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There are many applications of wood plastic composite in daily life, especially in the construction wood industry. Extruded products of different sizes and shapes increase the diversity of wood plastic composite materials. When the profile is not required to have a continuous sheet structure or the components have a complicated structural design, the wood plastic composite profile can be formed by injection molding or compression molding. Processors sometimes have to face the problem of how to completely fill the wood plastic material during processing. In order to solve this problem, they need to reduce the amount of wood filler to increase the fluidity of the melt.
Since 200°C is the upper limit of the processing temperature for wood plastic composites, some resins with melting points above 200°C, such as PET, cannot be used for wood plastic composites. Water vapor will degrade the performance of the composite material and also help to breed microorganisms, so it must be removed before using wood filler. The wood filler should be dried before processing and molding, and the moisture content after treatment is generally required to be less than 1 to 2%. Wood plastic composite materials processing machinery is required to be equipped with feeding equipment, drying equipment, extrusion equipment and molding equipment, as well as some necessary downstream equipment such as cooling water tanks, traction equipment and cutting equipment. Treatment requires appropriate additives to modify the surface of the polymer and wood flour to improve the interface affinity between wood flour and resin. The dispersing effect of high-filled wood powder in molten thermoplastics is poor, which makes the melt fluidity poor and the extrusion molding process is difficult. Surface treatment agents can be added to improve the fluidity to facilitate extrusion molding. The plastic matrix also needs to add various additives to improve its processing performance and the use performance of its products.
During the process of wood plastic composite feeding, the wood powder has a fluffy structure, and it is not easy to feed the extruder screw, especially when the wood powder contains more water, the phenomenon of "bridging" and "sticking" often occurs. The instability of wood plastic composite feeding will cause extrusion fluctuations, resulting in lower extrusion quality and output. Feeding is interrupted, and the residence time of the material in the barrel is prolonged, causing the material to burn and change color, which affects the internal quality and appearance of the product. Use forced feeding device and reasonable conveying method to ensure the stability of extrusion. Configuration design During the extrusion process of wood plastic composites, the configuration of the screw plays a very important role. The reasonable screw structure can reduce the friction between the screw and the wood fiber, produce appropriate shear and dispersion mixing, so that the material system containing a large amount of wood powder can be well and uniformly plasticized. In addition to ensuring the smooth transition of the runner design and reasonable flow distribution in the mold design and cooling setting, wood plastic composites have higher requirements for pressure building capacity and temperature control accuracy.
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