| Stereocomplex poly（lactic acid）（PLA SC）has a melting point of 230°C,which can significantly enhance the thermal resistance of PLA materials.Also,PLA SC has high mechanical properties,good hydrolysis resistance and solvent resistance because of special crystal structure.Numerous scholars have carried out researches on the methods of regulating the crystallization of PLA SC,and controlled the SC crystallization by changing the main factors such as chain structure,blend ration and crystallization conditions.In these studies,the preparation methods of PLA SC were solution mixing and melt blending,the isomeric polymers were mixed in molecular level.when the distance of these isomers increased,the crystallization behaviors of PLLA/PDLA were not clear yet.In this study,a simple and easy-to-use physical processing technology—electrospinning have been used to prepare PLLA/PDLA electrospun fiber samples,which with different molecular distances of PLLA and PDLA by different electrospinning methods.The crystallization behaviors of PLLA/PDLA asymmetric blend film and PLLA/PDLA asymmetric fibers which were prepared by different electrospinning methods,i.e.,spinning by mixed solution（DL-A）,side by side mode（DL-B）,and double spinnerets（DL-C）were systematically studied by differential scanning calorimetry（DSC）and wide-angle X-ray diffraction（WAXD）.And the effects of electrospinning and the change of molecular distance between PLLA and PDLA on the crystallization behavior of PLLA/PDLA blends were discussed.As well as,the effect of SC distribution on the crystallization behavior of HC was discussed,too.The results are as follows:（1）The crystallization behavior of PLLA/PDLA asymmetric blend electrospun fibers was different from that of PLLA/PDLA asymmetric blend film.The electrospun fiber has more obvious glass transition and cold crystallization peak.In the electrospun fiber,the molecular chains of PLLA and PDLA were arranged more orderly,which is more conducive to the formation of SC crystallization.Therefore,theΔHSC of the electrospun fiber samples in each proportion was significantly higher than that of the corresponding blend film samples,and gradually increased with the increase of PDLA content.When the mass ratio of PLLA and PDLA was 40/60 or 50/50,only SC was formed in the fibers.The confinement of HC was also more obvious because of the nano size of the fiber and the confinement of the SC.（2）In the three groups of PLLA/PDLA asymmetric electrospun fibers,the molecular distance between PLLA and PDLA followed the order of DL-A<DL-B<DL-C,while the mass ratio of PLLA and PDLA was the same,ΔHSC followed the order of DL-A>DL-B>DL-C.TheΔHSC of each group of samples increased with the increase of PDLA content,whileΔHHC was decreasing.In DL-A,when the content of pdla is low,HC was formed first,and then SC is formed.When the content of PDLA increased,SC was formed first,and then HC was formed or no HC was formed directly.In DL-B,HC was formed at about 100°C,and SC was formed at about 140°C.In DL-C,HC was formed first in a single fiber,and SC was formed in HC melting process or after HC melted.（3）The distance between PLLA and PDLA was different because of different spinning methods.In addition to the content of SC,the distribution of SC would be further affected,too.The crystallization rate of HC in PLLA/PDLA blends was affected by the content and distribution of SC at the same time.In DL-A,SC would form a physical crosslinking network to limit the formation of HC.the content of SC was higher,the crystallization of HC was slower.In DL-B,SC was only formed at the contact surface of PLLA and PDLA solution,and the physical crosslinking network was only formed at this interface.Compared with DL-A,the restriction on the molecular chain or segment of the enantiomers on both sides of the interface was not obvious,and the crystallization rate of HC decreased slightly with the increase of SC content.in DL-C,SC was formed at the intersection of PLLA and PDLA fibers,these SC were distributing like stars,and the distance between SC crystals was far and no easy to from physical cross-linking.These SC can effectively promote the formation of HC as nucleating agent.With the increase of SC content,the crystallization rate of HC was increased.In the presence of SC,the crystallization rate of HC in the same proportion samples of PLLA/PDLA electrospun fibers follows the order of DL-A<PLLA<DL-B<DL-C. |
