Polydimethylsiloxane vi -poly(vinylidene fluoride) (PDMS vi -PVDF) composite membranes were prepared using asymmetric PVDF hollow-fiber membranes as the substrate where a very thin layer of silicone-based coating material was deposited via a developed dip coating method. The preparation of the composite membranes under various conditions were investigated. In the optimal coating procedure, homogenous and stable oligo-PDMS vi coating layers as thin as 1-2 m were successfully deposited on the surface of PVDF membranes. The developed PDMSvi -PVDF composite membranes were applied for separation of a wide variety of volatile organic compounds (benzene, chloroform, acetone, ethyl acetate, and toluene). The results showed that the PDMS vi -PVDF hollow-fiber composite membranes that had been developed exhibited very high removal efficiency (Ͼ96%) for all the VOCs examined under favorable operating conditions.

ABSTRACT:The sorption equilibria and kinetics of three volatile organic compounds (VOCs)-benzene, chloroform, and acetone-in a newly developed divinyl-terminated poly(dimethylsiloxane) (PDMS vi )-oligo polymer were studied. The PDMS vi -oligo polymer was prepared from a hexane solution consisting of PDMS vi as the polymer, oligosilylstyrene as the crosslinker, and a platinum-divinyltetramethyldisiloxane complex as the Karstedt catalyst. The sorption uptake of each VOC by the polymer was measured gravimetrically at different VOC partial pressures at a constant temperature and at different temperatures between 24 and 50°C. The rate of VOC sorption was monitored until equilibrium was established. The solubility coefficient increased when the VOC activity increased, and the results revealed that the PDMS vi -oligo polymer was a good sorbent for the three VOCs examined. Relatively high solubilities of these VOCs were obtained in this polymer in comparison with those reported for conventional silicone rubbers. The Flory-Huggins model fit the observed equilibrium sorption isotherms of the benzene and chloroform systems very well, whereas the Koningsveld-Kleinjtens variation law had to be combined with the Flory-Huggins model to describe the sorption isotherm of acetone in the polymer film. The rates of sorption of the three VOCs in the polymer samples were generally rapid and controlled by Fickian diffusion. The diffusivities of benzene, chloroform, and acetone at 24°C, determined with the diffusion equation, were approximately 10 Ϫ6 cm/s. The sorption and diffusion data revealed that the newly developed PDMS vi -oligo polymer was an excellent sorbent for the three VOCs examined.