Effect of crystal melting on water vapor permeability of shape-memory polyurethane film

Crystal melting of shape memory polyurethane (SMPU) film is investigated using polarizing optical microscopy, scanning electron microscopy, differential scanning calorimetry, and temperature variable wide-angle x-ray diffractometry. Water vapor permeability (WVP) at different temperatures is measured. The results show that the SMPU film is dense with crystalline soft segments. Crystal melting of soft segments takes place when the temperature increases from 10 to 50degreesC. At the same temperature range, the WVP of SMPU film increases significantly. After investigating the relationship between the relative changes in amorphous area and temperature, we can conclude that crystal melting of soft segments leads to increases in the amorphous area, resulting in a significant increase in water vapor permeability.