Effect Of Foaming Process And Crystallization On Microcellular Foaming Behavior Of Pcl/pla Blends

As an important part of tissue engineering technology,the materials of tissue engineering scaffolds should be biocompatible and biodegradable,and their morphology and structure should meet the requirements of high cell density,small cell size and high porosity connectivity.The preparation of microporous materials is the key technology of tissue engineering scaffolds.Polylactic acid(PLA)and polycaprolactone(PCL),as biomaterials approved by FDA in the United States,have renewable plant origin,Biodegradability and biocompatibility.PLA is suitable for tissue with high modulus.PCL is suitable for tissue with lower modulus.Different performance requirements of tissue engineering scaffold materials can be satisfied by different mixture ratio of PCL/PLA blends.The batch micro-foaming technology with supercritical fluid has been widely concerned in the preparation of tissue engineering scaffolds because of the green environment.The PCL/PLA blends was investigated systematically,and the influence of foaming process,mixture ratio and PLA crystallization on the foaming behavior of PCL/PLA blends was analyzed.The influence laws of foaming process,ratio and crystallization on the foaming behavior was obtained,and it was of great significance for controling the foaming process to obtain the ideal morphology and properties of the PCL/PLA blends.The main work and conclusions are as follows:1.Effect of foaming process and ratio on foaming behavior of PCL/PLA blends.PLA and PCL biomaterials were blended to obtain different proportions PCL/PLA(70/30,80/20,30/70,20/80)blend systems.The process range of foaming temperature was determined by DSC.Based on the batch microcellular foaming technology,the effects of saturation pressure,foaming temperature,saturation time and material ratio on the cell morphology(cell size,cell density and porosity)of microcellular foamed materials were analyzed by a single factor experimental method.The results showed that with the increase of saturation pressure,the diameter of cell becomes smaller and the cell density of microfoamed material increases.With the increase of foaming temperature,the cell diameter of the microcellular foamed materials becomes larger and the density of the cell decreases.With the increase of the saturation time,the size of the cell increases and the density of the cell is reduced.When the saturation time is too long,the solubility of gas in polymer reaches the maximum and the change of cell morphology tends to be stable.2.Investigation of crystalline morphology of PLA and PCL/PLA blends.The crystallization of PLA,PLC and their blends was studied systematically by isothermal cold crystallization and isothermal melting crystallization at different crystallization temperatures.The results showed that isothermal cold crystallization and melting crystallization between Tg and Tm both occurred for PLA.At the same temperature,the growth rate of spherulites of melt crystallization is faster than that of isothermal cold crystallization,and the spherulite morphology is better,but no crystallization occurred during isothermal crystallization of PCL.Melting Crystallization of PLA/PCL blends pccured between T_g and T_m of PLA.The nucleation of PLA spherulites can be promoted when the PCL was added.With the increase of temperature,the nucleation rate decreased,the growth rate of spherulites increased,which resulted in the size of spherulites increased and the number of spherulites decreased.3.The effect of crystallization on the foaming behavior of PLA.Uncrystallized PLA samples and isothermal crystallization PLA samples were selected for batch microcellular foaming,and the effect of crystallization morphology on cell morphology was analyzed.The results indicated that cold crystallization occurred in the microcellular foaming process of uncrystallized PLA samples.The spherulites were also found in the microcellular foamed materials of isothermal crystallization PLA samples,and the microcellular structure appeared both in the spherulites and the amorphous region between the spherulites.Under the same foaming process,cell diameter in the microcellular fomed materials of PLA crystallized samples was smaller in than that of the uncrystallized PLA samples.