The effect of moisture absorption on the physical properties of polyurethane shape memorypolymer foams

Abstract

The effect of moisture absorption on the glass transition temperature (Tg) and the stress/strain behavior of network polyurethane shape memory polymer (SMP)foams has been investigated. With our ultimate goal of engineering polyurethane SMPfoams for use in blood-contacting environments, we have investigated the effects ofmoisture exposure on the physical properties of polyurethane foams. To the best of ourknowledge, this study is the first to investigate the effects of moisture absorption at varyinghumidity levels (non-immersion and immersion) on the physical properties ofpolyurethane SMP foams. The SMP foams were exposed to differing humidity levels forvarying lengths of time, and they exhibited a maximum water uptake of 8.0% (bymass) after exposure to 100% relative humidity for 96 h. Differential scanningcalorimetry results demonstrated that water absorption significantly decreased theTg of the foam, with a maximum water uptake shifting theTg from67 to 5 °C. Samples that were immersed in water for 96 h and immediately subjected to tensile testingexhibited 100% increases in failure strains and 500% decreases in failure stresses; however,in all cases of time and humidity exposure, the plasticization effect was reversibleupon placing moisture-saturated samples in 40% humidity environments for 24 h.