The extrusion molding process of wood-plastic composite materials is divided into one-step extrusion molding process and two-step extrusion molding process.The one-step extrusion molding process of wood-plastic composite materials does not go through the intermediate granulation stage, and the treated wood fibers, thermoplastics and other additives are directly put into the extruder,The mixing, plasticizing and extrusion molding of materials are all completed in one or a group of equipment.In the two-step extrusion molding process of wood-plastic composite materials, it is necessary to first mix and granulate wood fibers, thermoplastics and additives, and then extrude the product. The pelletizing and shaping stages are separated in the two-step extrusion process, allowing for more flexible processing.
During the two-step extrusion molding process, often due to improper raw material ratio or process parameter setting, the product has poor appearance and performance, such as tearing of the material side wall or shark skin disease. Therefore, it is very important to study the process parameters of two-step extrusion molding to improve the appearance performance of wood-plastic composites.
Using wood flour and HDPE as raw materials, the wood-plastic composite material is processed by the method of twin-screw extruder granulation and single-screw extruder molding. During the processing, it is found that the comprehensive performance of the wood-plastic composite material is better when the speed is 40r/min and the temperature is 130°C, 135°C, 145°C, 152°C, 157°C, and 170°C.
The traditional two-step extrusion process is: mixing - granulation - molding. In the experiment, polyethylene plastic was used as a granular product. According to the traditional process, uneven mixing may occur, resulting in the existence of granular substances on the surface, which affects the appearance of the product. Therefore, the experiment added the secondary mixing process in the processing process, mixing-granulation-mixing-molding, so that the materials can be further mixed evenly, and the appearance performance of wood-plastic composite materials can be improved.