WOOD PARTICLE BOARDS

[0001 ] The present invention relates to wood particle boards and a method for their production.

[0002] A wood particle board is a composite material manufactured from wood particles, for example wood chips, sawmill shavings and/or saw dust at varying particle sizes held together by a binder and used especially for the manufacture of furniture, such as cabinets, kitchens and bathroom furniture. Generally, wood particle board (which is sometimes referred to as "chipboard") is produced by mixing wood particles and a binder composition, e.g. a thermo-curable resin, subsequently forming the resulting mixture into a sheet or mat and compressing said sheet or mat under elevated temperatures. In order to improve the visual appearance and/or durability, a veneer or melamine layer may be applied to the board's surface(s).

[0003] According to one aspect, the present invention provides a method of manufacturing a wood particle board as defined in claim 1 . The dependent claims define preferred or alternative embodiments.

[0004] The presence of the non-carbohydrate polyhydroxy component of the binder composition may be useful to i) facilitate an even distribution of the binder composition over individual wood particles and/or over a collection of wood particles which are mixed or processed together and/or ii) provide an appropriate quantity of moisture for the resinated wood particles. A binder composition that cannot easily flow or be distributed may lead to clumping of resinated wood particles and/or to a non-homogenous material mix at entry into board press. The non-carbohydrate polyhydroxy component may act as a lubricant and/or a non-drying liquid; this may reduce or prevent clumping of the resinated wood particles. [0005] The resinated wood particles may be mixed or tumbled, for example in a bunker, prior to being formed in to a mat; the non-carbohydrate polyhydroxy component may facilitate binder distribution over surfaces of the wood particles during such mixing. Furthermore, the use of a non-carbohydrate polyhydroxy component may avoid the necessity of providing additional water or diluting the binder composition to facilitate binder distribution and thus avoid the generation of undesired quantities of steam during subsequent curing. [0006] The non-carbohydrate polyhydroxy component may be selected from: a diol, a triol, a polyol, an organic compound containing multiple hydroxyl groups and mixtures thereof. It may comprise, comprise at least 50 wt% or consist essentially of glycerol, polyethylene glycol, polypropylene glycol, trimethylolpropane, pentaerythritol, polyvinyl alcohol, partially hydrolyzed polyvinyl acetate, fully hydrolyzed polyvinyl acetate, or mixtures thereof. Glycerol is particularly preferred because it can be acquired as a cost efficient waste product from other industrial processes, is bio based and is non-hazardous chemical.

[0007] The non-carbohydrate polyhydroxy component may have a viscosity when measured at 20°C which is:

- greater than or equal to: 10 cP, 50 cP, 100 cP or 250 cP or 500 cP or 750 cP or 1000 cP or 1250 cP; and/or

- less than or equal to: 10000 cP or 7500 cP or 5000 cP or 2500 or 2000 cP or 1500 cP;

notably when the viscosity is measured at 20°C. The viscosity of the non- carbohydrate polyhydroxy component and of the binder composition is measured by rotational viscometry notably using a Brookfield viscometer. One such viscosity measurement involves applying a torque through a calibrated spring to a spindle immersed in a test fluid, the amount of viscous drag indicated by the spring deflection providing a measure of the viscosity.

[0008] The non-carbohydrate polyhydroxy component may be used in a quantity of:

- at least 0.1 % or at least 1 %, or at least 2% or at least 5 % and/or

- no more than 25% or no more than 20% or no more than 15%

by weight based on the total weight of the binder composition.

[0009] The term "binder composition" as used herein means all ingredients applied to the wood particles and/or present on the wood particles, notably prior to curing, (other than the wood particles themselves and any moisture in the wood particles), including reactants, solvents (including water), the non-carbohydrate polyhydroxy component(s) and additives. The term "dry weight of the binder composition" as used herein means the weight of all components of the binder composition other than any water that is present (whether in the form of liquid water or in the form of water of crystallization).

[0010] The binder composition applied to the wood particles comprises uncured reactants which cure and cross-link to form a cured binder which holds the particles of the wood particle board together. The binder composition comprises starting materials that will form a thermoset resin upon curing. The reactants may comprise components selected from the group consisting of: protein(s), starch(es), cellulose, carbohydrate(s), gum(s), natural resin(s), bitumen(s), natural rubber(s), synthetic rubber(s), phenolic(s) such as tannin or lignin, notably present in a quantity of at least 30%, at least 40%, at least 50%, at least 60% , at least 70% or at least 80% by dry weight based on the total dry weight of the binder composition.

[001 1 ] The binder composition is preferably free of, or comprises no more than 5 wt% or no more than 10 wt% urea formaldehyde (UF), melamine urea formaldehyde (MUF) and/or phenol formaldehyde . [0012] The binder composition is preferably a binder that does not comprise any added formaldehyde. It may be "substantially formaldehyde free", that is to say that it liberates less than 5 ppm formaldehyde as a result of drying and/or curing (or appropriate tests simulating drying and/or curing); more preferably it is "formaldehyde free", that is to say that it liberates less than 1 ppm formaldehyde in such conditions.

[0013] Advantageously, the binder composition may be a carbohydrate based binder composition. The combination of this with the non-carbohydrate polyhydroxy component(s) has been found to provide an advantageous combination of bond strength, notably without penalizing cure speed, whilst facilitating manufacturing processes. The binder composition may comprise (a) reducing sugar reactant(s) and nitrogen-containing reactant(s) and/or (b) curable reaction product(s) of reducing sugar reactant(s) and nitrogen-containing reactant(s). The reducing sugar reactants may be provided in the form of reducing sugars and/or generated in situ, notably from a carbohydrate reactant which yields reducing sugar(s) in situ, for example due to application of heat and/or presence of a catalyst or further reactant. [0014] The binder composition may comprise a binder composition as described in any of WO 2007/014236, WO 2009/019232, WO 2009/019235, WO 201 1/138458, WO 201 1/138459 or WO 2013/150123, each of which is hereby incorporated by reference. [0015] The nitrogen-containing reactant(s) and the reducing sugar reactant(s) (or their reaction product(s)) may be Maillard reactants that react to form Maillard reaction products, notably melanoidins when cured. Curing of the binder composition may comprise or consist essentially of Maillard reaction(s). The cured binder composition may comprise melanoidin-containing and/or nitrogenous- containing polymer(s); it is preferably a thermoset binder and is preferably substantially water insoluble.

[0016] The reducing sugar reactant may comprise: a monosaccharide, a monosaccharide in its aldose or ketose form, a disaccharide, a polysaccharide, a triose, a tetrose, a pentose, xylose, an hexose, dextrose, fructose, a heptose, a sugar, molasses, starch, starch hydrolysate, cellulose hydrolysates, reaction product(s) thereof or mixtures thereof. The reducing sugar reactant(s), or carbohydrate reactant(s) that yield the reducing sugar reactant(s) may have a dextrose equivalent of at least about 50, at least about 60, at least about 70, at least about 80 or at least about 90. The reducing sugar reactant may comprise or consist of high fructose corn syrup (HFCS).

[0017] As used herein, the term "nitrogen-containing reactant " means any chemical compound, or mixture of compounds, which contain(s) at least one nitrogen atom and which is/are capable of reacting with the at least one reducing sugar reactant. The nitrogen-containing reactant may be selected from NH3, an inorganic amine or an organic amine comprising at least one primary amine group, as well as salts thereof. It may comprise NH3 used as such (e.g. in form of an aqueous solution), or an inorganic and organic ammonium salt, for example ammonium sulfate (AmSO ₄ ), ammonium phosphate, e.g. diammonium phosphate, ammonium chloride, ammonium nitrate or ammonium citrate. [0018] The nitrogen-containing reactant may be a polyamine. Herein, the term "polyamine" includes any organic compound having two or more amine groups, which may independently be substituted or unsubstituted. For example, the polyamine may be a primary polyamine. As used herein, a "primary polyamine" is an organic compound having two or more primary amine groups (-NH2). Within the scope of the term primary polyamine are those compounds which can be modified in situ or isomerize to generate a compound having two or more primary amine groups (-NH2). The primary polyamine may be a molecule having the formula H2N-Q-NH2, wherein Q is an alkanediyl, cycloalkanediyl, heteroalkanediyl, or cycloheteroalkanediyl, each of which may be optionally substituted. For example, Q may be an alkanediyl group selected from -C2-C24-, an alkanediyl group selected from -C2-C9-, or an alkanediyl group selected from -C3-C7-. According to a preferred embodiment, Q is a C6 alkanediyl. According to another embodiment, Q may be a cyclohexanediyl, cyclopentanediyl or cyclobutanediyl, or a divalent benzyl radical. In this context, it should be noted that certain authors prefer using the term "alkyl" instead of the chemically more correct "alkanediyl" nomenclature; the same chemical group is meant.

[0019] As used herein, the term "alkanediyl" means a chain of carbon atoms, which may optionally be branched, preferably of limited length, including -C1-C24-, -C1-C12-, -Ci-Cs-, -C1-C6-, and -Ci-C ₄ -. Shorter alkanediyl groups may add less lipophilicity to the compound and accordingly will have different reactivity towards the reducing sugar reactant and/or solubility.

[0020] As used herein, the term "cycloalkanediyl" means a chain of carbon atoms, which may optionally be branched, where at least a portion of the chain is cyclic and also includes polycyclic structures, for example, cyclopropanediyl, cyclopentanediyl, cyclohexanediyl, 2-methylcyclopropanediyl, 2-ethylcyclopentanediyl, adamantanediyl. Furthermore, the chain forming cycloalkanediyl is advantageously of limited length, including -C3-C24-, -C3-C12-, -C3-C8-, -C3-C6-, and -C5-C6-. Shorter alkanediyl chains forming cycloalkanediyl may add less lipophilicity to the compound and accordingly will have a different behavior.

[0021 ] As used herein, the term "heteroalkanediyl" means a chain of atoms that includes both carbon and at least one heteroatom, and is optionally branched. Examples of such heteroatoms include nitrogen, oxygen, and sulfur. In certain variations, said hetero-atoms also include phosphorus, and selenium. In one embodiment, the heteroalkanediyl is a polyether. As used herein, the term "cycloheteroalkanediyl", includes a chain of atoms that includes both carbon and at least one heteroatom, such as heteroalkanediyl, and may optionally be branched, where at least a portion of the chain is cyclic. Particularly, examples of cycloheteroalkanediyl include divalent tetrahydrofuryl, pyrrolidinyl, tetrahydropyranyl, piperidinyl, morpholinyl, piperazinyl, homopiperazinyl, quinuclidinyl.

[0022] Herein, the term "optionally substituted" means the replacement of one or more hydrogen atoms with other functional groups. Such other functional groups may include amino, hydroxyl, halo, thiol, alkyl, haloalkyl, heteroalkyl, aryl, arylalkyl, arylheteroalkyl, nitro, sulfonic acids and derivatives thereof, carboxylic acids and derivatives thereof.

[0023] The primary polyamine may be a diamine, triamine, tetramine, or pentamine, for example: a triamine selected from a diethylenetriamine, 1 - piperazineethaneamine, or bis(hexamethylene)triamine; triethylenetetramine; or tetraethylenepentamine.

[0024] One feature of the primary polyamine is that it may possess low steric hindrance. For example, 1 ,2-diaminoethane, 1 ,4-diaminobutane, 1 ,5- diaminopentane, 1 ,6-diaminohexane, 1 ,12-diaminododecane, 1 ,4- diaminocyclohexane, 1 ,4-diaminoben-zene, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1 -piperazine-ethaneamine, 2-methyl- pentamethylenediamine, 1 ,3-pentanediamine, and bis(hexamethylene)triamine, as well as 1 ,8-diaminooctane have low steric hindrance.

[0025] Preferably, the nitrogen-containing reactant comprises or consists of 1 ,6- diaminohexane (hexamethylenediamine, HMDA) or 1 ,5-diamino-2-methylpentane (2-methyl-pentamethylenediamine).

[0026] In another embodiment, the nitrogen-containing reactant comprises or consists of a polyether-polyannine, which may be a diamine or a triamine, for example a trifunctional primary amine having an average molecular weight of 440 known as Jeffamine T-403 Polyetheramine (e.g. Huntsman Corporation). [0027] In a further embodiment, the nitrogen-containing reactant may comprise or consist of a polymeric polyamine, for example chitosan, polylysine, polyethylene imine, poly(N-vinyl-N-methyl amine), polyaminostyrene, polyvinyl amine (which can be a homopolymer or a copolymer).

[0028] The reducing sugar reactant(s), may make up:

- at least 30%, preferably at least 40%, preferably at least 50%, more preferably at least 60%, more preferably at least 70%, even more preferably at least 80% by dry weight of the binder composition; and/or

- less than 97%, more preferably less than 95 % by dry weight of the binder composition.

[0029] The nitrogen-containing reactant(s) may make up:

- less than 50% or 40%, preferably less than 30%, more preferably less than 25% by dry weight of the binder composition; and/or

- at least 2.5%, preferably at least 5%, more preferably at least 10% by dry weight of the binder composition.

[0030] The binder composition may comprise (i) at least 25%, and preferably at least 40%, at least 50% or at least 60% by dry weight of: (a) reducing sugar reactant(s) and nitrogen-containing reactant(s) and/or (b) curable reaction product(s) of reducing sugar reactant(s) and nitrogen-containing reactant(s).

[0031 ] The ratio of carbonyl groups in the reducing sugar reactant(s) to reactive amino groups in the nitrogen-containing reactant(s) may be in the range of 5:1 to 1 :2. For example, the ratio of carbonyl groups to reactive amino groups may be in the range of 5:1 to 1 :1 .8, 5:1 to 1 :1 .5, 5:1 to 1 :1 .2, 5:1 to 1 :1 , 5:1 to 1 :0.8 and 5:1 to 1 :0.5. Further examples include ratios such as 4:1 to 1 :2, 3.5:1 to 1 :2, 3:1 to 1 :2, 2.5:1 to 1 :2, 2:1 to 1 :2 and 1 .5:1 to 1 :2.

[0032] Herein, the term "reactive amino group" means any amino group in the nitrogen-containing reactant(s) which is capable of reacting with the carbohydrate component. Specifically, examples of such reactive amino groups include primary and secondary amino groups, amide groups, imine and imide groups, as well as cyanate and isocyanate groups.

[0033] The binder composition may include ester and/or polyester compounds. [0034] The binder composition may comprise one or more adjuvants, for example waxes, dyes release agents and formaldehyde scavengers (notably urea, tannins, quebracho extract, ammonium phosphate, bisulfite).

[0035] The binder composition may be applied to the wood particles, in the form of an aqueous composition, preferably an aqueous solution or dispersion, notably in which the dry weight of the aqueous binder composition makes up: > 40 wt% , > 45 wt% , > 50 wt% , > 55 wt% or > 60 wt% and/or < 95 wt%, < 90 wt%, < 85 wt% or < 80 of the total weight of the aqueous binder composition. The presence of the non- carbohydrate polyhydroxy component(s) is particularly advantageously when the binder composition is used at a high solid content, notably > 55 wt%, to facilitate even distribution of the binder composition over the resinated wood particles despite the high solid content.

[0036] The binder composition, notably in the state in which it is applied to the wood particles may have a viscosity which is:

- greater than or equal to: 10 cP, 25 cP, 50 cP, 75 cP or 85 cP or 95 cP or 105 cP or 1 15 cP or 125 cP; and/or

- less than or equal to: 250 cP or 225 cP or 200 cP or 175 cP or 150 cP;

notably when the viscosity is measured at 20°C.

[0037] The term "wood particle" used herein means wood particles or fibers, including wood chips, wood flakes, sawmill shavings and saw dust or mixtures thereof. The wood particles may have granular sizes of 0.05 - 10 mm or 1 - 10 mm. The wood particle board may be a multi-layer wood particle board; in this case, the particles used for the core layer may have granular sizes between 0.05 - 10 mm or 1 - 10 mm and the surface layer particles may have a granular size less than 1 .5 mm. The aforementioned granular sizes are in respect of at least 90% by weight of the wood particles, preferably at least 95% by weight. Wood particles from both virgin wood and/or reclaimed wood may be used; the wood may comprise, but are not limited to, birch, beech, alder, pine, spruce tropical wood or wood mixtures. Preferably, the wood particles contacted with the binder composition have a moisture content of less than 8%, less than 6% or less than 5% moisture, for example due to pre-drying; they may be pre-dried to a moisture content of 1 to 5% moisture, e.g. 2 to 4% moisture or 1 .5 to 3.5% moisture. [0038] The particle boards of the invention may comprise boards commonly called particle boards or oriented strand boards or medium density fiber boards or high density fiber boards.

[0039] The wood particle boards, notably once cured, may comprise at least 70%, at least 80%, at least 90% or at least 95% by weight of wood particles.

[0040] The wood particle boards, notably once cured, may comprise at least 0.025 %, at least 0.05%, at least 0.075% or at least 1 % and/or less than 5%, less than 4%, less than 3% or less than 2 % of the non-carbohydrate polyhydroxy component(s) by dry weight of the finished particle board. When the particle is a multi-layer board in which the non-carbohydrate polyhydroxy component(s) is not present in all of the layers, the above result may be obtained in respect only of the layer(s) containing the non-carbohydrate polyhydroxy component(s).

The quantitative determination of the non-carbohydrate polyhydroxy component(s) may be made by HPLC (high-pressure liquid chromatography) after an extractive process. The extractive process may consist of a sample of the finished particle board broken into a small piece (for example 2 g) and placed into hot water. The sample in the hot water may be sonicated in an ultrasonic bath (for example during 15 minutes) and then the extrac may be filtered and introduced to a HPLC column. For quantification of glycerol, or other low molecular weight non-carbohydrate polyhydroxy component, an example of a suitable column may be a Luna NH2 (250mm ^* 4.6mm ^* 5 microns) eluted with a mobile phase of 10% water and 90% acetonitrile.

[0041 ] The thickness of the wood particle board may be > 5 mm, > 8 mm, > 10 mm, or > 15 mm and/or < 100 mm, < 80 mm, < 60 mm, < 50 mm, < 45 mm or < 25 mm. Preferred thicknesses are in the range of 10 to 45 mm or 16 to 22 mm. The length of the particle board may be > 1 .5 m, > 2 m, > 2.5 m or > 3 m and/or < 8 m, < 6 m or < 5 m. The width of the particle board may be > 1 m, > 1 .2 m, > 1 .5m or > 1 .8 m and/or < 4 m, < 3 m or < 3.5 m.

[0042] The wood particle boards may have edges which are trimmed and/or cut and/or machined; they may be piled up and provided as a package comprising a plurality of boards arranged and/or bound together, for example to facilitate transport; the package may comprise an enveloping film, for example of a plastics material.

[0043] The binder composition may be applied to the wood particles as a single binder composition, for example by all ingredients of the binder composition being mixed together before being applied as a single spray or projection to the wood particles. Alternatively, two or more portions of the binder composition may be applied separately. For example, the non-carbohydrate polyhydroxy component may be applied to the wood particles separately from the rest of the binder composition. The binder composition may be applied to the wood particles by spraying, for example by passing the wood particles through a spray of the binder composition or by spraying the binder composition over the wood particles whilst the wood particles are being mixed. Preferably, the wood particles are mixed subsequently to application of the binder composition, for example by tumbling, notably in a mixer or bunker. Mixing of the wood particles with the binder composition may comprise applying the binder composition to the wood particles, preferably with subsequent additional mixing of the wood particles, for example by tumbling.

[0044] During the curing of the wood particle board, the internal temperature of the board, notably the temperature at the centre of the board in its thickness direction, may be raised to a temperature of:

a) > 100 °C, > 1 10 °C , > 1 15 °C , > 120 °C, > 130 °C or > 140 °C, and/or b) < 200 °C, < 180 °C, < 170 °C or < 160 °C.

The curing temperature may range from 1 10 °C to 280 °C. Further examples of the curing temperature include ranges of 1 10 to 260 °C, to 240 °C, to 220 °C or to 210 °C.

[0045] The mat of resinated particles may be pressed, e.g. in a hot press, at a pressure which is > 20 bar, > 25 bar or > 30 bar and/or < 80 bar, < 75 bar, < 70 bar or < 65 bar to obtain a cured particle board.

[0046] The mat of resinated particles may be pressed at a press factor in second per mm of thickness of the wood particle board which is > 2 seconds/mm, > 3 seconds/mm, > 4 seconds/mm or > 5 seconds/mm and/or < 60 seconds/mm, < 40 seconds/mm, < 30 seconds/mm or < 20 seconds/mm to obtain a cured particle board. Thus, the press-time may depend on the thickness of the wood particle board.

[0047] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying images of which:

Fig 1 is a representation of a wood particle board made in accordance with the invention; and

Fig 2 is a representation of a comparative example. [0048] Example 1

Two wood particle boards, samples A1 and A2, of length and width 300 x 300 mm having a thickness of 16 mm and a target density of 650 kg/m ³ were prepared.. Once dried to a residual moisture content of about 3.5 wt% (based on oven dried wood weight) the wood particles were sprayed with the binder composition and thoroughly mixed by tumbling:

Both wood particleboards were three layer particle boards and were made with Urea Formaldehyde (UF) resinated core chips at a 62:38 ratio of core:surface wood chip mass. The UF was 95.5 parts by weight (66.72g, 66% solid) of UF resin and 4.5 parts by weight (3.81 g, 52% solid) ammonium nitrate catalyst Surface layer binder composition of Sample A1 : According to the invention

43.5 parts by weight (19.2 g) of dextrose monohydrate (DMH 90.9 wt% dextrose and 9.1 wt% water of crystallisation), 43.5 parts by weight (17.45 g, 100% solid) of fructose, 13.00 parts by weight (7.45 g, 70 wt% in H ₂ O) of HMDA (hexamethylenediamine, 1 ,6-hexanediamine) and addition of 5 parts by weight (2.91 g, 69% solid) glycerol. The solid content was 69 wt%

Surface layer binder composition of Sample A2: Comparative example

43.5 parts by weight (19.2 g) of dextrose monohydrate (DMH 90.9 wt% dextrose and 9.1 wt% water of crystallisation), 43;5 parts by weight (17.45 g, 100% solid) of fructose, 13.00 parts by weight (7.45 g, 70 wt% in H ₂ O) of HMDA (hexamethylenediamine, 1 ,6-hexanediamine)

The solid content was 69 wt%. A mass of coated wood particles adapted to achieve a target board density of 650 kg/m ³ was transferred into a forming box in order to form board samples of 300x300x16 mm. The loading of the binder composition is of 10 % on surface chips and 7.5% on core chips. Board samples were pressed under 56 bar, to a thickness of 16mm using metal stops, at a target platen temperature of 230 °C for a given time period such as to reach a press factors of 7 s per mm thickness for a 16 mm thick board

Fig 1 shows the particle board of sample A1 .

Fig 2 shows the particle board of sample A2.

[0049] The comparative example of Sample A2 in Fig 2 shows that several spots are clearly visible. These spots are believed to be dumpings of the wood particles with binder due to poor binder distribution. Such clumping can lead to non- homogeneous properties of the wood particle board, notably affecting bond strength and/or breaking resistance.

[0050] Fig 1 shows reduced presence of spots.