An aqueous dispersion for binding and coating applications

Abstract

According to an example aspect of the present invention, here is provided an aqueous dispersion, and a film thereof, comprising an extract comprising suberin, and a dispersant comprising hemicellulose grafted with organic acids or their anhydrides. Further, there is provided a method of manufacturing such aqueous dispersion or film. In addition, the present invention relates to the use of such aqueous dispersion and film.

Description

AN AQUEOUS DISPERSION FOR BINDING AND COATING APPLICATIONSFIELD

[0001] The present invention relates to an aqueous dispersion, and a film thereof. In particular, the present invention concerns a novel aqueous dispersion comprising suberin and a hemicellulose-based dispersant, especially a hemicellulose grafted with organic acids.

[0002] The present invention also concerns a method of producing such aqueous dispersion and its use for binding and coating applications.BACKGROUND

[0003] Paper and paperboard are renewable packaging materials but they do not as such have the required barrier properties to provide protection for example against moisture, oxygen, volatile aroma, grease and oil, as well as impact of light. At present, the required barrier properties are achieved especially by extrusion plastics (e.g. polyethylene), aluminium, and / or fluorochemicals, resulting in poor end-product recyclability and increasing safety concerns in food packaging materials. Typically, such barriers used are multilayer structures.

[0004] Also latexes are commonly used as coating materials. Latexes (elastomers) are soft amorphous polymers, which are commonly formulated as water-based dispersions (latexes) and used in numerous products, e.g., converted paper, packaging materials, coatings, textiles and car tyres. However, the commercial products are mainly oil-based, such as styrene-butadiene, styrene-acrylate and polyvinyl-acetate copolymers.

[0005] Currently, fossil fuel-based polymer materials for coating applications put a great threaten to environment and human’s health. Thus, there is a pressing need for alternative bio-based polymer materials to replace the source of oil-based materials.

[0006] For example, suberin is a complex and wax-like biopolymer that consists of long-chain fatty acids and glycerol. In particular, suberin is a mixture of hydrophobic and lipophilic biopolymers and is one of major components of outer cell walls of certain plant tissues, such as cork and bark, and can be derived from waste generated by agriculturalindustries. Suberin is known to provide barrier properties in plants due to its high hydrophobicity, making it a promising material for use in barrier coatings on fibre-based packaging. However, such use has not been yet implemented.

[0007] However, there is a need to improve the functional properties of biopolymers for more demanding packaging applications. In particular, there is a clear need for new thermoplastic bio-based elastomers to replace the petroleum-derived synthetic polymers which are the main ones currently in use.SUMMARY OF THE INVENTION

[0008] It is an aim of the present invention to reduce or even completely to eliminate the above-mentioned problems of oil-based raw material use encountered in the art.

[0009] This invention provides an aqueous dispersion comprising suberin and a hemicellulose-based dispersant. The hemicellulose-based dispersant is in particular hemicellulose grafted with organic acids or their anhydrides. By mixing such hemicellulose derivative, i.e. modified hemicellulose, with suberin, an aqueous dispersion can be provided which is suitable for various end-use applications. Thus, it has been surprisingly found in the present invention that combination of the hemicellulose derivative and suberin provides improved barrier and binding properties.

[0010] The aqueous dispersion of the present invention finds uses in the paper, paperboard and packaging industry as well as broader in coating and surface treatment products.

[0011] According to a first aspect of the present invention, there is provided an aqueous dispersion comprising an extract comprising suberin and a dispersant comprising hemicellulose grafted with organic acids or their anhydrides.

[0012] According to a second aspect of the present invention, there is provided a method of manufacturing an aqueous dispersion comprising an extract comprising suberin and a dispersant comprising hemicellulose grafted with organic acids or their anhydrides. The method comprises the steps of providing a hemicellulose, providing organic acids or their anhydrides, grafting the hemicellulose with the organic acids or their anhydrides toobtain a hemicellulose-based dispersant, and mixing the hemicellulose-based dispersant with an extract comprising suberin.

[0013] According to a third aspect of the present invention, there is provided a film formed by the aqueous dispersion described above or by the method described above.

[0014] According to a fourth aspect of the present invention there is provided uses for such aqueous dispersion and film.

[0015] More specifically the present invention is characterized by what is stated in the independent claims. Some specific embodiments are defined in the dependent claims.

[0016] Thus, the present invention is at least partly based on the idea that hemicellulose derivative -based dispersant, in particular surfactant, is used to stabilize suberin fatty acids into an aqueous dispersion. Suberin-based aqueous dispersions have not been earlier reported since suberin cannot be easily dispersed in water due to its hydrophobic nature. The hemicellulose grafted with organic acids or their anhydrides acts in the aqueous dispersion through a steric stabilization mechanism.

[0017] The present invention provides a sustainable and safe barrier coating and binder composition comprised of hemicellulose-based dispersant and suberin, especially for fiber-based packaging materials. Suberin is a natural binder and barrier material that is usually burnt for energy in a pulp mill, whereas in the present invention it has been surprisingly utilized in producing aqueous dispersions. Hemicellulose, in turn, is an underutilized side-stream from paper pulping process. Use of hemicellulose to replace fossil-based chemicals reduces the environmental footprint of the packaging material or binder composition thereof, and further improves recyclability of fiber-based packaging materials. Both suberin and hemicellulose are bio-based materials.

[0018] Thus, the present invention utilizes waste streams from pulping and biorefinery industries to produce novel bio-based and biodegradable aqueous dispersions for barrier coatings and paints.

[0019] In general, aqueous dispersion coatings have several benefits, including increased barrier properties and those can be produced solvent-free. Thus, compared to conventional extrusion coatings, dispersion coatings also have lower environmental costs and are often suitable for re-pulping or composting when using bio-based polymer.

[0020] The present invention overcomes the challenges of the prior art with a unique dispersion morphology, wherein the hemicellulose-based dispersant allows for generating sufficiently small suberin particle size in the dispersion to enable its coating as a thin barrier layer. Thus, the hemicellulose indirectly improves the coating by acting as a dispersant, in particular as a surfactant, creating a homogeneous dispersion between suberin and water.

[0021] The material of the present invention satisfy both the demand of a low film formation temperature and a sufficient flexibility of the barrier layer thus providing required binding and barrier properties for the end-use purposes.

[0022] Further features and advantages of embodiments will become evident from the following description of preferred embodiments in which reference is made to the attached drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIGURE 1 is a schematic depiction of the preparation of the aqueous dispersion according to an embodiment.

[0024] FIGURE 2 shows a reaction mechanism of the esterification reaction according to an embodiment.

[0025] FIGURE 3 shows the measured surface tensions of hemicellulose derivatives.

[0026] FIGURE 4 shows the measured Turbiscan stability index for two hemicellulose-based dispersants.

[0027] FIGURE 5 shows the water contact angle for a suberin coating obtained by use of a hemicellulose-based dispersion in comparison to reference samples.EMBODIMENTS

[0028] DEFINITIONSIn the present context, the term "bio-based" refers to a material that comprises, consists or essentially consists of a substance (or substances) derived from living matter (biomass) andeither occur naturally or are synthesized. In some embodiments, a part or all of the biobased material or bio-based raw-materials are obtained from renewable sources, such as from biomass, including lignin.

[0029] In the present context, the term ’’degree of substitution”, abbreviated ”DS”, refers to the average amount of substituent groups (mmol) attached per gram of the derivative of hemicellulose.

[0030] As used herein, the term “about” refers to the actual given value, and also to an approximation to such given value that would reasonably be inferred to one of ordinary skill in the art, including approximations due to the experimental and / or measurement conditions for such given value.

[0031] Unless otherwise stated, properties that have been experimentally measured or determined herein have been measured or determined at room temperature.

[0032] Unless otherwise indicated, room temperature is 23 °C.

[0033] Unless otherwise stated, properties that have been experimentally measured or determined herein have been measured or determined at atmospheric pressure.

[0034] According to an embodiment there is provided an aqueous dispersion comprising suberin, and a dispersant comprising hemicellulose grafted with organic acids or their anhydrides. In particular, there is provided an aqueous dispersion comprising an extract comprising suberin, and a dispersant comprising hemicellulose grafted with organic acids or their anhydrides.

[0035] Suberin is a complex polyester biopolymer found in the inner face of the primary cell walls in aerial and root parts of plants. In particular, suberin is found in the outermost layer of bark. Main molecular components of suberin are polyaliphatics and polyaromatics. The aliphatic domain is an insoluble polyester largely comprised of fatty acids and glycerol, whereas the aromatic domain is derived from phenylpropanoid. Thus, suberin is typically derived from bark or cork by extraction, wherein it is part of a bark or cork extract that may also comprise other components of bark or cork, such as betulin, tannins and / or glucose.

[0036] Thus, in one embodiment, the aqueous dispersion comprises bark and / or extract comprising suberin. In one embodiment, the extract may comprise only suberin.

[0037] Suberin is mixed with a dispersant, preferably surfactant, in order to be able to provide a suberin-based aqueous dispersion by improving separation of the suberin particles in water to prevent their settling and / or clumping. Typically, the dispersant acts as a surfactant lowering the surface tension between two phases, i.e. suberin particles and water in this case. Preferably, the dispersant enables forming a homogeneous aqueous dispersion comprising suberin with small average particle size.

[0038] According to one embodiment, suberin has an average particle size of less than 10 um, preferably 0.05 to 5 um, in the aqueous dispersion. The average particle size being measured by laser diffraction particle size analyser (Mastersizer, Malvern Panalytical).

[0039] According to one embodiment, the dispersant comprises a hemicellulose derivative, in particular hemicellulose grafted with organic acids or their anhydrides. Such hemicellulose derivative is an amphiphilic hemicellulose derivative achieved by grafting naturally occurring organic acids, in particular fatty acids, on hemicellulose. Anhydride of an organic acid is a chemical compound derived by the removal of water molecules from an organic acid. Thus anhydrides of organic acids have two acyl groups bonded to the same oxygen atom.

[0040] Hemicelluloses are branched polysaccharides found in plant cell walls. They play an important role in the structural integrity of the plant cell wall and can be isolated from a variety of plant sources. According to one embodiment any hemicellulose can be used. In particular, wood-derived hemicellulose is used.

[0041] According to one embodiment, hemicellulose is obtained by extraction, membrane filtration, hydrolysis, biosynthesis routes or by the combination thereof.

[0042] In one embodiment hemicellulose is selected from the group of galactoglucomannan (GGM), xylan, arabinogalactan, arabino-glucuronoxylan, xyloglucan, betaglucan, alpha-glucan or a combination thereof, preferably from the group of GGM, xylan, and mixtures thereof.

[0043] In a preferred embodiment, hemicellulose is galactoglucomanna (GGM) or xylan, especially GGM. Galactoglucomannan is a hemicellulose that is predominantly found in softwoods, and it exhibits desirable properties, such as high solubility in water and possesses emulsifying capacity, which makes it highly suitable for use as a surfactant.Compared to conventional surfactants, GGM-based surfactant has several advantages, such as reduced environmental impact, low toxicity and improved biodegradability.

[0044] According to one embodiment, the hemicellulose is derived from spruce, by using a spruce extract that is rich in galactoglucomannans. Spruce extract can be produced through pressurized hot water extraction, for example.

[0045] According to one embodiment, the hemicellulose is in its native form. According to another embodiment, hemicellulose is purified hemicellulose, which increases the weight percentage of the hemicellulose in the hemicellulose composition by removal of impurities. In one embodiment, hemicellulose is purified by ethanol precipitation method.

[0046] In one embodiment, the hemicellulose is grafted with organic acids or their anhydrides through esterification reaction. The reaction mechanism of the esterification reaction according to an embodiment is shown in Figure 2.

[0047] According to one embodiment, the organic acids comprise fatty acids, resin acids or a mixture thereof. The organic acids are preferably naturally derived organic acids. Organic acids can have any chain length.

[0048] According to one embodiment, the organic acids have a chain length in the range of C2 to C20, preferably in the range of C6 to Cl 8, such as C9 to C14. Thus, the chain length of the organic acid can be, for example, from C2, C4, C6 or C9 to Cl 4, Cl 5, Cl 6, Cl 8 or C20. Without being bound by this theory, the chain length of the organic acids may have some effect on the surface activity of the grafted hemicellulose-derivative. It may be that shorter organic acids chain lengths (Cl 5 and shorter) exhibit a greater reduction in surface tension compared to those grafted with longer chain, such as Cl 8 and longer. On the other hand, in tests carried out with the dispersion of the present disclosure, a dispersion prepared with GGM grafted with a C18-fatty acid as dispersant showed better storage stability over time when compared to a dispersion prepared using GGM grafted with Cl 4- fatty acid as dispersant, although both remained stable for a much longer time than carried out under test conditions.

[0049] In some embodiments, the organic acid is a fatty acid. Fatty acids are carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. The hemicellulose can thus be grafted with a fatty acid having an aliphatic chain in the above disclosed ranges, such as from C4 to C20, or from C4 to Cl 6. Preferably, the aliphatic chainis unbranched. Naturally occurring fatty acids typically have an unbranched chain of an even number of carbon atoms, ranging from 4 to 28 carbon atoms.

[0050] According to one embodiment, the organic acids are selected from the group of mystiric acids, stearic acids and a mixture thereof.

[0051] According to one embodiment, the organic acids are activated organic acids. In one particular embodiment, the organic acids are activated with carbonyldiimidazole (CDI). CDI is a preferred activator since it enables mild reaction conditions. However, also other activators can be used.

[0052] In one embodiment, CDI reacts with an organic acid "connecting” an imidazole group temporarily to the organic acid, resulting in an activated organic acid that can be grafted onto hemicellulose chain, wherein the imidazole group is released. In general, activated organic acids are more reactive than non-activated organic acids.

[0053] In one embodiment, at least 70 wt.%, preferably at least 80 wt.%, more preferably at least 90 wt.%, of the organic acids or their anhydrides are activated, calculated from the total weight of the organic acids and their anhydrides.

[0054] After mixing the suberin, in particular an extract comprising suberin, with the dispersant, a stable aqueous dispersion is obtained comprising suberin evenly dispersed in water, and hemicellulose derivative acting at the interface of suberin and water. The hemicellulose derivative dispersant, preferably acting as a surfactant, facilitates breakdown of suberin aggregates into smaller and more uniform particles in a water phase.

[0055] According to one embodiment, the amount of the hemicellulose-based dispersant depends on the degree of organic acid substitution on the hemicellulose, its corresponding hydrophilic-lipophilic balance (HLB) value and surface tension.

[0056] The hemicellulose derivative can be present in the dispersion in an amount up to 100 wt.% with respect to the weight of dry suberin, i.e., both components can be present in equal amounts. According to one embodiment, the amount of hemicellulose derivative is 0.1 to 50 wt.%, preferably 0.5 to 20 wt.%, more preferably 1 to 10 wt.% with respect to weight of dry suberin. Thus, the content of hemicellulose derivative can be, for example, from 0.1, 0.5, 1, 3, 5 or 8 wt.% up to 10, 15, 20, 25, 35, 50, 75 or 100 wt.% with respect to the weight of suberin, when calculated based on the dry weight.

[0057] In some embodiments, the suberin content of the dispersion is from 1, 3, 5, 10, and 15 wt. % up to 5, 10, 15, 20, 25, 30, 35, or 40 wt.%, such as from 1 to 10 wt. %, from 3 to 20 wt.%, or from 15 to 30 wt.%. The extract comprising suberin is preferably the main solid component of the dispersion, as a high suberin content contributes to improved water stability and thus better barrier properties of the treated material, in particular a suberin containing film obtained thereon. In coating applications, a suberin content of up to around 25-30 wt.% can be used without reaching a too high viscosity.

[0058] According to one embodiment, the total solid content of the aqueous dispersion is in the range of 5 to 55 wt.%, preferably 15 to 50 wt.%, more preferably 20 to 40 wt.%, calculated from the total weight of the dispersion. The total solids content can be chosen according to the intended end use, such as in coating applications, or as binder, adhesive, or in composite materials.

[0059] In some embodiments, the dispersion comprises further solid components, such as mineral pigments.

[0060] The liquid phase of the aqueous dispersion, i.e., the dispersion medium, is preferably comprised of or essentially comprised of water. Thus, in some embodiments, the percentage of water is at least 90 wt.%, preferably at least 95 wt.-%, most suitably at least 97 wt.%, based on the total weight of the liquid phase.

[0061] According to some embodiments, the pH of the dispersion is from 5.5 to 8, preferably from 6 to 7, more preferably 6 to 6.5. Thus, the pH can be, for example, from 5.5, 5.8 or 6 up to 6.5, 7 or 8. Without pH adjustment, the pH may become lower than 5.5, which in turn tend to increase the degree of shear induced agglomeration. Agglomerates formed at a low pH can block any grooves in the metering rod of a coater, or other metering element, resulting in poor coating quality. Any agglomerates present on the coated surface will also cause coating defects. Furthermore, a too low pH is corrosive for the equipment. However, since suberin has high acidic strength, and thus, a relatively large amount of alkali is needed to neutralize the pH of the dispersion upon suberin addition, it might not be motivated to increase the pH above the upper limits disclosed. Especially since an excess of alkali in the dispersion can cause a saponification reaction, a neutral or slightly acidic final pH can be preferred.

[0062] The present invention also concerns a method of producing an aqueous dispersion, in particular the aqueous dispersion described by the above embodiments. Thus the above embodiments also relate to the present method.

[0063] The method comprises grafting hemicellulose with organic acids or their anhydrides and mixing such dispersant with suberin, in particular an extract comprising suberin, to obtain an aqueous dispersion.

[0064] According to an embodiment the method comprises the steps of providing hemicellulose, providing organic acids or their anhydrides, grafting the hemicellulose with the organic acids or their anhydrides by esterification reaction to obtain a hemicellulosebased dispersant, and mixing the hemicellulose-based dispersant with suberin, in particular with an extract comprising suberin, especially with a bark and / or cork extract comprising suberin. By preparing the hemicellulose dispersant separately, the conditions for the grafting can be optimized to, for example, reach a desired degree of substitution. Additionally, the ratio of dispersant to suberin can be optimized for the intended end use of the dispersion. Furthermore, the formation of undesired by-products can be prevented and it is ensured that the grafting takes place with the intended organic acid or its anhydride.

[0065] According to one embodiment the method comprises a step of providing isolated hemicellulose. In a preferred embodiment, the hemicellulose is obtained by extraction, membrane filtration, hydrolysis, biosynthesis routes or by the combination of those. Also other synthesis routes of hemicellulose can be used.

[0066] According to one embodiment, the hemicellulose is provided in dissolved form. The hemicellulose can be dissolved, or partially dissolved, in a solvent or mixtures of solvents. Thus, the hemicellulose can be dissolved or dispersed in water, in organic solvent, or in mixtures of water and organic solvent. In particular, hemicellulose is dissolved in an organic solvent. Any suitable organic solvent can be used. However, according to a preferred embodiment, hemicellulose is dissolved in dimethyl sulfoxide (DMSO). DMSO is a relatively low toxic polar solvent that is well suitable for dissolution of hemicellulose.

[0067] According to one embodiment, the organic acids or their anhydrides are provided in dissolved form, in particular dissolved in an organic solvent. Any suitable organic solvent can be used. However, according to a preferred embodiment, organic acids are dissolved in tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO), or in a mixturethereof. In particular THF is an ideal non-polar solvent for organic acids that dissolved organic acids already at room temperature. DMSO typically requires temperatures higher than a room temperature.

[0068] According to one embodiment, the hemicellulose and the organic acids are separately dissolved in an organic solvent(s) and then the solutions are combined for the grafting reaction.

[0069] According to another embodiment, the hemicellulose and the organic acids are simultaneously dissolved in the same organic solvent or solvent mixture.

[0070] According to a third embodiment, the hemicellulose is added to the organic acid solution.

[0071] According to one embodiment, the organic acids are dissolved at room temperature. In particular, the organic acids are dissolved in THF at room temperature.

[0072] According to one embodiment, the organic acids are dissolved at a temperature of at least 40 °C, preferably of at least 60 °C, such as at 65 °C, at atmospheric pressure. In one embodiment, the dissolving temperature depends on the used solvent. In a particular embodiment, the organic acids are dissolved in DMSO in such temperatures.

[0073] According to one embodiment, the method comprises providing activated organic acids. In a preferred embodiment, the organic acids are activated with carbonyldiimidazole. Typically, organic acids or their anhydrides are first dissolved and then reacted with the activator, such as carbonyldiimidazole.

[0074] Next, the hemicellulose is grafted with the organic acids or their anhydrides, especially with activated organic acids or their anhydrides, by esterification reaction to obtain a hemicellulose-based dispersant.

[0075] According to one embodiment, the grafting, i.e. esterification reaction, is carried out at a temperature of at least 40 °C, especially at a temperature of at least 60 °C, in an atmospheric pressure. Preferably, the esterification reaction is carried out in an inert atmosphere. The esterification can be carried out at a pH in alkaline or in acidic range, preferably in an alkaline range.

[0076] In a preferred embodiment, the esterification reaction occurs effectively when both the hemicellulose and the organic acids are provided in dissolved form, especially dissolved in an organic solvent. Thus, according to one embodiment, the grafting, i.e. esterification reaction, is carried out in an organic solvent medium, preferably the organic solvent medium comprising at least DMSO and optionally THF. In one preferred embodiment, the esterification reactions occurs in DMSO solution. Thus, if both hemicellulose and organic acids are dissolved in DMSO, only one solvent is required.

[0077] In one embodiment, the organic solvent medium of the esterification reactions comprises a mixture of DMSO and THF. In one embodiment, the DMSO / THF weight ratio is in the range of 1 : 1 to 3 : 1 , preferably 2:1.

[0078] According to an embodiment the hemicellulose-based dispersant has a degree of substitution of up to 3, in particular up to 2, for example of about 0.05 to 0.5, such as 0.1 to 0.4. The degree of substitution is measured by proton nuclear magnetic resonance with dimethyl sulphoxide as solvent.

[0079] According to an embodiment the hemicellulose has a number average molecular weight of 2,000-500,000 g / mol, preferably 3,000-50,000 g / mol, more preferably 5,000-20,000 g / mol, in particular 3,000-10,000 g / mol and a weight average molecular weight of 3,000-1,000,000 g / mol, preferably 4,000-50,000 g / mol, in particular 5,000- 30,000 g / mol as measured by a high-performance size exclusion chromatography.

[0080] According to an embodiment the hemicellulose-based dispersant, i.e. grafted hemicellulose, has a number average molecular weight of 2,000-500,000 g / mol, preferably 3,000-50,000 g / mol, more preferably 3,000-20,000 g / mol, in particular 3,000-10,000 g / mol, and a weight average molecular weight of 3,000-1,000,000 g / mol, as measured by a high- performance size exclusion chromatography.

[0081] According to one embodiment, the organic solvent(s) are removed from the formed dispersion by any known method, such as evaporation or distillation. Preferably, organic solvent(s) are removed before mixing the formed hemicellulose-based dispersant with the suberin, in particular an extract comprising suberin.

[0082] According to one embodiment, the formed hemicellulose-based dispersant is pre-treated before mixing with the suberin. In one embodiment, the hemicellulose-based dispersant is precipitated, preferably in acetone. In a further embodiment, the precipitatedhemicellulose-based surfactant can be optionally isolated through filtration, and / or optionally dried. Drying is preferably performed in a vacuum desiccator, such as in a vacuum oven.

[0083] According to one embodiment, the hemicellulose-based dispersant is diluted with water before mixing with the suberin. According to some embodiments, the hemicellulose-based dispersant is dispersed in water and / or alkali solution to a solids content of 1 to 25 wt.%, such as 1 to 5 wt.%, calculated based on the dry weight of the hemicellulosebased dispersant, before mixing the hemicellulose-based surfactant with suberin.

[0084] Next, the hemicellulose-based dispersant and the suberin are mixed, in particularly mixed until a homogeneous, and preferably transparent, dispersion is obtained. In one embodiment, while mixing, preferably with a mixer with an emulsification screen, suberin is slowly added to ensure that no lumps are formed.

[0085] In one embodiment, suberin is added into a water diluted hemicellulose solution. In particular, suberin is gradually added into such solution.

[0086] In one embodiment, suberin (or an extract comprising suberin) is added in solid form, preferably suberin is used in the form of freeze dried suberin or as a wet suberin cake.

[0087] In another embodiment, suberin is melted prior to adding into the hemicellulose solution. In one embodiment, suberin is melted at about 80 °C (at a temperature higher than melting temperature of suberin) and then added into a water diluted hemicellulose solution.

[0088] According to one embodiment, the mixing is continued for about 10 to 60 minutes, such as 20 to 30 minutes.

[0089] According to one embodiment, the mixing speed is over 10 000 rpm. The mixing speed can be, for example, 10 000 to 14 000 rpm, preferably from 10 000 to 12 000 rpm to avoid foaming.

[0090] In some embodiments, the pH of the suberin dispersion is adjusted, preferably by addition of alkaline solution, such as NaOH. In preferred embodiments, the pH of the dispersion is adjusted to from 5.5 to 8, preferably from 6 to 7, and more preferably from 6 to 6.5. Thus, the pH can be adjusted to, for example from 5.5, 5.8 or 6 up to 6.5, 7 or 8. Without pH adjustment, the pH may become lower than 5.5, which can increase the degreeof shear induced agglomeration. Agglomerates formed at a low pH can block any grooves in the metering element of the coater and form defects on the coated surface, resulting in poor coating quality. Furthermore, a too low pH is corrosive for the coating equipment. However, if the pH is increased to quickly or using excessive alkali, such as NaOH, saponification will occur, causing foaming. When the dispersion contains bubbles as a result of the foaming, these may cause pinholes in a coating obtained therefrom, impairing the quality and water stability of the coating. Thus, the optimal pH of the obtained suberin dispersion lies within the above ranges, as these will provide a dispersion that can withstand share forces without agglomeration and simultaneously produce a high quality and uniform coating. Suberin has high acidic strength, and thus, a relatively large amount of alkali is needed to neutralize the pH of the dispersion upon suberin addition. Therefore, and in particular to avoid saponification, it can be beneficial to use a neutral or slightly acidic pH in the final dispersion.

[0091] In some preferred embodiments, the pH is adjusted in an aqueous dispersion of hemicellulose-based dispersant prior to mixing with an extract comprising suberin. The pH can be adjusted by addition of alkaline solution, such as an NaOH solution, to an aqueous dispersion of hemicellulose-based dispersant. In tests carried out in the context of the present disclosure, it has been found that dispersions stabilized with hemicellulose grafted with organic acids, in particular fatty acids, undergo a dramatic increase in viscosity if the pH is adjusted as a final step of the dispersion preparation. Thus, the pH of the aqueous dispersion of hemicellulose-based dispersant can be increased up to around 12.5, as a nonlimiting example, and then neutralized upon addition of suberin. With this order of addition and pH adjustment, the viscosity of the dispersion does not increase.

[0092] Further, the present invention concerns a film formed by the aqueous dispersion or by the described method. In particular embodiment, the present invention concerns a coating formed by the aqueous dispersion or by the described method on a porous substrate.

[0093] Thus, according to one embodiment the method further comprises casting and drying the formed aqueous dispersion into a film.

[0094] In some embodiments, the method further comprises curing the film at a temperature of 75 to 130°C, such as from 75, 80, 90, or 100°C up to 110, 115, 120 or 130°C.In particular, a curing temperature of 90 to 120°C, more preferably 100 to 115°C, was found to reduce the water sensitivity of the film.

[0095] In some embodiments, the method further comprises curing the film during a curing time of 0.2 to 96 hours. Thus, the curing time can be from 0.2, 0.5, 1, 2, 4, 8, 16 or 24 h up to 4, 12, 24, 48, 72 or 96 h. A prolonged curing time, such as a curing time of from 4 to 96 h, preferably 8 to 48 hours, was found to in combination with a temperature in the above disclose range to further reduce the water sensitivity of the film.

[0096] According to one embodiment, there is provided a bio-based film formed by the aqueous dispersion described above, comprising suberin together with a hemicellulose grafted with organic acids or their anhydrides, or by the method described above, comprising the steps of providing hemicellulose, providing organic acids, grafting the hemicellulose with the organic acids or their anhydrides by esterification reaction to obtain a hemicellulose-based dispersant, and mixing the hemicellulose-based dispersant with suberin.

[0097] In preferred embodiments, the film is subjected to a curing step as described above. Curing in said temperature ranges, in particular a prolonged curing step in said temperature ranges, improves the water stability of the film, such as a coating on a fibrous surface.

[0098] In some embodiments, the film has been cured at a temperature of 75 to 130°C, preferably 90 to 120°C, more preferably 100 to 115°C. Particularly in the preferred ranges, a high-quality film can be obtained, producing coatings with improved wet strength.

[0099] In further some embodiments, the film has been cured during a curing time as disclosed above. Thus, in some preferred embodiments, the film has been cured during a curing time of 4 to 96 h, preferably from 8 to 48 h. In particular in combination with the curing temperatures as disclosed herein, such a prolonged curing time results in improved quality of the film obtained in coating applications. Especially the wet strength of the dry film is improved under such treatment. Thus, a film cured at the temperatures presented above, preferably for a prolonged curing time, will in coating applications result in a more durable coating that is harder to remove by rubbing the surface when compared to coatings obtained without a curing step carried out under said conditions.

[0100] According to an embodiment the thickness of the film is 300-300 m, preferably 50-150 pm, in particular 80-150 pm.

[0101] According to one embodiment the aqueous dispersion, or a film thereof, provided as described above is used for coating applications, such as coatings for paper, paperboard or sand paper, preferably in food-packaging or in pharmaceutical packaging, in water treatment as a membrane and for cosmetics packaging. Thus, according to one embodiment, the aqueous dispersion can be used to form a membrane for water purification application.

[0102] According to one embodiment the aqueous dispersion, or a film thereof, provided as described above is used as a binder, such as binder in pigment coatings or paints, or as an adhesive, such as an adhesive for gluing wood and wood products, or composites.

[0103] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0104] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0105] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0106] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0107] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0108] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.

[0109] The following non-limiting example illustrates an embodiment.EXAMPLESExample 1 : Preparation of hemicellulose derivative

[0110] Spruce extract rich in galactoglucomannans was used as a source of hemicellulose. The spruce extract was produced through pressurized hot water extraction. The spruce extract was first precipitated in ethanol to remove potential impurities and to ensure proper modification. The extract was then filtered and re-dissolved in water before undergoing two additional rounds of precipitation in ethanol. After purification, the extract was dried in a vacuum oven at 40 °C.

[0111] The weight percentage (wt.%) of the GGM composition increased slightly (from 75 wt.% to 82 wt.%) during the purification process, which indicates that impurities were effectively removed through EtOH precipitation step, resulting in a higher concentration of hemicellulose in the purified sample.

[0112] Method 1 (dissolving fatty acids in THF):

[0113] Fatty acids were dissolved in tetrahydrofuran (THF) at room temperature and then 1,1 -carbonyldi-imidazole (CDI) was added thereto (1.2 eq) to activate the fatty acids. The solution was left for stirring until no more carbon dioxide was produced, and an additional hour was waited to ensure proper fatty acid activation. Afterwards, the solution was precipitated in water before filtering and drying in a vacuum oven at a temperature of 40 °C for 12 hours, resulting in a colorless powder.

[0114] Next, the purified GGM was modified in a separate reaction step by dissolving it in a mixture of DMSO and THF (weight ratio 2:1) together with the activated fatty acids (2 eq.). Imidazole (4 eq.) was added as a catalyst. The reaction was left for 15 hours at 50 °C. Afterwards, THF was removed through rotary evaporation, and the solution was precipitated in acetone. The resulting precipitates were isolated through filtration and dried in vacuum in a vacuum oven at a temperature of 40 °C in order to obtain a hemicellulosebased dispersant.

[0115] Method 2 (dissolving fatty acids in DMSO):

[0116] Fatty acids were dissolved in DMSO at a temperature of 65 °C and activated by adding CDI (1 eq.) under constant stirring until no more carbon dioxide was produced, and an additional hour was waited to ensure proper fatty acid activation. Activation of the fatty acids resulted in the formation of imidazole as a side product, where there was no need for the addition of imidazole as a separate catalyst. Further, with this method, the purified GGM could then be directly dissolved in the same DMSO and mixed for an additional 15 hours at a temperature at 65 °C. The mixture was precipitated in acetone and isolated through filtration before being dried in a vacuum oven at a temperature of 40 °C in order to obtain a hemicellulose based dispersant.

[0117] Activation of fatty acids was ensured by1H NMR spectroscopy by comparing the signals of the terminal CHs-groups of the fatty acids at 0.88 ppm and the signals of the imidazolde ring at 7.11, 7.50 and 8.18 ppm. The conversions were calculated and found tobe approximately 90 wt.% when using the first synthesis method and approximately 80 % when using the second synthesis method. Both synthesis routes of activated fatty acids were deemed suitable for the esterification of GGM, as described above.

[0118] Results, i.e. yield and degree of substitution (DS), of the esterification of GGM with Cl 4- and Cl 8- chain length fatty acids are shown in table 1. These hemicellulose-based dispersants were synthesized with the first synthesis method.

[0119] Table 1 : Yield and degree of substitution (DS) of the esterification of GGMExample 2: Preparation of a suberin-based aqueous dispersion and a coating thereof

[0120] The hemicellulose-based dispersant of example 1, produced by method 1 or 2 was used to disperse suberin which was extracted from bark. The hemicellulose was added at 10 % by weight with respect to the weight of dry suberin and the final solid content of the suberin-hemicellulose dispersion was adjusted to 30 wt.%, calculated from the total weight of the dispersion.

[0121] Freeze-dried hemicellulose-based dispersant was first added to dilution water under vigorous stirring until a clear homogeneous solution was obtained. Suberin (freeze- dried or aqueous cake) was then added in small amounts to this solution under vigorous stirring to avoid formation of clumps and the stirring was continued until a homogenous dispersion was obtained. A mixer (stirrer) with a fine emulsification screen running at over 10.000 rpm is preferred to obtain a homogeneous dispersion.

[0122] This hemicellulose stabilized suberin dispersion was coated onto a paper or paperboard using a sheet coater and dried in the oven at 80 - 100 °C. The resulting paper orpaperboard had approximately 10 - 25 g / m2of dry suberin coating and the water vapor transmission rate was between 12 - 25 g / m2 / day.Example 3 : Surface tension measurements

[0123] Surface tension of the hemicellulose derivatives (i.e. grafted GGM solutions) of example 1 (with fatty acid equivalent 0.14) were measured. The GGM derivatives and unmodified GGM as a reference were diluted into 5 different concentrations 10, 5, 1, 0.5 and 0.1 mg / mL. Surface tensions were measured using a tensiometer equipped with a platinum ring. The measured surface tensions are shown in Figure 3.

[0124] It was observed that GGM derivative grafted with shorter fatty acid chain length (Cl 4) exhibited a greater reduction in surface tension compared to GGM derivative grafted with longer chain length (Cl 8). However, both chain lengths contributed to the reduction of surface tension indicating that they are effective surface-active agent. Similar results were obtained for samples produced according to method 2 of example 1.

[0125] Example 4: Stability of suberin dispersions

[0126] Turbiscan analyses were carried out determine the stability of the obtained suberin dispersion containing GGM grafted with C14 and C18 fatty acids as dispersant, respectively, both with an acid equivalent of 0.14. The dispersant was prepared according to the process presented in example 1, with the exception that the hemicellulose-based dispersant was added in an amount of 5 wt.% with respect to dry suberin.

[0127] By the Turbiscan analyses, the storage stability of the dispersion is measured using static multiple light scattering (SMLS). Changes in the transmission and backscattering of light is recorded along the height of a vial containing the sample. Sedimentation, aggregation, and creaming will result in changes that are detectable by the instrument before they can be seen by the human eye. From the recorded date, a value called Turbiscan index is obtained, which can be used in evaluation of the stability of the sample. The lower the index, the better the stability. The index is given as a function of time. Figure 4 shows that the suberin dispersion stabilized with galactoglucomannan grafted with Cl 8 fatty acid (acid equivalent of 0.14) (C18-0.14 fa-g-GGM) was more stable during a four-hour period than the samples stabilized with galactoglucomannan grafted with C14 fatty acid (acid equivalent of 0.14) (C14-0.14 fa-g-GGM).

[0128] However, in the context of the stability tests, it should be noted that the suberin dispersions remained stable during much longer periods, although the tests were limited to a four-hour analysis. No visible phase separation or sedimentation could be observed even after several months of storing. Without being bound by theory, it is likely that the hemicellulose creates a network structure in the suberin dispersion, preventing sedimentation and creaming. During storage, the dispersions tend to form a gel, which can be made fluid again with mild agitation.Example 5: Water contact angle

[0129] The water contact angle of suberin-based dispersions was measured using Kruss Mobile Surface Analyzer. The measurements were carried out for the suberin dispersion obtained according to example 1, using 5 wt.% GGM grafted with C18-fatty acid as dispersant (acid equivalent of 0.14 (FA-GGM, Cl 8 (0.14)) with respect to the weight of dry suberin. Reference measurements were carried out for an ethanol-based suberin dispersion, as well as an uncoated reference.The results are presented in Figure 5. From the results it can be seen that the aqueous suberin dispersion performed better than the ethanol-suberin dispersion in which no surfactant was present.INDUSTRIAL APPLICABILITY

[0130] The aqueous dispersion according to the current invention can be used as glues, adhesives and binders. Particularly, they can be used as glues and adhesives in wood-based products such as plywood or as binders in applications such as pigment coatings and paints. The films according to the current invention can be used as films in packaging materials, such as to replace aluminum foil, PE, PP, PVDC or EVOH, for food, cosmetics and pharmaceuticals or as barrier coatings for paper and paperboard.ACRONYMS LISTCDI 1,1 -carbonyldi-imidazoleDMSO Dimethyl sulfoxideDS Degree of substitution GGM GalactoglucomannanTHF Tetrahydro furan

Claims

CLAIMS:

1. An aqueous dispersion comprising an extract comprising suberin, and a dispersant comprising hemicellulose grafted with organic acids or their anhydrides.

2. The aqueous dispersion according to claim 1, wherein the hemicellulose is galactoglucomannan (GGM), xylan, arabinogalactan, arabino-glucoronoxylan, xyloglucan, betaglucan, alpha-glucan or a combination thereof, preferably GGM or xylan.

3. The aqueous dispersion according to claim 1 or 2, wherein the hemicellulose is obtained by extraction, membrane filtration, hydrolysis, biosynthesis routes or by the combination thereof.

4. The aqueous dispersion according to any of the preceding claims, wherein the organic acids or their anhydrides comprise fatty acids, resin acids or a mixture thereof, preferably organic acids are naturally derived fatty acids.

5. The aqueous dispersion according to any of the preceding claims, wherein organic acids have a chain length in the range of C2 to C20.

6. The aqueous dispersion according to any of the preceding claims, wherein the organic acids or their anhydrides are activated organic acids or their anhydrides.

7. The aqueous dispersion according to any of the preceding claims, wherein the organic acids, preferably fatty acids, or their anhydrides are activated with carbonyldiimidazole.

8. The aqueous dispersion according to any of the preceding claims, wherein the hemicellulose is grafted with organic acids or their anhydrides through esterification reaction.

9. The aqueous dispersion according to any of the preceding claims, wherein the amount of hemicellulose is 0.1 to 50 wt.%, preferably 0.5 to 20 wt.%, more preferably 1 to 10 wt.% with respect to weight of dry suberin.

10. The aqueous dispersion according to any of the preceding claims, wherein the total solid content of the aqueous dispersion is in the range of 5 to 55 wt.%, preferably 15 to 50 wt.%, more preferably 20 to 40 wt.%, calculated from the total weight of the dispersion, the rest preferably being water.

11. The aqueous dispersion according to any of the preceding claims, wherein the pH of the dispersion is from 5.5 to 8, preferably from 6 to 7, more preferably 6 to 6.5.

12. A method of producing an aqueous dispersion, comprising the steps of- providing a hemicellulose,- providing organic acids or their anhydrides,- grafting the hemicellulose with the organic acids or their anhydrides by esterification reaction to obtain a hemicellulose-based surfactant, and- mixing the hemicellulose-based surfactant with an extract comprising suberin.

13. The method according to claim 12, comprising providing isolated hemicellulose, preferably obtained by extraction, membrane filtration, hydrolysis, biosynthesis routes or by the combination thereof.

14. The method according to claim 12 or 13, comprising providing hemicellulose in dissolved form, preferably dissolved in an organic solvent, in particular in dimethyl sulfoxide (DMSO).

15. The method according to any of claims 12 to 14, comprising providing the organic acids or their anhydrides dissolved in an organic solvent, such as tetrahydrofuran (THF), dimethyl sulfoxide (DMSO) or a mixture thereof.

16. The method according to any of claims 12 to 15, comprising providing the organic acids or their anhydrides dissolved in DMSO, preferably the organic acids or their anhydrides aredissolved in DMSO at a temperature of at least 40 °C, more preferably at a temperature of at least 60 °C, such as at least 65 °C, at atmospheric pressure.

17. The method according to any of claims 12 to 16, comprising activating the organic acids or their anhydrides before the grafting, preferably the organic acids or their anhydrides are activated with carbonyldiimidazole.

18. The method according to any of claim 12 to 17, wherein the grafting, i.e. the esterification reaction, is carried out in an organic solvent medium, preferably the organic solvent medium comprising at least DMSO and optionally THF.

19. The method according to any of claim 12 to 18, wherein the grafting, i.e. esterification reaction, is carried out at a temperature of at least 40 °C, especially at a temperature of at least 60 °C, in atmospheric pressure, preferably in an inert atmosphere.

20. The method according to any of claims 14 to 19, wherein the organic solvent or solvents are removed from the dispersion by any known method, such as evaporation or distillation, before mixing the hemicellulose-based surfactant with suberin.

21. The method according to any of claims 12 to 20, wherein the hemicellulose-based dispersant is precipitated in acetone and isolated through filtration, and optionally dried, preferably in vacuum desiccator, before mixing the hemicellulose-based surfactant with suberin.

22. The method according to any of claims 12 to 21, wherein the hemicellulose-based dispersant is dispersed in water and / or alkali solution to a solids content of 1 to 25 wt.%, such as 1 to 5 wt.%, calculated based on the dry weight of the hemicellulose-based dispersant, before mixing the hemicellulose-based surfactant with suberin.

23. The method according to any of claims 12 to 22, wherein the pH of the dispersion is adjusted to from 5.5 to 8, preferably from 6 to 7, more preferably 6 to 6.5.

24. The method according to claim 23, wherein the pH is adjusted in an aqueous dispersion of hemicellulose-based dispersant prior to mixing with an extract comprising suberin.

25. The method according to any of claims 12 to 24, wherein the hemicellulose-based surfactant and suberin are mixed until a homogeneous dispersion is obtained.

26. A film formed by the aqueous dispersion according to any of claims 1 to 11 or by the method according to any of claims 12 to 25.

27. A film according to claim 26, wherein the film has been cured at a temperature of 75 to 130°C, preferably 90 to 120°C, more preferably 100 to 115°C.

28. A film according to claim 26 or 27, wherein the film has been cured during a curing time of 4 to 96 h, preferably 8 to 48 hours.

29. Use of the aqueous dispersion according to any of claims 1 to 11, the aqueous dispersion obtained by the method according to any of claims 12 to 25, or the film according to any of claim 26-28, for coating applications, such as coatings for paper, paperboard or sand paper, preferably in food packaging or in pharmaceutical packaging, in water treatment as a membrane and for cosmetic packaging.

30. Use of the aqueous dispersion according to any of claims 1 to 11, the aqueous dispersion obtained by the method according to any of claims 12 to 25, or the film according to any of claims 26-28, as a binder in pigment coatings or paints, or as an adhesive, such as adhesive for gluing wood and wood products, or composites.

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