Use of a temperature sensitive surface gel to reduce fouling

Numerous surface modification strategies have been developed to improve the fouling resistance of filtration membranes. A novel approach in which a temperature sensitive polymer gel is deposited on the surface is reported. The gel switches from an expanded, lower permeability, fouling-resistant hydrophilic state to a collapsed, higher permeability, fouling-prone hydrophobic state as the temperature is increased. By alternating between these two states, it is hypothesized that fouling can be reduced while minimizing the permeability reduction due to the surface modification. The hypothesis was tested by depositing a hydroxypropyl cellulose (HPC) gel on the surface of the cellulose acetate ultrafiltration membranes (Osmonics SN32) using divinyl sulfone (DVS) as a crosslinker. Unmodified and modified membranes were used to filter yeast and the HPC suspensions. To induce the hydrophobic-hydrophilic transition, the feed was switched alternately between room temperature and 60°C solutions. The experimental results support the hypothesis. Unmodified membranes fouled severely when operated at room temperature, 60°C, or oscillating between the two temperatures. The modified membranes fouled severely at 60°C but little fouling occurred at room temperature or with temperature oscillation. The results suggest that permanent surface modification is not required to reduce the fouling rates. Transient fluctuations in the surface chemistry and the structure are equally effective. Moreover, one can achieve higher filtration rates in transient operation because pores possess a larger effective diameter/higher permeability in the collapsed state than the expanded state.