| As a renewable as well as biodegradable thermoplastic polyester,Poly?lactic acid??PLA?is considered as the most promising substitute for those petroleum polymers due to its excellent physical properties and high cost performance.However,the poor heat resistance,stiffness and long modeling circle of PLA has badly limited the applications of PLA.Regulating PLA crystallization behavior is vital to control the degradation rate,heat resistance,optical properties,mechanical properties and barrier properties of PLA.Hence the investigations on controlling the crystallization of PLA has attracted lots of attention.In this present work,based on the investigation of miscibility and interaction between PLA and Li TFSI?lithium bis?trifluoromethanesulphonyl?imide?,crystallization behavior of PLA/Li TFSI blends was discussed,for which a novel mechanism that regulating the crystallization of PLA and its stereocomplex with the pre-ordering effect by Li TFSI was proposed.And then PLLA/PDLA/Li TFSI/CNT nanocomposites were prepared.The main content of this work will be introduced as follows:?1?The interaction and miscibility between PLA and Li TFSI.The investigation on the morphology and structure of PLLA/Li TFSI blends with Fourier transform infrared spectroscopy?FTIR?.scanning electron microscope?SEM?and small angle X-ray scattering?SAXS?revealed that there is strong interaction between PLA and Li TFSI and it originates from the hydrogen bond between SO2 and CF3 group of the anion TFSI-with CH3 and CH group of PLA molecules.Moreover,Li TFSI completely resolves in PLA when blended with PLA and there is no phase separation in PLA/Li TFSI blends when cooling down from melts.?2?Investigation on regulation of PLLA crystallization by Li TFSI.The crystallization behavior of PLLA/Li TFSI blends was investigated with differential scanning calorimeter?DSC?and polarized light microscope?PLM?.It was revealed that the crystallization of PLLA is enhanced by a minor content of Li TFSI.Especially with the optimum content of Li TFSI at 0.5%,the nucleation of PLLA crystallization is greatly enhanced.However,the increasing content of Li TFSI in PLLA/Li TFSI blends is followed by a weaker enhancement effect on PLLA crystallization.And the crystallization is even hindered in PLLA/Li TFSI blends when the content of Li TFSI is 10%.The results of In-situ FTIR analysis suggested that the enhancement on nucleation process of PLLA crystallization with a minor content of Li TFSI was achieved by a preordering effect on PLLA molecules in melt state.The population distribution of PLLA chain conformers in melt state is dependent on the content of Li TFSI,due to the strong interaction between Li TFSI and PLLA.And a minor content of Li TFSI induces a higher population of gt conformer?103 helix?of PLLA molecules in melt state,which reduces the nucleation barrier of PLLA crystallization,therefore the nucleation of PLLA crystallization was significantly enhanced.While a high content of Li TFSI induces a much lower population of gt conformer of PLLA melt,which consequently impedes the crystallization of PLLA.?3?Investigation on the regulation of the crystallization of PLLA/PDLA stereocomplex by Li TFSI.The results of DSC analysis for PLLA/PDLA/Li TFSI blends revealed that the crystallization behavior of PLLA/PDLA stereocomplex is depended on different contents of Li TFSI in PLLA/PDLA/Li TFSI blends.With the Li TFSI content of 0.5%,crystallization of homogeneous crystals in racemic PLLA/PDLA blends is enhanced due to the synergistic effect on accelerating the formation of?-form crystals by both minor content of PLA stereocomplex and Li TFSI in Li TFSI in PLLA/PDLA/Li TFSI blend.And the increasing content of Li TFSI in Li TFSI in PLLA/PDLA/Li TFSI blends is followed by a higher crystallinity of PLA stereocomplex.Until the content of Li TFSI is added up to 10%,there is exclusive formation of PLA stereocomplex,without homogeneous crystals in Li TFSI in PLLA/PDLA/Li TFSI blend.According to the further investigation by In-situ FTIR,the high content of Li TFSI in Li TFSI in PLLA/PDLA/Li TFSI blends induced a pre-ordered structure in melt,which helps to avoid the conformation regulation process before the formation of PLA stereocomplex.Thus the induction period of the formation of PLA stereocomplex is much shortened with a high Li TFSI content in Li TFSI in PLLA/PDLA/Li TFSI blends.?4?Investigation on the structure and properties of PLLA/PDLA/Li TFSI/CNT nanocomposites.PLLA/PDLA/Li TFSI/CNT nanocomposites were prepared by melting blending,and the structure and properties of nanocomposites were investigated.It was revealed that CNT is well dispersed in PLLA/PDLA/Li TFSI/CNT blends with the help of Li TFSI Furthermore,the investigation on the crystallization of composites revealed that Li TFSI and CNT synergistically enhance the crystallization of PLA stereocomplex in PLLA/PDLA/Li TFSI/CNT composites.And the results of electrical conductivity test suggested a lower percolation threshold and a better conductivity in PLLA/PDLA/Li TFSI/CNT composites than it in those composites without Li TFSI. |
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