Preparation of a novel thermo responsive PSF membrane, with cross linked PVCL-co-PSF copolymer for protein separation and easy cleaning

Abstract

An amphiphilic thermo responsive cross linked polyvinylcaprolactam-co-polysulfone (PVCL-co-PSF) copolymer was synthesized via solution polymerization of vinylcaprolactam (VCL) in PSF solution by use of three different initial ratios of PSF to VCL monomer. After the synthesis of the copolymer, the required amount of PSF was dissolved in PVCL-co-PSF copolymer solution. The presence of copolymer in the blended membrane was confirmed by Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Blended membranes showed enhanced pure water flux, hydrophilicity and evident thermo sensitivity. The hydration capacity for the modified membrane decreased from 279 to 161 mg cm⁻³ when the temperature changed from 25 to 40 °C. The hydration capacity of the modified PSF membrane compared to the plain PSF membrane increased from 127 to 279 mg cm⁻³, and the adsorbed protein amount decreased from 0.14 mg cm⁻² to 0.03 mg cm⁻² at 25 °C. The reversible volume phase transition of PVCL around the lower critical solution temperature (LCST) was used as an environmentally-friendly approach for membrane cleaning. A temperature change water elution hydraulic cleaning for the modified membranes around the LCST of the PVCL-co-PSF copolymer brushes was proposed (as shown in Fig. 7). Following the alternating temperature-change (40 °C/25 °C) cleaning, flux recoveries of about 92.5% (in the case of BSA) and 95% (in the case of HA) were obtained for the modified PSF membrane (the flux recoveries of the plain membrane were only about 39% and 36% after BSA and HA ultrafiltration, respectively).