RU2356728C2 - Method for manufacture of plates from composite material - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: stated invention is related to method for manufacture of construction materials and may be used in woodworking, furniture and construction industry. Technical result is achieved in method for manufacture of wood-particle boards from woodworking industry wastes. Method includes fractioning of filler, filler treatment with ingredient that increases compatibility of filler with binder with further drying. Then modified wood particles are combined with polyethylene by means of previous mixing and heating with further rolling in rollers with roll diametre of 180 mm and gap of 1 mm in between. Then prepared mass is pressed in die mold of hydraulic press at the temperature of 130-140°C and pressure of 5 MPa. Wood-polymer composition is filled with ingredient that increases compatibility of polar wood filler with non-polar thermoplastic binder in the form of secondary polyethylene, such as copolymer of 4-vinyl cyclohexen and maleic anhydride (CBM). At that the ratio of components is as follows, wt %: secondary polyethylene - 59.0-70.5; wood particles - 27-38; CBM - 2.5-3.0.

EFFECT: increased physical-mechanical properties of boards from wood-polymer composite, namely improved thermodynamic compatibility of components and growing stability of wood-polymer compositions under variable humidity conditions of products operation, and also improved technological and ecological conditions of composite materials manufacture.

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Description

The invention relates to the production of building materials and can be used in the woodworking, furniture and construction industries.

A known method of manufacturing a particle board based on carbamide-formaldehyde resins modified with latex compositions includes treating the particles with a composite binder followed by hot pressing (I. Iosifov et al. Properties of particle boards based on carbamide-formaldehyde resins modified with latex compositions. Higher forestry institute, Sofia, IX Symposium, 9, 1989, pp. 185-189).

The disadvantages of this method are the use of styrene-butadiene latexes that do not contain carboxyl groups, thickening additives in the form of latex with a high content of methacrylic groups, as well as the absence of an active filler capable of effectively adsorbing residual formaldehyde. Emission from finished plates of this compound, which has carcinogenic and mutagenic properties, makes the use of plates in construction extremely difficult and virtually eliminates their use in the furniture industry.

The closest in technical essence to the method of manufacturing a composite material (S.S. Glazkov, E.N. Levykin, M.V. Enyutina. / Wood-polymer compositions based on secondary materials of industry. // Proceedings of universities. Chemistry and chemical technology. - 2001. - T.44. - Issue 2. - S.142-145), which includes several stages: fractionation of the filler, processing of the studied fraction with a solution of SKEPT in nefras, followed by drying, combining the modified wood particles with polyethylene by pre-mixing and heating following by rolling on laboratory rollers with a roll diameter of 180 mm and a gap of 1 mm between them, pressing the resulting mass in the mold of a PG-60 hydraulic press at a temperature of 130-140 ° C and a pressure of 5 MPa, the WPC contains these components in the following ratio, wt.%:

recycled polyethylene 59.0-70.5 wood particles 27-38 SKEPT 2.5-3.0.

Sawdust was used as wood waste, which is produced in large quantities in woodworking industries from circular saws, sawmills, etc. Recycled polyethylene raw materials in accordance with TU 63-476-32-90 ″ Raw polymer secondary raw ″ was an obsolete film and film products.

The disadvantages of this method are the relatively low indicators of strength and water resistance of the plates, as well as technological and environmental negative aspects associated with certain requirements on the composition of the initial components of the composite binder.

The objective of the invention is to increase the physico-mechanical properties of the plates on the basis of improving the thermodynamic compatibility of components and increasing the stability of wood-polymer compositions (WPC) under variable-humidity conditions of use of products, as well as improving the technological and environmental conditions for the manufacture of composite materials.

To solve this problem, in the known method of manufacturing WPC, including fractionation of the filler, processing the filler with a solution of SKEPT in nefras, followed by drying, combining the modified wood particles with polyethylene by pre-mixing and heating, followed by rolling on laboratory rollers with a roll diameter of 180 mm and a gap between them 1 mm, pressing the resulting mass in the mold of a PG-60 hydraulic press at a temperature of 130-140 ° C and a pressure of 5 MPa, is introduced into the WPC as an ingredient, Collapsing compatibility with polar wood filler apolar thermoplastic binder in the form of recycled polyethylene synthetic rubber instead of the ethylene-propylene (EPDM), a copolymer of 4 - vinylcyclohexene and maleic anhydride (CBM) in the following ratio, wt.%:

recycled polyethylene 59.0-70.5 wood particles 27-38 CBM 2.5-3.0.

A positive effect of the proposed technical solution, namely, an increase in the strength and water resistance of the finished plates, is achieved by introducing into the composition of the WPC as an ingredient that improves the compatibility of the polar wood filler with a non-polar thermoplastic binder in the form of secondary polyethylene, a copolymer of 4-vinylcyclohexene-1 and maleic anhydride (CBM). At the same time, ethylene-propylene synthetic rubber (SKEPT) (SKEPT - 40TN TU. 2294-022-05766-801-2002 SKEPT according to TU.38.103252-92), as well as nefras solvent necessary for preparing a solution of this component, are excluded from the composition of the KDP.

The latter significantly improves the technological and environmental conditions of the manufacturing process of plate composite materials, because excludes the use of solvents related to highly volatile and flammable liquids.

The resulting effect from the use of the proposed binder composition can be explained as follows.

As noted above, the processing of wood filler in the form of sawdust can be carried out with aqueous solutions of a copolymer of 4-vinylcyclohexene-1 with maleic anhydride, which significantly improves the environmental characteristics of the process.

The resulting effect from the use of this impregnating material can be explained as follows. Synthetic polymer (CBM) is a linear reactive oligomer containing anhydride reaction groups in an amount of 6-36% wt. per oligomer macromolecule. In the presence of moisture, the anhydride groups transform into carboxyl groups, which then dissociate according to the following scheme:

In the impregnation of woody CBM particles containing polar oxygen-containing groups, in the best case carboxylic, the residual moisture content in the wood filler is high. Moisture promotes the dissociation of carboxyl groups with the removal of a hydrogen cation. At the same time, a small amount of moisture (determined by the content of adsorbed, bound moisture in the wood microcapillaries) is sufficient for dissociation, since the same amount of water is released again when salts are formed, and it again causes dissociation, etc. according to the following scheme:

1.nR ₁ COOH + nH ₂ O → nR ₁ COO ^- (H ₂ O) _x + nH ⁺ (H ₂ O) _nx ;

2. Me ^{n +} + nH ₂ O → Me (OH) _n → Me ^{n +} + nOH ^- ;

3. Ме ^{n +} + nR ₁ COO ^- + nH ⁺ + nOH ^- → (R ₁ COO) _n Me + nH ₂ O,

where Me is any polyvalent metal;

R ₁ - the remainder of the macromolecule of a copolymer of 4-vinylcyclohexene-1 with maleic anhydride (CBM), resulting from the electrolytic dissociation of a macromolecule of a polymer stabilizer.

Water in this case is a kind of catalyst in the salt formation reaction between oxides and acid groups. In the interaction of metal cations and anions of CBM acid residues, chemical ionic bonds can arise, providing very high adhesion of the contacting bodies. This process is promoted by an increase in temperature at the stage of drying the treated wood particles and their heat-hardening, when high temperature provides closer and closer contact of the CBM oligomer macromolecules.

At the same time, structuring takes place not only between CBM molecules, but between CBM molecules and wood containing functional groups (mainly hydroxyl) in cellulose and lignin that can efficiently interact with CBM carboxyl groups to form a high-strength single oligomer-wood, ″ crosslinked system ″ Chemical bonds. Due to the noted features of the reactive CBM oligomer, wood filler modified with this product is characterized by a higher level of physical and mechanical properties. Moreover, having the structure and properties of a surfactant, CBM is able, along with a marked increase in the strength characteristics of wood filler, to also change the chemical nature of the surface of wood particles, which is manifested in an increase in free surface energy and hydrophobicity.

The adherence of bodies under known conditions can be accompanied by stronger bonds than intermolecular ones: chemical bonds can form between the contacting molecules, which are known to be hundreds of times stronger than Van der Waals forces.

Ionic forces can occur, for example, in contact with metals and drying oils, drying oils in the presence of a metal-containing desiccant. The reaction of carboxyl groups of drying oil with metal cations occurs with the formation of an ionic chemical bond.

Thanks to the latter, a sufficiently high density of polymer “packing” is achieved in the interfibrillar and intercellular spaces of wood.

It should also be noted that, unlike the prototype, where the SKEPT copolymer was obtained using vinyl ethylene and propylene monomers, in which the only double bond disappears during the polymerization, the proposed solution uses a copolymer containing, along with functional carboxyl groups, a reactive unsaturated bond in the lateral cyclohexene group. Therefore, in addition to the noted advantages, this product will be capable of oxidative structuring in comparison with the prototype. If the copolymer is structured inside the wood particles according to the above mechanism, then outside, under conditions of high temperature (140-160 ° C) and atmospheric oxygen, additional oxidative polymerization will proceed according to the following scheme.

Under the action of air oxygen, a homolytic cleavage of the CH bond occurs with the formation of radicals:

RH + O ₂ → R ^· + O ^· OH

and subsequent interaction with another oxygen molecule:

R ^· + O ₂ → ROO ^·

^{ROO · + R'H → ROOH + R} '·

ROOH → RO ^· + O ^· H

Since free radicals accumulate in the system, an increase in the molecular weight of low molecular weight copolymers, as well as the formation of spatially structured copolymers, occurs due to radial polymerization of the remaining double bonds of the copolymer macromolecules.

Thus, this polymer product combines high penetration due to low molecular weight, the ability to chemical structuring due to the presence of reactive functional groups and has the effect of self-hardening in the presence of residual (sorption) moisture of the wood filler according to the above mechanism.

4-Vinylcyclohexene-1 is the main unsaturated compound (more than 70% wt.) Of bottoms of rectification of the return solvent, which is formed in large quantities in the production of butadiene rubber on metal complex catalysts. Currently, in the conditions of the Voronezh OJSC Voronezhsintezkauchuk, a process has been established for the isolation of 4-vinylcyclohexene-1 from bottoms, followed by use as an individual compound, including a monomeric one. This invention will serve as an additional incentive for the qualified use of recycled materials and increase the efficiency of the existing enterprise.

The method is as follows.

The manufacture of pressed plates from composite material included several stages: fractionation of the filler, treatment of the studied fraction with a solution of a substance that increases the compatibility of the hydrophilic filler with hydrophobic polyethylene, the combination of modified wood particles with polyethylene by pre-mixing and heating, followed by rolling on laboratory rollers with a roll diameter of 180 mm and the gap between them is 1 mm, pressing the resulting mass in the mold of a hydraulic press brand PG-60 When a temperature of 130-140 ° C and a pressure of 5 MPa.

Single-layer plates with a thickness of 12 mm are made. After pressing, each plate is cooled in an upright position without blowing at room temperature. Plate tests were carried out no earlier than 5 days after manufacture.

In accordance with the above technology, plates were obtained according to the prototype (example 1) and the proposed method, changing the composition of the composite material (examples 2-6 of table 1).

Table 1 Components The content of components, wt.% According to the example 1 (prototype) 2 3 four 5 6 Recycled polyethylene 64.75 55.00 60.00 65.00 70.00 75.0 Wood particles 30.50 43.75 37.50 30.00 22.50 15.0 SKEPT 2.75 - - - - - CBM - 1.25 2,50 5.00 7.50 10.0

Plates with different composition of the composite material, manufactured according to the above technology, were tested for physical and mechanical properties and the content of free formaldehyde. The performance of the tested boards are shown in table 2.

table 2 Indicators Examples 1 (prototype) 2 3 four 5 6 Bending Strength, MPa 11.80 9.26 12.90 15.3 13.5 11,2 Tensile strength parallel to the reservoir, MPa 7.12 6.45 7.87 9.56 8.64 7.10 Thickness swelling,% in 30 days 1.00 1,52 0.74 0.65 0.81 1.12 Water absorption by weight,% for 30 days 1.70 2,51 1.55 1.23 1.17 2,34 Density, kg / m ³ 720 750 810 820 815 760 The content of free formaldehyde, mg / 100 g of sample 3.42 1,02 2.02 2.48 3.42 1,02

As follows from the data in table 2, the plates obtained by the proposed method have higher strength characteristics and water resistance, and the emission of formaldehyde does not exceed the level of the prototype.

Claims (1)

A method of manufacturing chipboards from wood processing industry waste, including fractionation of the filler, processing of the filler with an ingredient that improves the compatibility of the filler with a binder, followed by drying, combining modified wood particles with polyethylene by pre-mixing and heating, followed by rolling on laboratory rollers with a roll diameter of 180 mm and a gap between them of 1 mm, pressing the resulting mass in the mold of a hydraulic press brand PG-60 at at a temperature of 130-140 ° C and a pressure of 5 MPa, they are introduced into the WPC as an ingredient that increases the compatibility of the polar wood filler with a non-polar thermoplastic binder in the form of secondary polyethylene, a copolymer of 4-vinylcyclohexene and maleic anhydride (CBM) in the following ratio, wt.%:
recycled polyethylene 59.0-70.5 wood particles 27-38 CBM 2.5-3.0