Tuning the properties of breathable polyurethanes through chemical crosslinking

Abstract

AbstractThe present work aims at improving the properties of waterproof breathable polyurethane membranes by introducing chemical crosslinks. A series of crosslinked polyurethanes were prepared by chain extension of prepolymer containing varying amounts of a triisocyanate‐based crosslinker (0–15% wt/wt). Thin polyurethane films (~40 μm) were prepared by a solution casting technique and the effect of introducing the crosslinker on thermal, mechanical characteristics was established. Crosslinking led to an increase in glass transition temperature. All crosslinked polyurethanes exhibited a sub‐ambient Tg. Both tensile and tear strengths were found to improve with crosslinking. Crosslinking (15% wt/wt) led to an increase in waterproofness from 112 ± 11 mbar to 574 ± 23 mbar, while the breathability reduced from 1246 ± 52 g/m2/day to 678 ± 32 g/m2/day. Polyurethane membranes containing 10% crosslinker exhibited an optimal balance of waterproofness and breathability, where the film was found to possess a water vapor transmission rate (WVTR) of 834 ± 37 g/m2/day with a hydrostatic pressure of 490 ± 18 mbar. This was subsequently coated on a cotton–polyester fabric to fabricate a breathable textile which was found to exhibit a WVTR of 663 ± 18 g/m2/day and a hydrostatic pressure of >3 bar, which was suitable for practical applications.