The Primary Influencing Elements In The Processing Process Of Wood-Plastic Composites

The Primary Influencing Elements in the Processing Process of Wood-Plastic Composites

(1) Forming temperature

The main influence of temperature is barrel temperature and die temperature. Barrel temperature has a decisive influence on the mixing results of composite materials. Low temperature leads to uneven plasticization of plastics, inadequate mixing and difficult movement of the mixing body in the barrel. High temperature leads to easy degradation of plastics, easy burning of wood flour and smoking. The temperature of the barrel has the main influence on extrusion forming. Low temperature and excessive pressure of the head make it difficult to extrude the finished product, and then easy to form blockage. High temperature makes the extruded product not compact and excessively high temperature. Foaming can be foamed without extrusion, which can not form a better bubble nucleus and affect the quality of the finished product.

On the premise of abundant plasticization, low temperature extrusion should be adopted. Equipment such as screw and moulding die should also have low-temperature extrusion characteristics, so that the capping vessel has superior shape and smaller diameter. The temperature of feeding section should be controlled below 165 C, the shrinkage section and homogenization section should be between 160 and 180 C, and the die and die should be set below 160 C.

(2) Screw speed

The influence of screw speed on extrusion foam is mainly manifested in the following aspects: first, the higher the screw speed, the greater the pressure in the extruder, and then the more conducive to nucleation, the more nucleated bubbles and the higher the foaming rate. However, when the pressure is too high, the development of nucleated foams is restrained, affecting the abundant development of foams; secondly, the higher the screw speed, the stronger the shearing effect, the easier the foams merge or crack when the shearing effect is too strong, affecting the foam quality and the composition of low-density foam plastics; thirdly, the screw speed is too high or too low, making the staying time too short or too long, easy to occur early foaming or foaming agent differentiation is not sufficient. Such phenomena affect the average precise cell structure. Therefore, under the condition that other factors remain unchanged, the screw speed has an optimum value, usually between 12 and 18 r/min.

(3) Extrusion pressure

Lack of extrusion pressure will result in rough appearance and low strength of the finished product. Higher extrusion pressure can not only control the gas-containing melt in the die not to foam earlier, but also make the pressure difference in the die surface larger, and then make the pressure drop speed higher, which is conducive to bubble nucleation, the number of nucleated bubbles increased, and the foaming rate also increased, which is conducive to obtaining the average precise bubble structure. However, high extrusion pressure has an effect on the development of cell. In order to obtain suitable die pressure, the screw speed, head temperature and die shape can be adjusted.