WO2015150750A1

WO2015150750A1 - Polysaccharide-based materials

Info

Publication number: WO2015150750A1
Application number: PCT/GB2015/050915
Authority: WO
Inventors: Andrew Peter Abbott; William WISE
Original assignee: University Of Leicester
Priority date: 2014-03-31
Filing date: 2015-03-26
Publication date: 2015-10-08
Also published as: GB201405796D0; GB2527023A

Abstract

There is provided a plastic or gel material comprising a mixture of: (a) a compound of formula (I) or a mixture of two or more compounds of formula (I), (M^a+)c(X^b-)d or a hydrate thereof, wherein c and d can be 1, 2 or 3, M^a+ is a Group I or II metal cation, X^b- is a monovalent, bivalent or trivalent anion; (b) one or more uncharged organic compounds, each of which compounds comprises at least one oxygen atom and at least one hydrogen atom that is capable of forming a hydrogen bond with X^b-; and (c) one or more polysaccharides, wherein each polysaccharide is a polymer of pyranose monomers, at least 30% of which monomers are in the α-anomeric conformation. There is also provided articles formed from such materials, uses of such materials and processes for forming such materials.

Description

Polysaccharide-Based Materials

This invention relates to plastic or gel materials based upon certain polysaccharides (pyranose-based polysaccharides containing at least 30% of the pyranose monomers in the a-anomeric form). This invention also relates to uses of such materials, processes for their preparation as well as to articles comprising such materials. These materials have particular application as binders for fiberized materials, and in particular for composite wood materials such as particle board, fibre board, MDF, chipboard and plywood. The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgment that the document is part of the state of the art or is common general knowledge.

Cellulose-based composites are major materials for the worldwide construction industry. Most buildings contain cellulose-based composites as a significant component. A significant advantage of cellulose-based composites is that they typically use waste products from the pulp and timber industries and so they are significantly less expensive than virgin timber. Typically, they are constructed of wood particles which are held together with 20% by weight of a thermoset resin.

The current UK market for wood products is listed in Table 1.

(Table 1 from Timber Trade Federation Statistical Review 2010).

Almost all of the resins used in fibreboard are either urea-formaldehyde (UF) or phenolformaldehyde (PF). The main concern with the use of these resins is the slow release of formaldehyde, which is a known carcinogen, often into an enclosed domestic environment. These formaldehyde-based resins have ideal properties for board use as they are simple to prepare and inexpensive. They do not readily degrade which is a service advantage. However, the fact that they do not degrade is also an environmental disadvantage. Fibreboard is widely used for short-term applications making it a significant environmental contaminant.

There is a need for alternative binders which do not release carcinogens and which are ideal for use due to their simplicity and low manufacturing costs. An innovative, alternative approach is to use a thermoplastic starch (TPS) as the binder. Surprisingly it has been found that mixtures of common hydrogen bond donors and salts can be used to plasticise starch. This thermoplastic material can be melted and injection moulded and acts as a good resin for forming composite woods such as medium density fibre board (MDF), particle board and chipboard. This type of resin provides an inexpensive, recyclable, compostable, fire-retardant alternative to the formaldehyde-based resins.

TPS can be used as an effective binding agent for a variety of cellulose-based particles to produce environmentally benign biodegradable boards. Types of cellulose-based particles include wood fibre, wood flour and wood particles. The fibres in the wood flour prevent crack propagation at low wood content and produce materials with a similar strength to MDF.

The starch-based materials can be machined in the same way as MDF but also have the advantage that they can be formed using vacuum or injection moulding. The starch-based materials are recyclable, which reduces their environmental impact in short-term constructs.

The starch-based boards are qualitatively superior to fire retardant (Class 0) MDF and eminently superior to standard MDF. A major processing advantage is that the wood- fibre/flour/particle and starch mixtures can be blended and stored long in advance of board production removing the necessity to have an active urea-formaldehyde (UF) process of board manufacture. Polymeric materials containing starch and plasticisers such as polyols are known (see, for example, WO 2008/071717 and WO 2008/090195). However, such materials do not contain salts of Group I and II metals or anions such as tetraborate or chloride. Further, these known materials require the presence of polymers other than polysaccharides to achieve acceptable mechanical properties.

We have now found, surprisingly, that plastic materials may be formed from a polysaccharide that is a polymer of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation, through mixing that polysaccharide with an uncharged, organic H-bond donor / acceptor and a salt of Group I or II metals.

According to the present invention there is provided a plastic or gel material comprising a mixture of:

(a) a compound of formula (I) or a mixture of two or more compounds of formula (I),

or a hydrate thereof, wherein

c and d can be 1 , 2 or 3,

M^a+ is a Group I or II metal cation,

X^b" is a monovalent, bivalent or trivalent anion;

(b) one or more uncharged organic compounds, each of which compound comprises at least one oxygen atom and at least one hydrogen atom and that is capable of forming a hydrogen bond with X^b" and or M^a+; and

(c) one or more polysaccharides, wherein each polysaccharide is a polymer of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation.

When used herein, the term "plastic material' refers to a material that can be moulded or pressed (i.e. a material that has the property of plasticity).

The term used herein "gel" refers to a semi-solid to almost solid colloid of a solid and a liquid.

In accordance with the present invention, the mixtures described herein can be used as resins and/or glues. The skilled person would understand the term "resin" to mean solid or semisolid viscous substances which are used principally as varnishes and adhesives. The skilled person would understand the term "glue" to mean an adhesive substance used for sticking objects or materials together. As will be appreciated by those skilled in the art, the term "ductile" refers to the ability of a material to be deformed plastically without fracture. Ductility of the plastic material can be determined, for example, by measurement of elongation to break. This can be done, for example, by taking a standard size of sample, such as a 10 mm diameter cylindrical sample between 3 and 5 cm long, securing one end of the sample to a fixed anchor and the distal end of the sample to a mobile anchor, applying force to the mobile anchor so as to move it away from the fixed anchor (thereby applying strain along the length of the sample) and then measuring the force required to extend the sample as well as the percentage elongation of the sample at fracture. By way of such measurements, not only can information be obtained on elongation to break of the plastic material, but also on the tensile strength (including the Ultimate Tensile Strength) of that material. Embodiments of the present invention relating to the plastic material include those in which the elongation to break of the plastic material (e.g. when measured at a temperature of 298 K) is at least 1 %, such as 2%, 5%, 10%.

Further embodiments of the present invention relating to the plastic material include those in which the Ultimate Tensile Strength of the plastic material (e.g. when measured at a temperature of 298 K) is from 10 to 10,000 kN/m², preferably from 10 to 1000 kN/m², more preferably from 20 to 700 kN/m² or more preferably from 30 to 450 kN/m².

Component (a)

In certain embodiments of the present invention, component (a) is a mixture of two or more compounds of formula (I) or, particularly, a compound of formula (I). In such embodiments, M^a+ may be a cation such as Na⁺, K⁺, Li⁺, Ca²⁺or Mg²⁺ as defined in respect of formula (la) above.

Anion X^b" is any monovalent, bivalent or trivalent inorganic anion. Embodiments of the invention include those in which X^b" is an inorganic anion selected from the list comprising halide, chlorate, perchlorate, bromate, nitrate, nitrite, cyanide, cyanate, thiocyanate, hydrogencarbonate, carbonate, sulfate, hydrogensulfate, pyrosulfate, sulfite, hydrogensulfite, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate, hexafluorophosphate, tetrafluoroborate, borate, diborate, triborate, tetraborate, carboxylate (e.g. any one of formate, acetate, trifluoroacetate, propionate, isobutyrate, heptanoate, decanoate, caprate, caprylate, stearate, acrylate, caproate, propiolate, ascorbate, citrate, glucuronate, glutamate, glycolate, a- hydroxybutyrate, lactate, tartrate, phenylacetate, mandelate, phenylpropionate, phenylbutyrate, benzoate, chlorobenzoate, methylbenzoate, hydroxybenzoate, methoxybenzoate, dinitrobenzoate, o-acetoxybenzoate, salicylate, nicotinate, isonicotinate, cinnamate, oxalate, malonate, succinate, suberate, sebacate, fumarate, malate, maleate, hydroxymaleate, hippurate, phthalate, terephthalate and the like) and sulfonate (e.g. any one of benzenesulfonate, methyl-, bromo- or chloro-benzenesulfonate, xylenesulfonate, methanesulfonate, trifluoromethanesulfonate, ethanesulfonate, propanesulfonate, hydroxyethanesulfonate, 1- or 2- naphthalene-sulfonate, 1 ,5- naphthalenedisulfonate and the like).

Particular embodiments of the invention that may be mentioned include those in which X^b" is a mono or divalent anion, such as a monovalent anion selected from the list above (e.g. an anion selected from the list comprising fluoride, chloride, bromide, iodide, nitrate and acetate (such as bromide or, particularly, chloride or tetraborate)).

Optionally, wherein component (a) is a hydrated metal salt. Component (b)

The term "organic" will be well understood by those skilled in the art. Thus, when used herein, the term "organic" includes references to uncharged chemical compounds (other than carbon, oxides of carbon, or acids of (bi)carbonate, cyanide, cyanate, thiocyanate or fulminate), whose molecules contain carbon.

The term "uncharged", when used herein in relation to component (b), refers to organic molecules (compounds) that do not bear a permanent positive or negative (electrostatic) charge on any atom within the molecule. In this respect, uncharged organic compounds are those that comprise a single, covalently-bonded molecule and that are not separated into cationic and anionic components.

Whether a compound contains a hydrogen atom that is capable of forming a hydrogen bond with M^a+ and /or X^b" will either be evident to those skilled or can be determined by methods known to those skilled in the art (see, for example, Paul D. Beer, Philip A. Gale and David K. Smith, Supramolecular Chemistry (Oxford Chemistry Primers), Oxford University Press, Oxford, 1999, and especially Chapter 3 (pages 31 to 42) and the references cited therein). For example, a titration can be conducted in which anion X^b" is added to the dissolved compound and changes in a physical property connected with the H-atoms of the compound (e.g. a spectroscopic signal, such as an infrared or ¹ H NMR signal) are monitored. For instance, the compound in question may be dissolved in a deuterated solvent (such as deuterated chloroform, dichloromethane or acetonitrile) and changes in the ¹ H NMR signals from that compound monitored when aliquots of sodium tetraborate are added to the solution.

According to one embodiment of the present invention each compound forming component (b) can have:

(i) a melting point greater than -20°C (e.g. from -20 to 200, 180, 160 or, particularly, 140°C); and/or

(ii) a molecular weight of less than 200 g/mol (e.g. from 45 to 200, 180, 160, 140 or, particularly, 120 g/mol).

In these and other embodiments, the compound forming component (b) may be an amide or polyol.

When used herein in connection with component (b), the term "amide" includes references to compounds containing a -C(0)N(H)- structural fragment. Further when used herein in connection with component (b), the term "polyof includes references to compounds containing two or more hydroxyl (-OH) groups.

Thus, embodiments of the present invention include those in which component (b) is a one or more compounds of formula (Ilia) and/or one or more compounds of formula (1Mb),

HO-Y-OH (1Mb)

wherein:

R⁸ represents H, Ci_-4 alkyl (which latter group is optionally substituted by one or more F atoms), phenyl (which latter group is optionally substituted by one or more substituents selected from halo, Ci_-4 alkyl and Ci_-4 alkoxy) or N(R⁹)R¹⁰;

R^8a represents H or Ci_-4 alkyl (which latter group is optionally substituted by one or more F atoms);

R⁹ and R¹⁰ independently represent H or Ci_-4 alkyl (which latter group is optionally substituted by one or more F atoms);

Y represents C2-10 alkylene or C₄-8 cycloalkylene optionally (i) substituted by one or more substituents selected from F, OH, SH, N(R¹¹)R¹² and C1-4 alkyl (which latter group is optionally substituted by one or more substituents selected from F and OH), and/or

(ii) interrupted by one or more groups selected from O, S and NR¹³; and

R¹¹ to R¹³ independently represent H or C1-4 alkyl (which latter group is optionally substituted by one or more substituents selected from F and OH).

Embodiments of the present invention that may be mentioned include those in which: (1) R⁸ represents H, CF₃, or, particularly, methyl, phenyl, NH₂, N(H)CH₃ or N(CH₃)₂; (2) R^8a represents methyl or, particularly, H;

(3) a represents

C2-6 alkylene (e.g. C2-6 n-alkylene) optionally substituted by one or more (e.g. one, two, three or four) OH groups, or

C5-6 cycloalkylene substituted by one or more (e.g. five or six) substituents selected from OH and C1-2 alkyl (which latter group is optionally substituted by two OH groups or, particularly, one OH group).

Further embodiments that may be mentioned include those in which:

(1) R⁸ represents methyl, phenyl, N(H)CH₃ or, particularly, N H2;

(2) R^8a represents methyl or, particularly, H;

(3) a represents unsubstituted C2 alkylene or C₃-6 n-alkylene optionally substituted by one or more (e.g. one, two, three or four OH groups).

In certain embodiments of the present invention, the compound of formula (1Mb) is a compound of formula (IV),

R^Y is H or OH; and

p is 0 to 4 (e.g. 1 , 2, 3 or 4).

Thus, particular embodiments of the present invention that may be mentioned include those in which component (b) is one or more compounds selected from the list comprising benzamide, acetamide, /V-methylurea, Λ/,Λ/'-dimethylurea urea, glycerol, mannitol, xylitol, ethylene glycol and propylene glycol (e.g. one or more compounds selected from the list comprising benzamide, acetamide, /V-methylurea, Λ/,Λ/'-dimethylurea urea, glycerol, mannitol, xylitol and propylene glycol), or, alternatively, one or more compounds selected from the list comprising acetamide, glycerol or, particularly, urea. Component (c)

As detailed above, component (c) is one or more polysaccharides, wherein each polysaccharide is a polymer of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation.

A pyranose monomer is a monomer of a pyranose polysaccharide that is based upon a (tetrah dro)pyran ring. tetrahydropyran

In polysaccharides, pyranose monomers are linked together by the formation of ether bonds involving an -OH group attached to a C-atom that is also attached to the O-atom of the (tetrahydro)pyran ring. This -OH group can be present in the cyclic monomer group in one of two conformations, namely the a- and the β-anomeric conformations (illustrated below by use of a particular "chair" conformation of the pyranose ring).

a-anomer (3-anomer

(OH axial) (OH equatorial)

The C-atom in the above-depicted structures to which the two O-atoms are attached is called the anomeric carbon, and also represents a chiral centre when the molecule is locked in the ring conformation. In this respect, it is to be noted that the formation of the ring is reversible in aqueous solution for pyranose monomers, due to interconversion of the molecules between linear (hydroxyaldehyde) and cyclic (hemiacetal) forms.

The polysaccharides employed as component (c) according to the present invention contain pyranose monomeric units, at least 30% of which monomers are in the a-anomeric conformation. The a-anomeric conformation in a polysaccharide is illustrated below by reference to the structure of amylose (which is used as an illustrative example only).

a-anomeric conformation in amylose

(illustrative example)

In amylose, the ether bonds are formed between the 1- and 4-positions of pyranose monomer (i.e. between the anomeric carbon and the C-atom in the 4-position in the ring relative to that carbon). Such linkages are described as a(1→4). However, the polysaccharides employed in the present invention may contain any ether linkages found in polysaccharides derived from natural sources, such as α(1→6), β(1→4) and/or β(1→6), provided that at least 30% of the pyranose monomers are present in the a-anomeric conformation.

Embodiments according to the present invention that may be mentioned include those in which the or each polysaccharide of component (c) comprises:

one or more of amylose, amylopectin, agarose and agaropectin;

a mixture of amylose and amylopectin; or

a mixture of agarose and agaropectin. Particular embodiments that may be mentioned in this respect include those in which component (c) is:

one or more polysaccharides (e.g. one polysaccharide) selected from the list comprising agar and a starch; or

one or more polysaccharides (e.g. one polysaccharide) selected from the list comprising agar and a starch selected from the list comprising corn starch, potato starch, wheat starch, tapioca starch and soluble starch.

Embodiments of the present invention that may be mentioned include those in which the one or more polysaccharides of component (c) each comprise a minimum of 30 (e.g. a minimum of 40, 50, 75, 100, 200, 300, 500, 1000, 10000 or 20000) pyranose monomer units. Further embodiments of the present invention that may be mentioned include those in which the weight average molecular weight of the or each of the one or more polysaccharides of component (c) is at least 4 kDa (e.g. at least 6, 8, 12, 16, 32, 48, 60, 100, 300 or, particularly, 500 kDa).

Particular embodiments of the present invention that may be mentioned include those in which:

polysaccharide component (c) is the sole polymeric component of the plastic or gel material; or

the plastic or gel material is substantially free of polymers that are not polysaccharides (or that are not polysaccharides that are polymers of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation). The term "substantially free", when used herein in relation to certain polymers, includes references to plastic or gel materials according to the first aspect of the invention that comprise at most 10% (e.g. at most 9, 8, 7, 6, 5, 4, 3, 2, 1 , 0.5, 0.1 or 0.01 %) by weight of polymers that are not polysaccharides (or that are not polysaccharides that are polymers of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation).

Other embodiments of the present invention that may be mentioned include those in which the plastic or gel material is substantially free of water.

For the avoidance of doubt, the present invention encompasses embodiments wherein the gel or plastic material contains components described through a combination of any two or more embodiments of the invention that are detailed above and that are not mutually exclusive. Thus, for example a particular embodiment of the first aspect of the invention is a plastic or gel material comprising a mixture of:

(a) one or more compounds selected from the list comprising a Group I or II salt;

(b) one or more compounds selected from the list comprising an amide and a polyol; and

(c) one or more polysaccharides, the or each polysaccharide comprising one or more of amylose, amylopectin, agarose and agaropectin. Component (d)

The plastic material described above can optionally contain a composite component as a major or minor constituent. This can be a constituent that provides a functional property such as anti-static, lubricating or colouring agent. Alternatively it can be a filler such as wood dust, wood fibre, wood flour, wood particles, chalk or carbon black. Particularly this material will contain a plant fibre such as wood, miscanthus, hemp, bagasse, coir, jute, sisal, cotton. In accordance with the present invention, the plastic or gel material can be used as a substitute for thermoset resins such as urea-formaldehyde or phenol formaldehyde in particle board, medium density fibre-board or plywood.

Of particular note are the materials based on the description of components (a), (b) and (c) above, have thermoplastic properties and are unlike thermoset resins commonly used in fibre and particle boards. Using the composition described according to the present invention imparts the ability to partially re-melt some of the material allowing it to be recycled. Many of the components described in (a), (b), (c) and (d) are biodegradable allowing the composite material to be composted at end-of-life. Furthermore, by using hydrate salts such as borax for component (a), this can impart fire retardant properties to the material which is of particular importance for wood-based composites.

Further, another particular embodiment of the first aspect of the invention is a plastic or gel material comprising a mixture of:

(a) one or more compounds (e.g. one compound) selected from the list comprising sodium tetraborate, sodium chloride, sodium bromide, sodium acetate, calcium chloride and magnesium chloride each optionally in their hydrate form e.g. CaCl2.2H20;

(b) one or more compounds (e.g. one compound) selected from the list comprising benzamide, acetamide, /V-methylurea, Λ/,Λ/'-dimethylurea, urea, glycerol, mannitol, xylitol and propylene glycol; and

(c) one or more polysaccharides (e.g. one polysaccharide) selected from the list comprising agar and a starch.

In still a further embodiment of the present invention, the plastic or gel material is one in which:

the molar ratio of component (a) to component (b) is from 1 : 10 to 1 :1 , particularly, from a lower limit such as 1 :4, the ratio of the combined mass of components (a) and (b) to the mass of the polysaccharide component (c) is from 1 :2 to 4: 1.

Other embodiments of the present invention that may be mentioned, include those in which component (a) forms at least 7.5% by weight of the plastic or gel material (such as at least 10, 12.5, 15 or 20% by weight of said material). When the fibre- or particle- based material is of plant origin e.g. wood, help, flax, coir etc. then the natural water content of these components may increase the overall water content of the finished material to typically 20%.

A particular embodiment of the present invention relates to plastic or gel materials in which: component (b) is a one or more compounds of formula (Ilia) and/or one or more compounds of formula (1Mb); and

the plastic or gel material is substantially free of polymers that are not polysaccharides (or that are not polysaccharides that are polymers of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation).

Other embodiments of the invention that may be mentioned relate to plastic or gel materials defined by a combination of this particular embodiment with any one or more embodiments of present invention that are detailed above and that are not mutually exclusive.

In addition to components (a), (b), (c) and (d), the plastic or gel material of the present invention may contain one or more further additives. Additives that may be mentioned in this respect include those selected from the list comprising fillers, stabilizers, anti-wear agents and blowing agents. Depending upon the nature of the additive, the additive may be incorporated into the plastic or gel material according to the present invention either: by mixing the additive with any one or more of the precursor components of the material (i.e. components (a), (b), (c) and (d)) before those components are converted to the plastic or gel material; or

by mixing the additive with the plastic or gel material after that material has been formed from its precursor components (e.g. using conventional blending techniques).

Alternatively, additional materials may be combined with the plastic or gel material, such as structurally reinforcing materials. Thus, according to a further aspect of the present invention, there is provided a composite material comprising:

(A) a plastic or gel material according to any one of the above-described embodiments of the present invention; and

(B) another material.

The other material mentioned at (B) above may be a natural material (e.g. plant-derived material, such plant material employed as a source of polysaccharide component (c)), a ceramic, a glass, and/or a synthetic material such as a plastic, a resin or carbon fibres or nanotubes. In certain embodiments according to the present invention, the other material is:

(i) a structurally reinforcing material; or

(ii) one or more materials selected from the list comprising cellulose fibres, wood fibres, wood flour, wood particles, lignin fibres, carbon fibres, glass fibres or ceramic powders.

In accordance with the present invention, the composite material can be a composite wood (also known as an engineered wood, man-made wood or manufactured board) which includes, but is not limited to MDF, particle board, chipboard and plywood. Composite wood are manufactured by binding or fixing the strands, particles, fibres, veneers or boards of wood, together using the plastic and gel materials described herein as resins and/or glues.

The composite material according to the present invention may be formed either:

(I) by mixing the other material with any one or more of the precursor components of the plastic or gel material according to the present invention (i.e. components (a), (b) and (c)) before those components are converted to the plastic or gel material;

(II) by mixing the other material with the plastic or gel material of the present invention after that material has been formed from its precursor components (e.g. using conventional techniques for forming composites of plastics with other materials); or

(III) by premixing components (a), (b) and (c) to form a viscous liquid and then sprayed through heated nozzles over component (d) and this material is then formed by the application of both heat and pressure. This process is similar to the resination technique currently used to apply resins to fibres in particle and fibre board manufacture.

The plastic or gel material according to the present invention may be prepared by a process comprising providing a mixture of components (a), (b) and (c), as described above. Thus, according to a further aspect of the present invention there is provided a process for preparing a plastic or gel material of the present invention, said process comprising:

providing a mixture of

(a) a compound of formula (I) or a mixture of two or more compounds of formula

(I), as defined above,

(b) one or more uncharged organic compounds, each of which compounds comprises at least one oxygen atom and at least one hydrogen atom that is capable of forming a hydrogen bond with anion X^b" of the compound of formula (I);

(c) one or more polysaccharides, wherein each polysaccharide is a polymer of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation; and optionally one or more additives, wherein the mixture is heated until the plastic or gel material is formed; or

(ii) for the preparation of foamed, plastic materials of the present invention, a mixture of components (a), (b) and (c) is provided, optionally an additive as defined in (i) above, and a volatile material, and then the mixture is heated until a plastic material is formed and the volatile material has volatilised and imparted a foamed structure to the plastic material. Formation of the plastic or gel material according to the present invention can be determined, for example, by inspection of the properties of the mixture (of components (a), (b) and (c) and, optionally (d)) after heating.

As components (a), (b) and (c) are all non-plastic, the conditions (e.g. temperature and duration of heating) required to form the plastic or gel material can easily be determined for any given mixture of such components. However, preferable conditions that may be mentioned include:

heating the mixture to a temperature from 50 to 200°C, such as from 75 to 190°C or from 100 to 180°C (e.g. 150°C or 160°C);

· heating the mixture for any length of time from 30 seconds to 600 minutes, such as from 30 seconds to 240 minutes, from 1 to 180 minutes or from 2 to 120 minutes (e.g. from 3 to 30 minutes); and/or

heating the mixture under atmospheric pressure or, alternatively, under elevated pressure (e.g. from 200 to 2,000 kPa, such as from 900 to 1 ,100 kPa).

When both heat and pressure are used to form the material according to the present invention, they may both be conveniently applied by way of a heated press. When used herein, the term "volatile material" includes references to materials that, at atmospheric pressure (e.g. 101.325 kPa) and upon heating to moderate temperatures (e.g. a temperature in the range from 50 to 180°C), convert from solid or liquid form to entirely gaseous form. In this respect, volatile materials that may be mentioned include volatile organic solvents such as any one or more compounds selected from the list comprising water, dichloromethane, diethylether, ethanol, ethylacetate, hexane, pentane and acetone.

For the avoidance of doubt, components (a), (b) and (c), as well as the optional additives, may take any of the definitions provided above in relation to the present invention.

Further, in the processes according to the present invention, the ratios of components (a), (b) and (c) may be the same as those described in relation to the plastic or gel material according to the present invention.

The components (a), (b) and (c) may be mixed in any order. For example, components (a) and (b) may be mixed together first and then component (c) added to the mixture so formed. As another example, components (a), (b) and (c) may be mixed together simultaneously.

In an alternative embodiment, component (c) may be replaced by a source of one or more polysaccharides, wherein each polysaccharide is a polymer of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation. For example, polysaccharides from natural sources (e.g. plant materials such as grains, tubers and fruits) may be employed in unrefined state to form a plastic, gel material or a composite according to the present invention.

In this alternative embodiment, the source of one or more polysaccharides, wherein each polysaccharide is a polymer of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation (e.g. a natural source such as grains, tubers and fruits) is contacted with components (a) and (b) (which components are optionally pre-mixed together) and then heated until a plastic, gel material or a composite material according to the present invention, is formed.

In relation to the above, suitable natural sources of polysaccharides that are polymers of pyranose monomers, at least 30% of which monomers are in the α-anomeric conformation include natural sources of agar and starches, such as corn, wheat, tapioca, potato peel, banana peel, orange peel, algae from the genera Gelidium and Gracilaria or the seaweed Sphaerococcus euchema. When such a natural source of polysaccharide is employed, any residual materials from that natural source (e.g. materials, such as cellulose, that are not polysaccharides that are polymers of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation) may either be:

retained in the material formed by the process of the alternative embodiment of the present invention (thereby providing a composite material according to the present invention); or

separated from the plastic or gel material formed from the one or more polysaccharides that are polymers of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation (thereby providing a plastic or gel material according to the present invention).

In another alternative embodiment, composite materials according to the present invention may be formed by providing a mixture of components (a), (b), (c) and another material, and optionally an additive, and then heating that mixture until the composite material is formed. In this alternative embodiment, the other material may be, for example a structurally reinforcing material, such as one or more materials selected from the list comprising cellulose fibres, wood fibres, wood flour, wood particles, lignin fibres, carbon fibres, glass fibres or ceramic powders. The gel, plastic materials and composite material of the present invention have, due to their mechanical and physicochemical properties, a wide variety of uses, such as for packaging materials. Thus, according to another aspect of the invention, there is provided the use of a plastic, gel material or a composite material according to the present invention as a packaging material.

Furthermore, the gel or plastic materials according to the present invention can be used as a resin, glue, binder or adhesive. In particular, the materials can be used as a resin or binder for fiberized materials, including but not limited to wood. Articles prepared from the plastic or gel materials of the present invention may be provided with a coating (e.g. a hydrophobic coating) in order to improve their resistance to water. Thus according to a further aspect of the present invention there is provided an article wherein the article comprises a plastic, gel material or a composite material according to the present invention, that is coated with a water-resistant (e.g. hydrophobic) material.

Embodiments of this aspect of the invention include articles wherein the coating of water- resistant material covers at least 50% (e.g. at least 60, 70, 80, 90, 95 or 99%, such as 100%) of the exposed surfaces of the plastic, gel or composite material. In this respect, the term "exposed surfaces", when used herein, includes references to surfaces of the plastic, gel or composite material that, at room temperature and atmospheric pressure, are accessible to (externally-introduced) liquid water or water vapour.

When used herein, the term "water-resistant materia?' includes references to materials that, at a temperature of 298 K, have a solubility in water of less than 50 ppm (or less than 50 mg/L, such as less than 25, 10, 5 or 1 mg/L). Examples of water-resistant materials that may be mentioned include waxes (e.g. waxes based upon molecules containing at least 20 C-atoms, such as from 20 to 30 C-atoms), hydrophobic polymers (e.g. polyvinylacetate) and polymers such as polyvinylalcohol. Specific waxes that may be mentioned in this respect include those selected from the group consisting of paraffin wax, beeswax, bayberry wax, candelilla wax, caranday wax, castor bean wax, shellac wax, spermaceti wax, sugar cane wax and wool wax (lanolin).

It has been found that the application of pressure to plastic or gel materials of the present invention can modify the physical and/or mechanical properties of those materials (e.g. by increasing translucency, elasticity, toughness and/or hardness, and/or by decreasing ultimate tensile strength and/or Young's Modulus of the material). Thus, according to another aspect of the present invention there is provided a method of modifying physical and/or mechanical properties of a plastic or gel material, said method comprising the step of applying elevated pressure to the plastic or gel material.

When used herein,, the term "applying elevated pressure" includes references to applying above-atmospheric pressure (i.e. pressure above 101 ,325 Pa, such as from 2 x 10⁵ to 1 x 10⁷ Pa (2 to 300 bar)) to the material. The pressure may, for example, be conveniently applied by placing the plastic or gel material between two parallel metal plates and using elevated pressure to force the plates towards each other. The materials according to the present invention have the advantages that:

they may be prepared entirely from renewable, natural materials (e.g. materials that do not derive from fossil fuels, such as polysaccharide-containing food waste); they may be prepared entirely from materials that are non-toxic (e.g. non-toxic to humans);

they may be completely biodegradable / compostable;

they may biodegrade to materials that are harmless to the environment (e.g. to non- toxic materials);

they may by prepared by simple processes (including: energy- and/or material- efficient processes; process involving a small number of steps such as one- or two-step processes; one-pot processes; and/or processes not requiring chemical modifications of a natural polysaccharide constituent of the materials);

· they may have mechanical properties that render them suitable for a wide variety of applications;

they may be prepared either directly in the form required (e.g. a form not requiring further processing, such as moulding, laminating or re-casting) or in a form that is easy to manipulate;

· they may be recoverable and/or recyclable (e.g. by simple processes such as dissolution / reformation);

they may be stable to heat and/or flame resistant; and/or

they may be electrically conductive. Without wishing to be bound by theory, the advantageous mechanical properties of the materials according to the present invention are believed to derive from the conversion (by use of components (a) and (b)) of the polysaccharide (component (c)) from its largely crystalline native form to a stable, essentially amorphous form having reduced inter- and/or /^'nfra-chain H-bonding.

Brief Description of the Figures

Figure 1 shows a photograph of a sample of 40 wt % starch, 35.5 % glycerol and 24.5% borax pressed at 130 °C for 5 minutes.

Figure 2 shows samples of wood fibre bound using starch, glycerol and borax as a binder. The top sample comprises 45% wood fiber, 10% starch, 22.1 % glycerol and 22.9% borax. The bottom sample comprises 50% wood fibre, 10% starch, 19.7% glycerol and 20.3% borax. Figure 3 is a photograph showing the recycling procedure for a sample comprising 42% woodflour, 13% starch, 26.6% glycerol and 18.4% borax. Photographs: (a) shows a fresh block, (b) shows the sample ground to a fine powder and (c) shows a repressed block. Figure 4 is a graph showing the ultimate tensile strength of samples of wood fiber bound with 40 % woodfibre, 20% starch and 20% modifier where the modifier was (from I to r) glycerol, and then glycerol with different salts; borax, CaCl2.2H20, MgC .ehbO and NaCI.

The above starch-based product formed according to the present invention have been found to be less expensive to produce, are less dense and are advantageously more resistant to moisture.

Claims

1. A plastic or gel material comprising a mixture of:

or a hydrate thereof, wherein

c and d can be 1 , 2 or 3,

M^a+ is a Group I or II metal cation,

X^b" is a monovalent, bivalent or trivalent anion;

(c) one or more polysaccharides, wherein each polysaccharide is a polymer of pyranose monomers, at least 30% of which monomers are in the a-anomeric conformation, and wherein the plastic or gel material is substantially free of polymers that are not polysaccharides.

2. The plastic or gel material as claimed in Claim 1 , wherein the compound of formula (I) is selected from the list comprising sodium tetraborate, sodium chloride, sodium bromide, sodium acetate, calcium chloride and magnesium chloride each in either its hydrate or anhydrous form.

3. The plastic or gel material as claimed in any one of Claims 1 or 2, wherein the plastic or gel material comprises at most 5% by weight of polymers that are not polysaccharides.

4. The plastic or gel material as claimed in any one of Claims 1 to 3, wherein the plastic or gel material comprises at most 10% by weight of water.

5. The plastic or gel material as claimed in any one of Claims 1 to 4, wherein component (b) is one or more compounds selected from the list comprising acetamide, N- methylurea, Λ/,Λ/'-dimethylurea urea, glycerol, mannitol, xylitol, ethylene glycol and propylene glycol.

6. The plastic or gel material as claimed in any one of Claims 1 to 5, wherein the polysaccharide of component (c) comprises one or more of amylose, amylopectin, agarose and agaropectin.

7. The plastic or gel material as claimed in Claim 6, wherein component (c) is one or more polysaccharides selected from the list comprising agar and a starch.

8. The plastic or gel material as claimed in any one of Claims 1 to 7, wherein the material comprises a mixture of:

(a) one or more compounds selected from the list comprising sodium tetraborate, sodium chloride, sodium bromide, sodium acetate, calcium chloride, magnesium chloride or the hydrates thereof;

(b) one or more compounds selected from the list comprising benzamide, acetamide, /V-methylurea, Λ/,Λ/'-dimethylurea urea, glycerol, mannitol, xylitol and propylene glycol; and (c) one or more polysaccharides selected from the list comprising agar and a starch.

9. The plastic or gel material as claimed in any one of Claims 1 to 8, wherein the material further comprises an additive selected from the list comprising fillers, stabilizers, anti-wear agents, blowing agents, foodstuffs, food dyes and pharmacologically active agents.

10. The plastic or gel material as claimed in any one of Claims 1 to 9, wherein the molar ratio of component (a) to component (b) is from 1 :6 to 3: 1.

1 1. The plastic or gel material as claimed in any one of Claims 1 to 10 wherein the ratio of the combined mass of components (a) and (b) to the mass of the polysaccharide component (c) is from 1 :3 to 9: 1.

12. Use of the plastic or gel material as claimed in any one of Claims 1 to 11 as a resin or glue.

13. A composite material comprising:

(A) a plastic or gel material as defined in any one of Claims 1 to 1 1 ; and

(B) another material.

14. The composite material as claimed in Claim 13, wherein the other material is selected from the list comprising cellulose fibres, wood fibres, wood flour, wood particles, lignin fibres, carbon fibres, glass fibres or ceramic powders.

15. A composite wood comprising the composite material as claimed in Claims 14.

16. The composite wood as claimed in Claim 15, wherein the composite wood is MDF, particle board, chipboard or plywood.

17. A process for preparing a plastic or gel material as defined in any one of Claims 1 to 12, said process comprising:

(i) providing a mixture of

(a) a compound of formula (I) or a mixture of two or more compounds of formula

(I),

(b) one or more uncharged organic compounds; and

(c) one or more polysaccharides,

and optionally one or more additives,

and then heating the mixture until the plastic or gel material is formed; or

(ii) for the preparation of foamed, plastic materials, providing a mixture of components (a), (b) and (c), and optionally an additive, as defined in (i) above, and a volatile material, and then heating the mixture until a plastic material is formed and the volatile material has volatilised and imparted a foam structure to the plastic material.

18. The process as claimed in Claim 17, wherein the mixture is heated to a temperature from 100 to 180°C for a duration of from 2 to 30 minutes.

19. An article comprising a plastic or gel material as defined in any one of Claims 1 to 12, a composite material as defined in Claim 13 or Claim 14, or a composite wood as defined in Claim 15.

20. An article as claimed in Claim 19, wherein the article is coated with a water-resistant material.

21. A coated article as claimed in Claim 20, wherein the water-resistant material is polyvinylacetate, polyvinylalcohol or a wax selected from the group consisting of paraffin wax, beeswax, bayberry wax, candelilla wax, caranday wax, castor bean wax, shellac wax, spermaceti wax, sugar cane wax and wool wax (lanolin).