RU2132769C1 - Method of preparing molding material for manufacturing facing layer of chipboards - Google Patents

Abstract

FIELD: manufacture of building materials. SUBSTANCE: hydrolysis lignin and wood filler, prior to be mixed with urea- formaldehyde resin, are subjected to joint treatment with 25% ammonium hydroxide aqueous solution. Weight ratio of ammonium hydroxide solution to mixture of hydrolysis lignin and wood filler (on conversion to absolutely dry substances) ranges from 1:20 to 1: 5. Treatment is carried out at 70-100 C for 15-25 min and followed by drying to moisture content 9-12% at 100-130 C. Amounts of starting components of molding material are the following, wt %: urea- formaldehyde resin 8-13, hydrolysis lignin 20-39, and wood filler 53- 67. EFFECT: increased water resistance and strength of chipboards, simplified technology. 3 cl, 3 tbl

Description

 The invention relates to the woodworking industry, and in particular to compositions for producing the outer layers of wood boards, and can be used for the production of building materials, for example structural-facing, decorative and heat-insulating chipboards.

 Known press mass for the manufacture of the outer layers of multilayer chipboards containing urea-formaldehyde resin, sulfate soap, ammonium chloride and peat [1]. The disadvantages of this press are reduced water resistance of the facing layers.

 Known press mass, including binder and grinding dust treated with the residue from hydrolysis of peat [2]. The disadvantage of this mass is also the lack of resistance to water due to the high hydrophilicity of grinding dust.

 Closest to the claimed invention is a press mass for the manufacture of the facing layer of particle boards, including urea-formaldehyde resin, hydrolysis lignin and wood filler (hydrolyzed sawdust) [3]. The disadvantage of this method is the high labor and energy intensity of the process of hydrolysis of sawdust, requiring original and expensive hardware design. The strength properties of materials obtained from such a press mass are not high enough. In addition, the low content of hydrolysis lignin in the press mass does not allow it to be disposed of in large quantities.

 The purpose of the invention is to increase the water resistance and strength of lined chipboards.

This goal is achieved by the fact that before mixing with urea-formaldehyde resin, hydrolytic lignin and wood filler are subjected to joint processing with a 25% aqueous solution of ammonium hydroxide, and the ratio of the aqueous solution of ammonium hydrate and a mixture of hydrolysis lignin and wood filler in terms of abs. dry matter is in the range from 1:20 to 1: 5 wt.%. The treatment is carried out at a temperature of 70 - 100 ^o C for 15-25 minutes

After processing, the resulting mass is dried to a moisture content of 9 - 12% at a temperature of 100 - 130 ^o C. The initial components of the press mass are contained in the following ratio, wt.%: Urea-formaldehyde resin 8 - 13, hydrolysis lignin 20 - 39, wood filler 53 - 67.

 When treated with an aqueous solution of ammonia, the lignohydrocarbon complex of wood undergoes destruction, with the breaking of chemical bonds. As a result, active functional groups are freed. A significant amount of low-methylated lignin and substances extracted with the alcohol-benzene mixture are formed, which are able to enter into condensation reactions during heat treatment. The effect of ammonia water on hydrolysis lignin causes a change in its chemical activity. Activation products differ from the original lignin in a higher content of hydroxyl and carboxyl groups and low in methoxyl groups. That is, lignin activation products have a high reactivity. In addition, the proposed treatment provides plasticization of wood and lignin. Due to this, during hot pressing, the area of contact zones between the particles increases. This creates the prerequisites for the formation of an additional number of bonds per unit volume of the product. The interaction of the degradation products of hydrolytic lignin and wood filler begins already in the processing and continues actively during drying.

The resulting polymer-like substances in their physical properties resemble aldehyde oligomers of the resol type. Drying is carried out at a temperature of 80 - 100 ^o C, as at a higher temperature in the mass irreversible polycondensation processes begin. Upon drying, the activation products pass into a state similar to the rezitol, their agglomeration occurs. After treatment with ammonium oxide hydrate and drying of the activated starting ingredients, they are mixed with the resin in a high-speed mixer. Along with the grinding of solid components, agglomerates are destroyed. After controlling the moisture from the press mass, the facing layers of chip-adhesive packages are formed, pressed and subjected to hot pressing, during which complex polycondensation processes occur, the chemical interactions of the starting components and the newly formed products through the methylol groups of the resin, hydroxyl - wood, hydroxyl and carboxyl groups of activated lignin and wood degradation products. As a result, synthetic resin, polymer-like substances and the products of their interactions go into a state of resite with the formation of strong and water-resistant chemical bonds, providing high-quality materials.

 The proposed method for the manufacture of the facing layer of particle boards is implemented as follows.

 They take hydrolytic lignin and wood filler (e.g. sawdust) of the initial moisture content. In the reactor they are mixed and activated with ammonium hydroxide, while stirring vigorously. The mass is then dried and combined with a urea-formaldehyde resin in a high-speed mixer. The resin is sprayed. Apply resin brand KF-B GOST 14231-88 in the form of a 50% aqueous solution.

 According to the described technology, press masses are prepared that differ in activation and drying modes, activator consumption, and component ratio (see Tables 1 and 2 at the end of the description).

 From the press masses obtained by the proposed method, the outer layers of chip-adhesive packages were formed, which were then subjected to hot pressing by traditional technology. The pressed products were conditioned under standard conditions for 10 days.

 Physical and mechanical tests were carried out according to GOST 10634 - 88 and GOST 10635 - 88. The size and number of test samples was determined according to GOST 10633 - 78. The samples were made of plates with a thickness of 19 mm. The test determines the density, tensile strength under static bending, water absorption by weight and swelling in thickness in 24 hours. When tested for water resistance, the samples are preliminarily subjected to special preparation, which consists in impregnating the ends with a synthetic waterproof glue of cold curing.

 The test results are given in table. 3 (see the end of the description).

 From the table. 3 it can be seen that the physicomechanical parameters of particle boards with facing layers of press material obtained by the proposed method are superior to those of plates faced with a known mass (prototype). The greatest effect is achieved with the joint activation of hydrolytic lignin and wood filler with the claimed ratio of components, the amount of ammonium oxide hydrate, processing and drying modes.

 The synergistic effect, which is manifested in an increase in the properties of materials after the joint activation of wood and lignin (examples 1-9), is explained by the fact that the newly formed substances interact with each other and form a new thermosetting product.

Its presence has a positive effect on the properties of finished products. Reducing the consumption of ammonium oxide hydrate, temperature and reducing the processing time lead to the fact that activation is slow and shallow, the reactivity of the press mass increases slightly (example 10). The increase in the duration of activation does not provide a significant increase in the reactivity of the press mass (example 11). At temperatures above 100 ^o C (example 11) in the activation products irreversible polycondensation processes begin to develop, and the properties of the products fall. An increase in the ratio of ammonium oxide hydrate and lignin with a filler of more than 1: 5 leads to an increase in the moisture content of the activated mass and, as a result, to an extension of the drying process, which negatively affects the properties. Separate processing of lignin and wood filler does not achieve the desired effect (examples 12-13). An increase in the drying temperature leads to a deterioration in the properties of the finished products due to the fact that a significant part of the polymer-like products condenses before hot pressing or at the initial stage of this process (example 18).

 A decrease in temperature lengthens the pressing (example 17) without significantly improving the characteristics of the plates. High humidity (example 22) not only complicates drying, but also prevents the normal course of polycondensation processes, which is manifested in a decrease in the properties of materials. At a moisture content of less than 9%, the binder is absorbed into the inner layers of wood and lignin. A polymer deficiency occurs on the surface of the particles, the quantity decreases and the quality of the adhesive joints decreases (Example 21). The amount of resin less than 8 wt.% Does not provide the necessary strength and solidity of products (example 27). With a content of more than 13 wt.%, The latter is redistributed along the height of the material, concentrating in the lower layers, or generally flows onto a pallet. Together with it, the activation products and the fine fraction of the solid component are redistributed. The consequence of this is a decrease in density, an increase in the number of macro- and microvoids in the structure of the material. As a result, its strength decreases, and the water resistance deteriorates (Example 28). From the table. 2 shows that the proposed ratio of components provides an increase in the properties of materials to the greatest extent (examples 23-26).

 The technical advantages of the proposed method compared to the prototype [3] are the possibility of simplifying the technology of preparation of the press mass with a simultaneous increase in the physical and mechanical properties of the products. So, the static bending strength increased by 1.12 - 1.22 times, swelling in 24 hours and 30 hours decreased by 1.34 - 1.73 and 1.50 - 1.90 times, respectively, water absorption in 24 hours and 30 hours decreased by 1.16-1.45 and 1.15-1.75 times, respectively.

 High operational and aesthetic qualities of the plates can significantly expand the scope of their application. They can be used as decorative and facing material for exterior and interior decoration of industrial and civil structures, agricultural facilities, such as livestock farms. Large-tonnage waste of hydrolysis production — hydrolysis lignin — is utilized, and the possibility of using finely dispersed waste from mechanical processing of wood — sawdust and shavings — is created.

 This contributes to the rational use of raw materials of plant origin and the protection of the environment from the effects of these products. In addition, the proposed method contributes to the expansion of the raw material base of local building materials.

Sources of information
1. A.S. N 634967, m.cl. In 29 J 5/00, 1978.

 2. A.S. N 763151, m.cl. In 29 J 5/00, 1980.

 3. A.c. N 1065450, m.cl. C 08 L 97/02, 1984.

Claims (2)

1. The method of obtaining a press mass for the manufacture of the facing layer of particle boards, comprising mixing a urea-formaldehyde resin with hydrolysis lignin and wood filler, characterized in that prior to mixing with a urea-formaldehyde resin, the hydrolysis lignin and wood filler are subjected to joint treatment with a 25% aqueous solution of oxide hydrate ammonia at a temperature of 70 - 100 ^o C for 15 - 25 minutes, and the ratio of an aqueous solution of ammonium hydroxide and a mixture of hydrolytic lignin and wood filling in terms of abs. dry substance is set in the range from 1:20 to 1: 5 wt.%. 2. The method according to claim 1, characterized in that the starting components for mixing are taken in the following ratio, wt.%:
Urea-formaldehyde resin - 8 - 13
Hydrolytic lignin - 20 - 39
Woodfill - 53 - 67
3. The method according to claim 1 or 2, characterized in that after processing the hydrolytic lignin and wood filler with a 25% aqueous solution of ammonium hydroxide, they are dried at a temperature of 100 - 130 ^o C to a moisture content of 9 - 12%.

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