The influence of processing parameters on mechanical and morphological properties of TPVs base on natural rubber and polypropylene blends: A statistics approach

Abstract

Thermoplastic vulcanizates (TPVs) of natural rubber (NR) and polypropylene (PP) blends were prepared by the melt mixing process. The influence of the processing parameters (mixing temperature, mixing time, rotor speed, melt flow rate of PP, and blend ratio) on phase morphology and mechanical properties of PP/NR TPVs were investigated. The full factorial design used to be statistically verified to understand the basic parameters that govern the blend phase morphology during the melt-mixing process and clarify the relationship between the processing parameters on the properties of TPVs. The result reveals that all of the processing parameters were statistically significant for the tensile properties of the TPVs, excepted the rotor speed of the mixer. The most influencing factors for tensile properties were the composition of blend ratios and the melt flow rate of PP (MFI), respectively. Phase morphology indicated a two-phase structure in which NR cross-linked phase was dispersed as domains in the continuous PP matrix. TPVs prepared with PP for different melt flow rates (MFI 22 and 2 g/10 min) were showed the different domain size and size distribution of crosslinked rubber phase. The TPVs prepared with a composition PP with a melt flow rate of 2 g/10 min had a subjectively more finely-grain of dispersing rubber phase than with a composition PP with a melt flow rate of 22 g/10 min. Indicating that the fine-grain dispersion of NR cross-linked phase depends on melt viscosity ratio and degree of crosslinking in rubber phase, which obtained from the lower melt flow rate of PP (MFI 2 g/10 min) with a higher rotor speed of mixer. Furthermore, the optimization condition for the highest tensile properties was setting at the high level of mixing time (15 minutes), low level of the melt flow rate of PP (MFI 2 g/10 min), and high composition of blend ratio (50/50 of PP/NR).