FIELD OF THE INVENTION

The present invention is in the field of a method of modifying polymers produced by biological species, in particular microorganisms, by reacting un-modified biopolymer, a modified biopolymer obtained by said method, an adhesive comprising said modified biopolymer, a fibre reinforced composite comprising said modified biopolymer, and a fibre reinforce panel comprising said fibre reinforced composite.

BACKGROUND OF THE INVENTION

A fibre-reinforced composite (FRC) is a building material that consists of three components, namely fibres (for strength and stiffness) as a discontinuous or dispersed phase, a matrix (binder) as a continuous phase, and the fine interphase region, also known as the interface. For fibres use can be made of natural fibres, synthetics fibres, or a combination thereof. Examples thereof are flax, hemp, rice husk, rice hull, rice shell, cellulosic (waste streams), and plastic as ingredients. Fibres may need to be refined, blended, and compounded, such as in case of natural fibres from cellulosic waste streams. A high-strength fibre composite material in a polymer matrix can be formed thereby. The designated waste or base raw materials used in this instance are those of waste thermoplastics and various categories of cellulosic waste including straw, rice husk and saw dust.

In an alternative, e.g., to cellulosic waste streams, plant-based polymeric material, such as cellulose-based material thereof, may be used. Or a polyester may be formed directly from chemical products, such as by reacting an aliphatic polyalcohol and an aliphatic Poly carboxylic acid, such as is shown on W02020/152082 Al, WO 2020/212427 Al, and WO 2021/023495 Al, which material may be used for manufacturing a laminate and the like.

Naturally occurring materials such as cotton, starch, and rubber were familiar materials for years before synthetic polymers such as polyethene and Perspex appeared on the market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulphur. Ways in which polymers can be modified include oxidation, cross-linking, and end-capping. Such polymers may find application as fibre reinforced composite materials.

It is known that microorganisms are capable of producing biochemical compounds, such as lactic acid. Thereto typically a microbial culture is used. Therein microbial organisms reproduce in predetermined culture medium under controlled laboratory conditions. It is often essential to isolate a pure culture of microorganisms. A pure (or axenic) culture is a population of cells or multicellular organisms growing in the absence of other species or types. Remarkably also non-pure cultures are capable of producing chemical substances. Bacteria are capable of producing a wide variety of chemical substances, such as lactic acid, but also methane, and are therefore used in food industry, in waste treatment, and so on.

With the term “microbial process” here a microbiological conversion is meant.

Recently it has been found that biobased polymeric substances, such as extracellular polymeric substances (EPS), in particular polysaccharide comprising materials, obtainable from granular sludge can be produced in large quantities. These substances relate to biobased carboxylic acid-like chemicals, which may be present in an ionic form (e.g. cationic or anionic). Examples of such production methods can be found in W02015/057067 Al, and WO20 15/050449 Al, whereas examples of extraction methods for obtaining said biobased polymers can be found in Dutch Patent application NL2016441 and in WO2015/190927 Al. Specific examples of obtaining these substances, such as aerobic granular sludge and anam- mox granular sludge, and the processes used for obtaining them are known from Water Research, 2007, doi:10.1016/j.waters.2007.03.044 (anammox granular sludge) and Water Science and Technology, 2007, 55(8-9), 75-81 (aerobic granular sludge). Further, Li et al. in “Characterization of alginate-like exopolysaccharides isolated from aerobic granular sludge in pilot plant”, Water Research, Elsevier, Amsterdam, NL, Vol. 44, No. 11 (June 1 2010), pp. 3355-3364) recites specific alginate-like EPS in relatively raw form. Though initially the term “alginate-like”, or “alginate-like EPS” (ALE) was used, the biobased polymeric substances are found to be more complex in terms of chemical building blocks present therein. Therefore the term EPS is preferred. Details of the biopolymers can also be found in these documents, as well as in Dutch Patent applications NL2011609, NL2011542, NL2011852, NL2017470, and NL2012089. Also reference can be made to the Nereda® process. These documents, and there contents, such as characteristics (e.g. molecular weights, dynamic viscosity, shear rate, tensile strength, and flexural strength) of the biobased polymers, are incorporated by reference.

Quispe et al. (DOI : 10.1016/J.POLYMERTESTING.2020.107005) recites glycerolbased additives of poly (3 -hydroxybutyrate) films. Glycerol (G), polyglycerols (PGs), glycerol triacetate (GTA), and glycerol tributyrate (GTB) were studied as additives of poly (3 -hydroxy- butyrate) (PHB). The effect of different concentrations (5-30%) of these compounds on microstructure and final properties of PHB films were evaluated. Microscopic studies revealed that samples with G and PGs evidenced additives exudation. All studied additives decreased PHB melting temperature, facilitating its thermal processability. GTA and GTB addition induced a reduction in PHB glass transition temperature, demonstrating their plasticizing effect, an article by Bueno et al. (DOI: 10.1016/J.CARBPOL.2012.10.062) recite Synthesis and swelling behaviour of xanthan-based hydrogels. Xanthan chains were crosslinked by esterification reaction at 165 °C during short reaction times, such as of 7 minutes, either in the absence or in the presence of citric acid. Higher crosslinking density was obtained using citric acid, as evidenced by its lower swelling degree. CN 110 498 867 A recites water based fracturing fluids, in particular using a modified welan gum, thereto. The water-based fracturing fluid composition contains a thickening agent, a cross-linking agent, a fracturing auxiliary agent and water, and the water-based fracturing fluid composition is characterized in that the thickening agent is citric acid-modified welan gum.

Advantageously, in an initial step, granules of granular sludge can be readily removed from a reactor by e.g. physical separation, settling, centrifugation, cyclonic separation, decantation, filtration, or sieving to provide extracellular polymeric substances in a small volume. Compared to separating material from a liquid phase of the reactor this means that neither huge volumes of organic nor other solvents (for extraction), nor large amounts of energy (to evaporate the liquid) are required for isolation of the extracellular polymeric substances.

Extracellular polymeric substances obtainable from granular sludge (preferably obtained from granular sludge) do not require further purification or treatment to be used for some applications, hence can be applied directly. When the extracellular polymeric substances are obtained from granular sludge the extracellular polymeric substances are preferably isolated from bacteria (cells) and/or other non-extracellular polymeric substances. The granular sludge can be suitably produced by bacteria belonging to the order Pseudomonadaceae, such as pseudomonas and/or Acetobacter bacteria (aerobic granular sludge); or, by bacteria belonging to the order Planctomycetales (anammox granular sludge), such as Brocadia anammoxidans. Kuenenia stuttgartiensis or Brocadia fidgida or by betaproteobacteria, such as Candidatis Accumulibacter Phosphatis, or, by algae, such as brown algae.

Extraction of biopolymers from aerobic granular sludge is an emerging topic, and so far amongst others extraction with alkaline substances, such as Na2COs, NaOH or NaOCl, and likewise with compounds having two amine groups, have been suggested and implemented. The processes provide acceptable results for some further applications, but still produce a mixture of components present and need relatively harsh conditions. Na2COs is found to provide biopolymers with an number average molecular weight of 50-75 kDa, NaOH at a pH of 11-12 provides biopolymers with an number average molecular weight of 20-45 kDa, and NaOCl provides biopolymers with an number average molecular weight of about 120 kDa(100-150 kDa)[as determined with GPC/SEC, Shimadzu Nexpera GPC],

In an alternative to biological products, algae alginate (e.g. from seaweed) has found application in various products, especially as gelling agents. Calcium alginate wound dressings are used worldwide in view of creating a moist wound environment that encourages more effective healing. The alginate referred to here does not relate to a biopolymer of microbial origin.

In general it has been found difficult to further process products of biological origin, such as (these) microbial products, in particular biopolymers such as EPS, either in pure form as obtained from a reactor, or purified or extracted as indicated above.

So, practical application of biopolymers, such as alginate, has been limited. A problem with biopolymers is that upon further treatment water may need to be removed, which is difficult.

The present invention relates to a product comprising a modified biopolymer, such as the above modified extracellular polymeric substance, a method of producing said modified biopolymer, and further aspects thereof, which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to a method of obtaining a modified biopolymer comprising providing an amount of at least one un-modified biopolymer or providing at least one un-modified bio-polyester produced by at least one microbial species, such as an extra-polymeric substance, and (i) modifying the at least one un-modified biopolymer by reacting the unmodified biopolymer with at least one biodegradable and non-toxic es- ter-forming or ether-forming or anhydride-forming compound, wherein the ester-forming or ether-forming or anhydride-forming compound is capable of forming at least two of esters and/or ethers, wherein the ester-forming or ether-forming or anhydride-forming compound is selected from polyols, polyacids, such as poly carboxylic acids, poly alcohols, poly aldehydes, molecules comprising at least one OH-group and one COOH group, and combinations thereof, at an elevated temperature, during a reaction time of at least 10 minutes, therewith forming a modified biopolymer-compound ester and optionally amide and optionally ether. The reaction may be inter-biopolymer molecule, intra- biopolymer molecule, or both. Surprisingly the water, being produced by the reaction, and/or being present, can be removed and therefore does not substantially hinder the present modification. The reactive compound is preferably a polyol, or a polyacid. In this respect the prefix “poly” can also relate to “oligo”, that is 2-6, such as 3-4. It is important that in the reactive compound at least two ester-forming and/or ether-forming and/or anhydride-forming moieties are present, in order to modify the un-modified biopolymer. In an example, the extracellular polymeric substances comprise a major portion consisting of exopolysaccharides, and a minor portion, such as less than 30 % w/w, typically less than 10 %w/w, consisting of lipids and/or other components more hydro- phobic than the exopolysaccharides, such as proteins. In general, the phrase “at least two” implies two or more, in particular three or more, more in particular 4-6, such as the ester-forming and/or ether-forming and/or anhydride-forming moieties.

So inventors found that it is beneficial to include e.g. polyols like glycerol, sorbitol and analogous, and/or polyacids, for instance citric acid, to modify microbial biopolymer formulations, in particular to form complex 3D-structures, such as thermo-hardeners, or to form mixtures with a high polyfunctionality capable of forming such complex 3D-structure. In the case of Kaumera® (ALE) inventors established that 25% citric acid (CA) is about the stoichiometric amount to react with the available functional groups to form a Kaumera resin that can be cured at elevated temperature, such as at 140 C and higher, typically so as to yield a nonsoluble ester/amide covalently crosslinked network. In conjunction to this base formulation additionally citric acid and e.g. glycerol (GLY) can be included into the biopolymer to modify the plasticity or flow of the resin obtained. This can be in a non-stoichiometric ratio, although possibly stoichiometric ratios are better to get a complete reaction after curing. For CA/GLY this ratio may be about 3/1 in weight, based on the effective available acid groups (+2 in CA) and +3 OH in GLY. For the Kaumera polymer the level of acidity will influence the number of effectively available carboxylic groups in the polymer (COOH in acid ALE, for Na-ALE the carboxylic groups in the polymer do not participate). The Kaumera resin formulation of this generic type e.g. 75 Kaumera/25 CA + x%(3 CA/1 GLY) are suitable as a binder for e.g. fibre reinforced panel manufacturing. Analogously, the aliphatic PHBV polyesters obtained from e.g. vegetable waste composting can be modified using CA/GLY and similar additions, to cleave the polymer chains, and decorate the ends with branched acid or OH functional end- groups of the PHBV chains. This may be useful to control the degree of crystallization, the melting point of the formulation, and the 'tackiness' of the final mixture, after some esterifica- tion/cleavage at elevated temperature, again typically above 140C. These PHBV based formulations are considered useful for optimizing the polymer performance as a matrix resin, or in adhesives (solvent based, hot melt, and pressure sensitive adhesives). It is worth noting that glycerol can be replaced by analogous polyols like sorbitol (6 OH groups) in case of evaporation of the GLY at elevated temperatures, etc.

In a second aspect the present invention relates to a modified, plasticized, or functionalized biopolymer obtainable by a method according to the invention. It is considered an important advantage of the present method of modifying, and the modified biopolymers obtained thereby, that characteristics of the un-modified biopolymers can be adapted largely as desired. In other words, the biopolymers can be plasticized, or functionalized, or modified in general, with a specific application thereof in mind, such as the use as an adhesive compound, or the use in a fibre reinforced composite. Said modified biopolymer may have a melting point of >150 °C, and/or a tackiness of > 200 J/m2, and/or a glass transition temperature of < 50 °C (high temperature compostable), preferably < 40 °C, such as < 20 °C. For instance PHBV is < 0 C. A biopolymer PHBV based formulation that has a good hot melt and short-term tackiness properties is obtained.

In a further aspect the present invention relates to an adhesive comprising a biopolymer according to the invention, such as a solvent based adhesive, and a hot melt adhesive.

In yet a further aspect the present invention relates to a fibre reinforced composite comprising 1-70 wt.% of an adhesive according to the invention, and 30-99 wt.% fibres, in particular cellulosic fibres, hemp fibres, flax fibres, and viscose fibres, preferably wherein the composite is 50-90% cured.

And the invention relates, in a further aspect, to a fibre reinforced panel comprising a fibre reinforced composite according to the invention.

Thereby the present invention provides a solution to one or more of the above mentioned problems. Advantages of the present invention are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a method according to claim 1. The present method comprises (i) modifying the at least one un-modified biopolymer or providing at least one un-modified bio-polyester, (ii) plasticizing the at least one modified biopolymer or un-modified bio-polyester by reacting with an 0.1-35% stoichiometric amount of at least one biodegradable and non-toxic ester-forming or ether-forming or anhydride-form- ing compound, in particular 1-30 % stoichiometric amount, such as 5-25% stoichiometric amount, wherein the ester-forming or ether-forming or anhydride-forming compound is capable of forming at least two of esters and/or ethers, wherein the ester-forming or ether-forming or anhydride-forming compound is selected from polyols, polyacids, such as poly carboxylic acids, poly alcohols, molecules comprising at least one OH-group and one COOH group, and combinations thereof, at an elevated temperature, during a reaction time of at least 10 minutes, therewith forming a plasticized biopolymer-compound ester and optionally amide and optionally ether, and optionally (iii) functionalizing the at least one modified biopolymer or un-modified bio-polyester by reacting with an 0.1-35% stoichiometric amount of at least one biodegradable and non-toxic ester-forming or ether-forming or anhydride-forming compound, in particular 1-30 % stoichiometric amount, such as 5-25% stoichiometric amount, wherein the ester-forming or ether-forming or anhydride-forming compound is capable of forming at least two of esters and/or ethers, wherein the ester-forming or ether-forming or anhydride-forming compound is selected from polyols, polyacids, such as poly carboxylic acids, poly alcohols, molecules comprising at least one OH-group and one COOH group, and combinations thereof, at an elevated temperature, during a reaction time of at least 10 minutes, therewith forming a functionalized biopolymer-compound ester and optionally amide and optionally ether. In an alternative to reacting the un-modified biopolymer with the ester-, ether, or anhydride-forming compound one can also start with an un-modified biopolymer, in particular a bio-polyester. The bio-polyester is considered to be less reactive than an unmodified biopolymer having OH-groups available for reacting and optionally further groups for reacting. However, the bio-polyester can still be modified, such as plasticized, and/or functionalized, with at least one biodegradable and non-toxic ester-forming or ether-forming or anhydride- forming compound, typically under similar reaction conditions. In step of plasticizing a small fraction of the available reactive moi eties (or groups) is reacted, typically with an 0.1-25% stoichiometric amount of such reactive groups being available, preferably with an 1-8% stoichiometric amount, such as with an 2-5% stoichiometric amount thereof. In an alternative, or in addition, the modified biopolymer or bio-polyester can be functionalized in a similar manner, by reacting a small fraction of the available reactive moieties (or groups), typically with an 0.1-25% stoichiometric amount of such reactive groups being available, preferably with an 1-8% stoichiometric amount, such as with an 2-5% stoichiometric amount thereof. Depending on the selection of the reactive compound (ester-forming or ether-forming or anhydride-forming compound) plasticity and/or function of the biopolymer or bio-polyester can be modified.

In an exemplary embodiment of the present method wherein the un-modified biopolymer has various moieties or groups available for reacting, such as comprises OH-groups available for reacting and optionally at least one of NH _X groups for reacting, carboxylic groups for reacting, RSC Hx groups for reacting, RPC Hx groups for reacting, ester-groups for reacting, ether-groups for reacting, O-acetyl groups for reacting, which typically are ketone group, sulfone groups for reacting, sulfonate groups for reacting, sulphonamide groups for reacting, and combinations thereof. It is noted that biopolymers produced by at least one microbial species may vary in terms of molecular weight, in terms of functional groups and amounts thereof being present in the biopolymer, in terms of sequence of monomers, dimers, etc. The un-modified biopolymer and the ester-forming or ether-forming or anhydride-form- ing compound are preferably provided in a stoichiometric ratio of biopolymer: compound of 0.7:1 to 2:1, more preferably 1 : 1 to 1.5: 1. In an alternative during reacting the unmodified biopolymer and ester-forming or ether-forming or anhydride-forming an amount of 75-99.9 % of the stoichiometric ratio, which affectively is a too low ratio, preferably 80-95%, such as 85-90% of said stoichiometric ratio, of combined ester-forming and ether-forming and anhydride-forming compound is added. Such leads to “incomplete” reactions, or put different, partial modification of the un-modified biopolymer. Such partial modification may in fact be what is desired, having a specific application in mind.

In fact by selecting the amount of reactive compound, and/or a sequence of steps to be performed (such as plasticizing and functionalizing), the characteristics of the present unmodified microbial polymer can be modified as desired.

In an exemplary embodiment of the present method the polyol is selected from glycerol, trimethylolpropane, and pentaerythritol, from sugar alcohols ((CHOH) _n H2, where n = 4- 6), such as maltitol, sorbitol, xylitol, erythritol, and isomalt, and from polyvinyl alcohols (with formula (CH2CHOH) _n , wherein n<100, preferably wherein n<60, such as n<20),

In an exemplary embodiment of the present method the polyacid is selected from organic polyacids, such as dicarboxylic acids and tricarboxylic acids, such as citric acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and malonic acid.

In an exemplary embodiment of the present method in the step of (i) modifying by reacting the unmodified biopolymer the ester-forming or ether-forming or anhydride-forming compound is provided in a weight ratio compound:biopolymer of 1 : 10 to 1 : 1, preferably 1 :6 to 1 :2, such as 1 :5 to 1 :4.

In an exemplary embodiment of the present method the modified biopolymer is obtained at a temperature of > 100 °C, preferably > 140 °C, such as > 160 °C, and preferably < 185 °C. Typically the temperature is increased significantly, in order to speed up the reaction.

In an exemplary embodiment of the present method the modified biopolymer is reacted during 5-180 minutes, such as 10-60 minutes, such as 20-30 minutes, which is considered to be relatively quickly.

In an exemplary embodiment of the present method the pressure is < 1000 kPa, such as <100 kPa, in particular < 50 kPa, more in particular < 10 kPa, that is, under a reduced pres- sure, in particular under a reduced water pressure. As such water being formed during the reaction is removed rather easily.

In an exemplary embodiment of the present method is performed under a nitrogen atmosphere.

In an exemplary embodiment of the present method the un-modified biopolymer is selected from polysaccharides, wherein the saccharide is preferably selected from trioses, tetroses, pentoses, hexoses, heptoses, octoses, dodecyloses, from amino sugars, such as galactosamine, glucosamine, sialic acid, N-acetylglucosamine, from sulfosugars, such as sulfoqui- novose, and carrageenan, from ascorbic acid, and mannitol, from polyuronic acids, such as comprising glucuronic acid, d-Galacturonic acid, and mannuronic acid, poly sugar acids, such as comprising aldonic acid, ulosonic acid, uronic acid, aldaric acid, Glyceric acid (3C), Xy- lonic acid (5C), Gluconic acid (6C), Ascorbic acid (6C), Neuraminic acid (5-amino-3,5-dide- oxy-D-glycero-D-galacto-non-2 -ulosonic acid), Ketodeoxy octulosonic acid (KDO or 3-de- oxy-D-manno-oct-2 -ulosonic acid), Glucuronic acid (6C), Galacturonic acid (6C), Iduronic acid (6C), Tartaric acid (4C), meso-Galactaric acid (Mucic acid) (6C), and D-Glucaric acid (Saccharic acid) (6C), polymers comprising nonulosonic acid, such as sialic acid, such as alginate, inulin, starch, and celluloses, nitropolysaccharides, guar, and extracellular substances obtainable from granular sludge such as Kaumera, or wherein the bio-polyester is selected from polyhydroxy alkanoates (PHA), preferably wherein the PHA is formed from C2-C7 carboxylic acids, such as Poly(3-hydroxybutyrate-co-3 -hydroxy valerate) (PHBV), polylactic acid (PLA), and poly hydroxy butyrate (PHB), hybrid polymers thereof, and block- or co-polymers thereof , and combinations thereof. So, a large variety of microbial polymers can be used in the present invention for modification.

In an exemplary embodiment of the present method the un-modified biopolymer is anionic or cationic. In view of solubility in water such may be an advantage.

In an exemplary embodiment of the present method the un-modified biopolymer is a non-linear biopolymer.

In an exemplary embodiment of the present method the un-modified biopolymer has an average molecular weight of >5kDa (size exclusion chromatography), preferably > 10 kDa, more preferably >20 kDa, such as > 100 kDa. Size exclusion chromatography, such as by using a Shimadzu SEC, can be done using a suitable protocol, which are readily available. Such applies to other molecular weights as well.

In an exemplary embodiment of the present method the un-modified biopolymer has an average molecular weight of <1500kDa (size exclusion chromatography), preferably < 1000 kDa, more preferably <500 kDa.

In an exemplary embodiment of the present method the un-modified biopolymer has a multifunctionality, that is has different reactive groups, such as exemplified above. The multifunctionality introduces some complexity at the one end, but also offers versatility at the other end. In an exemplary embodiment of the present method the modified biopolymer-com- pound ester has an average molecular weight of >10 kDa.

In an exemplary embodiment of the present method the polyol and polyacid are provided in a molar ratio of available OH-groups in polyol: avail able acid groups in polyacid of 1 : 10 to 1:2, preferably 1 :5 to 1 :3.

In an exemplary embodiment of the present method a partial reaction is performed, such as forming an anhydride, thereby removing a H2O molecule, and still remaining reactive functionality of the COOH, which may be used later. In view of the multifunctionality and polymeric character of the present biopolymer clearly more than one water molecule per biopolymer molecule can be removed.

In an exemplary embodiment of the present method the modified biopolymer-com- pound ester is post-cured at a temperature of > 150 °C, preferably > 160 °C, such as > 170 °C.

In an exemplary embodiment of the present method the modified biopolymer-com- pound ester is post-cured during 5-120 minutes, such as 10-60 minutes, such as 20-30 minutes.

In an exemplary embodiment of the present method the un-modified biopolymer comprises 30-200 % free OH-groups, in particular 50-150%, and/or comprises 5-30% free COOH groups, in particular 10-25%, and/or comprises 1-10% free NH2 groups, in particular 5-8%.

In an exemplary embodiment of the present method the unmodified biopolymers have an number average molecular weight of 50-75 kDa, such as after extraction with Na2CCf have an number average molecular weight of 20-45 kDa, such as after extraction with NaOH at a pH of 11-12, or have an number average molecular weight of 100-150 kDa, e.g. about 120 kDa , such as after extraction with NaOCl [as determined with GPC/SEC],

In an exemplary embodiment of the present method the modified biopolymer is nonsoluble in water.

In an exemplary embodiment of the present method during (i) modifying, (ii) plasticizing, or (iii) functionalizing at least one further additive is provided, or a combination thereof.

In an exemplary embodiment of the present method during (i) modifying, (ii) plasticizing, or (iii) functionalizing at least one mono-carboxylic acid is provided, or a combination thereof.

In an exemplary embodiment of the present method 30-99 wt.% fibres are added to the modified or un-modified biopolymer, in particular cellulosic fibres, such as fibres of 0.2-7 mm length, in particular 1-5 mm in length such as 2-4 mm.

In an exemplary embodiment of the present method a water content of the modified or un-modified biopolymer is reduced, such as by hot-pressing at a temperature of 140-170 °C, in particular 145-160 °C, and/or under a pressure of 1-100 kN, in particular 10-30 kN, such as 15-20 kN, and/or during a time of 10-60 minutes, in particular 15-45 minutes, such as 38-42 minutes.

In an exemplary embodiment of the present method a water content of the modified or un-modified biopolymer is reduced by pre-drying of the modified or un-modi- fied biopolymer during a time of 10-240 minutes, in particular 60-180 minutes, at a temperature of 50-100 °C, in particular 70-80 °C.

In an exemplary embodiment the present fibre reinforce composite has a flexural modulus of 1-7 GPa (ASTM D790-17), and/or has a flexural strength of 5-30 MPa (ASTM D790-17).

The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

EXAMPLE S/EXPERIMENTS

The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying examples.

For a PHBV, treated with citric acid, and glycerol (in the given weigh ratios) the following adhesive properties were obtained:

Material Adhesion energy (J/m ² ) after 10 minutes

Paper on glass of PHBV (90:7.5:2.5) 427 J/m ²

Textile on glass of PHBV (90:7.5:2.5) 605 J/m ²

Textile on glass of PHBV (95:3.75: 1.25) 228 J/m ²

Post-it on glass 12.1 J/m ²

Sellotape on glass 245 J/m ²

Table 1 : adhesion energy measured on different materials.

In a further example a T _g of -6 to -10 °C, was obtained, depending on an amount on HV in the PHBV. A melting point of about 194 °C, a K of 1558°C/Da, and a t=0.4 in a Flory-Fox like Tm dependence was obtained. The melting temperature was > 150 °C for PHBV with small amounts of HV..

Kaumera (extracellular substances obtainable from granular sludge) films

Thin Kaumera/CA films were made at Chaincraft, by drying a solution of the two components. For DMTA testing, a film thickness of 100 to 200 pm was desired. Therefore, before a first iteration at creating the films, the thickness that would result from the drying process was calculated by using the geometry of the cupcake trays the films were to be made in and estimating the eventual density of the film. The assumptions in this calculation, however, were plenty, which resulted in insufficiently coherent films. Several batches were made, of which the last one is described here.

First, about 20 g of 12 weight % Kaumera solution was weighed off and diluted to 4% with demineralised water. Next, different amounts of citric acid were added to the solution, to get specific ALE/CA ratios. These mixtures were stirred for about 10 minutes before specific amounts were poured into cupcake trays. These were then dried in the oven at 40 °C for at least 24h. The amount of solution poured into the cupcake tray was based on the earlier calculations, but multiplied by 3 or 4, depending on the results of previous batches of films. Films were made with 0, 20, 22, 25, 29, 33, 40 and 50 weight % of citric acid.

After transporting them to Delft, the films were once again dried at 40 °C, this time in a vacuum oven, to remove any moisture. Afterwards, they were placed in a desiccator. Before testing, the films were cut into 3mm wide strips to be able to fit in the DMTA machine.

DMTA testing

For DMTA testing, the strips were manually cut to a length of approximately 2 cm to fit in the machine. Temperature sweep measurements were done for different temperature ranges in between -50 °C and 300 °C with a heating rate of 2 °C/min. The load was amplitude controlled, where the amplitude was set manually to be sure that the samples were in the linear regime. The load was always applied at 1 Hz. The machine used was a Perkin Elmer DMTA e7.

TGA testing

For TGA testing, small pieces of the films were used of around 8 mg. First, a temperature sweep test of 30 °C to 230 °C at 2 °C per minute was done on a pure Kaumera sample and a 25 weight % CA sample in order to identify temperatures at which different reactions would take place. Then, five more samples were subjected to a temperature sweep with isothermal steps at these temperatures so that the specific reactions would have the time to finish before others started. Doing so, individual reaction peaks could be deconvoluted in the timeweight graphs. The program had several heating steps at 2 °C per minute, and 30-minute isothermal steps at 90 °C, 115 °C, 160 °C and 220 °C. The full temperature range was 30 °C to 250 °C. The device used was a Perkin Elmer TGA 8000.

In an example the glass transition temperature is obtained by reading the temperature at the point where the storage modulus becomes 1.25 GPa, which is around 20 °C. The glass transition point was determined derived to be about 40 °C. For TGA an initial 2 °C/min sweep for the pure Kaumera and 25% CA samples are taken. This showed water released per CA reaction. The amount of water released per citric acid molecule, on average, can be calculated from this data. The higher this number is, the higher the degree of cross-linking, because a molecule reacting with a Kaumera chain releases 1 water molecule, whereas a citric acid molecule reacting with another releases only 0.5 water molecules per CA molecule. The upper limit will be 2, which is when each CA molecule reacts with a Kaumera chain on both sides. In these tests, the numbers were around 0.5 for 24w% samples, and 0.3 for 50w% samples. This indicates that the samples with a lower CA content, were more efficiently cross-linked than those with a higher content.

Testing of composites with Kaumera

The following composites were investigated: A set of 20 samples consisting of 64 g of citric acid, 160 g of ALE and 56 g of shredded toilet paper.

A set of 10 samples consisting of 46 g of citric acid, 160 g of ALE and 56 g of shredded toilet paper.

A set of 18 samples consisting of 64 g of citric acid, 160 g of ALE and 56 g of ReCell R cellulose. The 3 -point-bending test were performed at the mechanical lab in the faculty for maritime, mechanical and materials engineering at TU Delft. They were performed according to the standard ASTM D790-17, which was the most up to-date version of the ASTM standard for testing "Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials" (ASTM International, 2017), the strain rate, which was given as 0:01mm/mm/min by ASTM International (2017).. The tests were performed on a Zwick Z010 tensile tester, using a 10 kN load cell. The machine was operated using the Zwick/Roell TestXpert 2.0 software. Furthermore, a Mituyoto micrometer was used to measure the dimensions of the samples, and a pair of digital calipers was used to measure the support span. ReCell is a recycled cellulose fibre form sewage water.

Mean flex. Flex. Modulus Mean Max. Max. strength

Modulus Ef [MPa] StDev (MPa) Strength Sm [MPa] StDev [MPa]

Toilet paper, much citric acid 3080 288 8.64 0.71

Toilet paper, little citric acid 4283 387 11.2 1.30

ReCell 3486 243 9.94 0.87

Table 2, Results of 3 -point bend-testing

For an exemplary recipe, comprising 100 parts H-Ale, 30 parts citric acid, 6.6 parts glycerol, 5 parts bamboo powder and 25 parts of the above ReCell, the parts being on a weight basis, curing times and temperatures were investigated. Curing times were from >90 minutes for the lowest tested temperature of 140 °C to about 25 minutes for the highest tested temperature of 170 °C. A temperature of 160 °C with a curing time of 35-50 minutes was found optimal, e.g. in terms of almost no degradation of the product obtained.

In view of water content in the Kaumera/ALE, and in view of water formed by the reaction of e.g. citric acid with the Kaumera, such as due to esterification, extra care was taken to remove water before and during the reaction of Kaumera with he further ester-forming or ether-forming or anhydride-forming compound. Temperatures were varied from 140-170 °C, in particular 145-160 °C, and/or under a pressure of 1-30 kN, in particular 10-15 kN, and/or during a time of 10-60 minutes, in particular 15-45 minutes, such as 38-42 minutes. It was found that typically >90% of the sample was cured and in particular most (97%) to all of the sample was cured. Thereby uniform samples were obtained. Fibre reinforced composites formed by the present method typically had a flexural modulus Efl _ex of 1-7 GPa, such as 2-5 GPa, and a flexural strength Gf of 5-30 MPa using the 3-point bending test, typically 10-20 MPa.

SUMMARY OF THE FIGURES

Figs, la-b, 2-3, and 4a-b show exemplary reactions.

DETAILED DESCRIPTION OF THE FIGURES

Fig. la shows a schematic reaction between two biopolymers, left and right, having reactive groups for reacting. Shown are OH-reactive groups, COOH-groups, NH2-reactive groups, whereas other groups, such as RSO4Hx groups, RPO4Hx groups, ester-groups, ethergroups, O-acetyl groups, sulfone groups, sulfonate groups, and sulphonamide groups, are not shown, but may be present. Citric acid is added, and reacts under forming of two esters in the example. Likewise, the citric acid may react with one or more of the other reactive groups. In fig. lb a similar reaction as with the citric acid above is shown with glycerol.

Fig. 2 shows a schematic reaction between a modified biopolymer and a glycerol. The modified biopolymer is thereby functionalized. Likewise the modified biopolymer is plasticized. It is noted the terms “functionalize” and “plasticize” may at least partly overlap, depending e.g. on the type of biopolymer, reactant, reaction conditions, etc.

Fig. 3 shows a schematic “reaction” between a modified biopolymer and a glycerol. The glycerol is incorporated into the modified biopolymer. The modified biopolymer is thereby plasticized.

Fig. 4a shows a schematic reaction between an un-modified biopolymer, in this case polylactic acid, and citric acid. The citric acid reacts with an end-group of the polylactic acid. Therewith the polylactic acid is thereby functionalized. Likewise the modified biopolymer is plasticized.

Fig. 4b shows a schematic reaction between an un-modified biopolymer, in this case polylactic acid, and citric acid. The citric acid reacts with an intermediate group of the polylactic acid, effectively dividing the polylactic acid in two polymer chain parts, one with p monomers, and the other with q monomers, and the citric acid moiety in between. Therewith the polylactic acid is thereby functionalized.