The effect of moisture absorption on the glass transition temperature (T(g)) and stress/strain behavior of network polyurethane shape memory polymer (SMP) foams has been investigated. With our ultimate goal of engineering polyurethane SMP foams for use in blood contacting environments, we have investigated the effects of moisture exposure on the physical properties of polyurethane foams. To our best knowledge, this study is the first to investigate the effects of moisture absorption at varying humidity levels (non-immersion and immersion) on the physical properties of polyurethane SMP foams. The SMP foams were exposed to differing humidity levels for varying lengths of time, and they exhibited a maximum water uptake of 8.0% (by mass) after exposure to 100% relative humidity for 96 h. Differential scanning calorimetry results demonstrated that water absorption significantly decreased the T(g) of the foam, with a maximum water uptake shifting the T(g) from 67 °C to 5 °C. Samples that were immersed in water for 96 h and immediately subjected to tensile testing exhibited 100% increases in failure strains and 500% decreases in failure stresses; however, in all cases of time and humidity exposure, the plasticization effect was reversible upon placing moisture-saturated samples in 40% humidity environments for 24 h.

中文翻译：

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吸湿性对聚氨酯形状记忆聚合物泡沫物理性能的影响

已经研究了吸湿性对网络聚氨酯形状记忆聚合物 (SMP) 泡沫的玻璃化转变温度 (T(g)) 和应力/应变行为的影响。我们的最终目标是设计用于血液接触环境的聚氨酯 SMP 泡沫，我们研究了湿气暴露对聚氨酯泡沫物理特性的影响。据我们所知，这项研究首次研究了不同湿度水平（非浸泡和浸泡）下的吸湿性对聚氨酯 SMP 泡沫物理性能的影响。SMP 泡沫暴露在不同湿度水平下的时间长度不同，在暴露于 100% 相对湿度 96 小时后，它们的最大吸水率为 8.0%（按质量计）。差示扫描量热法结果表明吸水量显着降低了泡沫的 T(g)，最大吸水量将 T(g) 从 67 °C 转移到 5 °C。将样品浸入水中 96 小时并立即进行拉伸试验，其破坏应变增加 100%，破坏应力减少 500%；然而，在所有暴露时间和湿度的情况下，将饱和水分的样品置于 40% 湿度环境中 24 小时后，塑化效果是可逆的。