Effect of an organotitanate coupling agent on properties of calcium carbonate filled low-density polyethylene and natural rubber composites

Poor filler dispersion in a polymer matrix results in non-uniformity of the composite and hence changes its properties. This non-uniformity could be overcome by incorporating a suitable adhesion promoter and/or a coupling agent. Although titanate coupling agents are used in plastics, the use of a titanate coupling agent (CA) in rubberthermoplastic blends has not been studied in detail. Therefore, this study was aimed at incorporating a CA to natural rubber (NR) and low-density polyethylene (LDPE) blend through calcium carbonate (CaCO3) filler and thereby investigating the effect of CA loading on properties of the composites. In this study, a series of 70/30 NR/LDPE composites was formulated by varying the CA loading from 0 to 1.5 pphp (parts per hundred parts of polymer). CaCO3 loading was kept constant at 20 pphp. Brabender plasticorder was used to prepare composites at a temperature of 150 oC, and a rotor speed of 60 rpm. Physico-mechanical properties were evaluated according to ISO standards. Degree of swelling and gel content in p-xylene, water absorption, morphology, ageing, thermal and dynamic properties of the composites were investigated. Tensile strength, elongation at break and tear strength of the composites increased with the addition of CA and showed the best properties at a CA loading of 0.7 pphp. Hardness increased with the addition of CA, however, it decreased with the increase in CA loading. The highest gel content, retention of tensile properties and water resistance were also shown at 0.7 pphp loading. In overall, the composite at CA loading of 0.7 pphp showed better compatibility and the best properties.