A Study On The Crystallization Of Star-shaped Copolymer PLLA-ESO

Star-shaped copolymer PLLA-ESO and g-SiO2were prepared by ring-openingpolymerization and solution ring-opening polymerization. PLLA/nucleation agents (g-SiO2,Talc, TMC) composites were prepared by melt-blending. The effect of nucleation agents onthe isothermal crystallization kinetics, crystal morphology, thermal properties, mechanicalproperties, and heat resistance of PLLA-ESO and its composites were studied.The effect of nucleation agent on the isothermal crystallization kinetics of PLLA-ESOand its composites were investigated by differential scanning calorimetry (DSC) and theoptical polarimetry tester. It was found that PLLA-ESO and its composites showed amaximum crystallization rate at120°C. The Avrami exponent n value of all samples is inthe range of2.32to4.67. With increasing of the content of nucleation agents the k valuesof all samples decrease, whereas, the crystallization half-time values (t1/2) reduce. Theresults also indicated that TMC was an effective nucleating agent for PLLA-ESO. Theoverall crystallization rate and crystallinity of PLLA-ESO/TMC were higher than that ofPLLA-ESO/Talc and PLLA-ESO/g-SiO2.The crystal morphology of composites with theaddition of nucleation agents were investigated by polarized optical microscopy (POM). Itwas shown that the nucleus density increased significantly, the decrease in crystal size withaddition of nucleation agents. PLLA-ESO/g-SiO2and PLLA-ESO/Talc growed in sphericalform, however PLLA-ESO/TMC growed in needle crystal form.The effects of nucleation agent on the crystallization, thermal properties, mechanicalproperties, and heat resistance properties of PLLA-ESO and its composites were studied byDSC, X-ray diffraction (XRD), electron tensile tester and heat deflection temperature tester.The results indicated that the intense peak and the degree of crystallization of PLLA-ESObecame increase with the addition of nucleation agent. The cold crystallizationtemperatures (Tc c) of these composites were lower than that of neat PLLA-ESO. Moreover,the melting temperatures (Tm) and the glass transition temperature (Tg) of these compositesare almost as the same as that of neat PLLA-ESO. Compared with PLLA-ESO/TMC andPLLA-ESO/g-SiO2, PLLA-ESO/Talc exhibited good mechanical property. The largestvalue is achieved by PLLA-ESO/Talc with1wt%of Talc with an increase in tensilestrength of3.1%and in elongation of about294%. The tensile strength and elongation ofPLLA-ESO/g-SiO2nanocomposites possess maximum values at2wt%g-SiO2content. The tensile strength of PLLA-ESO/TMC composites possess maximum values at2wt%TMC content, meanwhile the elongation achieves the lower value. The HDT values ofPLLA-ESO composites were increasing with increasing nucleation agent loading, especialthe composites with heat treatment. The HDT value of PLLA-ESO/Talc was about119.5°C at10wt%Talc content. The HDT value of PLLA-ESO/TMC was about103.7°C at10wt%TMC content. The HDT value of PLLA-ESO/g-SiO2was about127.2°C at10wt%g-SiO2content.