SK94399A3 - Particle boards, fiber boards, flake boards and similar wood-based products, and the preparation process thereof - Google Patents

Abstract

An adhesive binder for bonding lignocellulosic particles, fibers and flakes of vegetable origin for the preparation of particle boards, fiber boards, flake boards and similar wood-based products, and the preparation process thereof, and the prepared fiber board or other end product by using said adhesive binder, and the process used for the preparation of said product. Said adhesive binder comprises an oxidized water soluble fraction derived from mechanical or chemimechanical pulping of lignocellulosic raw materials, and can further contain, e.g., lignin isolated from chemical pulping, or a surfactant. The preparation of the adhesive binder composition comprises the steps of separating a liquid effluent from wood raw material and concentrating and oxidizing said liquid effluent in an aqueous suspension containing an oxidase and introducing oxygen-containing gas into said suspension.

Description

FIBERBOARDS, FIBERBOARDS, PITCHED SHEET PANELS AND

SIMILAR WOOD BASED PRODUCTS AND METHODS OF PREPARING THEREOF

Technical field

The present invention relates to the manufacture of fiber boards and similar wood-based products, comprising only the distribution of lignocellulosic chips and fibers mixed and glued together by an adhesive binder. In particular, the present invention relates to novel adhesive binders, processes for their preparation, and fiber boards produced using said adhesive binders.

BACKGROUND OF THE INVENTION

The rapid increase in the production of particle board, chipboard and fiber board, especially medium density fiber board (the abbreviated MDF board), has in the past decade been requiring an inexpensive, bulk, and oil-independent adhesive. Lignin meets all these requirements and does not contain formaldehyde, which is traditionally considered a serious problem in the case of urea-formaldehyde (UF) adhesives. Natural lignin, as the main wood component, is neither hygroscopic nor water soluble. Since it has a polyphenol structure, lignin as an adhesive should be similar to phenol formaldehyde (PF) resins. This is true for natural lignin in wood, while technical lignins (lignosulfonate or kraft lignin) have serious limitations due to their low reactivity (kraft lignin) or their high hydroscopicity. During technical pulping, lignin becomes water-soluble due to degradation and chemical changes.

The use of sulphite leach (SSL) as an adhesive for paper, wood and other lignocellulosic materials is well known in the art and many patent applications have been filed over the past thirty years for the use of lignin products as adhesives for particle board, veneer and fiber board instead of conventional PF and 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 WO 93/25622, WO 94/1488, WO 95/23232 and WO 96/03546.

The main disadvantage that discourages the use of SSL as an adhesive for the production of fiber boards is its hygroscopicity. Therefore, it cannot seriously compete with other natural or synthetic adhesives. Furthermore, it has been shown that laccase enzymes and other peroxidases can be used as catalysts for the polymerization or curing of lignin (DE Patent No. 3,037

992, WO 96/03546). However, enzymes for generating radical reactions have so far shown limited success. The fibers and wood chips used in the production of 20% water and the used laccases to catalyze the polymeric bonding of the fiber board, natural lignin, however, are in the fiber board, contain 5 to need water to be able to effectively react required for large scale

Kraft lignin, as well as largely water-insoluble, is therefore formed in the production of two solid phases. Uneven spacing causes spotting and a significant failure of the plate's strength properties formed during the pressing stage.

For the above reasons, lignin-based production methods have not found any practical application to date.

Instead of lignin-based adhesives, it has been proposed to activate lignin in wood fibers by laccase and use these fibers without the use of additional binders for the production of fiber boards (EP Patent Application No. 0 565 109). The main problem with this technology is the long incubation time (up to 7 days).

Ingredients derived from one-year materials such as feruloylarabinoxylans may also be used as additions to the particle board adhesives. Therefore, according to Feldman et al. (WO 96/03546) wood fibers and chips spliced together using oxidized phenolic polysaccharides.

These xylans occur only in annual plants, not in soft or hardwood materials. They are not industrially available.

SUMMARY OF THE INVENTION

The present invention aims to overcome the problems related to the state of the art. In particular, it is an object of the present invention to provide a novel lignin-based adhesive for the preparation of particle boards, fiber boards and similar wood-based products. It is a further object of the present invention to provide novel particle board, fiber board and similar wood-based products. A third object is to provide a method of manufacturing an adhesive.

These and other objects, together with their advantages, regarding known lignin-based adhesives and methods for their preparation, which should become apparent from the description that follows, are achieved in the present invention as described and claimed herein.

It is known in the art that during mechanical refining of chips, a portion of the fibrous raw material is dissolved (about 1% by weight of the fiber). This fraction, which primarily contains the same chemical constituents as fibers (carbohydrates, extractables and lignin) / decontaminates the circulating water and effluent from the paper mill and increases the volumes of waste water to be treated. Various filtration and concentration methods are used to separate dissolved compounds from process waters. The result is a concentrated waste fraction without any practical use.

Surprisingly, it has now been found that the soluble lignin / saccharide fraction is particularly useful as an additive or adjuvant for gluing particle boards, fiber boards and similar composite wood-based products. Particularly good bonding is achieved when this fraction is polymerized by the enzyme laccase (or similar oxidase). The results are at the same level as those obtained with conventional phenolic or urea-formaldehyde resins.

Briefly, it has been found that an adhesive, usually externally manufactured, such as phenol-formaldehyde or urea-formaldehyde, can be replaced by natural wood-derived fractions separated in mechanical wood refining processes.

Thus, the adhesive binder comprises an oxidized, water-soluble fraction derived from mechanical or chemimechanical pulping of lignocellulosic raw materials.

A further advantage of this method is that the volumes of waste water that require extreme purification are reduced. In addition, MDF boards with excellent strength properties can be obtained.

The invention also relates to a process for preparing adhesive binder compositions comprising the steps of:

- separation of the effluent from mechanical or chemimechanical pulping of wood raw material,

- the concentration of this liquid to increase the dry matter content,

forming an aqueous suspension containing the dry matter and the oxidase, and

oxidizing said dry matter in the presence of an oxidase by suspending the oxygen-containing gas.

The present invention will now be explained in more detail with reference to the following detailed description and with reference to many 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 stages of manufacture, e.g. Particle and fiber boards provide bonding of chips, fibers or flakes. After thermal insulation during the manufacture of the board, the composition comprising the polymerized resin acts as a binder that holds the chips or fibers or leaf chips together.

The term "wood-based product" means any lignocellulose-based product, such as particle board, fiber board (including high and medium density fiber boards, i.e. hard MDF boards), chipboard, plywood and the like, consisting of chips, fibers or chips of vegetable origin, mainly derived from wood or annular or perennial plants, mixed and bonded together with adhesive binders.

Oxidative enzymes capable of catalyzing the oxidation of phenolic groups can be used to polymerize lignin and carbohydrate soluble wood fractions. 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 oxidation reactions using molecular oxygen as a substrate. Phenol oxidases (EC1.10.3.2 benyendiol: O ₂ oxidoreductase) catalyze the oxidation of o- and β-substituted phenolic hydroxyl amino / amine groups in monomeric and polymeric aromatic compounds. The oxidation reaction leads to the formation of phenoxy radicals and finally to the polymerization of lignin and possibly carbohydrate substances. Any enzyme that catalyzes the formation of biological radicals and secondary chemical polymerization of low molecular weight lignins, such as laccases, tyrosinases, peroxidases, or oxidases, can be used in the method of the present invention.

Specific examples of oxidases include the following: acases (E.C.1.10.3.2), catechol oxidases (E.C.1.10.3.1), tyrosinases (E.C.1.14.18.1), and bilirubin oxidases (E.C.1.3.3.5). Lacases are particularly preferred oxidases. They can 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 or mold or bacteria. Preferred peroxidases are those derived from plants, especially horseradish peroxidase and soybean peroxidase.

The terms " surfactant or " surfactant are used as synonyms to denote compounds that have an affinity for water and hydrophobic materials and thereby aid in the suspension of hydrophobic materials in water.

Soluble fraction derived from mechanical pulping

During industrial wood refining, wood raw material derived from different types of wood is refined, e.g. refined mechanical pulping (RMP), pressurized refining mechanical pulping (PRMP), thermomechanical pulping (TMP), pulp fiber (GW) or pulp fiber pulping (PGW) or chemithermomechanical pulping (CTMP), to which fibers separate from the fibers -seba.

During refining, a portion of the wood raw material (about 0.1 to 5%, typically about 0.5 to 2%) is dissolved in the aqueous phase, due to prevailing conditions such as high refining temperature. These dissolved fractions are composed of the basic wood components: cellulose, hemicellulose and lignin. The amount depends on the type of wood and the refining conditions used. Process water from mechanical pulping of softwood chips contains about 40 to 70% carbohydrates, 10 to 25% lignin and 1 to 10% extractables. In contrast to softwood, the hardwood pulping process water contains about 20 to 60% carbohydrates, 10 to 25% lignin, and 10 to 40% extractables. The percentages are given by example only and were calculated from the solids solids.

The fibrous fractions from the refining are collected and used further in the papermaking process. The dissolved fractions are separated from the fibers or are recirculated during the papermaking process. As mentioned above, in existing production processes, the formation of the dissolved fraction during mechanical or chemimechanical pulping is an increased environmental burden; the soluble fraction constitutes the main effluent stream which must be treated in external effluent treatment plants. Moreover, when recycled during the process, these fractions, due to the presence of solutes and colloids, cause serious problems in the manufacture of paper.

In the context of the present invention, it has been shown that the various components of the soluble fraction from mechanical or chemimechanical pulping of wood are always reactive with respect to oxidation in the presence of oxidizing enzymes. As evidenced by the results in Example 3, aqueous extracts of MDF fibers, the fractions dissolved during the preparation of TMP and PGW, and MDF process water can be enzymatically oxidized. Without being limited to any particular theory, it is believed that various oxidized compounds are formed, including, for example, phenoxy radicals, which provide adhesion to lignocellulosic chips and fibers and which are involved in polymerization reactions.

Production of adhesive

According to the present invention, the separated soluble fraction can be formulated into an adhesive binder by mixing with oxidase, thereby oxidizing and polymerizing the carbohydrates, lignin and extractables present. For this purpose, the soluble fractions are separated from the fibers and the aqueous phase is concentrated by filtration, ultrafiltration or evaporation or other suitable separation technique. The dry matter content of the soluble fraction is usually less than 10 wt%, often less than 5 wt%. As a result, it must be concentrated to a much higher degree before use. The dry matter content of the enzyme-treated adhesive composition is typically about 20 to 80 wt. %. The soluble fraction used to prepare the tacky binder preferably comprises about 10 to 70% carbohydrates and about 1 to 30% lignin, calculated on the dry solids of the water soluble fraction.

The enzyme used may be any one of the enzymes known to catalyze the oxidation and polymerization of aromatic lignin compounds such as laccase, tyrosinase or other oxidases. The amount of enzyme used varies depending on the activity of the enzymes and the amount of dry matter content of the composition. Generally, the oxidases are used in amounts of from 0.001 to 10 g protein / mg dry matter, preferably about 0.1 to 5 mg protein / g dry matter. The oxidase activity is about 1 to 100,000 nkat / mg, preferably over 100 nkat / g.

In the context of the present invention, oxygen has been found to play a critical role in the enzymatic polymerization of carbohydrates, extractables and lignin of any origin. This is particularly important for the preparation of adhesives for the production of fiber boards, particle board, chipboard and other similar wood-based products. Therefore, in addition to carbohydrates or lignin material, the presence of oxygen in sufficient quantities is also required. The oxidation reaction leads to the formation of oxidized radicals (e.g. phenoxy radicals) and finally to polymerization of the material.

In the known processes discussed above, only partial cross-linking was achieved due to an obvious limitation of oxygen availability. The limitation of the oxygen reaction is itself manifested by long reaction times and poor strength properties, resulting in a deterioration of the enzymatic polymerization result.

The oxygen supply can be increased in various ways, such as efficient mixing, foaming, supplying oxygen-enriched air, or oxygen supply to the solution by enzymatic or chemical means. Although any oxygen-containing gas may be used, it is preferable to use air, oxygen-enriched air, oxygen gas or compressed systems thereof.

Therefore, according to embodiments of the invention, the mixture comprising the soluble fraction and the enzyme is vigorously stirred in the presence of oxygen by e.g. aeration mixture. The stirring time is usually about 1 minute to 24 hours, more preferably about 5 minutes to 10 hours.

According to an alternative embodiment, the supply of oxygen is ensured by forming a sticky binder foam by mixing the soluble lignin fraction into water to form a mixture and bubbling the slurry through the gas to form bubbles having an average diameter of 0.001 to 1 mm, especially about 0.01 to 0.01 mm. The dispersion is preferably foamed to 1.2 to 10 times the original volume.

The foam is formed using a surfactant, which may be anionic, cationic or nonionic. The surfactant may therefore be selected from the group consisting of alkylsulfonate or alkylbenzenesulfonate, Tween® and other commercial polysorbate compounds, fatty acid soaps, lignosulfonates, sarcosinates, fatty acid amines or amines or polyoxyethylene alcohols and woody wood and wood-based substances. Foam stabilizers and solid surfactants such as CMC, gelatin, pectin, wood extractives and the like can be used to form the foam and increase its stability. A small amount of surfactant compounds is necessary, i. about 0.01 to 10%, especially about 0.05 to 5%.

The foam may be formed by foaming in a static foam generating device or in a turbulent foam generating vessel using known mixing technology.

In both of the above embodiments, the adhesive binders may be separated from the chip fibers, which are mixed with the adhesive binder by extruding or spraying the foam onto the fibers or chips. The adhesive binder can also be produced simultaneously by mixing the fibers or chips with the adhesive binder composition components. The adhesive binder composition is added either before or after drying the board fibers after refining. The composition is added to the chips, fibers or flakes in an amount of 0.1 to 30%, more preferably about 10% of the total dry matter.

According to a particularly preferred embodiment, the lignin is admixed to the binder prior to enzymatic oxidation. The amount of lignin may reach 1-99% of the dry weight of the composition, preferably the composition comprises 5-95% lignin and 95-5% soluble fraction (in which lignin is already contained). A portion of the lignin may be added in the form of fibers containing lignin.

As the results of Examples 4 and 5 below show, particle boards and MDF boards produced using adhesive binders containing 10% soluble fraction, 90% isolated kraft lignin and oxidase (laccase) provide boards having the same strength properties as the boards , prepared by conventional technology using UF resins. By replacing 1 to 50% of the isolated lignin with the saccharide / lignin fraction described herein, the cost of the natural resin binder can be greatly reduced.

The following non-limiting examples illustrate the invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Separation of the soluble fraction from mechanical pulping

The soluble fraction was isolated from soft or hardwood fibers after refining (TMP or PGW) and was concentrated by evaporation to various dry solids concentrations as necessary.

Example 2

Composition of soluble fractions

Composition of the soluble fraction of TMP softwood raw material obtained by the corresponding fraction of hardwood main constituents (Table 1).

process, using after refining or being analyzed for

composition % dry matter lignin 18 Extractable substances 5 carbohydrates 57 Reducing compounds 24 Identified sugars arabinose 1/3 galactose 1/9 glucose 7/2 xylose 0/7 mannose 10.8 Sugar acids 0.5

As can be seen, the main components are lignin and glucomannan, in approximately equal amounts.

In addition, however, several other ingredients have been identified. It is therefore not possible to conclude on the exact composition of the adhesive material. The corresponding dissolved hardwood fraction contained approximately the same amount of lignin (22%), but a higher amount of extractables (22%) and carbohydrates (40%) with much more glucose (20%).

Example 3

The reactivity of the soluble fraction for enzymatic polymerization from various processes oxidized by the oxidation value used were analyzed

Reactivity further efficiency of enzymes, bonding potential.

relative

Reactivity of dissolved wood - based fractions isolated for the ability to be described relative to polymerization and

The reactivities are compared with the corresponding values for known wood-based adhesive materials, kraft lignin and lignosulfonate. The results are shown in Table 2.

Table 2. Reactivity of dissolved fractions of PGW, TMP, spruce sawdust, pine sawdust and MDF fibers, measured by enzymatic oxidation using laccase; enzyme dose 20 gkat / l.

Dissolved fraction Consumption of O2 mg / g substrate PGW 0.2 TMP 4.1 Aqueous extract of spruce sawdust 12.8 Aqueous extract of pine sawdust 2.8 Aqueous extract of MDF fibers 7.5 Lignosulfonate 3.4 Sulfate lignin 2.5

Example 4

Bonding of MDF fibers with soluble fraction and mixture of soluble fraction with lignin in enzymatically catalyzed adhesive reaction

The soluble fractions produced by the softwood TMP as described in Example 1 were used as binder in the gluing of the particle and MDF board test panels. 4.0 g of soluble fraction or soluble fraction combined with lignin were vigorously stirred and aerated for 30 minutes with 4.0 g of laccase concentrate (4000 nkat activity / g) in 2.0 buffer of 2 M sodium acetate (pH 4.5). In the case of MDF panels, 5.5 g of the mixture was further sprayed or mechanically mixed with 20 g of dry fibers. The fibers or chips have already been treated with wax (Mobilex 54.60% emulsion in water) in an amount of 0.7% fiber dry matter. The reference tests were performed without laccase (water was used instead) and using commercial urea-formaldehyde resins.

For strength tests, panels of 50 mm x 50 mm x 2 mm (weight about 5 g) were prepared by pressing for 2 minutes at a pressure of 30 kp / cm ² and a temperature of 190 ° C. MDF panels, size 90 mm x 90 mm x 2 mm (weight about 22 g) were prepared by pressing for 2 minutes at 50 kp / cm ² at 190 ° C. After pressing, the panels were cut into 4 pieces (50 mm x 12 mm x 2 mm). These parts were tested for parallel tensile strength by a Zwick tester.

Table 3.

Small scale gluing test results for MDF fibers

Spoj ivo Tensile strength MPa Soluble fraction 22 ± 3 Soluble fraction + laccase 30 ± 4 Soluble fraction (10%) + lignin (90%) + laccase 38 ± 2 Water 15 + 2 Reference UF resins 40 ± 5

Example 5

Bonding of particle boards with soluble fraction and mixture of fraction and lignin

The gluing of the particle board test panels was carried out according to the procedure of Example 4, except that in the case of the particle board panels, 1.4 g of the mixture was either sprayed or mechanically mixed with 4.4 g chips of the particle board. For strength tests, panels of 50 mm x 50 mm x 2 mm (weight about 5 g) were prepared by pressing for 2 minutes at a pressure of 30 kp / cm ² and a temperature of 190 ° C. After pressing, the panels were cut into 4 pieces (50 mm x 12 mm x 2 mm). The results are shown in Table 4.

Table 4

Small scale gluing test results for shed boards

binder Tensile strength mpa Soluble fraction 3,8 ± 0.6 Soluble fraction + laccase 8.0 ± 0.4 Soluble fraction (10%) + Indulin AT (90%) + laccase 11.8 ± 0.4 Water 3.0 ± 0.5 Reference UF resin 12.5 ± 0.7

Claims (18)

PATENT CLAIMS 1. A particle board, fiber board, particle board or the like based on wood, characterized in that it comprises lignocellulosic chips, fibers, chips of vegetable origin, bonded together by an adhesive binder which contains a water-soluble fraction oxidized by oxidase and comes from from mechanical or chemimechanical pulping of lignocellulosic raw materials. Product according to claim 1, characterized in that the adhesive binder contains 10 to 70% carbohydrates and 1 to 30% lignin, calculated on the basis of the dry matter of the water-soluble fraction. Product according to claim 1 or 2, characterized in that the adhesive binder, together with the water-soluble fraction of lignin, is isolated during chemical pulping of lignocellulosic materials. Product according to claim 3, characterized in that the adhesive binder contains 5 to 95 wt. % water-soluble fraction and 95 to 5 wt. % lignin. Product according to claim 3 or 4, characterized in that the lignin in the adhesive binder is polymerized. Product according to any one of claims 1 to 4, characterized in that the adhesive binder composition comprises a surfactant. 7. A process for the preparation of wood-based particle boards, fiber boards or the like, characterized in that the chips, fibers and flakes of vegetable origin are bonded together by an adhesive binder containing a water-soluble fraction oxidized by oxidase and derived from mechanical or chemimechanical fibrillation of lignocellulose. raw materials. Method according to claim 7, characterized in that the chips, fibers or flakes of vegetable origin are joined together by an adhesive binder comprising a mixture consisting of an enzymatically oxidized, water-soluble fraction originating from mechanical or chemimechanical pulping and lignin. Method according to claim 7 or 8, characterized in that the adhesive binder composition is added to the board fibers before drying and after refining. . Method according to claim 7 or 8, characterized in that the adhesive binder composition is added after drying the board fibers after refining. Method according to any one of claims 7 to 10, characterized in that the adhesive binder composition is added to the chips, fibers or flakes in an amount of from 1 to 10% of the total dry matter. Method according to any one of claims 7 to 10, characterized in that the preparation of the adhesive binder composition comprises the steps of: - separation of the effluent from mechanical or chemimechanical pulping of wood raw material, - the concentration of this liquid to increase the dry matter content, forming an aqueous suspension containing said dry matter and an oxidase, and oxidizing the dry matter in the presence of an oxidase by introducing an oxygen-containing gas into the suppression. • The method according to claim 12 or 13, wherein the oxidase is a laccase or a peroxidase. Method according to claim 12 or 13, characterized in that the dry matter of the effluent is concentrated to a dry matter concentration of 20 to 60%. The method of any one of claims 12 to 14, wherein the effluent comprises process water from refining mechanical pulping, pressurized refining mechanical pulping, chemimechanical pulping, thermomechanical pulping, pulp or pressure pulp pulping, or chemithermomechanical pulping. A method according to any one of claims 12 to 15, characterized in that the oxygen-containing gas comprises air, oxygen-enriched air, oxygen gas or mixtures thereof. The method of claim 16, wherein the oxygen-containing gas is introduced into the supernatant by the foam. The method of claim 17, wherein the suspension is foamed to 1.2 to 10 times the original volume.