FI104835B - Lignin-based binders for the production of particle board - Google Patents

Description

104835

LIGGIN-BASED BINDERS FOR CHIPBOARD PREPARATION

The present invention relates to a binder according to the preamble of claim 1 for the production of particle boards and other similar wood-based products consisting of lignocellulosic particles, fibers or chips mixed with a binder and bound by a binder. The invention also relates to a process for the preparation of new lignin and / or carbohydrate based binders according to the preamble of claim 11 as well as particle boards and similar wood based products made using said binder.

10 The rapid growth in the production of particle board and fiber boards, particularly medium density fiber boards (hereinafter abbreviated MDF boards) over the last decades, has created the need for low cost, high availability, crude oil independent binders. Lignin meets these requirements well and does not contain formaldehyde, which has traditionally been considered a serious problem with urea-formaldehyde adhesives (UF). As a major component of wood, native lignin is neither hygroscopic nor water-soluble. However, during technical pulping, lignin becomes water soluble due to degradation and chemical changes.

• · · * '; The use of sulfite waste liquor (SSL) as a binder for paper, wood or other lignocellulosic materials is well known in the art, and several patent applications have been filed over the last three decades for the use of lignin products in particle board, plywood and. · · · ·: · For bonding fiber boards instead of traditional PF or UF adhesives, referenced in DE 3 037 992, 3 621 218, 3 933 279,4 020 969,4 204 793 and 4,306,439 and PCT applications published as WO 93/25622, WO 94/01488, WO 95/23232 and WO 96/03546.

The main disadvantage of using SSL as a binder in the manufacture of fiber boards is its hygro- • *: **: scopiness. For this reason, it cannot actually compete with others of natural origin. · · ·. with existing or synthetic adhesives. When used as an adhesive, SSL «· · •; · · | 30 can be converted to an insoluble form by curing. Chemically, curing lignin is a cross-linking process that results in the formation of new carbon-carbon and ether bonds between different lignin molecules or within a single macromolecule. Both intracellular and intermolecular cross-linking reactions reduce the solubility and swelling of lignin. Cross-linking can be achieved by either a condensation reaction or a radical coupling reaction. Condensation reactions require either high temperatures and long heating times or mineral acids that cause structural changes or carbonization in the wood particles. A method for cross-linking Iignosulphonates by radical combinations has recently been developed. In most cases, lignin requires cross-linking additives such as epoxides, polyisocyanates, polyols, polyacrylamides, polyethyleneimides, and aldehydes.

It has further been shown that laccase enzyme or other peroxidases can be used as lignin polymerization or curing catalysts (DE 3 037 992, WO 96/03546). However, the success of enzymes in radical reactions has so far been limited. Fibers and chips used in the manufacture of fibreboards contain 5-20% water, and the lacquers used need some water to effectively catalyze the polymerization required for the comprehensive bonding of the fibreboard. However, kraft lignin, like native lignin, is largely water-insoluble, and thus two solid phases are formed on the production line. The uneven distribution of solids results in sputtering and a significant deterioration in the strength properties of the sheet formed during the compression step.

: 20 ·: * '. * In addition, the use of isolated lignin is limited by the high cost of kraft lignin, which is close to the economic margin for chipboard.

For these reasons, lignin-based production processes have not so far led to significant practical applications.

This invention seeks to eliminate the problems associated with the prior art. In particular, it is an object of the present invention to provide a novel lignin-based adhesive for use in gluing chipboard and other wood-based products. Another object of the invention is to provide novel particle boards and similar wood-based products; : what. The third object is to provide a binder manufacturing process.

These and other objects, together with the known advantages of the lignin-based binders and their manufacturing processes, the advantages of which will be apparent from the following specification, are accomplished in accordance with the invention as described below and claimed.

In accordance with the present invention, lignin or lignin polymerized by oxidizing enzymes or a soluble carbohydrate fraction obtained by mechanical refining of lignocellulosic materials are added and mixed with lignocellulosic raw materials for pulp or chips or wood chips as a lignocellulosic feedstock.

Foamed UF and PF resins are known in the art. Said foams are used to improve process performance and product quality, particularly in high solids binders. Patent Application CA 2,114,258 describes the production of particle board 15 using foamed life blood and UF resin mixtures. DE 3,644,067 also describes the use of foamed materials for bonding fibers and chips to provide a homogeneous binder application in the case of fine particles (fibers or powders). T. Sellers describes in Forest Prod. J. 38 (1988) pp. 55-56 foam. : the superior performance of the UF and PF resins in the manufacture of particle board, especially for high solids contents. However, no reference has previously made reference to foaming of lignin-containing binder compositions.

The lignin-based binder composition of the present invention contains lignin and / or m | · · · * * An aqueous suspension of carbohydrates from the pulping process of lignocellulosic materials. The suspension is foamed 1.05 to 10 times, preferably 1.1 to 8 times, in particular 1.2 to 5 times the volume of the liquid mixture. It is preferable to use polymerized kraft lignin as the lignin component. Further, according to the present invention, the natural lignin contained in the wood fibers can be used to replace a substantial part of the lignin of the binder for the production of chipboard. Thus, these binders consist of an aqueous solution of carbohydrates obtained from the pulping process of fibers and lignin and / or lignocellulosic feedstock.

More specifically, the binder according to the invention is characterized in what is stated in the characterizing part of claim 1.

The process for preparing the binder according to the invention is in turn characterized by what is disclosed in the characterizing part of claim 11 and the particle boards and other wood-based products according to the invention are characterized by what is described in the characterizing part of claim 15.

The foam homogenizes the solid phase and the liquid phase, increases the viscosity of the mixture and prevents the settling of solids. The oxygen-containing foamed structure also provides additional oxygen to the oxygen-dependent oxidase-catalyzed lignin / carbohydrate polymerization. Due to its large volume, the foam covers the wood fibers and wood chips used in the manufacture of boards more homogeneously. This results in better strength values and better control over the use of binder in production.

15

The invention will be explained in more detail by the following detailed description and by reference to experimental examples.

In the context of the present invention, the terms "binder", "adhesive" and "resin" refer to [20] a chemical composition which, during the wet manufacturing process of a chip and fiber board, for example, causes adhesion between the chips or fibers. After thermal pressing in the manufacture of the boards, the composition containing the polymerized resin acts as a binder which holds the chips or fibers or chips together.

• · ·: T; 25 The term "wood-based product" means any product based on lignocellulosic material, such as particle board, fiber board (including both high and average density. ·.: Boards, eg hardboard and MDF), particle board, plywood and similar products. , consisting of chips, fibers or flakes of vegetable origin, in particular from wood or from annual or perennial plants, which have been mixed and bound together with binders. According to a particularly preferred embodiment, the present invention is used in the manufacture of particle boards and the like wood-based products in which 104835 wood particles can be crosslinked and bonded using fibers contained in a binder composition which are bound to the particles by a lignin-based binder.

The term "fibers" includes organic and inorganic fibers of any suitable material having a length to thickness ratio of greater than 6, preferably greater than 10, in particular greater than 20. It is preferable to use lignin-containing fibers since the lignin of the fibers is oxidized in the presence of oxidases and acts as a binder in a mixture of wood particles and binder foam, and particularly preferred lignocellulosic fibers are wood fibers or annual or perennial plants.

Such fibers can be obtained from wood or plants by mechanical pulping, pressurized mechanical pulping, thermomechanical pulping, pulping or pressurized pulping, or chemothermomechanical pulping. Further, the fibers used to make fiber boards (e.g., medium density or high density fiber boards) may be used in the manufacture of chipboard 15.

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 may be used. Inorganic fibers such as glass fibers, carbon fibers, gypsum fibers, etc.

', 20 can also be utilized.

: · [* Oxidizing enzymes catalyzing the oxidation of phenolic groups can be used to polymerize the carbohydrates in the soluble fractions of lignin and wood. These enzymes are oxidoreductases such as peroxidases and oxidases. "Peroxidases" are enzymes that catalyze an oxidation reaction using hydrogen peroxide as a substrate, while:>: "oxidases" are enzymes that catalyze an oxidation reaction using molecular oxygen as a substrate. Phenoloxidases (EC 1.10.3.2 benzene diol: oxygen oxides «:: <· · reductase) catalyze o- and p-substituted phenolic hydroxyl groups and. · · ·. oxidation of amino / amine groups in monomeric and polymeric aromatic t I «| 30 compounds. The oxidation reaction leads to the formation of phenoxy radicals and eventually to the polymerization of lignin and possibly carbohydrates. The enzyme used in the process of the present invention can be any enzyme that catalyses biological radical formation and secondary chemical polymerization of small molecule lignin, such as laccase, tyrosinase, peroxidase or oxidase.

Specific examples of oxidases include laccases (EC 1.10.3.2), catechol-5 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, for example, from bacteria and fungi of the following strains: Aspergillus, Neurospora, Podospora, Botrytis, Lentinus, Polyporus, Rhizoctonia, Coprinus, Coriolus, Phlebia, Pleurotus, Fusarium and Trametes.

10

Suitable peroxidases can be obtained from plants or fungi or bacteria. Preferred peroxidases are plant peroxidases, particularly horseradish peroxidase and soybean peroxidase.

The terms "surfactant" or "surfactant" are used interchangeably to refer to substances that have affinity for water and hydrophobic substances and thus help to suspend hydrophobic substances in water.

,. ·, 20 Binder component

As mentioned above, lignins of various origins can be used as the binder component of this foam-coated adhesive. In particular, isolated lignin, e.g. from sulfate, • teaspoon sulfite, ORGANOSOLV or MILOX processes may be used.

• · · 25 f j *. However, various soluble wood fractions can be used in addition to or instead of lignin.

: * · *: It is known in the art that during mechanical milling of chips, some of the fibrous raw material compounds are soluble (about 1% by weight of the fiber). This fraction primarily contains the same chemical components as the fibers (carbohydrates, extractives and lignin).

(·. T 30 By way of example, the soluble fraction of conifers contains about 40-70% carbohydrates, 10-25% lignin and 1-10% extractives, while the hardwood pulping process water contains about 20-60% carbohydrates, 10- 25% lignin and 10-40% extractives.

104835 7

It has been found that this soluble lignin / carbohydrate fraction obtainable by mechanical or chemimechanical pulping is particularly useful as a bonding or adjuvant for bonding particle boards, fiber boards and other similar wood-based composite products. Particularly good bonding results are obtained if this fraction (as in the case of 5 lignin) is polymerized with laccase (or equivalent) oxidase enzymes. The results are at the same level as those obtained with conventional phenolic or urea-formaldehyde resin.

It will be appreciated that a similar soluble fraction can be obtained by treating 10 lignocellulosic raw materials, such as wood fibers or sawdust, with hydrolases, e.g., cellulases, hemicellulases, and pectinases.

This invention relates to a foam-based technique for providing a good dispersion for various solids. Thus, effective contact during the economical production of particle board is achieved by the use of oxidase-activated lignin and / or carbohydrate-based binders in combination with wood fibers or other lignocellulosic fibers "" "0.1 to 50%, preferably 0.5 to 30%, and particularly preferably 1 to 10% by weight of kraft lignin or · '"[20 other similar lignin is replaced by fibers in foam-based oxidase

I

,,, in the activated formulation.

According to a preferred embodiment of the present invention Where wood-based fibers are used, the lignin and fibers are activated by oxidases and mixed with the chips as a foam to provide a good viscous suspension medium to form a uniform solid dispersion and thus: * · *: substantially improves the quality of the chipboard to be manufactured The use of foamed binders described in this invention also results in better application control and substantial savings in the use of the binder Foam is formed using a surfactant.

,,,.; The foamed, activated fiber and lignin / carbohydrate dispersion can be produced separately from the chips, which are blended into the foam by a known mixing technique, e.g., extrusion or spraying the foam onto the fibers or chips. Foam can also be produced by mixing fibers and chips with foam chemicals, lignin / carbohydrates, and lacquer.

According to the present invention, the foam is produced by dispersing a mixture of lignin and fibers in water 5 to form a suspension and bubbling gas through the suspension to form bubbles having an average diameter of 0.001 to 1 mm, in particular about 0.01 to 0.1 mm.

The foam is produced using a surfactant which may be anionic, cationic or nonionic. Thus, the surfactant may be selected from the group consisting of al-10 alkyl sulfonates or alkylbenzenesulfonates, Tween® and other commercial compounds, fatty acid soaps, lignosulfonates, sarcosinates, fatty acid amines or amines, or polyoxyethylene alcohols and wood and plant extracts. Foam stabilizing agents and solid surfactants such as CMC, gelatin, pectin, wood extractors and the like can be used to produce and improve foam stability.

A small amount of surfactant is needed, i.e. about 0.01-10%, especially about 0.05-5%.

While the foam may be produced by foaming in a static foam or turbulent foam cell using known mixing techniques. While any gas may be used in foaming, it is preferable to use oxygen containing gases such as air, oxygenated air, oxygen or pressurized systems thereof. The importance of the use of oxygen-containing gases is further discussed in more detail below.

The foam produced is substantially stable during handling, storage, transport and manufacture of wood-based products and has a density in the range of 0.1 to 0.9 kg / l. , in particular 0.2 · · · · · · · · - 0.7 kg / l and an average bubble size in the range of 0.005 to 0.1 mm, particularly 0.01 to 0.1 · · · · · mm, preferably 0.02 mm.

The process of the present invention can be used for all oxidase-catalyzed, previously unsuccessfully presented, oxidase-using enzyme-catalyzed gluing processes. The enzyme used may be any enzyme which catalyses the oxidation and polymerization of aromatic compounds or lignins, such as laccase, tyrosinase or other oxidase as mentioned above. The amount of enzyme used will vary depending on the activity of the enzyme and the amount of dry matter in the composition. Generally, 0.001 to 10 mg protein / g dry matter, preferably about 0.1 to 5 mg protein / g dry matter are used. The oxidase activity is from about 1 to about 100,000 nkat / g, preferably greater than 100 nkat / g.

In the context of the present invention, it has been found that oxygen plays a significant role in the enzymatic polymerization of lignin, regardless of the origin of the lignin. This is particularly important in the manufacture of binders for fiberboard, particle board and chipboard and other similar wood-based products. Thus, in addition to the aromatic reactant, oxygen is also required. The oxidation reaction leads to the formation of phenoxy radicals and eventually to polymerization of lignin.

In the prior art processes discussed above, cross-linking was only partially achieved due to obvious restrictions on oxygen availability. The limiting effect of oxygen on the reaction is clearly evident in the long reaction times used and the poor strength properties obtained, thereby weakening the result obtained by enzyme-assisted polymerization.

Oxygen can be introduced in a variety of ways, such as by efficient mixing, oxygen-enriched air, or introduction of oxygen by enzymatic or chemical means. However, according to the present invention, by foaming the suspension, the oxygen-containing gas has: : ** It is possible to provide enough oxygen to fully polymerize the lignin, while • · · '· 1 foamed structure gives the binder enough strength to prevent sedimentation of insoluble lignin or ... 25 polymerized lignin from the binder, causing problems in production and sheet product.

• · · · • · «« <'; This invention has considerable advantages. Thus, the foamed structure can be utilized. lignin and / or carbohydrates or polymerized lignin-bonded particle boards utilizing the binding properties of lignin or polymerized lignin, while the fibers act as interparticle crosslinkers. The oxygen-containing foamed structure adds more oxygen to the oxygen-dependent oxidase-catalyzed lignin / carbohydrate polymer due to its high volume and more homogeneous coating of wood fibers and wood particles in the manufacture of boards.

The following non-limiting examples illustrate the invention.

Example 1 10 Production of MDF Fibers MDF fibers were made from hardwood (Swedish birch) by milling birch chips in a conventional TMP process at a defibrator pressure of 4 bar.

15 Fiber quality to values by both Bauer McNett analysis and Pulmac stick analysis. The results are shown below:

Table 1. Fiber Properties Bauer McNett 20> 16 (> 1.19 mm) __ 1 ^ 6_ 16 - 30 (1.19 -0.595 mm) __ 25Λ_ 30 - 50 (0.595 - 0.297) __ \ 2A_; ··· 50- 100 (0.149 mm) __ 29 ^ 0_ <100 (<0.149 mm) 15.0 • · '·' 1 25 Pulmac stick content

Screening Plate 0.15mm 7.0 's' Screening Plate 0.25mm 0.8_ 30 · 104835 11

Example 2

Preparation of Particle Board This example illustrates the preparation of a foam-5 binder consisting of kraft lignin, laccase and wood fibers and the preparation of particle board with binder. The test has been performed on a laboratory scale.

Kraft lignin Indulin AT and 1 to 10% by weight of it replaced by the MDF fibers of Example 1 were used as an adhesive blend in the manufacture of chipboard specimens.

3.6 - 3.96 g of lignin and 0.04 - 0.4 g of MDF fibers were vigorously mixed and aerated for 30 min with 4.0 g of laccase growth solution (activity 4000 nkat / g) in 2.0 g of 2M sodium acetate buffer (pH 4.5). 1.4 g of the mixture was mechanically mixed with 4.4 g of chips. The chips were treated with 1% wax (Mobilex 54, 60% emulsion) of the 15 dry solids of the fibers. Reference tests were performed without laccase (water instead of laccase) and using commercial UF resins.

For strength tests, panels of 50 mm x 50 mm x 2 mm (weight about 5 g) · ... · were made by compressing at 30 kp / cm 2 at 190 ° C for 2 min.

After compression, the panels were cut into four sections (50mm x 12mm x 2mm). These pieces were tested for tensile strength (parallel to the surface) on a Zwick tensile strength apparatus.

4 »♦ · · * ·: t:: • • ♦» »* * f f f f« «« «« «« «« «« «« «« «« «« «« »·« 104835 12

Table 2. Results of chipboard bonding tests Foamed binder Tensile strength _MPa_

Water 3.0 ± 0.3 Indulin AT (10%) + MDF Fibers 8.5 ± 0.4 (90%)

Indulin AT (10%) + MDF fibers 11.9 ± 0.7 (90%) + laccase

Indulin AT 7.2 ± 0.4 10 Indulin AT + Laccase 12.7 ± 0.6

Reference UF resin 12.5 ± 0.7

As can be seen from the results shown in Table 2, up to 10% of the laccase-activated kraft lignin can be replaced as a binder with MDF fibers without significant degradation in strength properties. The particleboard produced by the process of this invention is quite comparable to conventional UF resin bonded sheet.

• • • • • • • • • • • • • • •

Claims (16)

104835 13 Lignin and / or carbohydrate-based binder composition for the manufacture of particle board and the like wood-based products, characterized in that the composition comprises a mixture of lignin-containing fibers and carbohydrates from the pulping process of the lignin and / or lignocellulosic materials, has been foamed l, l to ... 10 times the volume of the liquid mixture. Composition according to Claim 1, characterized in that the lignin comprises polymerized kraft 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. 15 Composition according to Claim 1, characterized in that the foam has a density of 0.1-0.9 kg / l, preferably 0.2-0.7 kg / l, and an average bubble diameter of 0.0001-0.1 mm , preferably 0.01 to 0.05 mm. '' 20 Composition according to one of Claims 1 to 4, characterized in that the fibers are lignocellulosic fibers from wood or from annual or perennial plants. The composition according to claim 5, characterized in that the fibers are obtained. mechanical treatment of wood or plants in the refiner by mechanical pulping, • · ·. ·: ·. 25 pressurized mechanical pulping, thermomechanical pulping, • · · '. • during pulping of pulp or pressurized pulp, or during pulping • · ... .... ';;. Composition according to Claim 6, characterized in that the fibers are obtained from the manufacture of fibers for the fiberboard. 104835 14 Composition according to Claim 1, characterized in that the fiber content is between 0.1 and 50%, preferably between 0.5 and 30% and in particular between 1 and 10% by weight of lignin. Composition according to Claim 1, characterized in that the foam contains from 0.1 to 10%, preferably from 0.2 to 5% by weight of the aqueous suspension. Composition according to any one of the preceding claims, characterized in that the composition contains oxidase or peroxidase, wherein the amount of oxidase is from 0.1 to 5 mg of protein / g of dry matter. 10 11. A process for the preparation of a lignin and / or carbohydrate based binder for particle board or similar wood-based products, characterized in that: - lignin and / or carbohydrates obtained from the pulping process of lignocellulosic raw materials are used, - or perennial plant-based fibers, - forming an aqueous suspension of lignin and / or carbohydrates and fibers, - activating the lignin and / or carbohydrates and fibers by oxidizing enzymes which catalyze the oxidation of phenolic groups, and foaming the aqueous suspension. A process according to claim 11, characterized in that - an aqueous suspension containing from 1 to 90% by weight of solids is formed comprising lignin, fibers and surfactants, and * · · V · 25 - foaming the aqueous suspension with oxygen containing gas 1.1 to 10 times the volume of the suspension by volume to give a foam containing 5 to 70% by weight of solids. The process according to claim 11 or 12, characterized in that the lignin ·: · · · · 30 comprises polymerized krafl lignin. 104835 15 Process according to Claim 12, characterized in that an aqueous suspension is formed containing lignin, fibers, oxidase and surfactants. 15. A particle board or other wood-based product, characterized in that it comprises 5 particles, fibers or chips of wood mixed with a binder according to any one of claims 1 to 10. A process for making a particle board or a similar wood-based product, characterized in that the wood particles, fibers or chips are blended with a lignin and / or carbohydrate-based binder according to any one of claims 1-10 such that the binder composition 20%. • • • • • • •••••••••••••484835