Effects of crystal structure of shape memory polyurethane film on water vapour permeability

The crystal structure of shape memory polyurethane film was investigated using POM, SEM, and DSC. The relative change of amorphous region at the different temperature was detected using WAXD. Water vapour permeability (WVP) at the same temperature range was also examined. The results obtained by POM and SEM SE1 and QBSD detectors show that the SMPU film is two-phase and non-porous. The water vapor permeable paths are the amorphous regions of the film. It is different from the two existing mechanisms of micro-porous and nonporous film. The crystal structure parameters of the SMPU film, such as the degree of the crystallinity, the size of the crystallites and the degree of phase separati on, would affect its water vapour permeability. It is the first time to use WAXD with adjustable temperatures to investigate the relationship between the relative change of amorphous region and water vapour permeability of the SMPU film. The result is that the increase of amorphous region gradually with the rising temperature is one reason to result in the increase in water vapor permeability accordingly.