Cure and mechanical properties of natural rubber-g-poly(methyl methacrylate)–cassava starch compounds

Graft copolymer of natural rubber and poly(methyl methacrylate) (NR-g-PMMA) was synthesized and used as a rubber component in the compounding formulation. Natural rubber air dry sheet (ADS) was also used to blend with the NR-g-PMMA. It was found that scorch time and cure time of the NR-g-PMMA–cassava starch and NR-g-PMMA–ADS–cassava starch compounds decreased with increasing levels of cassava starch. Also, the scorch time and cure time of NR-g-PMMA–cassava starch were longer than those of the NR-g-PMMA–ADS–cassava starch compounds. These results may be attributed to the levels of hydroxyl groups in the cassava starch and degree of unsaturation of the rubber component in the compounding formulation. It was also found that the cure rate index increased with the increase of the levels of cassava starch in the compounding formulation. Furthermore, the minimum and maximum torque and hardness also increased with the increase of cassava starch content. Decreasing trends of tensile strength, elongation at break and tear strength were observed upon increasing levels of the cassava starch. The inability of the cassava starch particles to support stress transferred from elastomeric phase and a rigid cassava starch–rubber interface might be the reasons for the decreasing trend.