The alternate temperature-change cleaning behaviors of PNIPAAm grafted porous polyethylene membrane fouled by proteins

Based on the reversible volume phase transition of Poly(N-isopropylacrylamide) (PNIPAAm) around LCST, a simple temperature-change cleaning method for PNIPAAm grafted porous polyethylene membrane fouled by bovine serum albumin (BSA) was proposed. It was found that after the temperature-change cleaning program between 25 and 35 degrees C, the fouling BSA could be eluted out easily by water from the graft membrane surface, and a flux recovery of 97.6% relative to that of the graft membrane before fouling was reached. The hydrophilicity and the rapidly stretching of PNIPAAm chains are considered responsible for loosing and shaking off the adsorbed BSA on graft membrane surface. However, the streaming potential measurements indicated a secondary BSA fouling occurring on the hydrophobic substrate membrane surface that was freshly exposed by the stretching PNIPAAm chains. The secondary BSA fouling was cleaned effectively with a streaming potential recovery of 99.1% by an alkali solution of 0.1 wt.% KOH also under the assistance of temperature-change cleaning method, and it is assumed that a higher enough graft density of PNIPAAm on substrate membrane surface was necessary to prevent the secondary BSA fouling. In the end, the above fouling condition and cleaning effects on graft membrane surface were further verified by ATR FT-IR analyses.