Crystallization Of PCL/PLA Blends And Its Effect On Microcellular Foaming Process

Polymer foams have great potential in tissue engineering,heat insulation and adsorption.The foaming properties of polymer materials are closely related to the matrix and crystal structure.Poly?lactic acid??PLA?and poly?caprolactone??PCL?are biodegradable materials,which are environmentally friendly and have become a research hotspot.By blending PCL and PLA,the crystallinity,melt strength and foaming properties of the blends were improved.Therefore,based on the isothermal crystallization and non-isothermal crystallization process,the influence of PCL on the crystallization of PLA and PLA on the crystallization of PCL were analyzed by differential scanning calorimetry and polarizing microscope.Furthermore,by using supercritical carbon dioxide micro-foaming technology,the influence of PLA crystal morphology and crystallinity on the microcellular morphology of PLA and PCL/PLA blends was analyzed,and the influence of PCL crystal on the microcellular morphology of PCL and PCL/PLA blends was analyzed.The main work and conclusions of this paper were as follows:1.Crystallization behavior of PCL/PLA blends.The blends of PCL and PLA were selected.With different isothermal temperature and cooling rate,the crystal morphology observed by polarizing microscope.The crystallinity was measured and the crystallization kinetics was calculated by differential scanning calorimetry.The effects of PCL on the morphology,crystallinity,nucleation and growth of PLA were analyzed.The effect of PLA on the crystallization behavior of PCL was analyzed by using the change of crystal morphology and crystallinity of PCL at different crystallization temperature.The results showed that:Compared with PLA,the effect of PCL on the crystallization of PLA was studied.In the isothermal crystallization process,the crystallization morphology and crystallinity of PLA were greatly affected by crystallization temperature.The PCL could promote the crystallization of PCL/PLA blends,improve the nucleation efficiency and the crystallinity,and reduce the crystal diameter.In the process of non-isothermal crystallization,the crystal of PLA sample was more perfect,and the crystal diameter was increased.In the PCL/PLA blends,PCL could promote the crystallization of PCL/PLA blends,increase the crystal number and the crystallinity,and reduce the crystal diameter.In the analysis of the effect of PLA on PCL crystallization,the effect of PLA on the crystallization process of PCL was studied by comparing PLA with the PCL sample.PLA could improve the crystallization temperature of PCL/PLA blends,increase the exothermic rate,the crystallization rate and relative crystallinity.When the proportion of PLA was higher,the effect of increasing the crystal diameter and reducing the crystal number were more obvious.With the proportion of PLA increasing,the crystallization of PCL/PLA blends was increased.2.The effect of PLA crystallization on Microcellular Foaming of PCL/PLA blends at low temperature.The effect of crystal morphology and crystallinity on the microcellular foaming of PLA and PCL/PLA blends was analyzed by using supercritical CO₂ microcellular foaming process.The results showed that:the crystal morphology produced during sample pretreatment could not only affect the distribution,diffusion and nucleation of Sc CO₂,but also improve the melt strength and viscoelasticity of the polymer.It is found that in PCL/PLA blends,the different of material ratio affected both the melt strength and the interface of heterogeneous polymer,which affected the nucleation and growth of the cell,making the cell structure of PCL/PLA?20/80?and PCL/PLA?30/70?samples more complete.In the PCL/PLA?40/60?blend,the island effect was formed because of the higher proportion of PCL phase,which made the micro-foaming morphology incomplete.3.The effect of PCL crystallization on Microcellular Foaming of PCL/PLA blends at low temperature.The effect of crystallization on the micro-foaming of PLA and PCL/PLA blends was analyzed by using supercritical CO₂ micro foaming process.The results showed that:Compared with PCL,PCL/PLA?80/20?and PCL/PLA?70/30?samples,the morphology of the crystallized samples was more uniform,and the open structure was easy to appear at the bottom of the bubbles.The higher melt strength of the crystallized sample could make the cell structure complete and improve the cell morphology.The results showed that PCL sample has smaller modulus,larger cell size and easier cell collapse.The addition of PLA phase as heterogeneous nucleation can improve the cell density,and the higher modulus in PCL/PLA blends could reduce the cell size.