Solvent effect and macrovoid formation in cellulose acetate phthalate (CAP)–polyacrylonitrile (PAN) blend hollow fiber membranes

Abstract

ABSTRACTThe interactions which govern the morphology of blend hollow fiber membranes is explored in detail in the present work. A hydrophilic (cellulose acetate phthalate) and a relatively hydrophobic polymer (polyacrylonitrile, critical surface tension 47.0 mJ/m2) blend in three solvents, viz., n‐methylpyrrolidone (NMP), dimethyl formamide (DMF), and dimethylsulfoxide (DMSO), has been selected as an example to understand the polymeric blend—solvent and nonsolvent interactions. The deviation intrinsic parameter ( ) is estimated as well as cloud point, linearized cloud point (LCP), and Fourier transform‐infrared (FT‐IR) analysis have been performed for the blend membranes. The analysis yields that is negative for both DMF and NMP indicating miscibility, whereas for DMSO it is positive indicating immiscibility. Cloud point and LCP analysis too reveal DMSO to be the poorest solvent and liquid‐liquid demixing is the governing phenomenon for the phase inversion. In depth interaction is conducted with help of FT‐IR spectra. The higher red shift of >C==O (1747 to 1665 cm−1) after complete phase inversion indicates stronger interaction in DMF and NMP, whereas, no shift in >C==O stretching in DMSO indicates weak or no interaction. This reveals that polymer blend‐solvent interaction is weak in case of DMSO than DMF or NMP. These observations manifest in DMSO membranes being most porous, with highest permeability and molecular weight cut off with poor tensile strength. On the other hand, NMP and DMF hollow fiber membranes yields denser structure with better mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44366.