Water vapor permeability of the polyurethane/TiO2 nanohybrid membrane with temperature sensitivity

A novel thermal‐sensitive polyurethane (TSPU)/TiO₂ nanohybrid membrane was successfully prepared via in situ process and used for controllable water vapor permeation. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) were employed to reveal the nanohybrid mechanism between TSPU and TiO₂ and the thermal sensitive characteristics of TSPU/TiO₂ nanohybrid membranes. FTIR analysis demonstrates that the highly active nano‐TiO₂ particles produced by the hydrolysis of the nanoprecursor (tetrabutyl titanate) have reacted with the active groups of TSPU. And some new peaks assigned to the Ti? O? C, Ti? C, and Ti? O? Ti bonds occur in the FTIR spectra of TSPU/TiO₂ nanohybrid membrane; these chemical bonds are believed to contribute to the higher mechanical properties of nanohybrid samples. DSC study indicates that nanohybridization does not disrupt the intrinsic phase‐separated structures and thermal‐sensitive characteristics of pure TSPU, the difference in behavior is the phase transition temperature (defined as switch temperature, T_s) of the reversible phase shifting from 50.1 to 53.4°C. SEM analysis shows that the nano‐TiO₂ particles are evenly distributed in TSPU and the size of the nano‐TiO₂ is lower than 100 nm. In addition, the water vapor permeability (WVP) of nanohybrid membrane is found to depend on the TiO₂ content. To be specified, when TiO₂ content is lower than 5.0 wt %, the nanohybrid samples show lower WVP at low temperatures and higher WVP at high temperatures than pure TSPU. Especially, when the temperature exceeds the T_s, for example from 50 to 60°C, the WVP of pure TSPU show improvement by 114%, whereas the WVP of the nanohybrid TSPU with 5.0 wt % TiO₂ content shows improvement by 145%, the latter shows more sensitivity to thermal stimuli. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008