Nanofiltration membrane prepared from polyacrylonitrile ultrafiltration membrane by low-temperature plasma: 5. Grafting of styrene in vapor phase and its application

Low-temperature plasma techniques have widely been used to modify surface properties of polymer membranes. The NF membranes were prepared from PAN UF membrane by Ar low-temperature plasma treatment and subsequent grafting of the monomer styrene in vapor phase. FTIR-ATR spectroscopy, DSC analysis and contact angle measurement were used to characterize the chemical and physical changes of PAN membranes modified by plasma-induced graft polymerization in vapor phase. FTIR spectra and DSC analysis revealed that hydrophobic monomer, styrene, was successfully grafted onto PAN UF membrane surface. DSC analysis also indicated that the average pore size decreased and the pore size distribution was narrowed with increasing graft time. The contact angle measurement results showed that the hydrophobicity of the grafted membrane was significantly increased. The filtration performances including permeation flux (J) and rejection (R) were determined with a mixture containing dewaxed oil (M_w ≈ 450 g/mol) and dewaxing solvent (toluene and methyl ethyl ketone) in the range of temperature. For the feed composition of 83.94 wt.% dewaxed solvent, the solvent in permeate solution was 98.42 wt.%, and the rejection of lube oil was up to 90.2%, which implied that these PAN membranes may be potentially used to recover the dewaxing solvent from the dewaxed lube oil.