Modification Of Poly(Lactic Acid) On Heat Resistance And Toughening

As a biodegradable polymer derived from biomass resources, poly（L-lactide） has gainedenormous attention, owing to its good biocompatibility, processability and reasonablemechanical properties. However, it should be noted that its poor thermal resistance andbrittleness greatly limit its application in the more demanding fields. Based on maintainingbiodegradability, blend modification of PLLA was adopted to improve its heat-resistant andtoughness, respectively, thus expanding the application. The main researchcontents and conclusions were as follows:(1) PLLA blends with different crystal structures were prepared by adding various nucleatorsand controlling the processing conditions. The aim is to improve the poor heat resistant of PLLA.The effects of different nucleators on the crystallization behavior and heat-resistance of PLLAwere studied systematically by differential scanning salorimetry(DSC), X-ray diffraction(XRD),heat deflection temperature tester（HDT）and dynamic mechanical analysis(DMA). It was foundthat poly(D-lactide)(PDLA)、 talcum powder(Talc)、 a multiamide compound (TMC-328,abbreviated as TMC in this article) can significantly improve the crystallization rate andcrystallinity of PLLA, thus improving thermal-resistant property. The heat deflectiontemperature of nucleated PLLA prepared at the mold temperature of120℃was up to130℃andthe mechanical properties increased simultaneously. Comparing to other nucleating agents, TMCwas much more effective at enhancing the crystallization rate and the blends containing TMCshowed the best heat resistance.(2) PLLA/poly (ethylene oxide)(PEO) blends were also prepared by melt processing. Theeffects of PEO with different molecular weight on microstructure and mechanical properties ofPLLA were systematically studied with the combination of DSC、XRD、scanning electron microscope(SEM) and universal testing machine. The results suggested that the compatibility oflow molecular weight PEO with PLLA was better than that of high molecular weight PEO at thesame composition, and PEO with low molecular weight could more significantly enhance thecrystallization rate of PLLA. Furthermore, PEO had a remarkable effect on the breakingelongation and impact strength of PLLA, which however depended very much on the molecularweight of PEO. The toughening effect of PEO with high molecular weight on PLLA wasobvious with the content of10wt%, while the tensile strength of blends slightly decreased.When the molecular weight of PEO reached2000kDa, the breaking elongation and impactstrength of the blends increased with increasing PEO content and the toughening effect was bestfor the bend containing30wt%PEO.