Synthesis of Teflon-FEP grafted membranes for use in water desalination

Grafting of vinyl monomers containing polar pendant groups such as -C=N of 4-VP and -C dropN of methacrylonitrile can impart desirable properties to t he Teflon-FEP. In the present work grafting of 4-vinyl pyridine (4-VP) and mythacrylonitrile (MAN) onto Teflon-FEP film has been carried out by preirr adiation method in aqueous medium. Optimum conditions for affording maximum percentage of grafting (Pg) have been evaluated. Maximum percentage of gra fting of 4-VP (16.35%) at a total dose of 51.62 KGy was obtained ata monome r concentration of 0.93 moles/L. For MAN maximum percentage of grafting (31 .70%) at a total dose of 49.90 KGy was obtained at a monomer concentration of 1.19 moles/L. Several grafting experiments were carried out in water-alc ohol medium to study the effect of alcohols on Pg of 4-VP and MAN. The foll owing order of different alcohols towards grafting of these monomers is obs erved. For 4-VP: Isopropanol > n-pentanol > ethanol > butanol > methanol. F or MAN: Isopropanol > ethanol > methanol > butanol > n-pentanol. In all bin ary water-alcohol systems percentage of grafting was found to decrease with increasing amount of alcohol as compared to that obtained in the aqueous m edium. The grafted Teflon-FEP films have been characterized by IR Spectrosc opy, scanning electron microscopy, swelling behaviour in different solvents , percentage area change following grafting and by permeability behaviour.