The performance of wood-plastic composite products is not only related to raw materials, but also has an inseparable relationship with the production process.It is difficult to mix the highly hydrophilic wood fiber and the strongly hydrophobic plastic evenly. In order to prepare products with superior physical properties, it is usually necessary to modify the plant fiber raw materials, which also puts forward higher requirements for WPC production and processing equipment. The molding process of wood-plastic composite materials includes injection molding process, extrusion molding process and compression molding process, and the most rapid development is extrusion molding process. Injection molding process, the material is stored at a certain temperature, the molten material fluid is conveyed by the screw under a certain pressure, injected into the mold cavity, cooled and formed under pressure, and then demolded and sampled to obtain a product of a certain shape. This method is usually selected for the production of complex structural parts and is one of the most important processing methods in industry.
The injection molding process can be simply divided into six steps: mold closing, glue injection, pressure holding, cooling molding, mold opening, and product removal. At present, the injection molding process has been better developed, and some emerging technologies have begun to be used, such as water-assisted injection molding, high-fill composite injection molding, micro-injection molding, and foam injection molding. The new molding process has injected new blood into the development of wood-plastic composite materials, and also brought new ideas to the processing of wood-plastic composite materials, while some traditional injection molding processes are coming off the production line.
The extrusion molding process refers to wood fiber materials and thermoplastics, which are melted by heating in extrusion equipment, and pressurized to make wood fibers and heated and melted plastics mixed and extruded.The molding process is simple, the preparation cycle is short, and the effect is remarkable. The screw extruder is the most commonly used molding equipment.However, the material should be mixed and granulated before extrusion, because the wood fiber with a fluffy structure is directly fed to the screw of the extruder, and the plant fiber and plastic are not easy to mix evenly, so the fiber must be dried or surface treated.The methods of fiber treatment mainly include coupling agent modification, surface spraying, dipping treatment, graft modification, compatibilizer, etc., and the treated fiber is mixed with plastic in a certain ratio, and put into the equipment for mixing and molding. This method has a better effect and has a certain use value when the requirements for the finished product are not too high.The extrusion molding method is specifically divided into one-step extrusion and two-step extrusion. One-step extrusion means that the mixing and molding process is completed in one step, and no granulation process is required;The two-step method must first be mixed and granulated, and then the compounded granules are plasticized and extruded.