Precipitated calcium carbonates as weathering enhancers and impact modifiers for rigid PVC siding and profiles

A study conducted to determine the suitability of calcium carbonate (CaCO₃) fillers in exterior PVC applications revealed that the surface-treated precipitated CaCO₃s of average particle sizes 0.5 micron and 0.07 micron, in fact, minimized the initial yellowing of PVC seen on weathering. It is hypothesized that these particle-size CaCO₃s, being optimum for light scattering, provide greater UV protection. Further, the high surface areas of these CaCO₃s increase the capacity to neutralize the HCl responsible for yellowing of the PVC. The optimum filler level is 5 to 10 phr. At this loading level, long-term impact strength is also retained.