Properties and Preparation of Peroxide Cured PP/ Low Crystalline MPE Thermoplastic Vulcanizate

Abstract

A peroxide cured polypropylene (PP)/metallocene polyethylene (mPE) blend to form a thermoplastic vulcanizate has been prepared. The mixing of mPE (40 wt%) and PP (60 wt%) containing a fixed amount of paraffin oil and various dosages of peroxide was performed to prepare the dynamic vulcanized blends using an internal mixer. Crystallinity remained largely unchanged for the PP, indicating the dominant role of the cured mPE domains on changes in the mechanical properties for the vulcanizates. Tensile strength decreased at first with increasing levels of peroxide concentrations, yet leveled off at higher levels of peroxide concentrations at all test temperatures. Tear strength generally decreased with increasing test temperatures and peroxide level. The values of the cutting strength were about two orders of magnitude smaller than the results obtained from tear measurements by reducing the crystalline yielding effect, owing to the confinement of the crack tip. However, the values of cutting strength attained were still slightly larger than those for conventional elastomers without a crystalline effect. The strength of these materials was mainly dominated by the crystalline yielding effect from PP or mPE, rather than the viscoelastic effect, even in this nano-fracture zone of deformation in the cutting measurement. Morphological observations from scanning electron microscopy (SEM) revealed decreasing numbers of etched cavities with increasing peroxide level after treatment with n-heptane.