Abstract
Poly(p-phenylene terephtalamide) (PPTA), a high-performance polymer with high modulus and good hydrophilicity, is often used as a reinforced material. However, due to its high crystallity, micro-phase separation often occurs in the blends. In this paper, PPTA/poly(vinylidene fluoride) (PVDF) compatible blend solution was synthesized by in situ polycondensation. Blend ultra-filtration membrane was prepared through the immersion phase inversion process. In order to obtain desired pore structure, the effects of different additives including hydrophilic polymer (polyethylene glycol (PEG)), inorganic salt (lithium chloride (LiCl)) and the surfactant (Tween-80) on the morphology and performance of PPTA/PVDF blend membranes were studied. The membrane formation process was investigated through ternary phase diagram (thermodynamics) and viscosities (kinetics) analysis. It was found that, with the increasing of LiCl content, a porous membrane structure with long finger-like pores was formed due to the accelerated demixing process which resulted in the increase of porosity and pore diameter as well as the enhancement of water flux and the decline of PEG rejection. When Tween content increased to over 3 wt%, dynamic viscosity became the main factor resulting in a decreased phase separation rate. The transfer of PEG and LiCl molecules onto membrane surface increased the surface hydrophilicity. The effect of Tween content on membrane hydrophilicity was also correlated with the compatibility of blend components.
Highlights
Due to its excellent chemical and mechanical properties, poly(vinylidene fluoride) (PVDF)ultrafiltration (UF) membrane has been widely used in water and wastewater treatment and bio-separation [1,2]
This paper aimed to explore the effect of different kinds of additives on the morphology and separation performance of PPTA/PVDF in situ blend membranes
Thermodynamic phase diagrams indicated that the addition of polyethylene glycol (PEG) or LiCl both deteriorated the thermodynamic properties of casting solution, while the negative effect of LiCl was more significant
Summary
Due to its excellent chemical and mechanical properties, poly(vinylidene fluoride) (PVDF). Ultrafiltration (UF) membrane has been widely used in water and wastewater treatment and bio-separation [1,2]. The strong hydrophobicity contributed to the flux decline and frequent back-flushing operation which will induce the deterioration of membrane mechanical strength and even membrane rupture. It is very important to enhance the hydrophilicity and mechanical strength of PVDF membrane. Poly(p-phenylene terephtalamide) (PPTA), a high-performance polymer with high modulus and good hydrophilicity, is often used as a reinforced material. Due to its high crystallity, micro-phase separation often happens during the conventional blending process. PPTA/PVDF blend membrane with excellent hydrophilicity was successfully prepared by in situ polycondensation to overcome the phase separation [3]
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