Water-vapor-permeable polyurethane for leather finishing

Water vapor permeability of leather is strongly depended on finishing materials - polyurethane and acrylic resin. On the basis, in this paper, a novel polyurethane (PU) film with high water vapor permeability (WVP) was achieved through chemical modification of PU. In the chemical modification, the effects of different types of chain extenders, the content of ethylene glycol (EG), the molecular weight (Mw) of poly ethylene glycol (PEG) as well as the content of PEG with molecular weight 300 g/mol (termed PEG300) on WVP and mechanical properties of PU films were investigated. The results indicated that for different chain extenders, such as 1, 4-Butane glycol (BDO), dimethylolpropionic acid (DMPA) and EG, the EG-based PU shows the highest WVP. The increase of EG content has positive effect on tensile strength and water. resistance but has negative effect on WVP and broken elongation. In the PEG series, when the PEG300, PEG400 and PEG600 were used as hydrophilic segments, relatively high Mw of PEG will decrease the WVP and water swelling degree of PU film. When PEG300 was selected as hydrophilic segment and EG as chain extender, higher contents of PEG300 are beneficial for tensile strength and broken elongation, but has little effect on WVP. TPU prepared from PEG300 as hydrophilic segments and EG as chain extenders, shows a WVP of 2680.5 g/m(2) (.) 24h, in contrast to widely used industrial product PU resin-7020 (the WVP is 1430.3g/m(2 .) 24h), the improvement of WVP reaches 87.4%. This Water-Vapor-Permeable Polyurethane shows a wide application in waterproof and breathable leather/PU leather-making.