Wood is mainly composed of cellulose, hemicellulose and lignin. Cellulose has high tensile strength and lignin has high compressive strength. The three major elements in wood not only make it elastic, but also have high toughness. Therefore, the lignocellulosic material is mixed with the plastic, and then placed in a special mold, under the conditions of high temperature and high pressure, through a special processing process, will be closely combined to form a new wood-plastic composite material.
The production of wood-plastic composite panels mainly has the following technological routes:
Extrusion process
Extrusion from a single or twin screw extruder allows continuous extrusion of sheets of any length. The process can be further divided into single-machine extrusion and two-machine composite extrusion sheet. The composite extrusion is to simultaneously extrude a layer of pure plastic on the surface of the wood-plastic sheet, and become a wood-plastic sheet used in special occasions.
Hot press forming process
Can form a certain size of discontinuous sheet, the processing technology is similar to the molding process of medium density fiberboard.
Extrusion process
A simultaneous extrusion and pressurization process using an extruder and a press. The length of the formed sheet is greater than that of the hot-formed sheet, and the comprehensive performance of the product is superior to that of the extrusion process.
The key to the control of wood-plastic composite processing technology is to prevent thermal degradation and scorch of plastics and sawdust during mixing and forming process. Sawdust as a thermal stability of organic matter is poor, and hemicellulose and lignin are easily decomposed and aerobic. When present, the smoke is discolored at about 200 °C. Therefore, in the formulation and process technology of wood-plastic composite panels, it is the key to the technology to solve the interface between wood powder and plastic resin.
The continuous mixing and manufacturing technology of wood-plastic composite materials is to use the coupling technology to combine wood powder, wood chips and thermoplastics, and to make high-strength composite materials by continuous mixing technology. Because wood fiber is used as reinforcing material, the product is on the surface. Hardness, mechanical strength, insect proof, waterproof, dimensional stability are good.
The processing of wood-plastic composite panels has significant technical characteristics compared with traditional wood processing and plastic processing. The wood-plastic composite panel production process is to process the selected wood powder after drying and other processes according to the formulation requirements of different uses. , crushing, processing according to the requirements of the profile processing by plastic processing extruder, and further processing into products, a variety of wood fiber can be processed from wood scraps, straw, rice husk, etc., especially waste wood powder, sawdust, crops The use of straw, etc., is undoubtedly a favorable protection for the social environment, not only conducive to the human living environment, but also the rational use of limited resources.
Technical performance
The wood-plastic composite board is made of 60% rice bran powder and 40% waste PE plastic. Its technical performance is as follows: tensile strength 5.8Mpa; bending strength 20.0Mpa; bending elastic modulus 1480Mpa; nail holding force ( Board surface) 1940N, (side) 1550N; water content 3%~5%; density 1.18g/cm3; (end surface) hardness 118 Mpa; 24 hour water absorption rate 0.36%; maximum thickness expansion ratio 0.28%; impact toughness 10.1KJ/ M2; longitudinal compressive strength 26.5Mpa.
Prospects
Wood-plastic composite panels combine the cost and performance advantages of wood and plastic, and the material has the advantages of corrosion resistance, no warping, easy maintenance, and very similar appearance to wood. Therefore, the wood powder is mixed and processed into a building and structure. Profiles have become one of the most active areas in the plastics extrusion industry. Recycling of waste plastics, plant straws, etc. is the recycling of resources, which can effectively reduce the amount of wood and protect the forest.
Wood fiber and plant fiber have sufficient sources, light weight and low price, low wear and tear on equipment, stable size of finished products, good electrical insulation, can be repeatedly processed, non-toxic, and biodegradable, and will not cause pollution to the natural environment. The thermoplastics are mainly polyolefins such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), and may be made of new materials, recycled materials, or composite materials of the two. The new wood-based materials produced from natural wood fiber waste and waste plastics are not only low-cost, but also contain no harmful substances such as formaldehyde, compared with the popular natural wood fiber-containing composite materials (such as composite flooring). .
Replacing wood with wood-plastic composites not only reduces the demand for wood, saves forest resources, but also alleviates the growing problem of white pollution. Through comprehensive utilization of waste resources, it turns waste into treasure, and turns harm into profit. It has high economic and social benefits, meets the requirements of scientific development and sustainable development, and conforms to the construction of a conservation-oriented society and the development of circular economy. Requirements have broad prospects for development.
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