Modification and Performance Enhancement of PVC Ultrafiltration Membrane by Grafting of Sulfonated Polystyrene

Hypothesis: In this study, modification of polyvinyl chloride ultrafiltration membrane was done and the modified membrane was used in the ultrafiltration process for oil-in-water separation. at first, PVC was dehydrochlorinated by sodium hydroxide. Then, the resulting dehydrochlorinated polyvinyl chloride (DHPVC) was grafted by styrene monomer and in the final step the grafted styrene was sulfonated by sulfuric acid. Ultrafiltration membranes were fabricated from PVC, DHPVC, styrene-grafted dehydrochlorinated polyvinyl chloride and sulfonated polymer by phase separation method and were evaluated, using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and pure water permeation flux, determination of mean pore size, porosity and water contact angle tests. The presence of grafted functional groups was confirmed by FTIR spectra. SEM images showed that all the membranes had fingerlike pores and the difference in shape of the pores was due to the thermodynamic instability and viscosity of the polymer solutions. Due to the higher hydrophilicity of the polymer, the sulfonated membrane showed significant increase in pore size and pure water flux, compared to other membranes. The DHPVC membrane showed the lowest contact angle because of the detachment of chlorine as a hydrophobic agent, but for the other membranes there was little difference in their contact angles which could be related to the surface roughness. Subsequently, the oil/water separation experiments were performed by the membranes. The modified membranes showed good performance in the separation of oil and water and had less fouling than the PVC membrane. The rejection of oil particles was 100% for all membranes except the sulfonated membrane. The rejection of oil particles by the sulfonated membrane decreased, because of the higher pore size and significant increase in the flux.