Synthesis of polyisoprene–montmorillonite nanocomposites via differential microemulsion polymerization and application of PIP–Mt in natural rubber

Polyisoprene–montmorillonite (PIP–Mt) nanocomposites with an average particle size of 30 ± 7.2 nm and narrow size distribution (20–50 nm) were successfully synthesized via differential microemulsion polymerization. X-ray diffractometry analysis revealed that PIP was intercalated in the Mt layers expanding the d spacing of the Mt layer from 3.1 nm to 3.8 nm. The SDS (surfactant) concentration, isoprene monomer (IP) to water ratio and Mt loading were all found to affect the IP conversion level, and the solid content and particle size of the obtained PIP–Mt nanocomposites. An IP conversion level of 81% and a solid content of 20% were achieved at 0.25 wt.% 2,2-azoisobutyronitrile (AIBN), 10 wt.% Mt, 10 wt.% SDS and an IP:H2O ratio of 0.24:1. These PIP–Mt nanocomposites could be used as an effective nano-filler in natural rubber (NR) latex for the preparation of NR/PIP–Mt composites, improving the mechanical properties compared to the unfilled NR. NR filled with PIP–Mt at 2 wt.% showed a 1.6 and 1.1 fold higher tensile strength and a modulus of elasticity at 300% elongation, respectively. Furthermore, NR/PIP–Mt composites at 2 wt.% Mt loading improved the thermal aging compared to unfilled NR, with an 87.6%, 96.2% and 84.0% retention of the tensile strength, elongation at break and modulus of elasticity, respectively compared to 52.5%, 88.9% and 58.8% for the unfilled NR.