plasticized wood materials with improved physicomechanical properties; produced by combined mechanical, thermal, and chemical processing of the raw material. Wood plastics are divided into pressed wood (lignoston), wood laminates (laminated birchwood, delta wood, wood-resin laminate, and arktilit), and wood-pulp plastics.
Pressed wood (plasticized) is natural wood (most often, birch; less frequently beech, hornbeam, or maple) compacted under a pressure of 15-30 meganewtons per sq m (MN/m2), or 150-300 kilograms-force per sq cm (kgf/cm2), at temperatures up to 120°C. The compacting is accomplished in various ways: by pressing the blank into a press mold of smaller diameter, by squeezing the “blank between the plates of a hydraulic press or in a hand mold, or by pressing plates of wood that have been bent in advance. To increase the moisture resistance and stability of the shape of wood plastics, wood blanks are impregnated with synthetic resins before compacting. Moisture-resistant pressed wood may be produced without impregnation by intensifying the heat treatment of the blank in the softening stage, in which case resinlike products of the change of lignin and hemicellulose are formed in the wood.
Pressed wood is produced in the form of boards, beams, slabs, and plugs. It has high impact resistance and plasticity and a low coefficient of friction and increased moisture resistance. Pressed wood is used to make machine parts that operate under impact loads, as well as parts that are resistant to friction.
Wood laminates are materials based on a thin sheet (single-ply veneer) of wood of deciduous species. To produce wood laminates, birch veneer (less frequently beech or linden veneer) is impregnated (sometimes coated) with solutions of thermosetting synthetic resins, dried, assembled into packets, pressed in hydraulic platen presses, and heated under a pressure of 10-17.5 MN/m2 (100-175 kgf/cm2) and a temperature of 120°-150°C. To increase the strength and elasticity of wood laminates, they are reinforced with metal mesh or foil or with rubberized fabric. The addition of graphite and oil improves the antifriction properties of the plastics. Wood-laminate blanks are worked mechanically (by sawing or shaving). Wood laminates have good electrical-insulation and mechanical properties, including antifriction properties, and are resistant to the action of many chemical reagents.
Wood laminates are used as a building material in machine building and shipbuilding and as electrical-insulation and structural material in the production of parts for high-tension equipment. They are suitable for manufacturing bending dies and chucks, and with water lubrication and at friction temperatures not over 60°C, they can be used as heavy-duty bearings.
Wood-pulp plastics are shaped one-piece molded parts or board materials made in press molds by hot molding of pulverized wood (sawdust, shavings, fibers, and veneer trimmings) that are impregnated with solutions of synthetic resins and then dried. In some cases the wood first undergoes partial acid hydrolysis or steaming under pressure, or it is treated with an alkali. Wood-pulp plastics have high mechanical strength and friction resistance and good electrical-insulation properties. These materials are used to produce shaped one-piece molded parts (bearing inserts and bushings, gears, cable boxes, electrical-insulation parts, and caps for fractionating columns) and parquet flooring slabs.
REFERENCESGenel’, S. V. Drevesnye plastiki v tekhnike. Moscow, 1959.
Pressovannaia drevesina i drevesnye plastiki v mashinostroenii: Spravochnik. Edited by A. G. Rakin. Moscow-Leningrad, 1965.