Abstract

A water-based thermally-responsive polyurethane (TRPU), based on the crystalline soft segment from the reaction of polycaprolactone diol (PCL) with isophorone diisocyanate (IPDI) and the crystalline hard segment from the reaction of IPDI -1,4-butanediol (BDO) together with dimethylolpropionic acid (DMPA), was synthesized and used in water vapour permeable leather finishing.

Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analyzer (DMTA), water swelling and water vapour permeability (WVP) were measured to evaluate how the structure of PU and the temperature influence the WVP of PU films and finished leathers.

In contrast to common polyurethane elastomer (PUE) with an amorphous reversible phase, the TRPU with a crystalline reversible phase shows a phase-separated structure and a phased transition temperature (Ttrans) at normal use temperature. The water swelling and water vapour permeability of both TRPU film and finished leather are found to depend on the inner structure of the polymers and the temperature. When the temperature exceeds the Ttrans, a significant increase of WVP from 4100g/m2/day to 10500g/m2/day was observed for finished leather in spite of some decrease of WVP compared with un-finished leather. Leather finished with common PUE appears to have a low WVP and only a slightly increased value over the temperature range.