Controllable modification of polymer membranes by long-distance and dynamic low-temperature plasma flow: Treatment of PE hollow fiber membranes in a module scale

A novel long-distance and dynamic low-temperature plasma (LDDLTP) setup was proposed for efficient modification of PE hollow fiber membranes in a module scale. The Ar plasma conditions (outside-in) were optimized by contact angle measurements. Contact angle variations along with fiber axial distance from the plasma inlet revealed that there was an effective treatment distance. Within this distance, almost all contact angles for outside membrane surfaces were close to 60°, far less than that of virgin membranes (about 120°). A RF power of 60W, a pressure of 20±2Pa and an exposure time of 120s were suitable for a selected LDDLTP flow of 0.4mLmin^-1. Under these conditions, the effective distance reached about 20cm after plasma treatment from double inlets for module 2 and no physical damage was observed. Moreover, this effective distance can be upgraded to about 42cm through increasing plasma inlet diameters (module 3). The changes in surface hydrophilicity were mainly due to implantation of a large amount of polar groups onto outside membrane surfaces. And the plasma-treated membranes not only reduced protein fouling and increased water flux, but also exhibited a good hydrophilic stability.