Cure Characteristics and Mechanical Properties of NR/ SBR Blends Filled with Nano-sized CaCO 3

Abstract

Four kinds of nano-sized calcium carbonate (CaCO₃) surface-modified with stearic acid, aluminate, titanate and aluminate-titanate complex coupling agents, were used to reinforce natural rubber (NR)/styrene-butadiene rubber (SBR) blends. The effects of surface modification and CaCO₃ content on the cure characteristics, swelling behaviour, and mechanical properties of NR/SBR blends were studied. The surface modification of CaCO₃ improved the processing and mechanical properties, and the stearic acid coated CaCO₃ (SA-CaCO₃) had finer dispersion and produced a better reinforcement effect than the other modified CaCO₃. Furthermore, a commercial high abrasion furnace carbon black (HAF) was used for comparison. The results showed that both CaCO₃ and HAF increased the cure rate, reduced the optimum cure time and improved the mechanical properties of NR/SBR blends at appropriate filler contents. The tensile strength of filled NR/SBR composites reached its maximum value when the SA-CaCO₃ content was 50 phr or the HAF content was 30 phr. The modulus at 200%, tear strength, and Shore A hardness of filled NR/SBR composites all increased with increasing filler content. The CaCO₃ reinforced the NR/SBR blends to some extent, though it was still not as effective as HAF.