Influence of precursor film microstructure on properties of HDPE microporous membranes prepared by stretching

Abstract

Oriented HDPE films having a stacked lamellar morphology were prepared to develop microporous membranes through cast film extrusion followed by stretching. Applying higher draw ratios (DR) and annealing the cast films improved crystal alignments remarkably. It was shown the improvement in c-axis orientation upon annealing was more significant for the films prepared with lower DR. Furthermore, applying Raman spectroscopy, the amorphous mass fraction of the films was obtained. Subsequently, considering a three-phase structure (i.e., crystal, amorphous and interphase), the interphase content of the films was also determined. A distinct DR dependence of the interphase content was noticed. It was observed that in addition to crystal perfection upon annealing, the amorphous phase fraction was also decreased due to possibly increase in free volume, promoting lamellar separation and cavitation during the subsequent stretching step. SEM images of the membranes surfaces as well as their normalized water vapor transmission rate (WVTR) values indicated a more uniform pore formation and increased permeability with DR. Furthermore, it was found that lower interphase content in the films with higher DR favors lamellar separation. However, permeability in the stretched precursor films with DR higher than a certain level (DR 5 93) was not improved significantly. Moreover, crystallinity and crystal orientation of produced membranes were investigated.

Cavitation‐Induced Stress Whitening in Semi‐Crystalline Polymers

“…Meanwhile, the appearance of voids sometimes is needed in some special fields, for example, creating microporous separation membranes. [57,58] cases. Cavities can be generated in the interspherulitic regions and inside the spherulites.…”

“…We emphasize the importance of cavitation triggered at large strain as it can be regarded as a signal to predict the ultimate life of the materials upon stretching. Meanwhile, the appearance of voids sometimes is needed in some special fields, for example, creating microporous separation membranes . Understanding the evolution of cavities during the deformation process can provide the possibility of finding an efficient way to promote, restrain, or even heal the cavities.…”

Influence of annealing treatment on the structure and properties of poly(4‐methyl‐1‐pentene)‐based films and membranes

“…In situ study of annealing effect on crystalline structure by SAXS, the crystalline phase thickness, the amorphous region, and the diffusion transition layer of HDPE were increased, and a linear relationship with the logarithm of the annealing time was proposed . In addition, annealing was normally an effective method to improve crystal orientation . Khonakdar and coworkers indicated that annealing increased the free volume as well as the crystal thickness .…”

“…In addition, annealing was normally an effective method to improve crystal orientation . Khonakdar and coworkers indicated that annealing increased the free volume as well as the crystal thickness . In general, annealing treatment played a significant role in crystal morphology of casting films and micropores morphology of stretched membranes.…”

Tailoring of thermal and mechanical properties of hollow glass bead‐filled polypropylene porous Films via stretching ratio and filler content

“…As for dry‐stretching, one of the main issues is to fabricate an appropriate initial row nucleated structure, since the pores are created as a result of lamellae separation . The effective processing parameters in dry‐stretching method including air cooling, roll temperature as well as the time and temperature chosen for annealing process . However, in particle stretching, the pores are formed at the interface of particles and matrix by hot stretching and there is no need to stretch the precursor film at low temperature .…”