Wood plastic products require appropriate additives to modify the surface of the polymer and wood flour to improve the interface affinity between the wood flour and the resin.
The high-filled wood powder has poor dispersion in the molten thermoplastic, which makes the melt flow poor, and the extrusion moulding process is difficult. A surface treatment agent can be added to improve the fluidity to facilitate extrusion moulding. Plastic substrates also require the addition of various additives to improve their processability and the performance of their products.
Wood plastic product feeding process
The wood powder structure is fluffy, and it is not easy to feed the screw of the extruder. Especially when the wood powder contains more water, the phenomenon of “bridge” and “holding rod” often occurs. Instability in the feed can cause extrusion fluctuations, resulting in reduced extrusion quality and yield. When the feeding is interrupted, the residence time of the material in the barrel is prolonged, which causes the material to burn and discolour, which affects the inherent quality and appearance of the product. The forced feeding device and the reasonable conveying method are adopted to ensure the stability of the extrusion.
Small molecules of volatile matter and moisture carried in wood flour can easily cause defects in the product, and the pretreatment cannot completely remove them. Therefore, the design of the exhaust system of the wood-plastic composite extruder is more important than that of the ordinary plastic extruder, and it is possible to carry out multi-stage exhaust if necessary. To a large extent, the better the exhaust effect, the better the quality of the extruded product.