Influence of lamellar structure on double yield behavior and pore size distribution in β nucleated polypropylene stretched membranes

Abstract

In this article, five b nucleated polypropylene (b-iPP) precursor films were prepared through crystallization within the temperature window of 110-135 C, and microporous membranes were fabricated by a successive biaxial stretching. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) showed that all the five b-iPP precursors, which were composed of parallel-stacked lamellae without fully developed spherulite, had similar crystallinity and extremely high contents of b-crystals. Thus, the influence of the lamellar structure on the stress-strain behavior of b-iPP precursors and the performance of such films upon stretching can be investigated. We first discovered a peculiar double yield phenomenon in b-iPP under tensile loading. Based on the detailed characterization of the morphological evolution during stretching, we found that a narrower b-lamellar thickness distribution would result in the delayed occurrence of a second yield point under tensile loading and a more uniform pore size distribution in the microporous membranes prepared from b-iPP.

Influence of annealing on stress–strain behaviors and performances of β nucleated polypropylene stretched membranes

“…In our previous study [45], we have proven that double yield behavior is pronounced in β-iPP when stretched at high strain rate, and is correlated with the lamellar thickness distribution, namely a narrower β lamellar thickness distribution would lead to a more homogeneous neck in cold drawing and a delayed occurrence of second yield point. The nominal stress-strain curves of the two β-iPP samples and the corresponding characteristic parameters during yield process are shown in Fig.…”

Synergetic effects of a matrix crystalline structure and chain mobility on the low temperature toughness of polypropylene/ethylene–octene copolymer blends

“…As is known, the b-form PP has no cross-hatch structure between lamellas, so its crystal slip ability is higher, which will result in higher cavitation ability in the amorphous phase and easier shear yielding of the crystalline phase. 4,7,11,32,38 Aer annealing, the mobility in the amorphous is improved with the segmental density decreased as discussed above, which will also lead to easier cavitation in the amorphous phase. The above results and discussions manifest that these two effects in the crystalline and amorphous phase could work together to enhance the cavitation ability, promote the shear yielding/plastic ow of the crystalline phase and thus improve the toughness synergistically.…”

“…[1][2][3][4][5] But its rather poor impact resistance strongly limits its wider applications, especially at temperatures below its glass transition temperature (around or below 0 C) when its amorphous phase is frozen in the glassy state. [5][6][7][8][9][10][11] A signicant amount of work has been carried out to improve the low temperature toughness of PP.…”

Influence of melt structure on the crystallization behavior and polymorphic composition of polypropylene random copolymer

“…The content of the b-crystal was determined according to standard procedures described in the literatures [9,[60][61][62][63][64], employing the following equation:…”