Effects of Coupling Agents on the Tensile Properties of Calcium Carbonate Filled LDPE Compatibilized with Maleic Anhydride-g-LDPE (Part I)

In this study many composites based on low density polyethylene (LDPE) with calcium carbonate (CaCO3) and maleic anhydride-grafted polyethylene (MAH-g-LDPE) as a compatibilizer have been investigated in order to study their behavior and the reinforcing mechanisms involved. Different types of chemical modifications of the filler surface were carried out in an attempt to enhance the interactions with the polymeric matrix by using silane and zirconate coupling agents. The compatibilizer was created using a single screw extruder by impregnating LDPE granulates with a solution obtained by dissolving in acetone the dicumyl peroxide used as the initiator for the grafting reaction, maleic anhydride as the grafting monomer, and triphenyl phosphine (TPP) as the stabilizer. Titration measurements indicated that the extent of grafting achieved was 0.21% by weight. The composites containing different concentrations of untreated CaCO3 and those treated with 2% of the compatibilizer were prepared by melt mixing using a two roll mill. It was found that the mechanical properties, which depended greatly on the state of the dispersion of the filler as well as the nature of the interface, were relatively better than the composites prepared by the humid method. Higher reinforcement was obtained with the composites treated with the zirconate coupling agent than those modified with the silane coupling agent.