| Shape memory polymer(SMP)is a kind of intelligent material which can respond automatically to environmental changes,while polylactic acid(PLA)matrix shape memory polymer is a kind of SMP with excellent mechanical properties,biocompatibility and biodegradability,received widespread attention of scientific research personnel,however,its brittleness and high glass transition temperature affect seriously its performance of shape memory,limiting its application in biomedical field.In this dissertation,in order to improve the toughness of PLA matrix SMP,lower its glass transition temperature and improve its performance of shape memory,PLA/TPU blend was prepared with blending different proportions of polylactic acid(PLA)and thermoplastic polyurethane(TPU),and PLA/TPU/TBC blend was prepared by means of blending different proportions of polylactic acid(PLA),thermoplastic polyurethane(TPU)and citric acid butyl ester(TBC),by means of melt-mixing method,improving the PLA's shape memory properties;Marc software was uses to simulate the shape memory of PLA matrix SMP before and after modified,and the mechanical behavior changes in the process of shape memory were compared and analyzed.In the study of toughening modification of PLA/TPU matrix shape memory polymer,when PLA/TPU blends are deformed under external forces,TPU elastomer particles can initiate crazes and stop its development in time,producing plenty of fine crazes inside the blend,while both the generation and blocking of the crazes consume a large amount of energy,thus improving the toughness of PLA.After adding 30%TPU,the elongation at break of PLA increased to 73.31%,and the impact strength increased to 20.34kJ/m~2,6.29 times and 3.94times higher than that of pure PLA.The toughening of TBC further improved the toughness of PLA/TPU blends for the reason that,after adding 10%TBC to the blends with PLA/TPU=70:30,the elongation at break and impact strength of the blends increased to224.78%and 38.05kJ/m~2,which were 24.19 times and 8.24 times higher than those with pure PLA.In the study of shape memory triggering temperature modification of poly(lactic acid)matrix shape memory polymer,PLA matrix SMP is a thermotropic shape memory polymer,and its shape memory recovering temperature is closely related to the glass transition temperature of the material.Due to the poor compatibility between TPU and PLA,the interface force between them is small,resulting in a less effect of TPU on the thermal properties of PLA.After adding 30%TPU,the glass transition temperature of PLA only decreased from 61.03?to 59.15?,however,after adding TBC to PLA/TPU blends,the glass transition temperature of PLA decreased significantly due to the good compatibility between TBC and PLA.The toughening of TBC decreases the mutual interaction of PLA molecular chains and lowers the barrier of thermal motion of PLA molecular chains,thus enabling PLA to change from a glassy state to a high-elastic state at a lower temperature.After adding 15%TBC in U10,the glass transition temperature of PLA was reduced to 32.08?,which was lower than the human body temperature of 37?.In other words,the shape recovery of PLA matrix SMP could be performed near the human body temperature,which was conducive to extend the application of PLA in the biomedical field.In the study of shape memory performance modification of PLA matrix shape memory polymer,the shape memory performance of pure PLA is poor due to its brittleness.Although the shape fixation rate of PLA is up to 98.31%,its shape recovery rate is extremely low,only55.64%.The shape memory performance of PLA is improved by means of melt blending modification.X-ray diffraction analysis showed that the crystallinity of PLA/TPU blends increased with the increase of TPU,and the crystallinity of PLA increased from 17.04%to25.01%after adding 30%TPU.After adding TBC to PLA/TPU,the crystallinity of PLA decreased gradually.The change of crystallinity changes the ratio of crystallinity and amorphous type in PLA matrix SMP,which will have a great influence on the shape memory performance of SMP.Shape memory experiment results show that through blending modification,PLA/TPU blend and PLA/TPU/TBC blend have a good bending shape memory properties,while its shape fixed rate is over 90%and the shape recovery rate is over 80%.The change trend of shape fixed rate and shape recovery rate of SMP with different proportion of PLA matrix is opposite,by contrast,the change trend of shape recovery rate is similar to the change trend of crystallinity,demonstrating the influence to shape memory performance of crystallinity and amorphous type.Based on viscoelastic theory,PLA matrix SMP before and after modified was applied to finite element simulation using the Marc software,obtained the reasonable three-dimensional relationship curve of stress-strain-temperature,comparing the relationship of stress-strain-temperature of PLA matrix SMP before and after modified in the process of shape memory,analyzing the relationship between stress-strain changing curve of different stages,stress-temperature changing curve of fixed cooling stage and strain-temperature changing curve of rising recovery stage,to investigate the effect of modification and improvement of PLA shape memory performance. |
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