Preparation of polyethylene microporous membranes with high water permeability from thermally induced multiple phase transitions

Microporous chlorinated polyvinyl chloride (CPVC) membranes were prepared via thermally induced phase separation process for the first time using diphenyl ether (DPE) as diluent. The CPVC/DPE blends exhibit upper critical solution temperature (UCST)‐type phase behavior, which undergoes liquid‐liquid phase separation followed by sol‐gel transition during cooling process. Therefore, the resulting CPVC membranes presented symmetric morphology with uniformly distributed cellular pores. The cloud point (liquid‐liquid phase separation temperature) decreased with increasing CPVC content, while the sol‐gel transition temperature showed an opposite trend. Both the growth rate of diluent‐rich phase droplets and the gelation rate of the CPVC/DPE blends increased by decreasing CPVC concentration or cooling rate, leading to an increase of the pore size in the final membranes. Results of water permeation tests confirmed that the water flux of the membranes have a significant dependence on their porosity and pore size, that is the water flux increased with the increase of porosity and pore size. Moreover, the CPVC microporous membranes prepared by the TIPS process showed a high mechanical strength and excellent acid/alkali resistance, which has presented a great potential for application in the fields of water and wastewater treatment. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44346.

Section: Resultssupporting

confidence: 67%

Section: Phase Diagram Of Cpvc/dpe Systemmentioning

confidence: 57%

Fabrication and characterization of chlorinated polyvinyl chloride microporous membranes via thermally induced phase separation process

Zhang

Mao

Bai

et al. 2016

“…A similar method to calculate the porosity was also used in the study in ref. 22. Table III shows the mechanical properties of the extracted fibers after the first-stage cold drawing of the gel-spun fibers.…”

Section: Porosity Determinationmentioning

confidence: 99%

Two‐stage drawing process to prepare high‐strength and porous ultrahigh‐molecular‐weight polyethylene fibers: Cold drawing and hot drawing

Liu

et al. 2015

High‐strength and porous ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers have been prepared through a two‐stage drawing process. Combined with tensile testing, scanning electron microscopy, and small‐angle X‐ray scattering, the mechanical properties, porosity, and microstructural evolution of the UHMWPE fibers were investigated. The first‐stage cold drawing of the gel‐spun fibers and subsequent extraction process produced fibers with oriented lamellae stacks on the surface and plentiful voids inside but with poor mechanical properties. The second‐stage hot drawing of the extracted fibers significantly improved the mechanical properties of the porous fibers because of the formation of lamellar backbone networks on the surface and microfibrillar networks interwoven inside to support the voids. With various processing conditions, the optimized mechanical properties and porosity of the prepared UHMWPE fibers were obtained a tensile strength of 1.31 GPa, a modulus of 10.1 GPa, and a porosity of 35%. In addition, a molecular schematic diagram is proposed to describe structural development under two‐stage drawing, including void formation and lamellar evolution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42823.

“…[1][2][3][4] There are various methods employed for the production of membranes and most of them are based on solvent casting (wet process) followed by phase separation induced by the addition of a nonsolvent to the polymer solution or through applying a temperature gradient. [5][6][7] However, the difficulty in solvent dissolution of the crystalline regions has limited the applicability of such polyolefins to the conventional solvent casting process. 4,8 Moreover, costly solvent recycling and solvent contamination are two drawbacks for the wet process.…”

Section: Introductionmentioning

confidence: 99%

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

Yadegari

Morshedian

Khonakdar

et al. 2017

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.