Impact modifiers and their influence in toughness and plate-out in highly filled rigid PVC formulations

Abstract

Impact modified rigid PVC formulations for the building and construction industry have evolved since their introduction in the 1960s. Formulations mainly consist of stabilised PVC with low levels of inorganic filler, pigment, and impact modifier. For outdoor applications n-butyl-acrylic grafted poly-methyl-methacrylate core/shell modifiers (AIM, a thermoset) and chlorinated polyethylene (CPE, a thermoplastic) modifiers are commonly used. It is known that CPE, especially the newer high molecular weight CPE products, are very efficient at high levels of filler (i.e. CaCO₃>8 phr). The high molecular weight CPE impact modifier has a synergistic effect with high CaCO₃ filler levels, boosting the impact strength of the final formulation. This effect is also seen at low temperatures, important in cold regions. This advantage has been exploited in the North American rigid PVC siding market; however, the European window profile market has kept CaCO₃ levels at 5–8 phr. There is a lack of knowledge around high molecular weight CPE in comparison with newer AIM in highly filled formulations, especially on how the impact modifier affects toughness and plate-out. A range of impact modifiers has been studied, focusing on their effects on impact strength (at room and low temperatures) and plate-out in formulations with high filler levels.