Processing window in impact-modified rigid PVC

A method is described for quickly evaluating the processing window of impact-modified rigid PVC formulations. This involves mixing the compound in a bowl mixer at various temperatures and to various levels of total work input. The impact properties are measured and plotted as a contour map versus melt temperature and work input, The melt temperature is the dominant factor in controlling the impact processing window. The total work input is a secondary effect, which mainly influences the system through shear heating effects on the melt temperature. This method was used to evaluate formulations with different impact modifiers and lubricant and filler levels. Impact modifier type, polyethylene wax, and filler concentrations are the dominant factors. The mechanisms involved are discussed.