NZ336668A

NZ336668A - Lignin and/or carbohydrate-based adhesives for particle board manufacture and method for preparation

Info

Publication number: NZ336668A
Application number: NZ336668A
Authority: NZ
Inventors: Liisa Viikari; Anneli Hase; Pia Qvintus-Leino; Kirsi Kataja; Simo Tuominen; Lars Gadda
Original assignee: Neste Chemicals Oy
Priority date: 1997-01-14
Filing date: 1998-01-14
Publication date: 2000-02-28
Also published as: FI970160A; EP0953030A1; KR20000070164A; HUP0200620A2; SK94199A3; BR9806909A; ID22657A; WO1998031764A1; PL334548A1; AU5664598A; FI970160A0; CA2277286A1; CN1250463A; FI104835B

Abstract

A lignin and/or carbohydrate based adhesive binder composition for particle boards and similar wood based products where a) the composition comprises a mixture of lignin containing fibers and lignin and/or carbohydrates obtained from a process of pulping lignocellulosic materials, and oxidative enzymes capable of catalyzing oxidation of phenolic groups and b) the mixture is being foamed to 1.1 to 10 times the volume of the liquid mixture. Also claimed is a method of preparing the binder an aqueous suspension is formed from the raw material and then foamed to form a binder.

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number 336668 WO 98/31764 PCT/FI98/00026 LIGNIN-BASED ADHESIVES FOR PARTICLE BOARD MANUFACTURE The present invention relates to the manufacture of particle boards and similar wood-based products comprising lignocellulosic particles, fibers or flakes mixed with and bonded 5 together with an adhesive binder In particular the present invention concerns novel Lgnin and/or carbohydrate -based adhesives and a preparation process thereof as well as particle boards manufactured using the adhesives The rapid increase in the production of particle boards and fiber boards, especially medium 10 density fiber boards (in the following also abbreviated MDF boards), during the last decades has created a demand for adhesives that are inexpensive, available in large quantities, and independent of crude oil Ligmn meets well these requirements and it does not contain any formaldehyde, which traditionally been considered a serious problem with conventional urea-formaldehyde (UF) adhesives As a major wood component, native ligmn is neither 15 hygroscopic nor soluble in water However, during technical pulping ligmn becomes soluble m water, due to degradation and chemical changes The use of spent sulphite liquor (SSL) as an adhesive for paper wood and other lignocellulosic materials is well-known in the art, and a large number of patent applications has 20 been filed during the last three decades for the use of ligmn products as adhesives for particle boards, plvwood and fiber boards instead of conventional PF or UF adhesives Reference is made to DE Patents Nos 3 037 992, 3 621 218 3 933 279, 4 020 969, 4 204 793 and 4 306 439 and PCT Applications published under Nos WO 93/25622, WO 94/01488, WO 95/23232 and WO 96/03546 25 The mam drawback of using SSL as an adhesive for fiber board manufacture is its hygroscopicity For this reason it cannot really compete with otner natural or svnthetic adhesives When SSL is applied as an adhesive, it can be convened to an insoluble substance by curing Chemically the curing of ligmn is a cross-linking process, which leads 30 to new carbon-camon and ether bonds between different lignm molecules or within one macromolecule Inter- as well as intramolecular cross-lmkmg reactions decrease the solubility and swelling of ligmn Cross-links in ligmn can be acnieved either bv condensation Printed from Mimosa 07/27/1999 11 27 37 page -3- WO 98/31764 PCT/FI98/00026 32 pt, or by radical coupling reactions For the condensation reactions, either high temperatures and long heating times or mineral acids are required, which cause structural changes or charring m the wood particles Recently, cross-linking of the lignosulphonate molecules by radical combinations has been developed In most cases additional cross-linking agents for ligmn are necessary, such as epoxides, polyisocyanates, polyols, poly(acryl amide)s, poly(ethylene lmine) and aldehydes Further, it has been shown that laccase enzymes and other peroxidases can be used as polymerization or curing catalysts of ligmn (DE Patent No 3 037 992, WO 96/03546) However, the enzymes for creating radical reaction have shown limited success so far Fibers and wood chips used in the production of fiber boards contain 5 - 20 % water and the laccases used need some water to effectively catalyze the polymerization reaction needed for extensive bonding of the fiberboard Kraft ligmn like native Iignin to its major part is, however, insoluble in water and thus two solid phases are formed on the production line An uneven distribution of the solids cause spotting and major failure in the strength properties of the board formed in the pressing stage A further problem relating to the use of isolated ligmn is the high price of kraft hgnin, which is near the limit for economical production of particle boards For the above mentioned reasons, lignm-based board production processes have not, so far, led to any major practical applications The present invention aims at eliminating the problems relating to the prior art In particular it is an object of the present invention to provide a novel lignin-based adhesive for use with particle boards and similar wood-based products It is another object of the present invention to provide new particle boards and similar wood-base/ products It is a third object to provide a method for manufacturing the adhesive It is a still further object of the piesent invention to at least provide a useful alternative These and other objects, together with the advantages thereof over known hgnin-based adhesives and processes for the preparation thereo apparent from the 21 DEC 1999 | RECEIVED WO 98/31764 PCT/FI98/00026 3 specification which follows, are accomplished by the invention as hereinafter described and claimed According to the present invention, hgnin or ligmn polymerized with oxidative enzymes or a 5 soluble fraction of carbohydrates obtained from mechanical refining of lignocellulosic materials, is added to and mixed with the fibers or chips or flakes used as lignocellulosic raw material of the ood-based product in the form of a foam to provide an even dispersion of the solids 10 Foamed UF and PF adhesives are known in the art Said foams are used for improving process performance and product quality especially in adhesives with high solid contents CA Patent Application No 2,114,258 describes particle board production by using foamed mixtures of UF resins and animal blood Also DE 3,644,067 descnbes the use of foamed materials in binding of fibers and flakes to produce a homogeneous adhesive application of 15 fine particles (fibres or powders) on the furnish T Sellers descnbes in Forest Prod J 38 (1988) p 55-56 the supenor performance of foamed UF and PF resins in particle board manufacture especially at higner solids content of the adhesive However, none of the prior art references mentions foaming of ligrun-containing adhesive compositions According to these references, the composition of the gas is not important either 20 The hgnin-based adhesive composition according to the present invention compnses an aqueous suspension of lignin and/or carbohydrates obtained from a process of pulping lignocellulosic materials The suspension has beerr foamed to 1 05 to 10, preferably 1 1 to 8, in particular to 1 2 to 5 times the volume of the liquid mixture It is preferred to use 25 polymerized kraft lignin as the ligmn component Furthermore, according to the present invention, natural lignin in wood fibers is used to replace a substantial part of the lignin in the adhesive binder intended for particle board production Thus, the present adhesive binders comprise an aaueous mixture of fibers together with lignin and/or carbohydrates obtained from a process of pulping lignocellulosic raw materials The fibers in the adhesive 30 binder as well as the added ligmn and/or other lignocellulosic material radical polymerize due to the effect of the enzyme m an even oxygen-containing foam matnx Instead of lignin. Printed from Mimosa 07/27/1999 11 27 37 page -5- WO 98/31764 PCT/FI98/00026 the use of native lignin -containing fibers of MDF or TMP types leads to savings in adhesive use, and, however, to a corresponding strength The foam will homogenize the solid phase and the liquid phase, increase the viscosity of the 5 mixture and prevent the sedimentation of the solids The oxygen-containing foamed structure will also provide more oxygen for the oxygen-dependent oxidase catalyzed hgmn/carbohydrate polymerization Because of its large volume, the foam will cover more homogeneously the wood fibers and wood particles in the preparation of the boards This will lead to better strength values and better contiol of the use of the adhesive in the 10 production The invention will now be explained in more detail with the aid of the following detailed description and with reference to a number of working examples 15 Within the context of the present invention, the terms "adhesive", "adhesive binder" and "resin" designate a chemical composition which, in the wet stages of the manufacture of, e g particle and fiber boards, provides adhesion between the particles or fibers After heat compression during board manufacture, the composition containing polymerized resin works as a binder which keeps the particles or fibers or flakes bonded together 20 The term "wood-based product" denotes any lignocellulose-based product, such as particle boards, fiber boards (including high and medium density fiber boards, i e hard boards and MDF boards), flake boards, plywood and similar products constituted by particles, fibers or flakes of vegetable origin, in particular derived from wood or annular or perennial plants 25 mixed with and bonded together with adhesive binders According to a particularly preferred embodiment the present invention is used for preparing particle boards and similar wood-based products in which wood particles can be crosslinked and joined together with the fibers of the adhesive composition, which will be attached to the particles by the hgmn-based adhesive 30 The term "fibers" encompasses organic and inorganic fibers of any suitable material having a length-to-thickness ratio of more than 6, preferably more than 10 in particular more than Printed from Mimosa 07/27/1999 11 27 37 page -6- WO 98/31764 PCT/FI98/00026 5 20 It is preferred to use lignm-containing fibers, because the lignin of the fibers will be oxidized in the presence of oxidases and work as an adhesive in mixtures of wood particles and the adhesive foam Particularly preferred lignocellulosic fibers are derived from wood or annular or perennial plants Such fibers can be obtained from mechanical refining of 5 wood or plants by refiner mechanical pulping, pressurized refiner mechanical pulping, thermomechanical pulping, groundwood or pressurized groundwood pulping, or chemi-thermomechanical pulping Furthermore, fibers from the preparation of fiber boards (e g medium density or high density fiber boards) can be used in the preparation of particle boards 10 In addition to the cellulosic fibers mentioned above, other natural fibers, such as cotton fibers, Abaca hemp fibers, sisal fibers, ramie fibers, flax fibers or jute fibers, can be used Inorganic fibers such as glass fibers, carbon fibers, gypsum fibers, etc can also be employed 15 For polymerizing lignin and carbohydrates of soluble wood fractions, oxidative enzymes capable of catalyzing oxidation of phenolic groups can be used These enzymes are oxidoreductases, such as peroxidases and oxidases "Peroxidases" are enzymes which catalyze oxidative reaction using hydrogen peroxide as their substrate, whereas "oxidases" 20 are enzymes which catalyze oxidative reactions using molecular oxygen as their substrate Phenoloxidases (EC 1 10 3 2 benzenediol oxygen oxidoreductase) catalyze the oxidation of o- and p-substituted phenolic hydroxyl and amino/amine groups m monomenc and polymeric aromatic compounds The oxidative reaction leads to the formation of phenoxy radicals and finally to the polymerization of lignin and possibly the carbohydrate matter In 25 the method of the present invention, the enzyme used mav be any of the enzymes catalyzing the biological radical formation and secondary chemical polymerization of low molecular weight ligmns, such as laccase, tyrosinase, peroxidase or oxidase As specific examples of oxidases the following can be mentioned laccases (EC 1 10 3 2), 30 catechol oxidases (EC 1 10 3 1), tyrosinases (EC 1 14 18 1) and bilirubin oxidases (EC 1 3 3 5) Laccases are particularly preferred oxidases They can be obtained from bactena and fungi belonging to, e g , the following strains Aspergillus Neurospora, Podospora, Printed from Mimosa 07/27/1999 11 27 37 page -7- WO 98/31764 PCT/FI98/00026 6 Botrytis, Lentmus, Polyporus, Rhizorlonia, Coprmus, Conolus, Phlebia, Pleurolus, Fusarium and Trameies Suitable peroxidases can be obtained from plants or fungi or bacteria Preferred peroxidases 5 are those which originate firom plants, in particular horseradish peroxidase and soy bean peroxidase The terms "surfactant" or "surface active agent" are synonymously used to designate compounds which have affinity to water and to hydrophobic (e g fatty) materials, thus 10 aiding the hydrophobic materials to suspend in water Adhesive component As mentioned above, lignin of different origins can be used as the adhesive component of 15 the present foamed adhesive binders In particular, isolated lignin of, e g, the sulphate, sulphite, ORGANOSOLV and MILOX processes can be used However, in addition to ligmn or instead of it, vanous soluble wood fractions can also be employed Thus, it is known in the art that dunng mechanical refining of chips, a part of tlie 20 compounds of the fibrous raw material is dissolved (about 1 % of the fiber weight) This fraction contains pnmanly the same chemical components as the fibers (carbohydrates, exti actives and lignin) To mention an example the soluble fraction of softwood chips contains some 40 to 70 % carbohydrates, 10 to 25 % lignin and 1 to 10 % extractives, whereas hardwood pulping process water contains some 20 to 60 % carbohydrates, 10 to 25 25 % lignin and 10 to 40 % extractives It has been found that this soluble lignin/carbohydrate fraction obtainable from mecnanical or chemimechanical pulping is particularly useful as an additive or adjuvant for gluing of panicles boards, fiber boards and other similar wood-based composite products 30 Particularly good gluing is acnieved if this fraction (as is the case with lignin) is polvmenzed with laccase (or similar) oxidase enzyme(s) The results are on the same level as those obtainable with conventional phenol or urea formaldehyde resins Printed from Mimosa 07/27/1999 11 27 37 page -8- WO 98,31764 PCT/E198/00026 7 It should be noticed that a similar soluble fraction can be obtained by treating lignocellulosic raw material, such as wood fibers or saw dust, with hydrolases, e g celluiases, hemicellulases and pectinases 5 Manufacture ot adhesive binder foam The present invention relates to foam-based technology for providing good dispersion of the different solids Thus, efficient contact during economical production of particle board is achieved using adhesive binders based on oxidase-activated ligmn and/or carbohydrates 10 together with wood fibers or other lignocellulosic fibers 0 1 to 50 %, preferably 0 5 to 30 % and in particular about 1 to 10 % by weight of the kraft lignin or similar ligmn is replaced bv fibers in the foam-based, oxidase-activated adhesive formulation According to the preferred embodiment of the present invention, in which wood-derived 15 fibers are used, ligmn and the fibers are activated by oxidases are mixed with the chips in the form of a foam that provides a good viscose suspending medium to form an even dispersion of the solids and hence improves substantially the quality of the particle board formed The use of the foamed adhesives as descnbed in this invention leads also to better control of the application and to substantial savings in adhesive use The foam is produced by the use of a 20 surface active agent The foamed, activated fiber and lignin/carbohydrate dispersion can be produced separately from the chips, which are mixed into the foam by known mixing technology, e g by extruding or spraying the foam onto the fibers or chips The foam can also be produced 25 simultaneously by mixing the fibers and chips with the foam chemicals, the lignin/carbohydrates and the laccase According to the present invention, the foam is produced by dispersing the mixture of iignm and fibers into water to form a suspension and bubbling a gas through the suspension to 30 form bubbles having a medium diameter of 0 001 to 1 mm, in particular about 0 01 to 0 1 mm Printed from Mimosa 07/27/1999 11 27.37 page -9- WO 98/31764 PCT/FI98/00026 8 The foam is produced by the use of a surface active agent that can be anionic, cationic or non-ionic Thus, the surfactant can be selected from the group consisting of alkylsulfonate or alkyl benzene sulfonate, Tween® and other commercial compounds, fatty acid soaps, lignosulfonates, sarcosmates, fatty acid amines or amines or poly(oxyetylene alcohol)s and wood and plant extractives Foam stabilizers and solid surfactants, such as CMC, gelatin, pectin, wood extractive and similar compounds, can be used to produce and enhance the foam stability A small amount of the surface active compounds is needed, i e about 0 01 to 10 %, in particular about 0 05 to 5 % 10 The foam can be produced by foaming in a static foamer or m a turbulent foam cell by using known mixing technology Although any gas can be used for foaming, it is preferred to use oxygen-containing gases, such as air, oxygen enriched air, oxygen or pressurized systems of these The importance of using oxygen-containing gases is discussed m further detail below 15 The foam produced is essentially stable during handling, storage, transport and manufacture of wood-based products and it has a density in the range of 0 1 to 0 9 kg/1, in particular about 0 2 to 0 7 kg/1, and a medium foam bubble diameter m the range of 0 005 to 0 1 mm, in particular about 0 01 to 0 1 mm, preferably about 0 02 mm 20 The method according to the present invention can be used for all oxidase-catalyzed, previously unsuccessfully suggested enzyme-catalyzed glueing processes using oxidases The enzyme used can be any of the enzymes catalyzing the oxidation and polymerization of aromatic compounds or lignins, such as laccase, tyrosinase, or other oxidases, as mentioned above The amount of enzyme used vanes depending on the activity of the enryme and on 25 the amount of dry matter content of the composition Generally the oxidases are used in amounts of 0 001 to 10 mg protein/g of arv matter, preferably about 0,1 to 5 mg protein/g of dry matter The activity of the oxidase is about 1 to 100,000 nkat/g, preferably over 100 nkat/g 30 In connection with the present invention it has been found that oxygen plays a decisive role m the enzymatic polymerization of lignin of any ongm This is important in particular for the production of adhesives for the manufacture of fiber boards, particle boards and flake Printed from Mimosa 07/27/1999 11 27 37 page -10- WO 98/31764 PCT/FI98/00026 9 boards and other similar wood-based products Thus, in addition to the aromatic reactant, also oxygen is needed The oxidative reaction leads to the formation of phenoxy radicals and finally to the polymerization of ligmn In the known methods discussed above, crosslinkmg was only partially achieved because of apparent limitations on the availability of oxygen The limitation of the reaction by oxygen manifests itself in the long reaction times used, and in the poor strength properties obtained, thus impainng the result of the enzyme-aided polymerization Oxygen can be supplied by vanous means, such as efficient mixing, air enriched with oxygen or introducing oxygen supplied by enzymatic or chemical means to the solution However, according to the pi esent invention, by foaming the suspension with an orygen-contaimng gas it is possible to provide the oxygen needed for full polymerization of the ligmn At the same time, the foamed structure gives enough strength tc the adhesive so as to prevent sedimentation of water-insoluble lignin or the polymerized lignin from the adhesive thus producing failure in the production and in the board product The present invention provides considerable advantages Thus, the foamed structure can be utilized in the preparation of particle boards of ligmn and/or carbohydrates or polymerized ligmn by utilizing the adhesive properties of the ligmn or polymerized lignin, whereas the fibers work as crosslinkers between the particles The foam will homogenize the inhomogenous solid phase and the liquid phase, increase the viscosity of the mixture and prevent the sedimentation of the solids and the fibers The oxygen-containing foamed structure will also provide more oxygen for oxygen-enhanced oxidase catalyzed lignin/carbohydrate polymerization Because of its large volume the foam will cover more homogeneously the wood fibres and wood particles m the preparation of the boards The adhesive binder is evenly distributed throughout the wood-based product, about 0 02 ± 0 002 0 2 ± 0 02 g/cm3, preferably 0 04 to 0 08 g/cm3 in any randomly selected volume unit of the product Printed from Mimosa 07/27/1999 11 27 37 page -11- WO 98/31764 PCT/FI98/0002fc 10 This leads to better strength values and better control of the use of the adhesive in the production The following non-limiting working examples illustrate the invention Example 1 Manufacture of MDF fibers MDF fibers were prepared from hardwood (Swedish birch) by refining birch chips m a 10 conventional TMP process at a refiner pressure of 4 bai The fiber quality was tested using both Bauer McNett analysis and a Pulmac shive analysis The results are shown below 15 Table 1 Fiber characteristics 20 Bauer McNett > 16 (>1 19 mm) 18 6 16-30(1 19-0 595 mm) 25 1 30-50 (0 595-0 297 mm) 124 50-100 (0 149 mm) 29 0 <100 (<0 149 mm) 150 Pulmac shive analysis Screen plate 0 15 mm 70 Screen olate 0 25 mm 0 8 25 Example 2 Manufacture of particles boards 30 This Example descnbes the preparation of a foamed adhesive consisting of kraft lignin, laccase wood fibre and the manufacture of particle boards from the adhesive The test has been earned out on laboratory scale Printed from Mimosa 07/27/1999 11 27 37 page -12- </div>

Claims

<div class="application article clearfix printTableText" id="claims">



WO 98/31764 

PCT/FI98/00026 

11 

Kraft hgnin Indulin AT and 1 - 10 % of its weight substituted with the MDF fibers of Example 1 were used as a binder mixture in particle board test panel manufacture 

3 6 - 3 96 g of the lignin was vigorously mixed with 0 04 - 0 4 g of MDF fibers and aerated 5 for 30 min with 4 0 g of laccase concentrate (activity 4,000 nkat/g) in 2 0 g of 2 M sodium acetate buffer (pH 4 5) 1 4 g of the mixture was mechanically mixed with 4 4 g of chips The chips had already been treated with 1 % of wax (Mobilex 54, 60 % emulsion) of the dry weight of the fibers The reference tests were performed without laccase (water was used instead) and using commercial ureaformaldehyde resins 

10 

For strength tests particle board panels of the size of 50 mm x 50 mm x 2 mm (weight about 5 g) were prepared by pressing 2 mm in 30 kp/cm2 of pressure and 190 °C of temperature After pressing, the panels were then cut into four pieces (50 mm x 12 mm x 2 mm) These pieces were tested for parallel tensile strength with Zwick tensile strength testing 15 equipment 

Table 2 Results of glueing tests for particle boards 

Foamed binder 

Tensile strength 

MPa 

Water 

3 0 +03 

Induhn AT (10 %) + MDF fibers 

8 5 ± 0 4 

(90 %) 

Induhn AT (10 %) + MDF fibers 

11 9 ± 0-7 

(90 %) + laccase 

Induhn AT 

72 ±04 

Indulin AT + laccase 

127 ±06 

Reference UF resin 

125 ±07 

As apparent from the results of Tabic 2, up to 10 % of laccase-activated kraft hgnin can be 30 substituted as an adhesive by MDF fibers without any significant loss in tensile strength The strength properties of particle boards prepared according to the present invention are quite comparable to those of conventional UF resin glued boards 

Printed from Mimosa 07/27/1999 11 27 37 page -13- 

12 

" ( 

WHAT IS CLAIMED IS: £. t) 

1 A lignin and/or carbohydrate -based adhesive binder composition for particle boards and similar wood-based products, wherein 

- the composition comprises a mixture of hgnin-contaimng fibers and hgnm and/or carbohydrates obtained from a process of pulping lignocellulosic materials, and oxidative enzymes capable of catalyzing oxidation of phenolic groups, and 

- the mixture is being foamed to 1 1 to 10 times the volume of the liquid mixture
2 The composition according to claim 1, wherein the lignin comprises polymerized kraft lignm
3 The composition according to claim 1 or 2, wherein the foam has a solids content of 1 

- 90% by weight
4 The composition according to claim 3, wherein the foam has a solids content of 5 to 70% by weight
5 The composition according to any one of claims 1-4, wherein the density of the foam is in the range from 0 1 to 0 9 kg/1, and the medium foam bubble diameter is m the range of 0 0001 to 0 1 mm
6 The composition according to claim 5, wherein the density of the foam is in the range from about 0 2 to 0 7 kg/1
7 The composition according to claim 5 or claim 6, wherein the medium foam bubble diameter is in the range of about 0 01 to 0 05 mm
8 The composition according to any one of the claims 1 to 7, wherein the fibers are lignocellulosic fibers derived from wood or annual or perennial plants
9 The composition according to claim 8, wherein the fibeis are obtained from mechanical refining of wood or plants by refiner mechanical pulping, pressurized refiner mechanical pulping, thermomechamcal pulping, groundwood or pressurized groundwood pulping, or chemithermomechanical pulping 

13 

V
10 The composition according to claim 9, wherein the fibers are obtained from the preparation of fibeis for fibei boards
11 The composition according to any one of the preceding claims, wherein the fiber content is 0 1 to 50% of the weight of the ligmn
12 ihe composition according to claim 11, wherein the fiber content is 0 5 to 30% of the weight of the ligmn
13 The composition according to claim 12, wherein the fiber content is 1 to 10% of the weight of the lignm
14 The composition according to any one of the preceding claims, wherein the foam contains surfactants in an amount of 0 1 to 10% by weight of the aqueous suspension
15 The composition according to claim 15, wherein the foam contains surfactants in an amount of 0 2 to 5% by weight of the aqueous suspension
16 The composition according to any one of the pieceding claims, wherein the composition contains an oxidase or a peroxidase, the amount of the oxidase being 0 1 to 5 mg protein/g dry matter
17 A method of preparing a lignin and/or carbohydrate -based adhesive mnder for particle boards and similar wood-based products, comprising the steps of 

- using hgnin and/or carbohydrates obtained from a pulping process of lignocellulosic raw materials as raw material, 

- using fibers based on wood or annual or perennial plants as raw material, 

- forming an aqueous suspension of the lignin and/or carbohydrates and the fibers, and 

- foaming the aqueous suspension to provide a foamed adhesive binder composition i, J : V / 

14
18 The method according to claim 17, comprising the steps of 

- forming an aqueous suspension containing 1 - 90 % by weight of solid matter comprising lignin, fibers and surfactants, and 

- foaming the aqueous suspension with an oxygen-containing gas to 1 1-10 times the volume of the suspension to provide a foam having a solids content of 5 - 70 % by weight
19 The method according to claim 17 or 18, wherein the lignin comprises polymerized la aft ligmn
20 The method according to claim 17 or 18, which comprises the step of forming an aqueous suspension containing lignin, fibeis, an oxidase and surfactants
21 Particle board or a similar wood-based product comprising wood particles, fibers or flakes mixed with an adhesive binder according to any one of the claims 1 to 16
22 A method of manufacturing a particle board or a similar wood-based pioduct, comprising the step of mixing wood particles, wood fibers or wood flakes with a ligmn and/or carbohydrate based adhesive binder according to any one of the claims 1 to 16 so as to incorporate 2 - 20% of the solids of the adhesive binder composition into the wood-based product
23 The composition according to claim 1, substantially as herein described with leference to either one of the Examples
24 The composition according to any one of claims 1-16, substantially as herein descnbed
25 The method according to claim 17, substantially as herein descnbed with reference to either one of the Examples
26 The method according to any one of claims 17-20, substantially as herein descnbed 

1 

i c r ' ^ 

Irv' / 

i 

• 15
27 The wood-based product according to claim 21, substantially as herein descnbed with reference to either one of the Examples
28 The wood-based product according to claim 21, substantially as herein descnbed
29 The method accoiding to claim 22, substantially as herein descnbed with reference to either one of the Examples
30 The method according to claim 22, substantially as herein descnbed 



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