| Poly(lactide acid)(PLA) is a biocompatible and biodegradable polyester, which are derived from renewable resources, is of great significance to solve the current energy and environmental problems. However, its low crystallinity and slow crystallization rate have limited the application area of PLA. Stereocomplexation between enantiomeric poly(L-lactide acid)(PLLA) and poly(D-lactide acid)(PDLA) has already been proved one of the most promising methods for increasing the properties of PLA since its first reported. Stereocomplex crystallization showed better properties in such as thermal stability and mechanical properties.Firstly, study the influence of force field and temperature field on the crystallization of sc-PLA during the preparation of PLLA/PDLA blend membrane. The results show that appropriate blending rate is in favor of the formation of stereocomplexation crystal(sc-PLA). In film casting period, full sc-PLA with higher crystallization degree can be obtained at lower(0oC) temperature. Proper increase of oscillation speed is beneficial to the formation of sc-PLA.Secondly, PLLA/PDLA during melt blending, study the blending temperature, blending number, molecular weight of the plasticizer and types of nucleating agent for the influence of sc-PLA formation. It is good for the formation of sc-PLA with PLLA/PDLA blend at such low temperature, there will be a small number of hc- PLA crystallization with the processing temperature higher than 190 oC. In terms of the status of the product, it is more conducive to spinning for the products with a processing temperature of 240 oC, but from the results of DSC and WAXD, the production rate and crystallinity of sc-PLA is not very high at this time. Sc-PLA formation rate and crystallinity will have a certain degree of improvement with a secondary processing at 240 oC, which use the products of a one time processing at 190 oC. Adding nucleating agent of TMC-306 and the molecular weight plasticizer of PEG can improve the production rate and crystallinity of sc-PLA with the equivalent proportion of PLLA/PDLA blending at 240 oC.Once more, The effects of the plasticizer PEG on the formation and crystallization behaviors of sc-PLA were investigated. When blend PLLA and PDLA were blended at 240 oC higher than the melting temperature of sc-PLA, both hc-PLA and sc-PLA formed in the blend. However, the WAXD and DSC analysis showed that exclusive sc-PLA crystallites without any hc-PLA crystallites could form after the incorporation of PEG. The isothermal crystallization behavior of sc-PLA indicated that PEG can accelerate the crystallization rate of sc-PLA. During the isothermal crystallization, the half crystallization time of sc-PLA decreased significantly at 10 wt% PEG content. What’s more, after the addition of PEG, the crystallization activation energy of sc-PLA decreased with 5 wt% PEG, while the chain mobility was improved and the combination of the chains of PLLA and PDLA accelerated the formation of sc-PLA. The presence of PEG decreased the spherulite density and increased the spherulites size, and the most perfect spherulite was obtained with 10 wt% PEG.In the end, The effects of the addition of PEG and/or TMC-306 on the formation and crystallization behaviors of sc-PLA were investigated. When blend PLLA and PDLA at the processing temperature higher than that of the melting temperature of sc-PLA, the formation of hc-PLA and sc-PLA both existed. However, the WAXD and DSC analysis showed that the exclusive sc-PLA crystallites without any hc-PLA crystallites can be formed after incorporation of PEG and/or TMC-306. The non-isothermal and isothermal crystallization kinetics indicated that PEG and TMC-306 can accelerate the crystallization rate of sc-PLA seperately. During the isothermal crystallization, the half crystallization time of sc-PLA significantly were significantly shortened by the coexistence of PEG and TMC-306. In addition, the crystallization activation energy of sc-PLA decreased after addition of PEG and/or TMC-306, especially for the sample of LDTP. At the same time, the stability of the crystals of sc-PLA maintained at a relatively stable level after the addition of PEG and/or TMC-306. The influence of PEG and TMC-306 on the morphologies of sc-PLA was investigated by polarized optical microscopy(POM). The presence of PEG decreased the spherulite density of sc-PLA and increased the size of spherulites, on the contrary, the presence of TMC-306 increased the spherulite density of sc-PLA and decreased the size of spherulites. With the coexistence of PEG and TMC-306, the nucleation density and spherulite size were in the middle of LDP and LDT. These results obviously evidenced that the cooperative effect of plasticizer PEG and nucleating agent TMC-306 on the crystallization of sc-PLA. |
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