High Moisture Permeability Polyurethane for Textile Applications

A polyurethane having both a high permeable property at warm temperatures, and a thermal insulate property at cold temperature was developed with significantly different levels of permeability within a narrow temperature range. The development was made in view of achieving a breathable, waterproof sportswear material that would react to variations in temperature and ultimately provide a higher level of comfort. This polyurethane was prepared by a solution polymerization process in N,N-dimethyl formamide (DMF). Having a Tg (glass transition temperature) set at room temperature the polyurethane has high permeability above the Tg and during the rubbery state, and has low permeability below the T8 and during the glassy state. In this study, properties of the polyurethane in terms of permeability, Tg, tensile strength and tensile modulus were examined. The hard segment contents, degrees of ethylene oxide (EO) concentration, types of polyols and their molecular weights, all key elements in determining the chemical structures, were chosen as the parameters. Permeability was found to increase with an increased concentration of EO. Tensile strength and tensile modulus were influenced by hard segment contents, and the type of polyols and their molecular weights. The Tg depended on the molecular weight of the polyols and hard segment contents. Finally, from the viewpoint of morphology, it was determined that the mechanism of the moisture permeability was different above and below the Tg, and the moisture permeability was also different above and below the Tg.