Mechanical, Thermal and Fire Retardant Characteristics of NR/PP/ATH Thermoplastic Vulcanizates

Abstract

Blends of natural rubber (NR) and polypropylene (PP) were melt-mixed with phenolic resin crosslinking agent to obtain thermoplastic vulcanizates (TPVs). The blend composition of NR and PP was at 60/40 %wt. Alumina trihydrate (ATH) was incorporated into the blends to improve the flame retardancy, and the effect of ATH incorporation at different levels (20 - 120 PHP, part per hundred polymers) on blend morphology, ATH dispersion, mechanical properties, thermal resistance and flame retardancy was investigated. Analyses by transmission electron microscopy (TEM) and energy dispersive X-ray-scanning electron microscopy (EDX-SEM) revealed the dispersed phase-like morphology of 60/40 NR/PP TPVs. The presence of ATH in the TPVs did not have much influence on morphology of 60/40 NR/PP blends. Increasing ATH content decreased the dispersion level of ATH, which caused a decrease of tensile strength and elongation at break. Furthermore, an addition of ATH into the NR/PP blends resulted in lower elastic recovery, but slight increase of hardness. It was also found that the ATH suppressed the intensity of mass loss rate of NR and PP, resulting slower thermo-oxidative decomposition process of the blend materials. Limiting oxygen index (LOI) and UL94-V rate were enhanced with more incorporated ATH content. According to the results present in this study, the addition level of ATH for development of flame retardant NR/PP blend-based TPVs with acceptable elastomeric properties was recommended at 100 PHP.