Tuning the properties of breathable polyurethanes through chemical crosslinking

The present work aims at improving the properties of waterproof breathable polyurethane membranes by introducing chemical crosslinks. A series of cross linked polyurethanes were prepared by chain extension of prepolymer containing varying amounts of a triisocyanate-based crosslinker (0-15% wt/wt). Thin polyurethane films (similar to 40 mu m) 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 T-g. 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/m(2)/day to 678 +/- 32 g/m(2)/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/m(2)/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/m(2)/day and a hydrostatic pressure of >3 bar, which was suitable for practical applications.

Automated summary

The present work focused on improving the properties of waterproof breathable polyurethane membranes by introducing chemical crosslinks. The introduction of a crosslinker led to an increase in glass transition temperature and improved tensile and tear strengths. The optimal balance of waterproofness and breathability was achieved with a polyurethane membrane containing 10% crosslinker, which was subsequently coated on a cotton-polyester fabric to create a breathable textile suitable for practical applications.