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The structural evolution during the linear low‐density polyethylene (LLDPE) film blowing has been studied with a combination of home‐made blown film apparatus and in situ WAXS and SAXS measurements. Analyzing the evolution of orientation parameters and crystallinity of the bubble shows that the blown film process can be divided into four regions. Distinctly different features of LLDPE bubble are observed in first three regions: (a) lower orientation parameters during the blown film process, (b) higher crystallinity is required to form a deformable crystalline crosslinked network, and (c) the weaker stretching effect and the difficulty of reaching equilibrium when the crystal network deforms. These results should provide a basis for understanding the poor blown film stability of LLDPE. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1404–1412 In situ WAXS and SAXS technique studies have been used successfully to investigate the structural evolution during the linear low‐density polyethylene (LLDPE) film blowing. It is found that the LLDPE blown film process can be divided into four regions. The higher crystallinity in the end of Region II and the weaker change of orientation in Region III are expected to explain the LLDPE blown film poor stability. [ABSTRACT FROM AUTHOR]

Aiming to reveal the stabilization mechanism of micropore embryos formed during cold stretching in high-density polyethylene films, samples are subsequently subjected to temperature elevation and strain holding at 25 °C, respectively. The corresponding structure evolution is tracked. It is found that after strain holding at 25 °C and subsequent strain recovery, inhomogeneously distributed cavities are produced, most of which can be healed as temperature is elevated to 110 °C. Consequently, only a small number of nonevenly distributed micropores are formed during the subsequent hot stretching. While for thermal pathway, micropores and fibrils can be formed as temperature is elevated. The hot stretching membrane exhibits uniformly distributed micropores and the micropores are well interconnected, indicating that micropores stabilized via temperature elevation are permanent and homogeneous. The results reveal different stabilization mechanisms of micropores via the thermal and mechanical pathways with regard to the distribution as well as the amount of permanent micropores. [ABSTRACT FROM AUTHOR]

Aiming to establish the relationship between structures of precursor film and its capability of pore formation, high density polyethylene (HDPE) precursor films are prepared under varied draw ratios and die temperatures, which are further subjected to stretching to generate microporous membranes. Structures like long period, lateral size of lamellae, orientation parameter, and fibril content of the precursor films are obtained by small/wide angle X-ray scattering (SAXS/WAXS), and morphologies of the microporous membranes are examined with scanning electron microscope. It is found that the content of fibrils and orientation parameter of lamellar stacks in the precursor films play counter effects on the capability of micropore formation. A critical window to balance the conflict is revealed with an optimal fibril content of about 6.4%, at which maximal porosity and most homogeneous porous structures are obtained. A schematic model is proposed to account for the role of the fibrils and the oriented lamellar stacks during pore formation, which may guide the production of high-performance HDPE microporous membranes. [ABSTRACT FROM AUTHOR]