Effect of Calcium Carbonate Properties on the Reinforcement of HMW-HDPE Film

Abstract

Pelleted concentrates based on linear low density polyethylene (LLDPE) were used to add 0, 7.5% and 15 wt% of different fine-ground, surface-treated calcium carbonate (CaCO₃) minerals to a high-molecular weight (HMW) high density polyethylene (HDPE) film resin. These dry blends were extruded into 13 μm thick film. Neck height and blow-up ratios (BUR) were varied to determine how the addition of CaCO₃ affected film property response to variations in these process conditions. Mineral addition yielded output rate increases of 5% at 7.5% CaCO₃ and 10% at 15% CaCO₃ while simultaneously decreasing melt pressure and motor load (current). Depending upon calcium carbonate grade, mineral loading and processing conditions, increases in dart impact strength and/or tensile yield strength were achieved. Calcium carbonate mineral grades also exhibited differences in the level of extrusion and bubble stability. Mineral reinforcement of HMW-HDPE films increases film coefficient of friction, which improves stacking of liners or merchandise bags.