SK94199A3 - Lignin-based adhesives for particle board manufacture - Google Patents

Abstract

The invention concerns a lignin-based adhesive binder composition for particle boards and similar wood-based products, comprising a foamed aqueous mixture of fibers and carbohydrates obtained from a process of pulping lignocellulosic materials, the mixture being foamed to 1.1 to 10 times the volume of the liquid mixture. The invention also concerns a method of preparing a lignin-based adhesive binder, comprising the steps of providing lignin isolated from a pulping process of lignocellulosic materials, providing fibers based on wood or annual or perennial plants, forming an aqueous suspension of the lignin and the fibers, and foaming the aqueous suspension to provide a foamed adhesive binder composition containing the solids in a homogeneous dispersion.

Description

LIGIN BASE BINDING DEVICE, METHOD OF PREPARATION, SINGLE BOARD AND SINGLE BOARD MANUFACTURING METHOD

Technical field

The present invention relates to the manufacture of particle board and similar wood-based products comprising lignocellulosic chips, fibers or flakes, mixed and glued together with an adhesive binder. In particular, the present invention relates to novel lignin and / or carbohydrate based adhesives, a method of preparation, and particle boards produced using adhesives.

BACKGROUND OF THE INVENTION

The rapid increase in the production of particle board, fiber board and chip board (MDF) over the past decades has created a demand for adhesives that are not expensive, are available in large quantities and are independent of crude oil. These requirements are well met by lignin, which also contains no formaldehyde, which has traditionally been considered a serious problem in conventional urea-formaldehyde (UF) adhesives. Native lignin, as the main wood component, is neither hygroscopic nor water soluble. During technical pulping, however, it becomes water-soluble due to degradation and chemical changes in lignins.

It is well known in the art to use a sulfite leach (SSL) as an adhesive for paper, wood and other lignocellulosic materials. During the last three decades, many patent applications have been filed for the use of lignin products as adhesives for particle board, plywood and fiber board instead of conventional PF and UF adhesives. Reference is made to DE patents 3 037 992, 3 621 218, 3 933 279, 4 020 969, 4 204 793 and 4 306

439 and PCT applications, issued under WO 93/25622, WO

94/01488, WO 95/23232 and WO 96/03546.

The main drawback of using SSL as a fiberboard adhesive is its hygroscopicity. Therefore, it cannot compete with other natural or synthetic adhesives. If SSL is used as an adhesive, it can be cured into an insoluble material. Chemically, curing of lignin is a cross-linking process that leads to the formation of new ether and C-C bonds between different lignin molecules or within a single molecule. Intermolecular and intramolecular crosslinking reactions reduce the solubility and swelling of lignin. Crosslinking in lignin can be accomplished either by condensation or by radical coupling reactions. Either high temperatures and long heating or mineral acids are required for the condensation reactions, causing structural changes or charring in parts of the wood. Recently crosslinking of lignosulfonate molecules by radical combinations has been found. In most cases, other crosslinking agents are necessary for lignin, such as epoxides, polyisocyanates, polzoles, poly (acrylamide) γ, poly (ethyleneimines) and aldehydes.

Furthermore, it has been shown that laccases and other peroxidases can be used as catalysts for polymerization or curing of lignin by enzymes (DE Patent No. 3,037,992, WO 96/03456). However, the use of enzymes to carry out radical reactions has not always been successful until now. The fibers and wood chips used to produce the fiber board contain 5 to 20% water and the used laccas need water to effectively catalyze the polymerization reaction needed for extensive bonding of the fiber board. However, sulfate lignin, largely similar to native lignin, is insoluble in water and thus two solid phases are formed during production. Uneven distribution of solids causes staining and distorts the properties of the plate formed in the press phase.

Another problem associated with the use of isolated lignin is the high cost of sulfate lignin, which is close to the economical production of particle board.

For the above reasons, the production of lignin-based boards has not so far led to any practical applications.

SUMMARY OF THE INVENTION

The present invention is directed to the elimination of problems related to the prior art. It is an object of the present invention to provide a novel lignin-based adhesive for use for particle board and similar wood-based products. It is a further object of the present invention to provide new wood-based particle board and similar products. A third object of the invention is to provide a method for manufacturing an adhesive.

These and other objects, together with their advantages over known lignin-based adhesives and processes for their preparation, which should be apparent from the following specifications, are achieved by the present invention as described and claimed herein.

In order to provide a uniform dispersion of solids, according to the present invention, lignin, lignin is polymerized with oxidizing enzymes or a soluble fraction of carbohydrates obtained from mechanical refining of lignocellulosic materials, added and mixed with the fibers, wood chips or flakes used as lignocellulosic base product wood in the form of foam.

Foamed UF or PF adhesives are known in the art. Said foams are used to improve process behavior and to improve product quality, especially in high solids adhesives. CA patent application no. No. 2,114,258 describes the production of a particle board using foamed mixtures of UF resin and animal blood. DE 3 644 067 also discloses the use of foamed materials in the bonding of fibers or flakes whereby a homogeneous adhesive application of fine particles (fibers or powders) to the papermaking material is produced. T. Sellers describes in Forest Prod. J. 38 (1998) pages 55 to 56 improved behavior of foamed UF and PF resins in the manufacture of particle board, especially as higher solids adhesives. However, none of the prior art discloses foaming of lignin-containing adhesive compositions. According to these references, the composition of the gas is not important.

According to the present invention, the lignin-based adhesive composition comprises an aqueous suspension of lignin and / or carbohydrates obtained in the pulping process of lignocellulosic materials. The suspension is foamed to a volume of 1.05 to 10, more preferably 1.1 to 8, especially 1.2 to 5 times higher than the volume of the liquid mixture. It is preferred to use polymerized sulfate lignin as the lignin component. Furthermore, according to the present invention, natural lignin in wood fibers is used to replace a substantial portion of the lignin in an adhesive binder for the manufacture of particle board. These adhesive binders comprise an aqueous mixture of fibers with lignin and / or carbohydrates obtained from the pulping process of lignocellulosic raw materials. Due to the effect of enzymes in the foam matrix, evenly containing oxygen, added use of lignin fiber radicals polymerize fibers and / or other

MDF or TMP in sticky lignocellulosic types containing native lignin instead of lignin, binder and material.

leads to savings in adhesive, but also to its corresponding strength.

The foam will homogenize the solid and liquid phases, increase the viscosity of the mixture and prevent sedimentation of the solid particles. The foamed oxygen-containing structure will also provide more oxygen for the O ₂ -dependent oxidases that catalyze lignin / saccharide polymerization. Due to the large volume of foam, the foam will cover more homogeneous wood fibers and wood chips when preparing the boards. This will lead to better force values and better control of the use of the adhesive during manufacture.

The present invention will now be explained in more detail by reference to the following detailed description and with reference to working examples.

In the context of the present invention, the terms " adhesive, " adhesive binder and " resin " refer to a chemical composition which, in the wet production stages, e.g. chip and fiber boards provide adhesion between chips or fibers. After thermal compression during the production of the board, the composition comprising the polymerized resin works as a binder that keeps the chips, fibers or leaf chips glued together.

The term "wood-based products" means any lignocellulose-based product, such as particle boards, fiber boards (including high and medium density fiber boards, ie heavy boards and MDF boards), chipboard, plywood and the like, consisting of chips , fibers or flakes of vegetable origin, mainly derived from wood or annular or perennial plants, which are mixed and glued together with an adhesive binder. According to a particular preferred process, the present invention is used to prepare wood-based panels and similar wood-based products in which the wood-chips can be cross-linked and bonded together with the fibers of an adhesive composition that will be glued to the wood-chip with a lignin-based adhesive.

The term "fibers" includes organic and inorganic fibers of any suitable material having a length to thickness ratio of greater than 6, more preferably greater than 10, especially greater than 20. It is preferred to use fibers containing lignin because the fiber lignin will be oxidized in the presence of oxidases and glue in a mixture of wood chips and glue foam. Particularly preferred lignocellulosic fibers are derived from wood or annular or perennial plants. These fibers can be obtained from mechanical refining of wood or plants by refining mechanical pulping, pressure refining mechanical pulping, thermomechanical pulping, pulp or pressure pulp pulping, or chemothermomechanical pulping. Further, fibers from the preparation of fiber boards (e.g., medium or high density fiber boards) may be used in the preparation of particle boards.

In addition to the cellulosic fibers mentioned above, other natural fibers can be used, such as cotton fibers, Abaca hemp fibers, sisal fibers, ramie fibers, rope fibers, or jute fibers. Inorganic fibers such as glass wool, carbon, gypsum fibers, etc. may also be used.

To polymerize lignin and carbohydrate soluble wood fractions, oxidative enzymes capable of catalyzing the oxidation of phenolic groups can be used. These enzymes are oxidoreductases such as peroxidases and oxidases. "Peroxidases are enzymes that catalyze oxidation reactions with hydrogen peroxide as their substrate, while" oxidases are enzymes that catalyze oxidation reactions with substrate molecular oxygen. Phenol oxidases (EC 1.10.3.2 Benzenediol: O2 oxidoreductase) catalyze the oxidation of o- and β-substituted phenolic hydroxyl and amino / amino groups in monomeric or polymeric aromatic compounds. Oxidation reactions lead to the formation of phenoxy radicals and to the polymerization of lignin, env. Carbohydrates. Any enzyme such as laccases, tyrosinases, peroxidase or oxidases catalysing the biological formation and secondary chemical polymerization of low molecular weight lignins can be used in the method of the present invention.

Specific examples of oxidases include the following enzymes: laccases (EC 1.10.3.2), catechol oxidases (EC 1.10.3.1), tyrosinases (EC 1.14.18.1) and bilirubinoxidases (EC 1.3.3.5). Particularly preferred oxidases are laccases.

They may be obtained from bacteria and fungi belonging, for example, to the following strains: Aspergillus, Neurospora, Podospora, Botrytis, Lentinus, Polyporus, Rhizoctonia, Coprinus, Coriolus, Phlebia, Pleurotus, Fusarium and Trametes.

Suitable peroxidases may be obtained from plants, molds or bacteria. Preferred peroxidases are those derived from plants, in particular horseradish peroxidase and soybean peroxidases.

The terms "surfactant" or "surfactant" are synonyms used to refer to compounds having affinity for water and hydrophobic (e.g., fatty) materials, thereby helping to dissolve hydrophobic materials in water.

Glue component

As already mentioned, lignin of various origins can be used as an adhesive component of foamed adhesive binders. In particular, isolated lignin, e.g. sulphate, sulphite or obtained from ORGANOSOLV and MILOX processes.

However, in addition to or instead of lignin, various soluble wood fractions may also be used. It is known in the art that part of the fibrous raw material compounds (about 1% by weight of fiber) are dissolved during mechanical chip refining. This fraction mainly contains the same chemical compounds as the fibers (carbohydrates, extractables and lignin). By way of example, the soluble softwood chip fraction contains about 10 to 70% carbohydrates, 10 to 25% lignin and 1 to 10% extractables, while the hardwood pulping process water contains 20 to 60% carbohydrates, 10 to 25% lignin and 10 to 40% extractables.

This soluble lignin-carbohydrate by mechanical or chemomechanical pulping has been found to be particularly useful as an additive or fraction obtainable from an adjuvant for gluing particle board, fiber board and other similar wood-based products.

In particular, effective bonding is achieved when this fraction (as in the case of lignin) is polymerized with laccase (or similar) oxidase enzyme (s). The results are at the same level as those obtained with conventional phenolic or urea-formaldehyde resins.

It should be noted that a similar soluble fraction can be obtained by treatment with hydrolases, e.g. cellulases, hemicellulases and pectinases for lignocellulosic raw material such as wood fibers or sawdust.

Production of adhesive binder foam

The present invention relates to a technology for providing a good dispersion of various foam-based solid particles. Therefore, efficient bonding during economical production of the particle board is achieved by using lignin-based and / or carbohydrate-based adhesive binders activated by oxidase together with wood fibers or other lignocellulose fibers. 0.1 to 50%, more preferably 0.5 to 30%, and in particular about 1 to 10% by weight of kraft lignin or similar lignin is replaced by fibers of a sticky, oxidase-activated foam-based formulation.

According to a preferred embodiment of the present invention, in which wood-derived fibers are used, lignin and oxidase-activated fibers are mixed with chips in the form of a foam which provides a good viscous suspending medium to form a uniform dispersion of solid particles thereby substantially improving the quality of the chips produced. board. The use of foamed adhesives as described in the invention results in better application control and substantial savings in adhesive. The foam is produced using a surfactant.

The foamed, activated fiber and lignin / carbohydrate dispersion can be produced separately from chips that are mixed into the foam by mixing technology, e.g. pressing or spraying the foam onto the fibers or chips. Foam can also be produced simultaneously by mixing fibers and chips with foam chemicals, lignin / carbohydrates and laccase.

According to the present invention, the foam is produced by dispersing a mixture of lignin and fibers in water to form a suspension and bubbling the suspension through gas to form bubbles having an average diameter of 0.001 to 1 mm, especially about 0.01 to 0.1 mm.

The foam is produced using a surfactant, which may be cationic, anionic or non-ionic. Therefore, the surfactant may be selected from the group consisting of alkylsulfonate or alkylbenzene sulfonate, Tween® and other commercial compounds, fatty acid soaps, lignosulfonates, sarcosinates, fatty acid amines or poly (oxyethylene alcohol) γ amines, wood and plant extractables. Foam stabilizers and solid surfactants such as carboxymethylcellulose (CMC), gelatin, pectin, extractables and the like can be used to produce and enhance foam stability. A small amount of surfactant is required, i. about 0.01 to 10%, especially about 0.05 to 5%.

The foam can be produced by foaming in a static foamer or in a turbulent foam cell using known mixing techniques. Although any gas can be used for foaming, it is preferred to use oxygen-containing gases such as air, oxygen-enriched air, oxygen, or pressure systems thereof. The importance of the oxygen-containing gases used is discussed in more detail below.

The foam produced is substantially stable during handling, storage, transport and production of wood-based products and has a density in the range of 0.1 to 0.9 kg / l, especially about

0.2 to 0.7 kg / L and a mean foam bubble diameter in the range

0.005 to 0.1 mm, in particular about 0.01 to 0.1 mm, more preferably about

0.02 mm.

The process of the present invention can be applied to all oxidase catalyzed, rather unsuccessful, adhesive processes. The enzymes used can be any of the enzymes that catalyze the oxidation and polymerization of the aromatic compounds or lignins, such as the laccase, tyrosinases or other oxidases mentioned above. The amount of enzyme used varies depending on the activity of the enzymes and the dry matter content of the composition. Generally, the oxidases are dry solids, more preferably the oxidase activity is greater than 100 nkat / g.

In relation to in amounts of 0.00 to about 0.1 to 5 mg about 1 to 100,000 mg protein / g protein / g dry matter.

nkat / g, more preferably in the enzyme critical adhesive boards of the found to origin

Therefore it is

The oxidation of the present invention was the polymerization of lignin of any role oxygen. This is particularly important in the production of fiber board, particle board and flake chips and other wood-based products, in addition to the aromatic reactant, the necessary oxygen, the reaction leads to the formation of phenoxy radicals and ultimately to the polymerization of lignin.

Due to the apparent limitation in the availability of oxygen, only partial cross-linking was achieved in the known methods discussed above. The limitation of the oxygen reaction is manifested in long reaction times and in poor strength properties obtained, thereby deteriorating the result of enzyme polymerization.

Oxygen can be delivered by various means, such as sufficient mixing, by air, oxygen-enriched, or by introducing oxygen into solution by enzymatic or chemical means. However, it is possible to provide the oxygen needed to modify the polymerization of lignin by foaming the suspension with an oxygen-containing gas. At the same time, the foamed structure gives sufficient adhesive strength and thus prevents sedimentation of the water-insoluble lignin or polymerized lignin from the adhesive, so that production and plate disturbances occur.

The present invention provides considerable advantages. The foamed structure can be used in the preparation of particle boards and / or carbohydrates or polymerized lignin using

The adhesive properties of lignin or polymerized lignin, while the fibers act as cross-linking factors between the chips. The foam will homogenize the non-uniform solid liquid phase, increase the viscosity of the mixture, and prevent sedimentation of solids and fibers. The foamed oxygen-containing structure will also provide more oxygen to the oxygen-catalyzed lignin / carbohydrate polymerization enriched in oxygen. In the preparation of the boards, the foam will, due to the large volume, cover the wood fibers and wood chips more evenly. The adhesive binder is evenly distributed by wood-based products, about 0.02 ± 0.002 to 0.2 ± 0.02 g / cm ³ , more preferably 0.04 to 0.08 g / cm ³ , in any randomly selected volume unit of product .

This leads to better force values and better control of the use of the adhesive in production.

The following non-limiting working examples illustrate the invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Production of MDF fibers

MDF fibers were prepared from hardwood (Swedish birch) by refining birch chips in a conventional TMP process, at a refining pressure of 4.10 ⁵ Pa.

Fiber quality was tested using as Bauer

McNett's analysis, as well as Pulmac's shear analysis.

The results are shown below.

Table 1. Fiber characteristics

Bauer McNett • si 6 (p.1 ₍ 1 Q mm) 18, 6 16-30 (1.19-0.595 mm) 25.1 30-50 (0.595-0.297 mm) 12.4 50-100 (0.149mm) 29, 4 ζ1 ΠΠ fzfi. 1 dQ mm) 15.0 Pulmata analysis of oazderia Sorting lead 0,15 7.0 Sorting plate 0,25 about 00

Example 2

Production of particle board

This example describes the preparation of a foamed adhesive comprising kraft lignin, laccase, wood fiber, and the manufacture of glue boards. The test was performed on a laboratory scale.

Indulin AT kraft lignin and lignin in which 1-10% by weight was replaced by MDF of Example 1 were used as a binder mixture for the manufacture of particle board test panels.

3.6 and 3.96 g of lignin were mixed intensively with 0.04 to 0.4 g of MDF fibers and aerated for 30 min. with 4.0 g lacase concentrate (4000 nkat activity / g activity) in 2.0 g 2M sodium acetate buffer (pH 4.5). 1.4 g of the mixture were mechanically mixed with 4.4 g of chips. The chips were already treated with wax (Mobilex 54.60% emulsion) at 1% fiber dry weight. Comparative tests were performed without laccase (instead of water) and with commercial urea-formaldehyde resins.

For strength tests they were pressed for 2 min. at a pressure of 30 kp / cm ² and a temperature of 190 ° C, prepared panels of mm x 50 mm x 2 mm (weight about 5 g). After compression, the panels were cut into 4 pieces (50 mm x 12 mm x 2 mm). These were tested for parallel tensile strength using a Zwick tensile strength tester.

Table 2. Glue test results for particle board.

Foamed binder Tensile strength Water in n + n _r ? Indulin AT (10%) + MDF ». 5-n.δ 90% Indulin AT (10%) + MDF 1 i Q + n 90 (%) + laccase Indulin AT i _r 9 + nA Indulin AT + Lacase 1 7. 7 + 0.6 Reference UF resin L2> .5 + n, 7

As can be seen from the results of Table 2, up to 10% of laccase-activated sulfate lignin can be replaced by MDF fibers without any significant loss of tensile strength. The strength properties of the chipboards prepared according to the present invention are comparable to those of boards bonded with conventional UF resin.

Claims (16)

PATENT CLAIMS A lignin and / or saccharide-based adhesive binder composition for particle board and similar wood-based products, characterized in that it comprises a mixture of fibers containing lignin and lignin and / or carbohydrates obtained from the pulping process of lignocellulosic materials and oxidative enzymes; capable of catalyzing the oxidation of phenolic groups, and the mixture is foamed to 1.1-10 times the volume of the liquid mixture. The composition of claim 1, wherein the lignin comprises polymerized sulfate lignin. Composition according to claim 1, characterized in that the foam has a solids content of 1 to 90%, preferably about 5 to 70% by weight. Composition according to claim 1, characterized in that the foam density is in the range of 0.1 to 0.9 kg / l, in particular about 0.2 to 0.7 kg / l, and the mean diameter of the foam bubble is in the range of 0 to 0.9 kg / l. 0001 to 0.1 mm, in particular about 0.01 to 0.05 mm. Composition according to any one of claims 1 to 4, characterized in that the fibers are lignocellulosic fibers derived from the wood of annual or perennial plants. Composition according to claim 5, characterized in that the fibers are obtained from mechanical refining of wood or plants by refining mechanical pulping, pressure refining mechanical pulping, pulp or pressure pulping pulp or chemothermomechanical pulping. Composition according to claim 6, characterized in that the fibers are obtained from preparing fibers for the fiber boards. Composition according to claim 1, characterized in that the fiber content is 0.1 to 50, preferably 0.5 to 30 and in particular 1 to 10% by weight of lignin. Composition according to claim 1, characterized in that the foam contains in an amount of 0.1 to 10, preferably 0.2 to 5% by weight of the aqueous suspension. Composition according to any one of the preceding claims, characterized in that the composition comprises an oxidase or peroxidase, the amount of oxidase being 0.1 to 5 mg protein / g dry matter. A process for the preparation of a lignin-based and / or carbohydrate-based adhesive binder for particle board and similar wood-based products, characterized in that it comprises the steps of: - the use of lignin and / or carbohydrates obtained from pulping processes of lignocellulosic raw materials as raw material, - the use of wood-based fibers, annual or perennial plants as raw material, forming an aqueous suspension of lignin and / or carbohydrates and fibers, and foaming the aqueous suspension to obtain a foamed adhesive binder composition. The method of claim 11, comprising the steps of: - forming an aqueous suspension containing 1 to 90% by weight of a solid containing lignin, fibers and surfactants, and - foaming the aqueous suspension with an oxygen-containing gas to 1.1 to 10 times the volume of the suspension to provide a foam with a solids content of 5 to 70% by weight. The method of claim 11 or 12, wherein the lignin comprises polymerized sulfate lignin. The method of claim 12, comprising the step of forming an aqueous suspension comprising lignin, fibers, oxidase, and surfactants. A particle board or similar wood-based product, characterized in that it comprises wood chips, fibers or flakes mixed with an adhesive binder according to any one of claims 1 to 10. A process for producing a wood-based particle board or the like, comprising the step of mixing wood chips, wood fibers or wood chip with a lignin-based adhesive and / or carbohydrate binder according to any one of claims 1 to 10, such as: to incorporate 2 to 20% of the solid components of the adhesive binder composition into the wood-based product.