Enhanced melt-recrystallization process of propylene-ethylene copolymer during the uniaxial stretching with the aid of isotactic polypropylene

The structural evolution of propylene-ethylene copolymer (coPP) and propylene-ethylene copolymer/polypropylene (coPP/iPP) films has been studied by in-situ WAXD/SAXS in a tensile process. Both coPP and coPP/iPP films show obvious melt-recrystallization during the deformation process. In the initial stage of stretching, the crystallinities of films decrease due to the stress-induced crystal fragmentation. After that, a large number of oriented crystals form in the late stage of the tensile process. Compared with that of coPP, the initial strain of recrystallization for coPP/iPP is smaller, and recrystallization-induced crystallinity (from 4.9% for coPP sample to 10.2% for coPP/iPP sample) and crystal orientation (from 0.75 for coPP to 0.93 for coPP/iPP) are improved. Structural evolution occurs in close relation to tensile rates. At low strain rate, molecular chains are easier to pull from the lattice, resulting in a significant decrease in crystallinity. At low strain rate, samples display stronger recrystallization in the late stage of stretching. Interestingly, there is a difference in the growth process for lamellae between coPP and coPP/iPP samples. For coPP samples, crystals grow on existing lamellae, leading to an increase in the average thickness of crystals. In contrast, recrystallization between lamellae tends to occur in coPP/iPP samples, leading to a decrease in average lamellar thickness and long period. [Display omitted] •Structural evolution of coPP and coPP/iPP blended films are studied using in-situ WAXD/SAXS in a tensile process.•The presence of iPP can enhance the melt-recrystallization process of coPP.•Low tensile rate causes large decrease in crystallinity at the beginning and strong recrystallization in the late stage.•The coPP samples crystallize epitaxially on the existing lamellae in the late stage of tensile process.•Embedded recrystallization between lamellar layers tends to occur in coPP/iPP samples.