing step was repeated.

[0393] The resulting product was then centrifuged for 5 minutes using a “SIA Centri 772 SEK” spin dryer (2800 rpm generating a g-force of 960) to remove as much free water as possible. The solid fraction was neutralised with a sodium-based alkali to adjust the pH to between 6.6 to 6.7, followed by drying to recover the final product. Drying was achieved by mixing the “wet” sample with propan-2-ol at a ratio of 1:1 in a sealed container and allowing to equilibrate for 5 minutes. The solvent was recovered by filtration and the solid portion centrifuged again for 5 minutes to remove any remaining excess liquid (all recovered solvent was recycled by evaporation for re-use). The centrifuged sample was then dried under vacuum (100 mbar) at a temperature of 70°C for approx. 2 hours. The particle size of the dried material was reduced further using a “Cosicosy” coffee grinder (350W) for 30 seconds to obtain a final particle size of approx. 500 pm.

[0394] Recovery after conversion from dry matter following washing: 97%.

[0395] Loss of dry matter: 3%. No alginate loss.

[0396] The final product was a brown / green granular material with a residual moisture content of less than 10%. When mixed with water and treated with a 20% calcium chloride solution, a firm highly cohesive gel was formed. This evidences the presence of sufficient alginate bearing G-blocks which are capable of forming a gel.

[0397] Free swelling and retention capacities were determined and compared to a sample of sodium polyacrylate (300 to 700 pm). The following results were obtained:

[0398] Example 16

[0399] Effect of salt on free swelling capacity of absorbent cellulose / alginate- containing materials of Examples 1 and 10 vs. sodium polyacrylate

[0400] Superabsorbent polymers such as sodium polyacrylate can absorb many times their own weight in pure water, typically in the range from at least 200 to 1000 times. This is not the case, however, where the water contains electrolytes such as salts which are known to restrict their capability to absorb free fluid. Industry standards require that superabsorbent polymers are tested for their free swelling capacity when exposed to 0.9% sodium chloride. This is representative of the functionality of these polymers in the presence of fluids that they may be expected to cope with when in use, such as in diapers or other incontinence products.

[0401] Tests were conducted to compare this loss in functionality for sodium polyacrylate against the absorbent cellulose I alginate-containing materials produced according to the invention. A sample of sodium polyacrylate was exposed to pure water and its free swelling capacity was measured. Another aliquot of the same sample was also exposed to a 0.9% solution of sodium chloride and its free swelling capacity measured. The difference between the two measurements was used to calculate the “%” loss of functionality when exposed to the 0.9% sodium chloride solution. As a comparison, the same experiment was performed with the materials produced in Examples 1 and 10. The results are set out in the following table:

[0402] As demonstrated, the sample of sodium polyacrylate loses 87.3% of its absorption capacity when exposed to a 0.9% sodium chloride solution. By comparison, the absorbent materials of Examples 1 and 10 show very little change in their free swelling capacity when exposed to a 0.9% sodium chloride solution. This demonstrates their resistance to electrolytic effects and evidences their suitability for use in the presence of electrolytes.

[0403] Example 17

[0404] Preparation and testing of composite materials containing absorbent cellulose / alginate-containing material of Example 1 with and without added calcium salt vs. composite materials containing sodium polyacrylate

[0405] Preparation and testing of absorbent composite material (no added calcium salt):

[0406] The dry cellulose I alginate-containing absorbent material produced in Example 1 was mixed with dry Kraft cellulose pulp PW411 to produce an absorbent composite material with a target composition of approx. 70 wt.% Kraft cellulose pulp 130 wt.% absorbent material. Once mixed the actual calculated composition was 63.8 wt.% Kraft cellulose / 36.2 wt.% absorbent.

[0407] From the masses of the individual components and their previously determined free swelling and retention capacities, the theoretical values for the final composition were calculated. The retention capacity of the combination was determined and compared to the theoretical figures and that of a sample of the Kraft cellulose pulp PW411. The following results were obtained:

[0408] Preparation and testing of absorbent composite material (with low dose calcium salt addition):

[0409] 3.01 g of Kraft cellulose pulp PW 411 was added to 300 ml of 0.11% calcium lactate solution and allowed to equilibrate for 5 minutes. The wet pulp was removed and squeezed to remove excess fluid then weighed to determine the total amount of lactate solution present in the wet mass. The wet pulp was then dried at 60°C under vacuum at 100 mbar for 6 hours to remove all excess water and provide a calcium-impregnated Kraft cellulose pulp. The calculated calcium lactate content of the dried pulp was 0.43 wt.%.

[0410] The dry cellulose I alginate-containing absorbent material produced in Example 1 was mixed with the calcium-impregnated Kraft cellulose pulp to produce an absorbent composite material with a target composition of approx. 70 wt.% Kraft cellulose pulp 130 wt.% absorbent material. Once mixed the actual calculated composition was 64.0 wt.% Kraft cellulose / 36.0 wt.% absorbent.

[0411] From the masses of the individual components and their previously determined free swelling and retention capacities, the theoretical values for the final composition were calculated. The retention capacity of the combination was determined and compared to the theoretical figures and that of a sample of the Kraft cellulose pulp PW411. The following results were obtained: Preparation and testing of absorbent composite material (with high dose calcium salt addition):

[0412] 3.09 g of Kraft cellulose pulp was added to 300 ml of 3.09% calcium lactate solution and allowed to equilibrate for 5 minutes. The wet pulp was removed and squeezed to remove excess fluid then weighed to determine the total amount of lactate solution present in the wet mass. The wet pulp was then dried at 60°C under vacuum at 100 mbar for 6 hours to remove all excess water and provide a calcium- impregnated Kraft cellulose pulp. The calculated calcium lactate content of the dried pulp was 13.52 wt.%.

[0413] The dry cellulose I alginate-containing absorbent material produced in Example 1 was mixed with the calcium-impregnated Kraft cellulose pulp to produce an absorbent composite material with a target composition of approx. 70 wt.% Kraft cellulose pulp 130 wt.% absorbent material. Once mixed the actual calculated composition was 64.3 wt.% Kraft cellulose 135.7 wt.% absorbent.

[0414] From the masses of the individual components and their previously determined free swelling and retention capacities, the theoretical values for the final composition were calculated. The retention capacity of the combination was determined and compared to the theoretical figures and that of a sample of the Kraft cellulose pulp PW411. The following results were obtained:

[0415] Preparation and testing of composite material based on Kraft cellulose pulp and industry standard sodium polyacrylate (300 to 700 pm):

[0416] Dry Kraft cellulose pulp and sodium polyacrylate were mixed with a target composition of approx. 70 wt.% Kraft cellulose 130 wt.% sodium polyacrylate. Once mixed the actual calculated composition was 66.6 wt.% Kraft cellulose 133.4 wt.% sodium polyacrylate. From the masses of the individual components and their determined free swelling and retention capacities, the theoretical values for the composite material were calculated. The retention capacity of the composite material was tested and compared to the theoretical figures. The following results were obtained:

[0417] Results and Discussion:

[0418] Figure 11 provides a comparison of the retention capacity of the composite materials tested in this Example. A further enhancement when using the alginate I cellulose-containing material according to Example 1 vs. sodium polyacrylate (“polyacrylate”) is observed when they are dispersed in a Kraft cellulose pulp matrix.

[0419] As expected, the measured values for the polyacrylate + pulp are close to the calculated theoretical values (theoretical 5.6 g / g vs. measured 5.7 g / g). This demonstrates that there is no interaction between these materials and that the pulp simply serves as a carrier for the superabsorbent polymer. However, this is not the case with the alginate I cellulose-containing material + pulp in which the measured values exceed the theoretical values by at least a factor of 2. The presence of calcium ions in the pulp further enhances the retention capacity of this composite material.

[0420] Example 18

[0421] Preparation and testing of composite materials containing absorbent cellulose / alginate-containing material of Example 11 with and without added calcium salt vs. composite materials containing sodium polyacrylate Preparation and testing of absorbent composite material (no added calcium salt):

[0422] The dry cellulose I alginate-containing absorbent material produced in Example 11 was mixed with dry Kraft cellulose pulp PW411 to produce an absorbent composite material with a target composition of approx. 70 wt.% Kraft cellulose pulp 1 30 wt.% absorbent material. Once mixed the actual calculated composition was 61 .5 wt.% Kraft cellulose / 38.5 wt.% absorbent.

[0423] From the masses of the individual components and their previously determined free swelling and retention capacities, the theoretical values for the final composition were calculated. The retention capacity of the combination was determined and compared to the theoretical figures and that of a sample of the Kraft cellulose pulp PW411 . The following results were obtained:

[0424] Preparation and testing of absorbent composite material (with low dose calcium salt addition):

[0425] 3.01 g of Kraft cellulose pulp PW 411 was added to 300 ml of 0.11 % calcium lactate solution and allowed to equilibrate for 5 minutes. The wet pulp was removed and squeezed to remove excess fluid then weighed to determine the total amount of lactate solution present in the wet mass. The wet pulp was then dried at 60°C under vacuum at 100 mbar for 6 hours to remove all excess water and provide a calcium-impregnated Kraft cellulose pulp. The calculated calcium lactate content of the dried pulp was 0.43 wt.%.

[0426] The dry cellulose I alginate-containing absorbent material produced in Example 11 was mixed with the calcium-impregnated Kraft cellulose pulp to produce an absorbent composite material with a target composition of approx. 70 wt.% Kraft cellulose pulp 130 wt.% absorbent material. Once mixed the actual calculated composition was 62.6 wt.% Kraft cellulose / 37.4 wt.% absorbent. From the masses of the individual components and their previously determined free swelling and retention capacities, the theoretical values for the final composition were calculated. The retention capacity of the combination was determined and compared to the theoretical figures and that of a sample of the Kraft cellulose pulp PW411. The following results were obtained:

[0427] Preparation and testing of absorbent composite material (with high dose calcium salt addition):

[0428] 3.09 g of Kraft cellulose pulp was added to 300 ml of 3.09% calcium lactate solution and allowed to equilibrate for 5 minutes. The wet pulp was removed and squeezed to remove excess fluid then weighed to determine the total amount of lactate solution present in the wet mass. The wet pulp was then dried at 60°C under vacuum at 100 mbar for 6 hours to remove all excess water and provide a calcium- impregnated Kraft cellulose pulp. The calculated calcium lactate content of the dried pulp was 13.52 wt.%.

[0429] The dry cellulose I alginate-containing absorbent material produced in Example 11 was mixed with the calcium-impregnated Kraft cellulose pulp to produce an absorbent composite material with a target composition of approx. 70 wt.% Kraft cellulose pulp 130 wt.% absorbent material. Once mixed the actual calculated composition was 65.1 wt.% Kraft cellulose 134.9 wt.% absorbent.

[0430] From the masses of the individual components and their previously determined free swelling and retention capacities, the theoretical values for the final composition were calculated. The retention capacity of the combination was determined and compared to the theoretical figures and that of a sample of the Kraft cellulose pulp PW411. The following results were obtained:

[0431] Preparation and testing of composite material based on Kraft cellulose pulp and industry standard sodium polyacrylate (300 to 700 pm):

[0432] A composite material based on dry Kraft cellulose pulp and sodium polyacrylate was prepared as set out in Example 17. From the masses of the individual components and their determined free swelling and retention capacities, the theoretical values for the composite material were calculated. The retention capacity of the composite material was tested and compared to the theoretical figures. The following results were obtained:

[0433] Results and Discussion:

[0434] Figure 12 provides a comparison of the retention capacity of the composite materials tested in this Example. A further enhancement when using the alginate I cellulose-containing material according to Example 11 vs. sodium polyacrylate (“polyacrylate”) is observed when they are dispersed in a Kraft cellulose pulp matrix.

[0435] As expected, the measured values for the polyacrylate + pulp are close to the calculated theoretical values (theoretical 5.6 g / g vs. measured 5.7 g / g). This demonstrates that there is no interaction between these materials and that the pulp simply serves as a carrier for the superabsorbent polymer. However, this is not the case with the alginate I cellulose-containing material + pulp in which the measured values exceed the theoretical values by at least a factor of 2. The presence of calcium ions in the pulp further enhances the retention capacity of this composite material.

[0436] While the invention has been described in detail with reference to specific embodiments thereof, it will be understood that various changes and modifications can be made without departing from the spirit and scope thereof.

Claims

1. Claims:

1. An absorbent article comprising an absorbent cellulose I alginate-containing material, wherein said material comprises cellulose fibres and alginate from a brown seaweed, and wherein said material is obtained by a process comprising at least the following steps:(i) providing a brown seaweed, or part thereof;(ii) dividing the brown seaweed, or part thereof, into a plurality of portions;(iii) washing the plurality of portions with water whereby to remove water- soluble components and recovering the residual wet residue;(iv) converting at least a portion of calcium alginate present in said residual wet residue into a water-soluble alginate whereby to provide a residue containing cellulose fibres and water-soluble alginate; and(v) de-watering said residue containing cellulose fibres and water-soluble alginate whereby to provide said absorbent cellulose I alginate-containing material as a dry residue.

2. An absorbent article as claimed in claim 1, wherein said material is obtained by a process in which the dry residue has a water content of less than about 20 wt.%, preferably a water content of about 5 to about 15 wt.%, based on the total weight of the dry residue.

3. An absorbent article as claimed in claim 1 or claim 2, wherein said material is obtained by a process which further comprises the step of reducing the particle size of the dry residue, for example by subjecting said dry residue to milling and / or grinding.

4. An absorbent article as claimed in any one of claims 1 to 3, wherein said material is obtained by a process in which the residue produced in step (iv) has a pH in the range of from about 4.5 to about 9, preferably from about 6 to about 7, preferably from about 6.5 to 6.7.

5. An absorbent article as claimed in any one of the preceding claims, wherein said material is obtained by a process which does not involve extraction and recovery of any alginate from the brown seaweed.

6. An absorbent article as claimed in any one of the preceding claims, wherein said material is obtained by a process in which the loss of dry matter from the residual wet residue produced in step (iii) is less than about 30%, preferably less than about 25%, for example less than about 15%.

7. An absorbent article as claimed in any one of the preceding claims, wherein said material is obtained by a process in which the loss of dry matter from the residual wet residue produced in step (iii) is less than about 10%, preferably less than about 5%, for example less than about 2%.

8. An absorbent article as claimed in any one of the preceding claims, wherein said material is in particulate form.

9. An absorbent article as claimed in claim 8, wherein said material has an average particle size in the range from about 250 to about 600 pm, preferably about 250 to about 500 pm.

10. An absorbent article as claimed in any one of the preceding claims, wherein said material has a free swelling capacity of from 5 to 60 g / g as measured according to the examples when using an aqueous fluid which is 0.9% NaCI dissolved in deionised water.

11. An absorbent article as claimed in any one of the preceding claims, wherein said material has a retention capacity of from 5 to 45 g / g as measured according to the examples when using an aqueous fluid which is 0.9% NaCI dissolved in deionised water.

12. An absorbent article as claimed in any one of the preceding claims, wherein said material is obtained by a process in which step (iii) comprises washing the plurality of portions with potable water, seawater, demineralised water or deionised water.

13. An absorbent article as claimed in any one of the preceding claims, wherein said material is obtained by a process in which step (iv) comprises at least the following steps: contacting the residual wet residue with an aqueous solution of a mineral acid whereby to effect exchange of native calcium ions with hydrogen ions to form alginic acid; recovering the resulting solid fraction; and contacting the resulting solid fraction with an alkali whereby to convert the alginic acid to a water-soluble form of alginate.

14. An absorbent article as claimed in claim 13, wherein said material is obtained by a process in which the step of contacting the residual wet residue with an aqueous solution of a mineral acid is effective to adjust the pH to about 1.5 to about 2, preferably to about 1.7 to about 1.9.

15. An absorbent article as claimed in claim 13 or claim 14, wherein said material is obtained by a process in which the mineral acid is hydrochloric acid or sulphuric acid.

16. An absorbent article as claimed in any one of claims 13 to 15, wherein said material is obtained by a process in which the step of contacting the solid fraction with an alkali is effective to adjust the pH to about 6 to about 10, preferably to about 6 to about 7.

17. An absorbent article as claimed in claim 16, wherein said material is obtained by a process in which the alkali is selected from sodium hydroxide, potassium hydroxide, ammonium hydroxide, potassium carbonate, sodium carbonate and mixtures thereof, preferably wherein the alkali is sodium carbonate.

18. An absorbent article as claimed in claim 17, wherein said material is obtained by a process in which the alkali is solid sodium carbonate or a solution of sodium carbonate, for example a saturated sodium carbonate solution.

19. An absorbent article as claimed in any one of claims 1 to 12, wherein said material is obtained by a process in which step (iv) comprises at least the following steps: contacting the residual wet residue with a weak organic acid, preferably citric acid; recovering the resulting solid fraction; contacting the resulting solid fraction with an aqueous solution of a mineral acid whereby to effect exchange of native calcium ions with hydrogen ions to form alginic acid; recovering the resulting solid fraction; contacting the solid fraction with an alkali whereby to convert the alginic acid to a water-soluble form of alginate.

20. An absorbent article as claimed in claim 19, wherein said material is obtained by a process in which the step of contacting the resulting solid fraction with an aqueous solution of a mineral acid is effective to adjust the pH to about 1.5 to about 2, preferably to about 1.7 to about 1.9.

21. An absorbent article as claimed in claim 19 or claim 20, wherein said material is obtained by a process in which the mineral acid is hydrochloric acid or sulphuric acid.

22. An absorbent article as claimed in any one of claims 19 to 21 , wherein said material is obtained by a process in which the step of contacting the solid fraction with an alkali is effective to adjust the pH to about 6 to about 7, preferably to about 6.5 to about 6.7.

23. An absorbent article as claimed in claim 22, wherein said material is obtained by a process in which the alkali is selected from sodium hydroxide, potassium hydroxide, ammonium hydroxide, potassium carbonate, sodium carbonate and mixtures thereof, preferably wherein the alkali is sodium carbonate.

24. An absorbent article as claimed in claim 23, wherein said material is obtained by a process in which the alkali is solid sodium carbonate or a solution of sodium carbonate.

25. An absorbent article as claimed in any one of claims 1 to 12, wherein said material is obtained by a process in which the step (iv) comprises at least the following steps: contacting the residual wet residue with a sodium chloride solution; separating the resulting solid fraction; and- washing the resulting solid fraction with propanol, preferably with at least 50% propanol, whereby to remove excess sodium chloride.

26. An absorbent article as claimed in any one of claims 1 to 12, wherein said material is obtained by a process in which step (iv) comprises at least the following steps: contacting the residual wet residue with a sodium citrate solution; adjusting the pH of the resulting mixture to about 6 to about 10, preferably to about 6 to about 7; and recovering the resulting solid fraction.

27. An absorbent article as claimed in claim 26, wherein said material is obtained by a process in which the step of adjusting the pH is performed by the addition of a sodium-based alkali.

28. An absorbent article as claimed in claim 27, wherein said material is obtained by a process in which the sodium-based alkali is sodium carbonate and / or sodium hydroxide, preferably sodium carbonate.

29. An absorbent article as claimed in claim 27, wherein said material is obtained by a process in which the step of adjusting the pH is performed by the addition of sodium hypochlorite.

30. An absorbent article as claimed in any one of claims 1 to 12, wherein said material is obtained by a process in which step (iv) comprises at least the following steps: contacting the residual wet residue with a solution containing sodium chloride and citric acid; separating the resulting solid fraction; andcontacting the resulting solid fraction with a sodium-based alkali whereby to adjust the pH to about 6 to 7.

31. An absorbent article as claimed in claim 30, wherein said material is obtained by a process in which the sodium-based alkali is sodium carbonate and / or sodium hydroxide, preferably sodium carbonate.

32. An absorbent article as claimed in any one of claims 1 to 12, wherein said material is obtained by a process in which step (iv) comprises at least the following steps: contacting the residual wet residue with a bleaching agent which contains sodium ions; and separating the resulting solid fraction.

33. An absorbent article as claimed in claim 32, wherein said material is obtained by a process in which the bleaching agent is sodium hypochlorite.

34. An absorbent article as claimed in any one of claims 1 to 12, wherein said material is obtained by a process in which step (iv) comprises at least the following steps: contacting the residual wet residue with a solution containing a calcium chelating agent, for example a sodium salt of ethylenediaminetetraacetic acid (EDTA); separating the resulting solid fraction; and contacting the resulting solid fraction with a sodium-based alkali whereby to adjust the pH to about 6 to 7.

35. An absorbent article as claimed in claim 34, wherein said material is obtained by a process in which the sodium-based alkali is sodium carbonate and / or sodium hydroxide, preferably sodium carbonate.

36. An absorbent as claimed in any one of claims 1 to 12, wherein said material is obtained by a process in which step (iv) comprises at least the following steps: contacting the residual wet residue with a bleaching agent which contains sodium ions;separating the resulting solid fraction; contacting the resulting solid fraction with an aqueous solution of a mineral acid whereby to adjust the pH to about 1.5 to about 2, e.g. to about 1.7 to about 1.9; separating the resulting solid fraction; and contacting the resulting solid fraction with a sodium-based alkali whereby to adjust the pH to about 6 to about 7.

37. An absorbent article as claimed in claim 36, wherein said material is obtained by a process in which the bleaching agent is sodium hypochlorite.

38. An absorbent article as claimed in claim 36 or claim 37, wherein said material is obtained by a process in which the mineral acid is hydrochloric acid or sulphuric acid.

39. An absorbent article as claimed in any one of claims 36 to 38, wherein said material is obtained by a process in which the sodium-based alkali is sodium carbonate and / or sodium hydroxide, preferably sodium carbonate.

40. An absorbent article as claimed in any one of the preceding claims, wherein said material is obtained by a process in which step (v) is carried out by solvent dehydration, direct drying or vacuum assisted drying.

41. An absorbent article as claimed in claim 40, wherein said material is obtained by a process in which step (v) is carried out by solvent dehydration, preferably using a solvent selected from propanol, acetone and ethanol, for example using propanol.

42. An absorbent article as claimed in any one of the preceding claims, wherein said material is obtained by a process in which the brown seaweed is selected from the group consisting of Laminaria spp., Fucales spp., Ascophyllum spp., Durvillaea spp., Ecklonia spp., Lessonia spp., Macrocystis spp., Sargassum spp., and Saccharina spp.

43. An absorbent article as claimed in claim 42, wherein said material is obtained by a process in which the brown seaweed is Laminaria hyperborea, Laminaria digitata orFucus serratus, preferably Laminaria hyperborea.

44. An absorbent article as claimed in any one of the preceding claims, wherein said material is obtained by a process in which the brown seaweed part is stipe or leaf.

45. An absorbent article as claimed in claim 44, wherein said material is obtained by a process in which the stipe is unpeeled.

46. An absorbent article as claimed in any one of the preceding claims, wherein the cellulose I alginate-containing material is formed or shaped into a sheet, layer, pad or film which forms part or all of said article.

47. An absorbent article as claimed in any one of claims 1 to 45, wherein the cellulose I alginate-containing material is incorporated into a fibrous carrier matrix which forms part or all of said article.

48. An absorbent article as claimed in claim 47, wherein the fibrous carrier matrix is provided in the form of a sheet, layer, pad or film.

49. An absorbent article as claimed in any one of the preceding claims which is a disposable absorbent article.

50. An absorbent article as claimed in any one of the preceding claims which is a wound dressing, a diaper, a feminine hygiene product, an incontinence pad, or a packaging material for food.

51. An absorbent article as claimed in claim 50, wherein said article is a diaper in which the absorbent cellulose I alginate-containing material is embedded within the fibrous matrix of an absorbent layer within the diaper.

52. An absorbent article as claimed in claim 50 which is a packaging material for meat, fish or fruit, for example a packaging material for fresh or frozen meat or fish, or fresh fruit.

53. A method of producing an absorbent article which is formed from or which incorporates an absorbent cellulose I alginate-containing material, wherein said material comprises cellulose fibres and alginate from a brown seaweed, said method comprising at least the following steps:(i) providing a brown seaweed, or part thereof;(ii) dividing the brown seaweed, or part thereof, into a plurality of portions;(iii) washing the plurality of portions with water whereby to remove water- soluble components and recovering the residual wet residue;(iv) converting at least a portion of calcium alginate present in said residual wet residue into a water-soluble alginate whereby to provide a residue containing cellulose fibres and water-soluble alginate;(v) de-watering said residue containing cellulose fibres and water-soluble alginate whereby to provide a dry residue;(vi) optionally reducing the particle size of the dry residue; and(vii) forming an absorbent article from the resulting absorbent cellulose I alginate-containing material or incorporating the resulting absorbent cellulose I alginate-containing material into an absorbent article.

54. A method as claimed in claim 53, wherein the absorbent cellulose I alginate- containing material is produced by a process as defined in any one of claims 1 to 45.

55. A method as claimed in claim 53 or claim 54, wherein the absorbent article is as defined in any one of claims 46 to 52.

56. Use of a cellulose I alginate-containing material as an absorbent, wherein said material comprises cellulose fibres and alginate from a brown seaweed, and wherein said material is obtained by a process as defined in any one of claims 1 to 45.

57. Use as claimed in claim 56, wherein said cellulose I alginate-containing material is formed, moulded or shaped into, or otherwise incorporated into an absorbent article as defined in any one of claims 46 to 52.

58. An absorbent cellulose I alginate-containing material, wherein said material comprises cellulose fibres and alginate from a brown seaweed, and wherein said material is obtained by a process as defined in any one of claims 1 to 45.

59. An absorbent cellulose I alginate-containing material as claimed in claim 58 which is in particulate form.

60. An absorbent cellulose I alginate-containing material as claimed in claim 59 having an average particle size in the range from about 250 to about 600 pm, preferably about 250 to about 500 pm.

61. An absorbent cellulose I alginate-containing material as claimed in any one of claims 58 to 60 having a free swelling capacity of from 5 to 60 g / g as measured according to the examples when using an aqueous fluid which is 0.9% NaCI dissolved in deionised water.

62. An absorbent cellulose I alginate-containing material as claimed in any one of claims 58 to 61 having a retention capacity of from 5 to 45 g / g as measured according to the examples when using an aqueous fluid which is 0.9% NaCI dissolved in deionised water.

63. A method of preparing an absorbent cellulose I alginate-containing material as claimed in any one of claims 58 to 62, said method comprising a process as defined in any one of claims 1 to 45.

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