The present invention relates to an adhesive system and a method of producing a wood based product.

Background

Formaldehyde based resins such as phenol-formaldehyde resin, melamine-formaldehyde resin and urea-formaldehyde resin are widely used as binders in the production of wood based products. Examples of such wood based products are composite products comprising layers glued together such as plywood, laminated flooring products and veneered products used in, e.g., furniture. Further examples of such wood based products are composite products such as particle-, chip- and fibreboards wherein wood chips and/or fibres, together with a binder, are pressed to form a board.

Upon curing a formaldehyde based resin, formaldehyde may be released both during the manufacture of the wood based product and also later during use of the product. Formaldehyde emission to indoor air is a major concern since many years for health reasons.

There is an increasing demand for formaldehyde-free wood adhesives which have sufficient water resistance and heat resistance making them suitable as alternatives to prior art adhesives containing formaldehyde based resins.

As an alternative to adhesive compositions comprising formaldehyde based resins, adhesives based on polymer latices of e.g. polyvinyl acetate are available.

EP 1908798 discloses a liquid dispersion comprising polymer particles composed of at least one monomer unit selected from ethylenically unsaturated monomers and diene unsaturated monomers while containing at least one crosslinkable unsaturated monomer; a vinyl alcohol polymer; a carboxyl group-containing vinyl alcohol polymer; and a crosslinking agent.

EP0587114 relates to an emulsion composition comprising an aqueous emulsion (A) obtained by emulsion polymerization of 100 parts by weight of an ethylenically unsaturated monomer in the presence of 1 to 15 parts by weight of a carboxyl group- modified polyvinyl alcohol as dispersant and a polyamide resin (B) such as polyamide epichlorohydrin. EP 2000485 relates to the use of (meth)acrylic acid amide(s) as comonomer(s) (b) for providing a formaldehyde-free aqueous polymer dispersion obtained by emulsion copolymerization of at least (a) vinyl ester monomer(s) and (b) comonomer(s) comprising said acrylic and/or methacrylic amide(s) derivatives in the presence of at least (c) fully hydrolyzed polyvinyl alcohol (PVOH), having an average degree of hydrolysis above 95.00 mol%, wherein the polymerization does not comprise comonomers derived from N- alkylol(meth)acrylic acid amides, and wherein the heat resistance, measured as WATT 91 value according to DIN EN 14257, is larger than the heat resistance obtained without using acrylic and/or methacrylic amide(s) derivatives (b).

JP 10-306266 relates to an adhesive composition obtained by incorporating (A) 100 parts by weight, on a resin basis, of a vinyl acetate resin-based emulsion prepared by emulsion polymerization between 100 parts by weight of vinyl acetate and 0.1-5 parts by weight of a carboxyl-containing monomer using polyvinyl alcohol as protective colloid with (B) 5- 100 parts by weight, on a resin basis, of an ethylene-vinyl acetate copolymer resin-based emulsion containing >25 weight-% of ethylene, (C) 1-20 parts by weight, on a resin basis, of an urethane resin-based emulsion, and (D) 0.5-10 parts by weight of an aminoethylated vinyl interpolymer of the formula -C-C(CH ₃ )-CO-O-[-C(Ri)-C(R ₂ )-N-] _n -H where R1 is H or methyl and R2 is a hydrocarbon group, or a polyamide-epichlorohydrin- based resin.

JP5009448 relates to an adhesive prepared by adding a crosslinking agent to a base consisting mainly of a copolymer emulsion comprising 5-80 wt-% vinyl acetate units and 95-20 wt-% acrylic ester units and/or methacrylic ester units and containing polyvinyl alcohol having primary hydroxyl, primary amino or secondary amino or a copolymer emulsion comprising vinyl pivalate units, primary hydroxy-containing vinyl compound units and ethylenically unsaturated monomer units and having a glass transition temperature of -10 ⁰ C or above. According to the Physical & Theoretical Chemistry Laboratory of Oxford University (http://msds.chem. ox. ac.uk/VI/vinyl_pivalate. html 13 July 2009) vinyl pivalate is a highly flammable, harmful (by inhalation, skin contact, or if swallowed), and irritating (to the eyes, respiratory system, and to the skin) substance that may cause cancer or heritable genetic damage.

For wood adhesives the cohesion strength of the dry bond, in particular under ambient temperature, is of paramount importance. In addition, there are further demands for high quality wood adhesives, among which the water resistance play a significant role. The D1-D4 scale of standard SS-EN 204:2001 is commonly used for classification of water resistance. It is an object of the invention to provide an adhesive system not being based on formaldehyde releasing components but still having high water resistance and heat resistance, in particular when used as a wood adhesive.

It is another object of the invention to provide an adhesive system that does not involve extensive use of carcinogenic or otherwise harmful or irritating substances.

These and other objects will become apparent from the present specification and examples.

The invention

One aspect of the invention relates to an adhesive system comprising

- an aqueous latex comprising dispersed particles of at least one polymer comprising at least one carboxylic group or at least one carboxylic anhydride group, or a combination thereof, said polymer being obtainable from monomers comprising vinyl ester monomers and (meth)acrylate monomers, with the proviso that said polymer does not contain 5 to 90 wt-% of vinyl pivalate units in combination with 0.2 to 15 wt-% of primary hydroxyl group-containing vinyl compound units, and

- a polyamine-epihalohydrin.

Said at least one carboxylic group or at least one carboxylic anhydride group may be introduced into or onto the polymer by way of carboxylation of the polymer; in the alternative, or - if more than one such group - complement, the group(s) may originate from monomer(s) making up the polymer; in the alternative, or - if more than one such group - complement, the group(s) may originate from a protective colloid used during the polymerisation, such as for instance carboxylated polyvinyl alcohol.

The polymer preferably comprise up to about 15 mole-% or from about 0.05 to about 10 mole-% of carboxylic groups based on the combined numbers of moles of monomer comprised in the polymer, or up to about 7.5 mole-% or from about 0.025 to about 5 mole-% of carboxylic anhydride groups based on the combined numbers of moles of monomer comprised in the polymer. The carboxylic or carboxylic anhydride groups may, for instance, originate from straight or branched C _3- - _I2 monocarboxylic acid monomers; straight or branched C4-12 dicarboxylic acid monomers; or straight, branched, or cyclic C _4- -I ₂ carboxylic anhydride monomers, wherein the carbon chain of said monomers contains at least one terminal, pendant, or internal ethylenic unsaturation. The carboxylic or carboxylic anhydride groups may e.g originate from ethylenically unsaturated carboxylic or carboxylic anhydride group containing monomers used at the preparation of the polymer. Such monomers may include one or more of acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, itaconic acid, itaconic anhydride, maleic acid, maleic anhydride, and fumaric acid, of which acrylic acid, methacrylic acid and mixtures thereof are particularly preferred.

By the term "adhesive system" as used herein is meant a combination of components which function as, and are intended to be used as, an adhesive when combined. In the term "adhesive" is herein also included the term "binder".

As used herein, the term "latex" is synonymous with "dispersion" and "emulsion" and refers to the product of a particular emulsion-polymerization reaction. In that regard, the term "latex" is typically understood to mean an aqueous or water-based polymer emulsion, without separation of the polymer product from the aqueous carrier (e.g., water) which may include other liquid as well as certain by-product components within the emulsion.

As used herein, the term "polymer" refers to the product of a polymerization reaction, and is inclusive of homopolymers, copolymers, etc.

As used herein, unless specified otherwise, the term "copolymer(s)" refers to polymers formed by the polymerization of at least two different kinds of monomers. As used herein, when a polymer is referred to as being obtainable from monomers, the monomers may be present in the polymer in a polymerized form of the monomers, or in a derivative form of the monomers.

The term "vinyl ester monomer" refers to any monomer of the formula I

O

Il

CH ₂ =CH-O-C-R (I) wherein R is a CrC ₃₀ organyl group. A non-exhaustive list of exemplary vinyl ester monomers comprise vinyl acetate, vinyl propionate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl laurate, vinyl chloroacetate, vinyl isobutyrate, vinyl caproate, vinyl stearate, vinyl versatate, and vinyl benzoate. However, it is preferred that vinyl pivalate or other harmful monomers are not included.

The term "(meth)acrylate" refers to both acrylate and methacrylate and combinations thereof.

The term "polyamine-epihalohydrin" as used herein refers to polyamine-epihalohydrin resins, including those that have been prepared with epihalohydrin, e.g. epichlorohydrin, as a reactant, either during the polymerisation or in the modification of an existing polymer. The polyamine may be a polyaminoamide. Such resins are widely used as wet strength agents in paper making and are commercially available, e.g. from Akzo Nobel under the trademarks Eka WS 320, Eka WS 320 RC, Eka WS 325, Eka WS XO, and Eka WS X14. Further, preparation thereof is disclosed in the literature, e.g. in any one of US 4450045, US 331 1 594, US 4336835, US 3891589, US 2926154, US4857586, US4975499, US5017642, US 5019606, US 5093470 and US 5516885.

In the art, polyaminoamide may also be referred to as polyamidoamine, polyaminopolyamide, polyamidopolyamine, polyamidepolyamine, polyamide, basic polyamide, cationic polyamide, aminopolyamide, amidopolyamine or polyaminamide. The polyaminoamide epihalohydrin resin may be in an aqueous solution, that further may comprise a water-miscible solvent such as methanol, ethanol or dimethyl formamide. The molecular weight can vary within wide ranges and Mw may, for example, be from about 10,000 to about 1 ,000,000 or higher, such as from about 50,000 to about 1 ,000,000. Epihalohydrins that can be used include epibromohydrin and epichlorohydrin, in particular epichlorohydrin. The polymers may be produced using, for instance, from about 0.5 to about 2 moles of epihalohydrin per mole of basic nitrogen in the polyaminoamide.

The polyaminoamide may be a reaction product of a polycarboxylic acid or a derivative thereof, such as a dicarboxylic acid or a derivative thereof, and a polyamine. Derivatives of carboxylic acids include e.g. anhydrides, esters and half esters. Exemplary polycarboxylic acids include saturated or unsaturated aliphatic or aromatic dicarboxylic acids. For the purpose of the invention, the term "carboxylic acid" is meant to include carboxylic derivatives, such as anhydrides, esters or half esters. The polycarboxylic acids may contain up to 10 carbon atoms, and may be chosen among oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid and derivatives and mixtures thereof.

The polyamine may, for instance, be chosen among polyalkylene polyamines, or mixtures thereof, satisfying the following formula: H ₂ N-(CR ¹ H) ₈ -(CR ² H) _b -N(R ³ )-(CR ⁴ H) _c -(CR ⁵ H) _C -NH ₂ (II) in which R ¹ -R ⁵ represent hydrogen or lower alkyl, preferably up to C ₃ and a-d represent integers from 0-4. Exemplary polyalkylene polyamines include diethylene triamine, triethylene tetra amine, tetraethylene penta amine, dipropylene triamine, and mixtures thereof. The polyamines of formula I may be combined with other polyamines or mixtures of other amines. The amines may, for instance, satisfy the following formulae IH-VIII:

H-(-NH-(CH ₂ ) _e -CR ⁶ H-) _f -NCH ₂ CH ₂ NH (III) R ⁷ R ⁸ N-(-(CH ₂ ) _g -CR ⁹ H-(CH ₂ ) _h -N(R ¹⁰ H -H (IV)

HR ¹¹ N-(CH ₂ ) _r CR ¹² H-(CH ₂ ) _k -OH (V)

HNR ¹³ R ¹⁴ (Vl)

H ₂ N-(CH ₂ ) _I -COOH (VII) (CH ₂ ) _m -NH-CO (VIII) in which R ⁶ -R ¹⁴ represent hydrogen or lower alkyl, preferably up to C ₃ , e-l represent integers from 0 to 4, and m represents an integer from 1 to 5. The polyamines may be used in combination with monoamines, i.e., compounds containing only one amine group (being a primary, secondary or tertiary amine group).

The polycarboxylic acid and the polyamine may, for example, be applied in a mole ratio of from 0.5:1 to 1.5:1 or from 0.7:1 to 1.4:1.

Preparation of polyaminoamides can be performed by any method known in the art, such as described in e.g. US 5902862. The polyamine may be reacted with from about 0.1 to about 3 moles of epihalohydrin per mole of secondary amine group in the starting polyamine, in particular with from 0.5 to 1.5 moles and specifically from 0.8 to 1 .2 moles per mole of secondary amine groups. A molar excess of epihalohydrin with respect to the secondary amine groups of the polyamine may be used in order to improve the stability of the final resin product.

The monomers for the polymer of the dispersed particles preferably comprise at least about 45 mole-% or from about 55 to about 99 mole-% of vinyl ester monomers. Said vinyl ester monomer may for instance be a vinyl acetate monomer.

The monomers for the polymer of the dispersed particles preferably comprise up to about 40 mole-% or from about 1 to about 35 mole-% of (meth)acrylate monomers, for example from 5 to 25 mole-% or from 10 to 20 mole-%. Said (meth)acrylate monomers may, for instance, be chosen among alkyl(meth)acrylates, hydroxyalkyl(meth)acrylates, alkyl di(meth)acrylates, epoxy(meth)acrylates, and combinations thereof.

More specifically said (meth)acrylate monomers may, for instance, be chosen among ethyl acrylate, methyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, methyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, cyclopentanyl methacrylate, 2- hydroxyethyl (meth)acrylate, 2-hydroxypropyl acrylate, tetrahydrofurfuryl acrylate, and combinations thereof. Even more specifically said (meth)acrylate monomers may, for instance, be chosen among n-butyl acrylate or methyl methacrylate, or a combination thereof, particularly methyl methacrylate. In an embodiment, additional monomers for internal crosslinking may be used, for examples in amounts up to 1 mole-% or up 0.5 mole-%. Examples of such monomers include ethylene glycol di(meth)acrylate, di(ethylene glycol) dimethacrylate, butylene g lycol d i m ethacrylate, 1 ,4-butanediol diacrylate, pentaerythritol triacrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane diallylether, allyl (meth)acrylate, diallyl maleate, triallyl (iso)cyanurate, and combinations thereof.

The polymer of the dispersed particles preferably comprise up to about 15 mole-% or from about 0.05 to about 10 mole-% of carboxylic groups based on the combined numbers of moles of monomer comprised in the polymer, or up to about 7.5 mole-% or from about 0.025 to about 5 mole-% of carboxylic anhydride groups based on the combined numbers of moles of monomer comprised in the polymer. The carboxylic or carboxylic anhydride groups may originate from ethylenically unsaturated carboxylic or carboxylic anhydride group containing monomers used together with the vinyl ester monomers and the (meth)acrylate monomers at the preparation of the polymer. Such monomers may, for instance, be chosen among straight and branched C _{3- 12} monocarboxylic acid monomers; straight and branched C _4- i ₂ dicarboxylic acid monomers; and straight, branched, and cyclic C4-12 carboxylic anhydride monomers, wherein the carbon chain of said monomers contains at least one terminal, pendant, or internal ethylenic unsaturation; included among such monomers are (meth)acrylic acid, crotonic acid, isocrotonic acid, itaconic acid, itaconic anhydride, maleic acid, maleic anhydride, and fumaric acid, of which acrylic acid, methacrylic acid or a combination thereof are particularly preferred.

The carboxylic or carboxylic anhydride groups may also originate from a carboxylic or carboxylic anhydride containing protective colloid used during the polymerisation, for example carboxylated polyvinyl alcohol.

In an embodiment of the invention the polymer of the dispersed particles is obtainable from monomers comprising vinyl ester monomers, (meth)acrylate monomers and carboxylic acid or carboxylic anhydride group containing monomers, the polymer being either free from any other kinds monomers or the content of any such other kinds of monomers being less than 1 mole%.

In an embodiment of the inventive adhesive system said aqueous latex comprising dispersed particles is comprised in a resin component, and said polyamine-epihalohydrin is comprised in a hardener component, said components being separate from each other.

The weight ratio of aqueous latex to polyamine-epihalohydrin may, for instance, be from about 100:0.3 to about 100:31 ; more specifically the weight ratio of aqueous latex to polyamine-epihalohydrin may, for instance, be from about 100:1.3 to about 100:23; even more specifically said weight ratio may, for instance, be from about 100:1 .3 to about 100:11.5; even further specifically said weight ratio may, for instance, be from about 100:1.3 to about 100:7.7; all weight ratios being dry:dry.

In an embodiment of the invention the aqueous latex comprised in the inventive adhesive system may be produced by way of emulsion polymerisation. For such polymerisation there are basically three different processes available: batch, semicontinuous and continuous. In a batch process all the reactants are added at the start of the reaction while in the semi-continuous process the components are added continuously throughout the reaction. In a continuous process, the components are added continuously during the process similarly to the semi-continuous process, but the product is removed at the same rate.

The polymerization procedure may be performed as well known in the art of emulsion polymerization. It may be carried out in an aqueous medium at a pH in the range of 3 to 7. To maintain the pH of the reaction mixture, a buffer may be added as is known in the art. Suitable buffers include alkali metal acetates, alkali metal carbonates, and alkali metal phosphates. The initiator system may, for example, be chosen among thermal initiators, redox initiators, or combinations thereof, for example potassium- or ammonium persulfates, tert-butyl hydroperoxide, cumene hydroperoxide, t-butylperbenzoate, t-butyl 2-ethyl perhexanoate, hydrogen peroxide and benzoyl peroxide. Suitable reducing agents of a redox initiator system include compounds such as sulphur compounds with a low oxidation state such as sulfites, hydrogen sulfites, alkali metal bisulfites, ketone adducts of bisulfites such as acetone bisulfite, alkali metal disulfites, metabisulfites and its salts, thiosulfates, formaldehyde sulfoxylates and its salts, reducing nitrogen compounds such as hydroxylamines, hydroxylamine hydrosulfate and hydroxylammonium salts, polyamines and reducing sugars such as sorbose, fructose, glucose, lactose and derivatives thereof, enediols such as ascorbic acid and isoascorbic acid, sulfinic acids, hydroxy alkyl sulfinic acids such as hydroxy methyl sulfinic acid and 2-hydroxy-2- sulfinactic acid and its salts. Redox initiators are typically used in combination with trace amounts of metal such as iron, for example supplied as ferrous sulphate. The polymer comprised in the inventive adhesive system may, for instance, have a weight average molecular weight of from about 100,000 to about 2,500,000 g/mol;

more specifically the polymer may, for instance, have a weight average molecular weight of from about 350,000 to about 2,000,000 g/mol, and even more specifically a weight average molecular weight of, for instance, from about 400,000 to about 1 ,600,000 g/mol.

The aqueous latex may furthermore comprises a protective colloid comprising a polymer chosen among, for instance, polyvinyl alcohol, hydroxyethyl cellulose, polyvinyl formamide, polyvinyl amine, a copolymer of two or more of said polymers, and combinations thereof. The protective colloid may be combined with another emulsifying agent, such as an anionic or non-ionic surfactant. In an embodiment of the inventive adhesive system the aqueous latex comprising dispersed particles is comprised in a resin component, and said polyamine-epihalohydrin is comprised in a hardener component, said components being separate from each other. The resin component may also comprise part of the polyamine-epihalohydrin.

The adhesive system may further comprise additives chosen among, for instance, preservatives, antifoaming agents, viscosity adjusting agents; fillers such as kaolin, calcium carbonate, wheat meal, soy meal, walnut shell meal; and other additives known to be suitable for use in wood adhesive formulations, including combinations thereof.

An aspect of the invention relates to an adhesive composition comprising the inventive adhesive system.

Another aspect of the invention relates to the use of the adhesive system according to the invention for producing a wood based product.

A further aspect of the invention relates to a method of producing a wood based product, comprising applying the inventive adhesive system onto one or more pieces of a wood- based material, and joining the one or more pieces with one or more further pieces of a material.

Still a further aspect of the invention relates to a wood based product obtainable by this method. By "wood-based materials" as used herein, is beside solid wood, also included wooden materials such as fibre-, chip-, and particleboard materials. The surfaces to be joined may be of the same or different type of wood based material.

The wood based material can be any type and form of wood based material such as chips, fibres, sheets, laminas, veneers, pieces etc.

In an embodiment of the inventive method the adhesive system comprises one component comprising said aqueous latex comprising dispersed particles, and another component comprising said polyamine-epihalohydrin, and the two components are applied onto the wood based material as separate components. The component comprising the aqueous latex may also comprise part of the polyamine-epihalohydrin. In one aspect of this embodiment the two components are applied in a sequence of time from each other, as a first component applied and as a second component applied onto the wood based material; in a specific aspect of this embodiment the first component applied comprises the aqueous latex comprising dispersed particles, and the second component applied comprises polyamine-epihalohydrin.

In another embodiment of the inventive method said aqueous latex comprising dispersed particles, and said polyamine-epihalohydrin, of said adhesive system are comprised together in a mixture. The inventive method may, for instance, comprise mixing wood based chips with the adhesive system, and joining the chips. As used herein the term "wood chips" includes chips, shavings, flakes, sawdust particles and any similar finely divided wood based material. The weight ratio between the polymer comprised in the adhesive system to chips may, for instance, be from about 1 :500 to about 1 :5; it may specifically be, for instance, from about 1 :100 to about 1 :10; even more specifically it may, for instance, be from about 1 :50 to about 1 :20. The moisture content of the chips before mixing with said polymer may, for instance, be from 0 to about 30 weight-%; it may specifically be, for instance, from 0 to about 10 weight-%: even more specifically it may, for instance, be from 0 to about 5 weight-%.

The moisture content of the mixture of chips and adhesive system at the beginning of the pressing may, for instance, be from about 3 to about 25 weight-%; it may specifically be, for instance, from about 5 to about 20 weight-%, and even more specifically it may, for instance, be from about 7 to about 15 weight-%.

The wood based product produced by the inventive method may, for instance, be a chip-, particle-, or fibre board, or an oriented strand board. The wood based chips may, for instance, be mixed with the adhesive system to form a mixture of chips and adhesive system, which is then pressed into a board.

The pressing may, for instance, take place at an elevated temperature. The pressing temperature depends on which wood based product intended to be manufactured but may be from about 50 to about 250 ⁰ C. The pressing time and pressing temperature are linked so that lower pressing temperatures generally require longer pressing times. The wood based product to be produced does also determine suitable pressing temperatures and pressing times. The pressing time may be at least about 10 s, specifically from about 10 s to about 60 minutes, more specifically at least about 30 s, even more specifically from about 30 s to about 30 minutes, even further specifically at least about 1 minute, and even yet more specifically from about 1 to about 15 minutes.

The adhesive system may, for instance, be applied onto a sheet-like material, and joined with a further sheet-like material.

The term "sheet-like material" as used herein refers to materials having dimensions in either the length or width directions, or both, that are much greater than the dimension of the material in the thickness direction; exemplary of sheet-like materials are laminae, boards, veneer, and the like.

An embodiment of the invention relates to a wood based product comprising pieces of wood based material joined with the inventive adhesive system; the wood based product may, for instance, be a laminated or veneered material; the wood based product may, for instance, also be a composite product such as e.g. a particle board, fibre board (such as MDF), chip board or oriented strand board.

The wood based product of the present invention may, for instance, be a laminated or veneered material, such as laminated flooring, veneered flooring, a veneered furniture material, plywood, a wall panel, a roofing panel, a laminated beam, or a composite product such as a particle board, fibre board, chip board or oriented strand board.

The wood based product may, for instance, be a composite product comprising wood based chips joined together with the inventive adhesive system. The invention is further illustrated by means of the following non-limiting examples. Parts and percentages relate to parts by weight respectively percent by weight, unless otherwise stated.

Examples

In the below examples the following chemicals were used:

Preparation of polymer latexes

Emulsion polymerisations were performed in an automated batch lab reactor of 1 litre. The reactor used was a LabMax from Mettler Toledo and the software program was Camile TG. The emulsion polymerisation started by introducing a protective colloid dissolved in water to the reactor. Next, a buffer was added to prevent the pH from decreasing excessively. The polymerisation was carried out as a semi-continuous reaction according to a pre-programmed recipe using two pumps to dose the monomer and initiator feed. The weight of the charged feeds was controlled by lab scales. The preprogrammed recipe also controlled the temperature of the reactor and stirring rate of the anchor type stirrer.

Four different recipes used for the emulsion polymerisation, specified in Table 1 , 2, 3 and 4 below.

Table 1

Table 3

Table 4

The polymer latexes produced are listed in Table 5 below. Table 5

Viscosities were measured by means of a Brookfield LVT spindle 4 at about 23 ⁰ C. Preparation of adhesive compositions and test specimens

The adhesive compositions produced are listed in Table 6 below.

Table 6

Tensile strength tests

The tensile strength of the adhesive compositions obtained in Example 2 was measured according to standard test SS:EN 204:2001 using a universal test machine Alwetron TCT50, and also according to WATT 91 , the "Wood Adhesives Temperature Test" (SS:EN 14257:2006).

Each of the listed adhesive compositions were spread on two boards which were pressed together for about 15 minutes at a temperature of about 75 ^° C.

The requirements for classifications D1 and D4 SS:EN 204:2001 are given in Table 7 below. The requirements are based on a mean value for ten pieces. Table 7

The tensile strength test values (in MPa) obtained are set forth in Table 8 below. Table 8