Study Of Shape Memory Behavior Of Polyurethane Responsive To Solvent Stimuli

Shape memory polyurethane (SMPU) have been widely studied recently fortheir excellent properties such as the wide range of shape-recovery temperature(from-30oC to70oC), high shape recoverability (maximum recoverable strain>400%) and good processing ability. Previous researches on SMPU were almostfocus on its recoverability on thermal condition. Recently, researchers found thatwater/moisture plays an important role in the recoverability of SMPU. But themechanism of this phenomenon is complex and still not clearly, so studys on themechanism is meaningful.This paper investigated the behavior of a kind of SMPU (MM3520) in fourdifferent solvents, the effects of temperature(before or after the glass transitiontemperature) on recoverability in solvents, the repeatability of the text and themechanism on solvent induced recoverability. On this basis, studys on the effects ofsalts in the recoverability of another SMPU (MM5520) have been done. The mainresearch contents were similar to solvent induced recoverability text. And wefocused on investigating the role of copper (II) chloride in solvent inducedrecoverability text thus obtaining the conclusion on this aspect.The text showed that before the glass transition temperature, recoverablebehavior relates to temperature and solvent, but when the temperature surpass theglass transition temperature, it is mainly influenced by solvent. Solvent determinesthe degree of recovery of MM3520. Repetition of text have few influence onmaterials. The FTIR (Fourier transform infrared spectroscopy) study indicates thepeak that represented hydrogen bonds between groups in polyurethane moves tolower frequency with the increase of immersion time. The hydrogen bonds betweensolvent molecules and tipical group in polyurethane have been formed. By the XRD(X-ray diffraction) experiments, effects of solvents on the condormation and latticeparameters have been found, and this results from the activity on hydrogen bonds.And then the role of hydrogen bonds have also been confirmed by the outcomes ofthermal analysis.When studying the behavior of salts in recovery text, we found that on the samecondition, SMPU added with copper (II) chloride performed better than the SMPUadded with sodium chloride. The function of salts is one-off event, after therecovery experiment, the surface of SMPU added with copper (II) chloride turned tored brown form black brown. By the observation of SEM, the processes of formationof surface in two different solvent were recorded. In water, oxidation was homogeneous, but in ethanol, this process happened in sequence. Though these twowith difference process, the ultimate surface topography were the same. The FTIRresults show the addition of copper (II) chloride reinforces the hydrogen bondsbetween solvent and polyurethane. The XRD results shows the mixtion of the tworaw materials results in the changing of lattice constant of copper (II) chloride, andafter immersed in solvents, some peaks vanish, that’s because copper (II) chlorideare dissolved by solvent. Then thermal analysis were used to analyze the glasstransition temperature and thermostability, the results are in accordance with theeffects of hydrogen bond in theory.