The hot mixing process of PVC foam board production is also the process of PVC mixture gelation. The unmixed PVC resin has different particle sizes and more small particles at room temperature, which will easily cause uneven plasticization during the extrusion process, thus affecting the quality of the PVC foam board. In the hot mixing process, PVC resin gradually melts, plasticizes and recrystallizes to form a network structure.
Temperature below 50℃
When the temperature of raw materials for the production of PVC foam board is below 50 ℃, PVC agglomerated powder particles and larger particles are friction, impact, although the apparent density does not change much, but the large stacked particles are shear broken gradually into small particles, and in the absorption of heat and mechanical energy after the activity increases, gradually combined with other particles, particle size increases
Temperature above 50℃
When the temperature is at 50-90℃, the blender ramps up faster, after that it ramps up slower and the diffusion, shearing and convection effects are more intense. When the material temperature reaches 115℃, the small particles of PVC resin become large and uniform, the small particles gradually disappear, and the edge of the particles become transparent and translucent due to partial gelation.
Under certain conditions, the degree of partial gelation of PVC resin pellets is determined by the temperature of the discharge material. When the material temperature reaches 120°C, the PVC pellets tend to stabilize and the degree of gelation increases.
The entire thermal mixing process PVC particles repeatedly combined and homogenized, the particle size increased, played a densification effect, so that the apparent density of PVC particles to reach the maximum, conducive to improve the extrusion yield, promote uniform plasticization of materials, improve the yield of plastic products with welding, impact properties and other properties.
Uniformity and dry flow of better PVC dry mix powder, PVC resin can be observed both particle refinement, particle size uniform morphological changes, but also shows the apparent density, part of the gelation characteristics.