Fracture behaviors of PP/mPE thermoplastic vulcanizate via peroxide crosslinking

Peroxide cured PP/metallocene polyethylene (mPE) to form a novel thermoplastic vulcanizate has been prepared. Metallocene polyethylenes with two different levels of comonomer contents were chosen for the investigation. The mixing of mPE (40 wt%) and PP (60 wt%) containing various dosages of peroxide was performed to activate dynamic cure using an internal mixer. Thermal behaviors remain largely unchanged for PP, indicating the dominant effect of cured mPE domains on mechanical properties for the vulcanizates. Tensile strength decreases at first with increasing the levels of peroxide concentrations yet increases again at higher level of peroxide concentrations at all test temperatures. Tear strength generally decreases with reduced energy dissipation and tends to level off at higher degree of cure. The values of cutting strength are comparable with the results for different types of materials and are generally two orders of magnitude smaller than the results from tear measurements. Strength of materials was clearly dominated by the crystalline yielding effect than viscoelastic effect, even in this nano-fracture zone of deformation in the cutting measurement. Morphological observations were also elucidated as well.