Smart temperature-controlled water vapor permeable polyurethane film

Aim of this study was to develop a temperature-controlled polyurethane (PU) film for the application in film coated clothes. The PU film should be a smart one that can control its water vapor permeability (WVP) through temperature change. The study was carried out by increasing the water vapor permeability of various breathable/waterproof PU films through variations of their hard-to-soft-segment ratio, PEG content, and isocyanate index; the thermal properties and morphologies were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). It was found that the WVP of the PU film (MDI/PEG/PBA/1,4-BD = 3:0.6:0.4:2) can control its WVP by temperature change by itself. The WVP of the PU film started to rise obviously at 18 °C which is near the material's glass transition temperature (23.88 °C). The result also showed that the PEG content affected the WVP dramatically; higher water permeabilities occurred at higher percentages of PEG in the main chain, but with concomitant decreases in the mechanical strengths. The most permeable PU film had a WVP of 6745 g/m2/day, a tensile strength of 29.38 MPa, and a tear strength of 112 kg/cm.