Influence of PLA stereocomplex crystals and thermal treatment temperature on the rheology and crystallization behavior of asymmetric poly(L-Lactide)/poly(D-lactide) blends
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Asymmetric poly(L-lactide)/poly(D-Lactide) (PLLA/PDLA) blends were prepared by adding small amounts of PDLA into the PLLA matrix with the formation of stereocomplex crystallites (sc-crystallites). Rheological results indicated that the PLLA/PDLA melt at lower temperatures (<Tm,sc, the melting temperature of the formed stereocomplex crystallites) underwent the transition from liquid-like to solid-like viscoelastic behaviors with increasing of the PDLA concentration, which was related to the sc-crystallites reserved in the melt of asymmetric PLLA/PDLA blends. Dissolution experiment indicated the presence of sc-crystallites network structure in the PLLA/PDLA blends, and the size of the sc-crystallite junction particles network increased with increasing of the PDLA concentration. DSC and POM studies indicated that the PDLA concentration and the thermal treatment temperature had a significant influence on the PLLA crystallizability behavior. At low thermal treatment temperature (<T m,sc ), reserved sc-crystallites showed an obvious promoting effect for PLLA crystallization. With increasing of the thermal treatment temperature, its promoting effect decreased due to melting of the sc-crystallites. This result suggests the sc-crystallites played two roles: nucleation sites and cross-linking points, and the two roles had a competitive relationship with change of the thermal treatment temperature and the PDLA concentration.
KeywordsStereocomplex Rheology Crystallization Poly(L-lactide) Poly(D-lactide)
The authors thank by the National Science Foundation of China (No. 51303149) for support. The research was also sponsored by the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University (CX201625) and the Natural Science Foundation of Shaanxi Province in China (No.2015JQ2045).
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