Temperature-sensitive polypropylene membranes prepared by plasma polymerization

Poly-N-isopropylacylamide (PNIPAAm) was grafted on polypropylene (PP) microfiltration membranes using plasma polymerization. The surface of the grafted membrane was evaluated by Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy pictures demonstrated that the PNIPAAm can be grafted either on the surface or in the pores of the membrane. The morphology of the grafted membrane can be adjusted through monomer concentration and polymerization time. Surface properties with a reversible response to temperature change were observed by measuring the dynamic contact angle. Below the low critical soluble temperature (LCST) of PNIPAAm, the grafted PP membrane exhibited a hydrophilic surface (advancing contact angle<40°). Above the LCST, the surface changed to hydrophobic properties (advancing contact angle>90°). We investigated the on–off characteristics of the grafted membrane by measuring water flux through the grafted membrane at different temperatures. The water flux can be varied from 25 to 7500 kg/m2 h, depending on the temperature and pressure drop. The swelling PNIPAAm chains block the pores of the microfiltration membrane, and the flux decreases (off status). The PNIPAAm chains shrink above the LCST and open the pores of the microfiltration membrane. Thus, the water flux increases (on status). The effect of pressure drop on the water flux of the grafted PP membrane was discussed. The rapid and remarkable changes in the pore size of the membrane may make it possible to use the grafted PP membranes as the carrier for a drug-delivery system. They would also be used as multifunctional separation membranes, control valves, and actuators.