Factors affecting the abrasiveness of filled rigid PVC dry blends

Abrasion due to the high speed mixing of rigid PVC dry blends filled with CaCO 3 was found to be a function of both the mixing conditions and type and level of CaCO 3 used. Laboratory scale tests showed that abrasion is a function of mix time, mix speed, and mixer blade geometry. These variables were standardized to develop a laboratory abrasion test using a Hockmeyer mixer equipped with a soft 3‐in diameter aluminum mixing blade. This procedure was used to investigate the effect of CaCO 3 property variables on abrasion during rigid PVC dry blending. Multiple linear regression analysis at 30 phr CaCO 3 showed that abrasion increased with filler top cut, mean, acid insolubles, and MgCO 3 content, but diminished with an increase in percent less than 1 micron fraction. A more generalized abrasion predictor model was developed by considering surface area to be a linear function of top cut, mean, and percent less than 1 micron properties. Abrasion was greatly minimized by using finer particle size, higher surface area CaCO 3 with low acid insoluble and magnesium carbonate levels. These criteria also aid in reducing the abrasive effects of TiO 2 during dry blending through a CaCO 3 /TiO 2 interaction.