Method for preparing a bioplastic unit and a bioplastic product

Abstract

The present invention relates to a method for preparing a bioplastic unit comprising the following steps: a) preparing a feed material of a polysaccharide originating from algae by adapting the viscosity of the feed material by removing or adding solvent during mixing or drying or squeezing or wetting or soaking, or by adapting size of the feed by grinding or downsizing into gravel-sized blocks or lumps, and optionally by adding additives, b) subjecting feed material(s) or the prepared feed material to a temperature above 20˚C below the boiling point of the solvent, preferably to a temperature above 10˚C below the boiling point of the solvent, c) while maintaining the increased temperature of step b), the pretreated material is shaped into a bioplastic unit by subjecting the pretreated material to an increased pressure e.g. during 3D printing, or extruding, or by pouring or injecting the pretreated material into a mould.

Description

[0001] Method for preparing a bioplastic unit and a bioplastic product

[0002] The present invention relates to a method for preparing a bioplastic unit from a soluble material which soluble polymer is solidified by removal of solvent, and to a bioplastic product having a tensile strength of at least 10 MPa.

[0003] Background of the invention

[0004] Numerous strategies and resources exist for production of biobased plastics wherein polysaccharides, proteins, and lipids are the primary feed ingredients. These feed ingredients are often sourced from renewable resources, such as corn, potatoes, vegetable oils, wood, food waste, and various cereal crops. Presently, the most prevalent types of bioplastics include starch-based versions, polylactic acid (PLA), poly-3-hydroxybutyrate (PHB), polyamide 11 (PA 11), and organic polyethylene (PE). Bioplastics derived from seaweeds are also increasingly becoming a focus.

[0005] Seaweeds are promising candidates for production of biobased plastics due to their filmforming capabilities. Products such as sachets, pouches, edible cups, wrappers, and plastic bags can be crafted from seaweed films. However, these films often present a key drawback in terms of mechanical strength and water resistance when compared to their non-seaweed counterparts. To expand the potential applications of seaweed films, seaweeds can be combined with other materials, enhancing the robustness and water-resistance of the seaweed-based material.

[0006] The present invention relates to a method for producing a novel biobased plastic from seaweed material which biobased plastic may be formed by a plurality of shaping processes such as injection moulding, 3D-printing, simple moulding or the like. Biobased plastic based on seaweed material is not normally thermoplastic as such which causes difficulties when securing the shape of the final product.

[0007] Injection moulding is a widely used manufacturing technique for creating complex and precise objects. Traditional injection moulding methods predominantly rely on solid materials or polymers having thermoplastic characteristics and having limited absorbency characteristics.

[0008] Another way of producing bioplastic units by the present invention, is to use 3D-printing. According to a traditional 3D printer builds up a 3D model one layer at a time, from the bottom upward, by repeatedly printing over the same area in a method known as fused depositional modelling (FDM). The printer creates a model over a period of hours by turning a 3D CAD drawing into lots of two-dimensional, cross-sectional layers, the printer deposits layers of molten plastic or powder and fuses them together and to the existing structure with adhesive or ultraviolet light. Traditionally, 3D printing has focused on polymers for printing, due to the ease of manufacturing and handling polymeric materials, the 3D printers may use thermoplastics i.e. plastics that melt when heated and turn solid when cooled, and typical materials are ABS (acrylonitrile butadiene styrene), PLA (polylactic acid), or PETG (polyethylene terephthalate glycol). However, 3D-printing may also be used with metals and ceramics as printing material.

[0009] US 5.121.329 discloses a 3D printer where the feed is supplied as a supply rod (46) which is pushed forward by a drive rod (52) being attached as an extension to piston (54) of a power cylinder (56). The supply rod (46) may comprise any thermoplastic material e.g. bees wax, casting wax, paraffin thermoplastic resins, metals or metal alloys. When supplying the feed to a surface, the supply rod (46) is heated within a heating head (84) to a predetermined temperature at which it will exceed the solidification temperature of the material of the supply rod (46) and melt to a flowable, fluid form.

[0010] CN11297999 A relates to 3D-printing of a thermoreversible hydrogel which hydrogel comprises a thermoreversible natural macromolecule such as gelatine, agar and carrageenan. The temperature of the thermoreversible hydrogel during printing is 35-50°C, and the gelatinized product is obtained by leaving the printed product in a low-temperature environment of e.g. 4°C. The feed material according to the present invention does not comprise gelatine, and also, the high temperature which in CN11297999 A is applied during mixing of agar with water, is according to the present invention maintained until the bioplastic unit is shaped.

[0011] Hence, the present invention provides an apparatus and a method for using non-melting materials for 3D printing, e.g. materials which are not thermoplastic polymers or metals or the like. Especially, the invention is suitable for non-melting materials which are made liquid by adding or controlling a solvent.

[0012] Summary of the invention

[0013] Thus, an object of the present invention relates to providing a biobased plastic from seaweed which plastic may be used to provide a bioplastic product having increased tensile and impact strength.

[0014] Thus, a first aspect of the invention relates to a method for a method for preparing a bioplastic unit comprising the following steps: a) preparing a feed material of a polysaccharide originating from algae by adapting the viscosity of the feed material by removing or adding solvent during mixing or drying or squeezing or wetting or soaking, or by adapting size of the feed by grinding or downsizing into gravel-sized blocks or lumps, and optionally by adding additives, b) subjecting feed material(s) or the prepared feed material to a temperature above 20°C below the boiling point of the solvent, preferably to a temperature above 10°C below the boiling point of the solvent,

[0015] - the sequence of step a) and b) is not significant, the steps may be combined or interchanged, after step a) and b) a pretreated material is obtained, c) while maintaining the increased temperature of step b), the pretreated material is shaped into a bioplastic unit by subjecting the pretreated material to an increased pressure e.g. during 3D printing, or extruding, or by pouring or injecting the pretreated material into a mould, d) after having shaped the pretreated material, the pretreated material is turned into a bioplastic unit by removing solvent from the pretreated material until the bioplastic unit has obtained a target content of solvent which target content depends on moulding method, purpose of the bioplastic unit and composition of the feed material.

[0016] According to any embodiment of the first aspect, the pretreated material may in step d) be subjected to heat, or ventilation or freezing, and / or to increased pressure or decreased pressure, to instigate vaporizing of solvent, or sublimation of solvent.

[0017] According to any embodiment of the first aspect, the bioplastic unit obtained at step d) may be subjected to a step e) according to which the bioplastic unit is post-treated by cutting, or grinding, or polishing and / or coating.

[0018] According to any embodiment of the first aspect, the prepared feed material of step a) and b) is not a thermoplastic material, the prepared feed material is a reversible absorbent material, and the viscosity of the prepared feed is controlled by controlling the content of solvent.

[0019] According to any embodiment of the first aspect, the prepared feed material of step a) and b) may not contain glycerine or at least may not contain glycerine in an amount large enough to provide the prepared feed material with thermoplastic characteristics.

[0020] According to any embodiment of the first aspect, the prepared feed material may comprise at least 50wt% solvent at the end of step a) and / or step b).

[0021] According to any embodiment of the first aspect, the pretreated material entering step d) may comprise a solvent content of at least 20wt%, or a solvent content of at least 40wt%, or a solvent content of at least 80wt%, and / or a solvent content of at most 90wt%.

[0022] According to any embodiment of the first aspect, the pretreated material entering step d) may have a temperature within 5°C of the boiling point of the solvent, e.g. the feed may have a temperature equal to or above 95°C if the solvent is water or an aqueous solution, and / or may have a temperature below 300°C, preferably at a temperature above 100°C and / or at a temperature below 290°C, if the solvent is water or an aqueous solution.

[0023] According to any embodiment of the first aspect, the feed material may comprise one or more polysaccharide(s) originating from red algae (Rhodophyta), preferably from an agarophyte, such as Gracilaria or Gelidium, producing hydrocolloid agar in its cell walls.

[0024] According to any embodiment of the first aspect, the feed material may comprise one or more polysaccharide(s) selected from the group of agar, alginate, carrageenan, furcellaran, ulvan, and the polysaccharide(s) may constitute from 50wt% to 100wt% of the total composition, e.g. from 75wt% to 100wt% of the total composition. According to any embodiment of the first aspect, the feed material entering step a) and b) may comprise at least 30wt% agar, or at least 50wt% agar, or at least 90wt% agar, or at least 95wt% agar, or at least 98wt% agar, and the solvent may be water or an aqueous solution.

[0025] According to any embodiment of the first aspect, the bioplastic unit obtained in step d) may have a tensile strength of at least 10 MPa, or at least 12 MPa, or at least 15 MPa, or at least 19 MPa, or at least 30 MPa, or at least 40 MPa, or at least 50 MPa.

[0026] According to any embodiment of the first aspect, step d) may be performed at a pressure below normal or ambient pressure being around 1 atm or 1013 mbar, e.g. the pressure may be below 900 mbar.

[0027] According to any embodiment of the first aspect, lignin or cellulose or hemicellulose fibres, i.e. fibres of bark, wood or leaves of plants, such as fibres of hemp or linseed may be added as additives in step a), the fibres may be one kind of fibres or a combination of fibres. Cellulose fibres are suitable to allow and maintain a higher content of oil in the bioplastic product, such oil may be linseed oil.

[0028] According to any embodiment of the first aspect, an inorganic or organic material in physical form of fibres or particles, selected from a group consisting of a salt such as a salt of calcium or natrium or magnesium is / are added as additives in step a), the additive may be one kind of additive or a combination of additives. The additive may be in form of comminuted calcium containing material such as shells e.g. seashells from mussels or clams. If the additive is an inorganic material such as seashells, no particles should be larger than 2 mm, preferably the particle size range should be below 1.5 mm.

[0029] The additive may provide the bioplastic unit with adapted hardness or flexibility, reduced flammability, resistivity to water-absorbance or even water repellent, having a ceramic appearance etc.

[0030] According to any embodiment of the first aspect, a 3D printer may be used in step c) to form a unit, which 3D printer may comprise an inlet (1) for feed, which feed is normally in a solid state, the feed is moved from the inlet (1) to a nozzle (3) by a pump such as a positive displacement pump (2). Alternatively, the prepared feed of step c) may be injected into a mould.

[0031] According to any embodiment of the first aspect, the material at the start of step d) may have a solvent content of 80wt% or less.

[0032] According to any embodiment of the first aspect, the pretreated material in step d) may be subjected to freeze drying, sublimation, or controlled heating to remove residual water, or simply freezing the materials to facilitate shape retention.

[0033] According to any embodiment of the first aspect, the hardened bioplastic unit obtained in step d) after hardening and further optional adaptation of the size and form, may be covered or coated by a waterproof coating such as a thermoplastic polyester (PLA - polylactic acid) or linseed oil or latex or another biodegradable polymer.

[0034] Another aspect of the present invention relates to a bioplastic product prepared by a method according to the first aspect having a tensile strength of at least 10 MPa, or at least 12 MPa, or at least 15 MPa, or at least 19 MPa, or at least 30 MPa, or at least 40 MPa.

[0035] Brief description of the figures

[0036] Figure 1 shows an embodiment of a 3D printer which may be used to prepare a bioplastic unit according to the invention.

[0037] Figure 2 shows another embodiment of a 3D printer which may be used to prepare a bioplastic unit according to the invention.

[0038] Figure 3A, 3B and 3C illustrate a method for moulding a bioplastic unit according to the invention.

[0039] Figure 4A, 4B and 4C illustrate another method for moulding a bioplastic unit according to the invention.

[0040] The present invention will now be described in more detail in the following.

[0041] Detailed description of the invention

[0042] Definitions

[0043] Prior to discussing the present invention in further details, the following terms and conventions will first be defined :

[0044] In general - This expression is used to describe features which may be used with all embodiments of the invention even though the feature(s) may be mentioned in the detailed part of the specification.

[0045] Non-melting materials - non-thermoplastic materials i.e. materials which do not become liquid at ambient pressure when the temperature is raised, non-melting materials may instead dry i.e. loose solvent, and / or char.

[0046] Bioplastic - In the context of the present document, a bioplastic is a polymer in form of a polysaccharide composed of smaller monosaccharides which polymer and / or monosaccharides originate from a natural or renewable biomass source such as algae.

[0047] Solvent - In the context of the present document, a solvent is a substance capable of dissolving the feed material into a homogeneous mixture thus creating a solution. Also, the solvent may be removed again from the final product.

[0048] It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention. The invention relates to method for creating units of a non-melting feed i.e. a feed which is not thermoplastic, and at least not thermoplastic in a state where it contains little or no solvent. The viscosity and state of a non-melting material may be controlled by controlling the content of solvent in the material by adding and / or removing solvent during the process. Removal of solvent may e.g. be done by controlling the temperature by either freezing or heating and / or by controlling ventilation, and the material may be liquefied e.g. by controlling agitation / kneading or comminution of the feed.

[0049] In general, a method for preparing af fixed unit of a non-melting feed comprises the below described steps.

[0050] First, a solid feed material is provided, the feed material may be in a state where it has a content of solvent or it may be in a dry state, and the feed material may be in form of gravel, particles, powder, shreddings, blocks or another comminuted, divided or subdivided form.

[0051] The feed material comprises a polysaccharide originating from algae. Preferably, the polysaccharide originates from red algae (Rhodophyta), preferably an agarophyte, such as Gracilaria or Gelidium, which produces hydrocolloid agar in its cell walls.

[0052] In general, at least 30wt% of the feed material is constituted of agar.

[0053] The feed material may be constituted of up to 100wt% (wt% of dry matter) polysaccharides e.g. one type of polysaccharide or a mixture of polysaccharides, especially a part of the polysaccharide may be cellulose. The cellulose component may originate from a waste product.

[0054] The feed material may also comprise additives where an additive is a component that constitute a smaller amount of the feed material, e.g. less than 20% by weight of the feed material, or less than 10% by weight of the feed material, or less than 5% by weight of the feed material, or less than 2% by weight of the feed material or less than 1% by weight of the feed material.

[0055] In general, an additive causes or enhances a particular effect of the final product or during the manufacturing process.

[0056] An additive may comprise or be constituted of lignin fibres such as hemp fibres which can act as a flame retardant in the final product or provide a filling component providing some flexibility in the final product.

[0057] An additive may comprise or be constituted of a hard and / or inert inorganic or organic material such as stone or granite powder or particles, or of comminuted marine shells such as clam shells which inorganic or organic material may increase hardness or durability of the final product or provide a more rigid structure to the final product.

[0058] Another additive may be a chemically active inorganic component such as a salt e.g. a calcium salt such as calcium sulphate or calcium carbonate, or a sodium or magnesium salt such as sodium sulphate or sodium carbonate or sodium chloride or magnesium sulphate or magnesium carbonate. Such inorganic components may function as stabilizer or emulsifier. An additive may also comprise an organic salt such as an organic sodium salt e.g. sodium citrate, sodium phosphate or sodium tartrate.

[0059] After providing a feed material, a solvent is added to the solid feed material and the feed material and solvent are mixed.

[0060] If the solvent content of the acquired feed material is too high, solvent may be removed from the feed material before the feed material and solvent is subjected to mixing. When solvent is added or removed to a desired content, it is possible to dissolve the polysaccharide feed material and bring the mixture into a fluid or liquid state by mixing or agitation.

[0061] The solvent may be water or an aqueous solution, and the water or aqueous solution may comprise one or more additives e.g. used to increase the solubility of the polysaccharide feed material or to adapt the viscosity of the liquified mixture.

[0062] Alternatively, the solvent may comprise an organic liquid such as an alcohol or a mixture of alcohols. Such an organic solvent may also comprise one or more additives for increasing the solubility of the polysaccharide feed material or for adapting the viscosity of the liquified mixture.

[0063] Normally, the content of solvent is at least 20wt% and at maximum 95wt% (weight% of dry matter). However, the optimal content of solvent depends both on the composition of the feed material and on the method which is used to form the final product.

[0064] During mixing of the solid feed material and the solvent - or before mixing is started -, the temperature of the feed material or of the mixture of feed material mixed and solvent is increased to a temperature above 20°C below the boiling point of the solvent. If the solvent is water or an aqueous solution the temperature will be around at least 80°C at atmospheric pressure, and normally the temperature is below 150°C at atmospheric pressure.

[0065] It is not clear why the increased temperature improves the quality of the final product but is its assumed that the relatively high temperature provided during the mixing or agitation process provide increased solubility and viscosity of the liquified feed material and makes it possible to produce a surprisingly dense and compact product.

[0066] The next step of the method is to shape the final product.

[0067] In general, the final product may be shaped by subjecting the feed material to an increased pressure, e.g. by injection moulding or by 3D-printing or by forcing the feed material into an open mould.

[0068] The last step of the method is to remove solvent from the final product to obtain a hard and dimensionally stable product. During this step, the pretreated material may be subjected to heat or freezing, and / or ventilation, and / or to increased pressure or decreased pressure, to instigate evaporation of solvent, or sublimation of solvent. The method used to remove solvent from the final bioplastic unit should be adapted to both the size and the production method of the bioplastic unit.

[0069] The residence time or treatment time in step d) depends on the following factors:

[0070] - the size of the bioplastic unit,

[0071] - whether the bioplastic unit is positioned in a mould and one or more surfaces therefore are covered by walls of the mould during step d), or whether the surfaces of the bioplastic unit are free and may be subjected to evaporation,

[0072] - the solvent used and the temperature and pressure in step d),

[0073] - the potential shrinking of the bioplastic unit.

[0074] Normally, the residence time in step d) is at least 1 hour, and it may be up to several days, e.g. 48 hours.

[0075] If the bioplastic unit has a small volume or has a large free-surface / volume ratio, then the shaped pretreated material in step d) may be left to the conditions of surroundings and evaporation of the solvent may then take place during resting of the unit, e.g. resting of the while increasing ventilation.

[0076] To increase the rate of removing solvent, the bioplastic unit may be subjected to heat by increasing the temperature during removal of solvent. Normally, the increased temperature will be between 30°C and 60°C in this step, and the increased temperature may be adapted

[0077] - either by increasing or decreasing the temperature - as the solvent content of the bioplastic unit decreases.

[0078] If the bioplastic unit in step d) is subjected to a reduced pressure, then cavities may be created in the bioplastic unit. Creation of cavities results in a material which has a lower density, although it may still be strong and have a hard outer surface. Reduced pressure is e.g. when water or an aqueous solution is used as solvent, and when the bioplastic unit is subjected to freezing during step d) i.e. the temperature is lowered to below 0°C, preferably below -10°C. Water is then removed by sublimation of water when the pressure is reduced to below ambient pressure, and the bioplastic unit then remains until the water has been removed.

[0079] Post-treatment of bioplastic unit, such as cutting, grinding, polishing or coating.

[0080] After having obtained the target content of solvent specified for the bioplastic unit, then the bioplastic unit may be subjected to post-treatment e.g. to make the unit appear appealing with a smooth surface of the desired dimensions, or to improve the water resistance of the unit by providing the unit with a water-tight coating or adding a substance reducing waterabsorbance. A water-tight coating may preferably be made of a non-toxic material of a natural origin such as linseed oil, latex, or the like.

[0081] 3D-printing and 3D-printer A 3D printer used to produce a final product according to the invention may comprise an inlet 1 for feed, which feed is normally solid or solidified, and means for moving the feed from the inlet 1 to a nozzle 3, which nozzle dispenses the liquified feed on a surface 7, when positioned on the surface 7 the liquefied feed solidifies to a 3D printed figure. The surface 7 may be stationary during operation while the nozzle 3 is moved horizontally and vertically during operation, alternatively the 3D printer may also be operated in a way where the nozzle 3 is kept stationary while the surface 7 is moved during operation.

[0082] The means for moving the feed from the inlet 1 to the nozzle 3 may comprise a positive displacement pump 2 such as a screw pump which forces the feed forward to the nozzle 3.

[0083] In general, a positive displacement pump 2, 5 moving the feed forward may provide a kneading and / or agitation of the feed as well as moving the feed forward, also, the pump 2, 5 may provide a complete or partial mixing with a solvent to liquify or lower viscosity of a solid or solidified feed during transport between the inlet 1 and the nozzle 3. The pump may comprise two or more pumps 2, 5 where e.g. a first pump 2 may feed a second pump 5 as illustrated in figs. 1 and 2. At least one pump 2, 5 may be a screw pump as this is a robust and inexpensive pump which is easy to control.

[0084] Fig. 1 shows an embodiment of a 3D printer according to the invention comprising an inlet 4 for solvent. The inlet 4 is shown to be close to the nozzle 3, but the inlet 4 for solvent may also be placed closer to the inlet 1 for feed. Alternatively, the nozzle 3 may comprise an inlet for solvent and, in general, the nozzle 3 may comprise heating means for increasing the temperature of the feed before leaving the nozzle 3.

[0085] Fig. 2 shows an embodiment of a 3D printer according to the invention which does not comprise a specific inlet for solvent. When 3D printing with this embodiment of a 3D printer, the solvent content of the feed in the reservoir 6 is adapted or controlled in such a way that the feed during transport may be kneaded or subjected to pressure to such an extent that the feed may be liquefied when passing into or through the nozzle 3.

[0086] Normally, the content of solvent of the feed is balanced between being as high as necessary to make the feed liquid and being as low as possible to allow for the feed to solidify quickly after having positioned the liquid feed on the surface 7 where the solid 3D printed figure is built.

[0087] The optimal content of solvent in the feed upon entering the 3D printing process depends on the type of feed, the type of solvent and the specific process. In general, the feed may comprise at least 50wt% solvent before entering through the inlet 1, or a solvent is added to increase the content of solvent in the feed to at least 50wt% while forcing the feed from the inlet 1 to the nozzle 3.

[0088] The embodiments of figs. 1 and 2 comprise two pumps, a first pump 2 comprising a horizontally positioned screw pump and a second pump 5 comprising a vertically positioned screw pump comprising an inlet for feed at an upper end and a nozzle 3 at a lower end. A 3D printer according to the invention may also comprise a feed reservoir 6 containing the solid or fluid feed during operation. Normally, the feed is solid or solidified feed and in form of a powder, a particulate material or gravel-sized units i.e. units of 2-20 mm, or a combination of such powder, particulate or gravel-sized material.

[0089] In general, a method for printing a model with a 3D printer according to the present invention comprises the following steps: a) preparing a feed of a non-melting material e.g. by mixing or drying or wetting i.e. adding solvent, or grinding or otherwise downsizing into gravel-sized blocks or lumps or in another way treating a feed, b) subjecting the prepared feed to a pumping action forcing the feed from the inlet 1 for feed in a 3D printer towards a nozzle 3, during pumping the feed is subjected to increased pressure and preferably to kneading and / or agitation, c) optionally solvent is added to the feed during transport to liquify or decrease viscosity of the feed, d) heating the feed to a temperature above ambient temperature and then forcing the feed through a nozzle 3, alternatively solvent may be added to the nozzle 3 as well.

[0090] The feed may have ambient temperature between step a) and step b), or alternatively, the temperature of the feed after step a) and before step b) may be increased to above ambient temperature and below 100°C, or to above ambient temperature and below 50°C.

[0091] According to a preferred embodiment, the feed may comprise a polysaccharide originating from algae such as agar, and the solvent may be water. According to this embodiment, the feed may comprise at least 60wt% water in step a), or a solvent is added to increase the content of water in the feed to at least 60wt% during step b) or c). When the feed leaves through the nozzle 3 in step d) the water content may be at least 70wt% and / or below 80wt%.

[0092] According to some embodiments, the feed passing through the nozzle 3 in step d) has a temperature within 5°C of the boiling point of the solvent or higher. If the solvent is water, then the temperature in step d) may be equal to or above 95°C and / or below 300°C, e.g. the temperature in step d) may be equal to or above 100°C and / or below 290°C.

[0093] After printing a 3D-model, the 3D-model may be subjected to freezing as freezing may provide a lightweight material. Also, it is possible to provide a lightweight material by producing a 3D-model comprising a 3D grid construction at least in one or more central areas or spaces. It is possible to combine these two features and 3D print a 3D-model comprising at least one or more internal and / or external areas comprising a grid construction according to the method of the present invention and afterwards subjecting the 3D-model to a temperature below 0°C for at least 10 minutes, preferably to a temperature below 10°C for at least 10 minutes. Preferably, the 3D-model is subjected to the low temperature for a period of at least 20 minutes, or at least 40 minutes, or at least 1 hour, or at least 2 hours.

[0094] Moulding

[0095] According to the present invention a bioplastic product may also be prepared by moulding and the method may then comprise the following steps: a) Preparing a mixture 10 comprising at least 5wt% of a polysaccharide originating from an algae and a maximum of 95wt% water, the polysaccharide may be in dry form such as powder or particulate form before being combining with the water. The mixture may comprise one or more additives where each additive may improve or add an effect to the final product. b) The mixture is then heated to a temperature of at least 80°C or to at least 100°C, e.g. to at least 200°C, or to at least 275°C for at least 20 minutes. The mixture may be stirred initially during this step, and the period for which the mixture is heated may last 1-40 minutes, or 20-30 minutes. After initial stirring the mixture may be left without stirring e.g. in an oven. During step b) the mixture may start to gelatinize, but heating the mixture to a high temperature, e.g. to a temperature above 180°C keeps the mixture liquid and allows the mixture to obtain close contact with the inner surfaces of the mould. A high temperature also results in increased coherence in the pre-hardened phase. c) Then the hot liquid mixture is poured into a mould 11 where the mixture is then allowed to cool to a temperature below 40°C, and normally to ambient temperature. During the cooling process, the mixture solidifies and hardens into a solid bioplastic product through cooling and dehydration. The hardening process may be speeded up by thermally isolating the mould from the surroundings thereby increasing the temperature during hardening.

[0096] Alternatively, the mould may be heated during hardening thereby further speeding up the hardening process. By controlling the temperature by isolation and heating and thereby control the time for the hardening process, it is possible to reduce occurrence of cracks in the final product.

[0097] During cooling and hardening in the mould, the bioplastic product may shrink. To prevent the bioplastic product from cracking, it is advantageous to do the casting in an open or at least partly flexible mould i.e. a mould where at least one side or surface of the product during casting either may not be present or may give-in or move to follow the size reduction of the hardening product unit. d) The final bioplastic product may be covered or coated by a waterproof coating such as a thermoplastic polyester (PLA - polylactic acid) or by another waterproof biodegradable polymer.

[0098] The mixture prepared in step a) may comprise a minimum of 6wt% agar, and / or a maximum of 40wt% agar, or a maximum of 10wt% agar, or a maximum of 8wt% agar.

[0099] The final bioplastic product obtained by the process is hard and may be rather brittle. To make the final bioplastic product less brittle, the mixture of step a) may comprise an additive in form of a softener such as glycerol. The content of softener will normally constitute less than 3wt% of the mixture and normally less than lwt% of the mixture. Also, the mixture may comprise at least around 0.1wt% of a softener in order to obtain the desired effect. However, the exact amount of softener to be added to the mixture will depend on which softener is used and the exact composition of mixture.

[0100] Also, the mixture may comprise an additive working as a fire- or flame-retardant component such as an inorganic or organic solid material in form of fibres or particles or powder having fire retardant characteristics. Lignin fibres such as hemp fibres or fibres of eelgrass (Zostera marina) may e.g. constitute a suitable fire retardant which provide a thermally resistant char layer in the bioplastic product.

[0101] In general, a fire- or flame-retardant additive constitutes less than 5wt% of a mixture, or event less than 3wt% of the mixture, and / or at least lwt% of a mixture depending on which fire retardant is used.

[0102] Normally, the mixture is not subjected to active cooling in step c), and step c) may therefore be allowed to continue until ambient temperature is reached. Step c) may last for at least 2 hours, preferably at least 3 hours, or at least 4 hours, or at least 5 hours and normally less than 30 hours. However, the exact optimal duration of step c) will depend on the size of the moulded product, the temperature at which the mixture was heated to in step b), and the physical shape of the mould i.e. whether the mould has an open side or a small opening for removal of vapor.

[0103] After having prepared a moulded bioplastic product, the moulded bioplastic product may be subjected to freezing as freezing may provide a more elastic and lightweight material. To obtain this elastic and lightweight characteristics, the bioplastic product may be subjected to a temperature below 0°C for at least 10 minutes, preferably to a temperature below 10°C for at least 10 minutes. Preferably, the moulded bioplastic product is subjected to the low temperature for a period of at least 20 minutes, or at least 40 minutes, or at least 1 hour, or at least 2 hours.

[0104] A mould 11 normally comprises an outlet 12 through which outlet 12 water is removed during step c). This outlet may be in form of an open side, or an open end or the like.

[0105] Normally, the mould 11 comprises both an inflexible part 13 which inflexible part 13 maintains a shape and position relative to the hardening mixture 10 or partly hardened product throughout the moulding process, and at least one open or flexible or removable part 14 which allows movement of at least one surface of the hardening product or which part 14 is removed during the moulding process after the mixture has partly solidified to allow the surface of the hardening product to give-in.

[0106] Normally a surface of a moulded bioplastic product which has faced an open side of a mould during moulding will be rough and will need a kind of after treatment in order appear smooth as the surfaces of the moulded bioplastic product which was facing an inner surface of the mould during moulding. The after treatment may comprise milling or grinding.

[0107] Figures 3A-3C illustrates a first moulding method according to the invention. Fig. 3A shows a container 15 containing a prepared mixture 10 having been heated as defined in step b), and a mould 11 comprising four inflexible sides 13 placed rectangularly, and an inflexible bottom part 13 having a carved pattern. Fig. 3B shows how the warm mixture 10 is poured from the container 15 into the mould 11. Fig. 3C shows how the mixture 10 has been filled into the mould 11 and completely covering the inflexible bottom part 13. The mixture 10 according to this embodiment is subjected to hardening while facing and being in contact with the four inflexible sides 13 and the inflexible bottom part 13 of the mould 11, these surfaces of the bioplastic product facing the inflexible sides and bottom part 13 will be smooth mirroring the inner surfaces of the mould. The surface of the bioplastic product facing the upper side 14 which is left open to allow unimpeded shrinking of the bioplastic product, will be rough and need grinding or similar to become smooth.

[0108] Figures 4A-4C illustrate a second moulding method according to the invention. Fig. 4A shows part of a mould 11 constituted of a central stick 13A and an end part 13B which parts comprises surfaces constituting inflexible sides in the mould 11 during moulding, during moulding the central stick 13A is fixed to the end part 13B. Fig. 4B shows a pipe 13C being fixed to the end part 13B while surrounding the central stick 13A, a prepared and heated mixture 10 may then be poured into the gap between the outer surface of the central stick 13A and the inner surface of the pipe 13C. When the mixture has solidified in the gap, then the pipe 13C is removed and the outer surface of the moulded bioplastic product is left to harden and to shrink without being in contact with a surface of the mould.

[0109] Example - moulding

[0110] A mixture is prepared by mixing 75 grams of agar agar with 1000 ml of water thereby creating a mixture having a content of 7,5wt% agar agar. No additives are added to the mixture.

[0111] After mixing, the mixture is initially stirred at room temperature and then the mixture is positioned in an oven at a temperature of 275°C for 20 minutes without stirring.

[0112] The mixture is still liquid after 20 minutes have passed, and the mixture is poured into a mould of the shape shown in the figures having an open top. The mould is placed in an isolated box for 4 hours.

[0113] After 4 hours, the mould comprising the moulded bioplastic product is removed from the isolating box. The moulded bioplastic product has reached ambient temperature and has become hard without any palpable elasticity, no cracks appeared during hardening.

[0114] The surface of the moulded bioplastic product facing the open top of the mould has become rough whereas the surfaces facing an inner surface of the mould have become smooth and even. Injection moulding

[0115] According to the present invention, a bioplastic product may also be prepared by injection moulding of a feed material.

[0116] An example of a feed material particularly suitable for injection moulding comprises alginic acid or an alginate salt such as sodium or calcium alginate prepared from seaweed. The feed material is formed by cross linking alginic acid or salt with calcium chloride to form a gel precursor.

[0117] To further enhance the feed materials properties, optional additives can be incorporated during the feed material formation process. Softeners such as hemp fibres can be included to improve flexibility. Fire retardants like salt may also be added to enhance safety characteristics.

[0118] Once the feed material precursor is prepared, it is ready for injection moulding. The feed material is injected into a mould using conventional injection moulding equipment. In many cases, it is beneficial to include a suitable feed helper to aid in the smooth flow of the sticky gel. This feed helper assists in preventing potential clogging or blockages in the feeding system during the injection process. However, alternative techniques or adaptations may exist that allow for successful injection moulding without the use of a feed helper, depending on the specific circumstances.

[0119] After having been subjected to injection moulding, the moulded material is dehydrated. However, a small amount of water may remain within the moulded material due to the materials absorbent nature. Excess water may be removed by either heating, freezing or ventilation, or the moulded material may just be left in a controlled environment such as at an increased temperature e.g. between 30-40°C.

[0120] As the moulded material is tightly pressed moulded material achieved during the injection moulding process, deformations caused by the removal of remaining water is significantly reduced.

[0121] The moulded material may be subjected to freeze-drying or sublimation drying to remove the residual water content.

[0122] Alternatively, the moulded material may simply be dehydrated either locked in a cast, or left free with acceptance of deformation, followed by a rehydration step, and then locked in a mould for a final dehydration, ensuring the desired shape is retained.

[0123] A freeze-drying process involves freezing the gel at low temperatures and then subjecting it to a vacuum conditions where "vacuum conditions" means that the pressure is lower than ambient pressure. The specific pressure may depend on the temperature, water content, the procedure used for preparing the gel and the pressure may vary during the procedure. Under vacuum conditions, the frozen water within the moulded material sublimates, transforming directly from a solid to a gas, resulting in a dehydrated structure of the moulded material. This process creates cavities inside the moulded material instead displacing the outer surfaces when water is removed, and thereby helps preserve the shape of the moulded material and minimize shrinkage.

[0124] According to the sublimation drying process there may be used controlled heating during the vacuum conditions. The frozen water within the moulded material turns into vapor without passing through a liquid phase, resulting in a dehydrated moulded material with preserved structure and integrity.

[0125] In general, a block of dehydrated moulded material may alternatively be used for CNC milling. The block of moulded material can be shaped precisely using computer-controlled machining, enabling the production of complex geometries and customized designs.

Claims

Claims1. Method for preparing a bioplastic unit comprising the following steps: a) preparing a feed material of a polysaccharide originating from algae by adapting the viscosity of the feed material by removing or adding solvent during mixing or drying or squeezing or wetting or soaking, or by adapting size of the feed by grinding or downsizing into gravel-sized blocks or lumps, and optionally by adding additives, b) subjecting feed material(s) or the prepared feed material to a temperature above 20°C below the boiling point of the solvent, preferably to a temperature above 10°C below the boiling point of the solvent,- the sequence of step a) and b) is not significant, the steps may be combined or interchanged, after step a) and b) a pretreated material is obtained, c) while maintaining the increased temperature of step b), the pretreated material is shaped into a bioplastic unit by subjecting the pretreated material to an increased pressure e.g. during 3D printing, or extruding, or by pouring or injecting the pretreated material into a mould, d) after having shaped the pretreated material, the pretreated material is turned into a bioplastic unit by removing solvent from the pretreated material until the bioplastic unit has obtained a target content of solvent which target content depends on moulding method, purpose of the bioplastic unit and composition of the feed material.

2. A method according to claim 1, wherein the pretreated material in step d) is subjected to heat, or ventilation or freezing, and / or to increased pressure or decreased pressure, to instigate vaporizing of solvent, or sublimation of solvent.

3. A method according to any previous claim, wherein the bioplastic unit obtained at step d) is subjected to a step e) according to which the bioplastic unit is post-treated by cutting, or grinding, or polishing and / or coating.

4. A method according to any previous claim, wherein the prepared feed material of step a) and b) is not a thermoplastic material, the prepared feed material is a reversible absorbent material, and the viscosity of the prepared feed is controlled by controlling the content of solvent.

5. A method according to any previous claim, wherein the prepared feed material comprises at least 50wt% solvent at the end of step a) and / or step b).

6. A method according to any previous claim, wherein the pretreated material entering step d) has a solvent content of at least 20wt%, or a solvent content of at least 40wt%, or a solvent content of at least 80wt%, and / or a solvent content of at most 90wt%.

7. A method according to any previous claim, wherein the pretreated material entering step d) has a temperature within 5°C of the boiling point of the solvent, e.g. the feed has a temperature equal to or above 95°C if the solvent is water, and / or at a temperature below 300°C, preferably at a temperature above 100°C and / or at a temperature below 290°C.

8. A method according to any previous claim, wherein the feed material comprises one or more polysaccharide(s) originating from red algae (Rhodophyta), preferably from an agarophyte, such as Gracilaria or Gelidium, producing hydrocolloid agar in its cell walls.

9. A method according to any of the claims 1-7, wherein the feed material comprises one or more polysaccharide(s) selected from the group of agar, alginate, carrageenan, furcellaran, ulvan, and constitutes from 50wt% to 100wt% of the total composition, e.g. from 75wt% to 100wt% of the total composition.

10. A method according to any previous claim, wherein the feed material entering step a) and b) comprises at least 30wt% agar, or at least 50wt% agar, or at least 90wt% agar, or at least 95wt% agar, or at least 98wt% agar, and the solvent is water or an aqueous solution.

11. A method according to any previous claim, wherein the bioplastic unit obtained in step d) has a tensile strength of at least 10 MPa, or at least 12 MPa, or at least 15 MPa, or at least 19 MPa, or at least 30 MPa, or at least 40 MPa, or at least 50 MPa.

12. A method according to any previous claim, wherein step d) is performed at a pressure below normal or ambient pressure being around 1 atm, or 1013 mbar, e.g. the pressure is below 900 mbar.

13. A method according to any previous claim, wherein an inorganic or organic additive is added in an amount of between lwt% and 49wt% of the total amount, e.g. in an amount of between lwt% and 30wt% of the total amount, or e.g. in an amount of between lwt% and 20wt% of the total amount.

14. A method according to claim 13, wherein the additive comprises lignin or cellulose or hemicellulose fibres, i.e. fibres of bark, wood or leaves of plants, such as fibres of hemp or linseed are added as additives in step a), the fibres may be one kind of fibres or acombination of fibres, or the additive comprises an inorganic comminuted calcium containing material such as seashells.

15. A method according to any previous claim, wherein an inorganic or organic material in physical form of fibres or particles, selected from a group consisting of a salt such as a salt of calcium or natrium or magnesium is / are added as additives in step a), the additive may be one kind of additive or a combination of additives.

16. A method according to any previous claim, wherein a 3D printer is used in step c) to form a unit, which 3D printer comprises an inlet (1) for feed, which feed is normally in a solid state, the feed is moved from the inlet (1) to a nozzle (3) by a pump such as a positive displacement pump (2).

17. A method according to any of the claims 1-15, wherein prepared feed in step c) is injected into a mould.

18. A method according to any previous claim, wherein the material at the start of step d) has a solvent content of 80wt% or less.

19. A method according to any previous claim, wherein in step d) is subjected to freeze drying, sublimation, or controlled heating to remove residual water, or simply freezing the materials to facilitate shape retention.

20. A method according to any of the previous claims, wherein the hardened bioplastic unit obtained in step d) after hardening and further optional adaptation of the size and form, is covered or coated by a waterproof coating such as a thermoplastic polyester (PLA - polylactic acid) or linseed oil or latex or another biodegradable polymer.

21. A bioplastic product prepared by a method of any of the claims 1-19 having a tensile strength of at least 10 MPa, or at least 12 MPa, or at least 15 MPa, or at least 19 MPa, or at least 30 MPa, or at least 40 MPa.

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