Study On Crystallizayion And Degradation Behavior Of 4a-PCL-b-PDLA And 2a-PLLA Blend System

Polylactic acid is the most important environmentally friendly polymer material.Because of its excellent biocompatibility,biodegradability and processability,it has received extensive attention in the field of daily necessities and biomedicine.However,due to defects such as slow crystallization rate and high production cost of polylactic acid materials,its further application is limited.Blend modification is an economical and practical method for modifying polylactic acid,in which the design of the modifier is particularly important.In recent years,polylactic acid modifiers with a "soft segment-hard segment" core-shell structure has been the research hotspot in this field,but their related modification mechanisms have not been studied,especially the "hard segment"(PDLA)matrix shape.The effect of the formation of composite crystals on the aggregate structure of the blend is for further study.This thesis designed and synthesized multi-arm block copolymer modifiers with different PDLA block molecular weights:four-arm polycaprolactone-b-dextran polylactic acid(4a-PCL-b-PDLA),using PCL as the soft segment,using PDLA as the hard segment and then blending with 2a-PLLA.With the increase of molecular of PDLA,the influence of the process from scratch to existence of the stereocomplex formed by block copolymer and PLLA on the crystallization and degradation properties of PLLA was especially discussed.The main work contents are as follows:First,a two-step ring-opening polymerization method was used to synthesize the 4a-PCL-b-PDLA block copolymer.Under the premise of keeping the number of arms and the PCL molecular weight unchanged,the molecular weight change of the PDLA block was adjusted,and then 4a-PCL-b-PDLA was blended with 2a-PLLA.The crystallization behavior of the blend was systematically studied in the process of non-isothermal crystallization and isothermal crystallization.Finally,the crystallization treatment of the blend film was studied based on the crystallization behavior.The degradation behavior focuses on the effect of the formation of stereocomplex on the crystallization and degradation properties of the blends.