Development of plasma and/or chemically induced graft co-polymerized electrospun poly(vinylidene fluoride) membranes for solute separation

Abstract

Nanofiber membranes were fabricated by electrospinning poly(vinylidene fluoride). The electrospun nanofiber membranes were further modified by grafting of acrylic acid (AA) and methacrylic acid (MAA) over the surfaces of the membranes. Plasma AA graft was attempted only, and the results indicated the partial membrane pore filling with grafted AA. For MAA grafting, chemically induced polymerization using benzoyl peroxide and hydrogen peroxide was attempted. The combination of plasma and chemically induced MAA graft polymerization was also attempted. The membranes were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and static contact angle (SCA) measurement. SEM surface analysis indicated partial pore narrowing of grafted membranes. The average pore size was reduced from 0.97μm for the untreated membrane to 0.15μm for the two step plasma and chemically induced grafted membranes. XPS analysis confirmed that grafting has taken place on the top surface of the membranes. The surfaces of the grafted membrane were significantly hydrophilic as observed by SCA. It was also found that the combination of plasma and chemically induced grafting using hydrogen peroxide was the most effective in terms of flux and selectivity. The grafting reduced the pore size by filling the pores of the original membranes by the graft polymers. This practice resulted in producing tight micro-filtration (MF) membranes from loose MF ones. An impressive high water flux of 150kg/hm2 at an operating pressure of 4 psig, and a 79% removal of polyethylene oxide (molecular weight 400kilo-Daltons) were achieved.