Influence of incorporation sequence of silica nanoparticles on morphology, crystallization behavior, mechanical properties, and thermal resistance of melt blended thermoplastic natural rubber

Abstract Thermoplastic natural rubber nanocomposites based on epoxidized natural rubber (ENR) and polypropylene blends at a fixed blend ratio of 50/50 wt% reinforced with small amount (2.5 wt%) of nanosilica (SiO ₂ ) were prepared by melt‐mixing through three different incorporation sequences in an internal mixer. The effects of incorporation techniques on morphology, crystallization behavior, mechanical properties, dynamic, rheological characteristics, and thermal resistance of thermoplastic natural rubber (TPNR) nanocomposites were investigated. It was found that the dispersion of nanosilica in TPNRs was significantly dependent on the incorporation sequence. In the case where SiO ₂ was premixed in ENR before blending with polypropylene (PP), the final morphology showed the good dispersion of SiO ₂ in ENR phase, while the SiO ₂ particles were localized near the PP interface when SiO ₂ was premixed the in PP first. Whereas, when the three components were simultaneously mixed, the SiO ₂ particles were mainly dispersed in the PP phase. It was also found that the improvements of Young's modulus, tensile strength, damping behavior, and thermal stability of TPNR nanocomposites were more pronounced when the SiO ₂ particles localized in ENR phase. By contrast, the presence of SiO ₂ particles in PP domain either near the interface or inside the PP phase affected the reduction in crystallinity of PP phase and showed a negative effect on mechanical properties due to the poor interface interaction between PP and SiO ₂ particles. POLYM. COMPOS., 33:1911–1920, 2012. © 2012 Society of Plastics Engineers