Water vapor permeability of cotton fabrics coated with shape memory polyurethane

In this paper, we have investigated the water vapor permeability of shape memory polyurethane (SMPU) coated cotton fabrics. The SMPUs were tailor made in order to obtain the phase transition temperature (soft segment crystal melting temperature) in the room temperature range. SEM studies were carried out in order to investigate the surface structure of coated and uncoated fabrics. The temperature sensitive water vapor permeability at soft segment crystal melting point was observed for SMPU coated fabrics. When the experimental temperature reached the soft segment crystal temperature of SMPU, an abrupt change of water vapor permeability of SMPU coated fabrics were observed. The significant change of water vapor permeability of SMPU coated fabrics is due to the phase change of SMPU which causes density changes inside the membranes due to micro-Brownian motion of soft segment, therefore, enhanced the water vapor permeability through the coated fabrics. The water vapor permeability of coated fabrics was also dependent on the primary structure of SMPU. When polycaprolactone glycol (PCL, Mn3000 g mol-1) was introduced in the polytetramethylene glycol (PTMG, Mn2900 g mol-1) based SMPU, the water vapor permeability decreases due to the increased interaction between the polymer chains due to presence of ester groups. In contrast increase of polyethylene glycol (Mn3400 g mol-1) in the SMPU backbone, the WVP increases due to the increasing hydrophilicity of the SMPU.