Unsaturated hyperbranched polyester as a surface modifier of CaCO3 and enhanced effect on mechanical properties of HDPE/CaCO3 composites

The unsaturated hyperbranched polyester (UH20) based on Boltorn™ H20 (H20) end‐capped with methacrylate groups and carboxylic acid groups was introduced to treat calcium carbonate (CaCO₃) as a new type of surface modifier by a wet‐coating technique. The interaction between CaCO₃ and modifier was proven to be due to the ionic character by FT‐IR after the extraction with acetone. The maximum amount of tightly bonded UH20 modifier was determined to be around 9% by thermogravimetric analysis (TGA). The incorporation of CaCO₃ coated with UH20 into high‐density polyethylene (HDPE) decreased the mechanical performance of HDPE/CaCO₃ composite in comparison with CaCO₃ coated with stearic acid. In the presence of a small amount of dicumyl peroxide (DCP), a greatly improvement of the notched impact strength as well the tensile strength of HDPE/CaCO₃ coated with UH20 composite was obtained. An enhanced effect in the mechanical performance of the composite between CaCO₃ coated with UH20 and HDPE matrix in the existence of DCP was suggested. Moreover, the morphological structures of impact fracture surface of the HDPE/CaCO₃ composites were studied by scanning electron microscopy (SEM) to confirm the possible mechanism for explaining the improvement of mechanical properties of the composite. Copyright © 2005 John Wiley & Sons, Ltd.