Mechanism of Significant Improvement of Large Strain Elasticity in Soft Propylene–Ethylene Random Copolymer via Blending with Hard Propylene–Ethylene Coplymer

The deformation behavior of propylene–ethylene copolymers with 23 mol % of ethylene (iPPcoE23) and its blend (90/10 w/w) (iPPcoE23b) with propylene–ethylene copolymer (6 mol % ethylene) (iPPcoE6) at room temperature was studied by in situ small-angle X-ray scattering and wide-angle X-ray diffraction techniques. The 10 wt % copolymer with 6 mol % ethylene counits dispersed as small domains in the matrix of iPPcoE23. During stretching, longer and thinner fibrils and better elasticity properties were shown in the blend iPPcoE23b at large strain regime. The higher elasticity for iPPcoE23b at large strain regime was ascribed to the weak ability of strain-induced crystallization due to cocrystallization of the crystallizable long chain sequences of iPPcoE23 with the high crystalline iPPcoE6 during cooling, leaving fewer long crystallizable sequences in the matrix in iPPcoE23b. In addition, the phase-separated domains contributed stronger network modulus in the late stage of stretching compared with that of the recrystallized network of iPPcoE23.