RU2800419C1 - Method for manufacturing form-stable wood boards - Google Patents

Abstract

FIELD: woodworking.

SUBSTANCE: perform preliminary heat treatment of wood particles, which takes 3-5 hours at a temperature of 200 to 240°C, then place the wood particles in a container filled with water and subject it to cavitation treatment in a hydrodynamic disperser. After cavitation treatment, impregnate it with organosilicon polymers by autoclave impregnation under a pressure of at least 5 MPa, with a total absorption value of 300 from 500 kg/m³ followed by drying to a moisture content of 6-8% at a temperature of 20 to 180°C.

EFFECT: improved physical and mechanical properties of wood-based panels and reduced energy costs of obtaining wood pulp.

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Description

The invention relates to the field of woodworking, and in particular to methods for producing wood-based panels without the use of binders for various purposes (from 200 to 1100 kg/m ³ ).

The invention can be used for the production of structural, heat and sound insulating products for construction, equipment or molds for the manufacture of large-format products: parabolic antennas, screens and other products operated in variable temperature and humidity conditions.

The first boards made from crushed wood without the use of binders, which are widely used, are wet pressed wood fiber boards [Laskeev, P.Kh. Production of wood pulp / P.Kh. Laskeev. - M.: Timber industry, 1967. - 580 p.]

A known method for the production of wood fiber boards in a wet way. It consists in the following: technological chips of the PV brand are prepared by hydrothermal and chemical processing. Chips are crushed on special machines (defibrators and refiners) into individual fibrillated fibers, which, mixed with water and additives, make up wood pulp for boards. This mass is subjected to hot pressing or convection drying, depending on the density of the boards. (Complex chemical processing of wood: textbook for universities / I.N. Koverninsky, V.I. Komarov, S.I. Tretyakov; ed. I.N. Koverninsky; Arkhang State Technical University - Arkhangelsk: ASTU, 2002. - 347 pp. - Bibliography: p. 342. - ISBN 5-261-00054-3).

The disadvantage of this method is that the manufacturing technology of fibreboard does not allow to obtain finished products with a thickness of more than 4 mm and a density of less than 350 kg/m ³ . The main disadvantage of this technology is the impossibility of obtaining waterproof boards with a low coefficient of linear thermal expansion (at least 15) and at the same time with a high anisotropy of properties in directions. Along with this, the cost of electricity for grinding is very high and often reaches more than 2000 kW per 1 m ³ of plates.

A known method for producing a wood press mass. According to this invention, a press mass in the form of vegetable raw materials (wood sawdust, cereal straw, etc.) is obtained by cavitation treatment. Vegetable raw materials (with a moisture content of 3-8%, a fraction of up to 1.25 mm) are placed in a container with water (hydromodulus equal to 10) without or with the addition of a hydrolyzing agent - sulfuric acid (concentration up to 1%). The mass is subjected to cavitation for various periods of time (from 15 to 120 minutes). The process is accompanied by spontaneous heating of the mixture to 95°C. (Patent RU No. 2381244, published on February 10, 2010, Bull. No. 4).

The disadvantages of this method are significant energy costs for drying the feedstock and the resulting wood fiber mass, the use of chemical reagents in the processing of plant materials. In this case, according to the invention, after cavitation treatment, drying of the press mass is necessary. The recommended pressing temperature and moisture content of the raw material does not provide conditions for the formation of bonds between the surface reaction centers of the lignocarbohydrate complex, which does not make it possible to obtain a material of medium and low density with high physical and mechanical properties. With a density of boards more than 1.5 times higher in comparison with materials made with the addition of synthetic binders, their mechanical properties are equal. With prolonged exposure to water on the material obtained without the addition of adhesives, its complete destruction occurs.

The closest invention for the same purpose is a method for producing wood-based panels. According to this invention, wood raw material is placed in a container with water, which is subjected to 40-60 times cavitation treatment in a hydrodynamic disperser with radially directed channels to obtain defibrated wood particles with a length of at least 1.5 mm, a thickness of 0.01 to 0.05 mm and a width of 0.03 to 0.06 mm and a high content of active reaction centers on the surface. (Patent RU No. 2541323 C1, published on February 10, 2015, Bull. No. 4).

This invention is aimed only at obtaining boards of medium density from 650 to 1000 kg/m ³ by hot pressing, with high water resistance, but this does not provide thermal stability and hydrophobicity of the surface and does not solve the problem of reducing energy costs when obtaining wood pulp with a large interfacial surface . The multiplicity of processing should be at least 40 times, which in turn does not allow to obtain a plate material with a density of 650 to 1000 kg/m ³ with acceptable physical and mechanical properties. In this case, the consumption of electrical energy is from 1500 to 2500 kW 1 m ³ plates.

The disadvantages of this method are the increased energy costs in obtaining wood pulp, low physical and mechanical properties of wood boards.

The invention solves the problem of obtaining form-stable wood boards under thermal and humidity effects, with a density of 300 to 1100 kg/m ³ with high physical and mechanical properties and reduced energy costs for obtaining wood pulp.

The reduction in energy costs in the production of wood pulp with a high interfacial surface is achieved due to preliminary thermal exposure, before hydrodynamic treatment, in combination providing adhesive interaction between wood particles with or without hot pressing. Density control from 300 to 1100 kg/m ³ can be varied both during hot pressing and by impregnating the boards with organosilicon polymers, which also makes it possible to increase their hydrophobicity.

The main feature that determines the similarity of the proposed invention with the features of the prototype is the use of hydrodynamic effects on wood.

This technical result is achieved by the fact that the method of manufacturing dimensionally stable wood boards, including the placement of wood particles in a container with water, which is subjected to cavitation treatment in a hydrodynamic disperser, according to the invention, the wood particles are preliminarily heat treated for 3-5 hours at a temperature of 200 to 240°C. After cavitation treatment, impregnation with organosilicon polymers is carried out by autoclave impregnation under a pressure of at least 5 MPa, with a total absorption value of 300 from 500 kg / m ³ , followed by drying to a moisture content of 6-8%, at a temperature of 20 to 180 ° C.

This makes it possible to obtain wood pulp with a large interfacial surface (specific surface up to 400 m ² /g).

The specific surface area at the main stages of obtaining wood pulp is presented in table 1.

After treatment in a hydrodynamic dispersant, wood pulp with a specific surface area of 200 to 400 m ² /g is formed into boards, which are dried by convection drying and have a density of 300 to 500 kg/m ³ . Plates from 800 to 1100 kg/m ³ are obtained by hot pressing. These boards have a porosity of 85 to 96%, which predetermines high water absorption and correspondingly low dimensional stability when water is absorbed.

Table 1

Specific surface area of wood pulp

Duration of heat treatment, h Multiplicity of passage through the disperser Specific surface area, m ² /g 0 0 130 3 2 142 4 3 190 5 5 217 3 2 264 4 3 295 5 5 320 3 2 360 4 3 381 5 5 390

To solve this problem, a mechanical barrier is required, that is, an increase in the density of the material and, accordingly, a decrease in the porosity of the material. However, as is known, an increase in density leads to an increase in linear thermal expansion. In the invention, this problem is solved by impregnation with organosilicon polymers by autoclave impregnation under a pressure of at least 5 MPa, with a total absorption value of 100 from 300 kg/m ³ , followed by drying to a moisture content of 6-8%, at a temperature of 20 to 180°C. The properties of the plates are presented in Table 2.

The method of manufacturing dimensionally stable wood boards is carried out as follows.

Initial wood particles: sawdust, shavings, specially crushed lumpy woodworking waste of coniferous or hardwood with a moisture content of 8 to 100% are fed to the heat treatment operation in a steam-air environment at a temperature of at least 200 ° C and a duration of 4 to 5 hours. After heat treatment, the particles are mixed with water at a temperature of at least 30°C, at a mass ratio, m.h.: from 6 to 12 and from 94 to 88, respectively. The resulting pulp is passed through cascade through 4 or 5 dispersers, while the size of the channels in the dispersers decreases from 11 mm to 6 mm, respectively. The resulting wood pulp is pumped by a pump into a container, from where it is dosed to a casting device. On the casting device, the moisture content of the mass is reduced to 170-250%. After this operation, the wood pulp acquires a strict geometric shape in the form of packages. Then, depending on the density of the plates, the resulting packages are sent to the operation of convective drying or hot pressing in a press. The modes of drying boards are detailed in [Study of the properties of low-density boards from mechanically activated wood particles without the use of binders / A. V. Namyatov, M. A. Bayandin, S. N. Kazitsin, V. N. Ermolin // Structure , properties and quality of wood - 2018: Proceedings of the VI International Symposium named after B.N. Ugolev, dedicated to the 50th anniversary of the Regional Coordinating Council on Modern Problems of Timber Science, Krasnoyarsk, September 10–16, 2018. - Krasnoyarsk: Publishing House of the Siberian Branch of the Russian Academy of Sciences, 2018. - P. 149-15].

Hot pressing of plates with a density of 500 kg/m ³ or more is carried out as follows: the resulting carpet on a mesh pallet is pressed in a hot flat press at a temperature of 190° to 220°C and a specific pressure of 1.6 to 4.0 MPa. The specific duration of pressing depends on the temperature of the process and the initial moisture content of the wood pulp and varies from 0.8 to 1.5 min/mm.

The resulting boards are loaded into an autoclave and impregnated under a pressure of at least 5 MPa, with a total absorption value of 100 to 300 kg/m ³ . After impregnation, the slabs are fixed vertically on a shelf and fed into a convection chamber, where drying is carried out at a temperature of 20 to 180 ° C until their moisture content is 6-8%.

Example 1

Wood particles ( sawdust, shavings, specially crushed lumpy wood waste) of coniferous or hardwood with a moisture content of 8 to 100% are fed to the heat treatment operation in a steam-air environment at a temperature of 250 ° C and a duration of 4 hours. After heat treatment, the particles are mixed with water at a temperature of at least 30°C, at a mass ratio, m.p.: 6 and 94, respectively. The resulting pulp is passed through cascade through 5 dispersers, while the size of the channels in the dispersers decreases from 11 mm to 6 mm, respectively. The resulting wood pulp is pumped by a pump into a container, from where it is dosed to a casting device. On the casting device, the moisture content of the mass is reduced to 250%. After this operation, the mass acquires a strict geometric shape in the form of packages. Then, depending on the density of the boards, the resulting packages are sent to the convective drying operation until the moisture content of the finished boards is 6-8%.

Example 2

Similar to example 1.

Wood particles (sawdust, shavings, specially crushed lumpy wood waste) of coniferous or hardwood with a moisture content of 8 to 100% are fed to the heat treatment operation in a steam-air environment at a temperature of 250 ° C and a duration of 4 hours. After heat treatment, the particles are mixed with water at a temperature of at least 30°C, at a mass ratio, m.p.: 6 and 94, respectively. The resulting pulp is passed through cascade through 5 dispersers, while the size of the channels in the dispersers, respectively, decreases from 11 mm to 6 mm. The resulting wood pulp is pumped by a pump into a container, from where it is dosed to a casting device. On the casting device, the moisture content of the mass is reduced to 250%. After this operation, the wood pulp acquires a strict geometric shape in the form of packages. Then, depending on the density of the boards, the resulting packages are sent to the operation of convective drying to a moisture content of the finished boards of 6-8%. Subsequently, they are impregnated with organosilicon polymers by autoclave impregnation under a pressure of at least 5 MPa, with a total absorption value of 300 from 500 kg / m ³ , followed by drying to a moisture content of 6-8%, at a temperature of 20 to 180 ° C.

Example 3

Similarly to example 1. Wood particles (sawdust, shavings, specially crushed lumpy woodworking waste) of coniferous or hardwood with a moisture content of 8 to 100% are fed to the heat treatment operation in a steam-air environment at a temperature of 250 ° C and a duration of 4 hours. After heat treatment, the particles are mixed with water at a temperature of at least 30°C, at a mass ratio, m.p.: 6 and 94, respectively. The resulting pulp is passed through cascade through 5 dispersers, while the size of the channels in the dispersers, respectively, decreases from 11 mm to 6 mm. The resulting wood pulp is pumped by a pump into a container, from where it is dosed to a casting device. On the casting device, the moisture content of the mass is reduced to 250%. After this operation, the mass acquires a strict geometric shape in the form of packages. Then, depending on the density of the boards, the resulting packages are sent for hot pressing with a specific duration of 0.8 to 1.5 min/mm and a specific pressure of 1.6 to 4.0 MPa to a moisture content of the finished boards of 6-8%.

Claims (1)

A method for manufacturing dimensionally stable wood boards, which includes placing wood particles in a container with water, which are subjected to cavitation treatment in a hydrodynamic disperser, characterized in that the wood particles are preliminarily heat treated for 3-5 hours at a temperature of 200 to 240°C, and after cavitation treatment, impregnation with organosilicon polymers is carried out by autoclave impregnation under a pressure of at least 5 MPa, with a total absorption value of 300 from 500 kg/m ³ , followed by drying to a moisture content of 6-8%, at a temperature of 20 to 180°C.