In the structure of wood-plastic material design, the first consideration is the choice of raw materials. Plastic varieties commonly used are polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), ABS and high impact polystyrene (HIPS) and so on. The main natural fiber for wood flour, rice husk, peanut shells, straw and other agricultural and forestry processing of waste, waste materials. The cellulose content of rice husk is higher than that of wood flour, and the content of water and lignin is lower than that of wood flour. The chemical composition is not as big as wood flour, and the quality of tree is relatively stable. And more important is to take into account the wood fiber fiber aspect ratio, degree of orientation, content and anisotropy and other factors. The fiber in the wood is long fiber, and the wood powder becomes the short fiber, the fineness of the wood powder finer, the better the uniformity, but the fiber length and aspect ratio will be greatly reduced, so the wood powder is generally considered the finer and better view Is not comprehensive, the key is the molecular orientation of the arrangement, that is, wood powder cellulose molecules should be arranged in a certain direction, can effectively improve the strength of rigidity.
Plant fiber orientation is the key technology of wood-plastic material production, from the morphological structure, this is a new generation of wood-plastic materials and the current wood-plastic products (such as fiberboard) the biggest difference. The fibers in the wood are long fibers, arranged in the direction of the trunk, so that the wood has excellent rigidity, strength and bending resistance. In order to make the powder fiber can play a similar effect of long fiber, wood flour or rice husk powder fineness, aspect ratio and content should be a series of regulatory matching. The study found that the use of wood flour, chaff with the distribution of fiber length bimodal approach to the length of the fiber to provide strength, short to improve the processing performance and surface finish approach, effectively solve the long fiber content is not high degree of orientation , Poor surface finish, processing difficulties and short fiber brittle, the intensity is not high a pair of contradictions.
Orientation is good or bad, although with the raw materials, the formula has a great relationship, but the decisive or by the equipment, mold and processing conditions to ensure that, so not any extruder can meet the requirements of the production of natural fiber wood profile. For the natural fiber composite wood material extruder, the design parameters and the general plastic profile extruder is very different, the material in the wood fiber content is high, poor mobility, the use of ejection method is ideal, that material in the screw Produce a huge pressure to promote, to overcome the nose pressure drop, the embryo from the top of the mold, the embryo away from the die, do not need stereotypes and cooling water, but this time the nose channel to long. Due to the large extrusion pressure, screw, gearbox, the motor is subject to great torque, this ejection method for the production of larger density products. For the smaller density of foam wood materials, the use of traction method, wood fiber content of not more than 50%, flexible process, through the formulation and adjustment of processing conditions to produce wood products texture, and can be supplemented by cooling technology, the resin Processing temperature to adapt to the characteristics of wood fiber is not high temperature, in the processing and production process, the requirements of the resin (plastic) fully plasticized, flow, but also the flow of fiber orientation, and does not operate the fiber. Only in this premise, in order to obtain the ideal imitation wood products.
Natural fiber composite wood material production process and fiber board pressing process is different from the basic hard PVC extrusion process is similar, mainly to increase the wood powder drying, grinding process. Drying of rice husk is easier, and the moisture content of wood flour is high, the moisture absorption capacity is strong, the drying and storage requirements are higher, and the crushing method should be selected according to the raw material and the final grain size. As the fineness of wood flour is not the finer the better, so to use the thickness of blending, bimodal distribution principle, it is important to be larger than the aspect ratio. The size of the aspect ratio, and the crushing method. In general, the grinding method is better than the hammering method. Extrusion molding must take into account the wood powder at high temperatures easily brittle, carbonized, the strength of the problem. Plant fiber temperature should not exceed 180 ~ 200 ℃, and the heating time should be as short as possible, so the processing temperature and extrusion process conditions must be synchronized with the temperature limit of wood flour.
Large-scale use of agricultural waste and a variety of plant fiber development of a new generation of wood-plastic materials, can be widely used in building decoration, packaging materials, cargo trays and a variety of common facilities of timber, to maintain the timber wood, wood, , Can be nailed, planer, can be bonded to the nature of wood, in the waterproof, anti-corrosion, fire is better than wood. Therefore, in the increasingly tense wood resources in China today, the development of wood and plastic with the dual advantages of reversible recycling of new wood-plastic materials, with significant social significance and economic value.