Shear field existing in polymer processing like injection molding,strongly influences the property of materials.It is shown that shear field dramatically enhances the nucleation rate and induces the orientation morphology during crystallization process.However,reports on the shear effect on semi-rigid chains such as Poly(lactic acid)(PLA)are rare.With regard to shear effects,enhanced nucleation rate with a spherulitic morphology in PLA after a step shear was observed(1 s-1,strain 125%,1s)1.Shear at low temperature just increases the spherulite density,and as shear temperature increases,typical spherulites change to cylindroid structures2.The nucleation rate and crystallization morphology after shear are also influenced by the chain structure of PLA(linear or branching)3.Kota Hemmi et al.4 investigated the acceleration of stereocomplex crystals(SC)growth under shear flow at 200℃.However,they didnt reveal the influence of shear on the formation of SC and alpha crystals.In the present work,we compared the crystallization behavior of SC in poly(L-lactic acid)(PLLA)/poly(D-lactic acid)(PDLA)blend(50/50,wt%)under quiescent and different shear conditions.From the results of isothermal crystallization,we conclude that shear field promotes the crystallization rate of SC and PLA homo-crystals.The density of SC spherulites is obviously increased after shear and cylinder-like morphology is also observed at high shear rate(Figure 1).The result of WAXS shows that the formation rate of SC is dramatically increased after shear especially under large shear rate(Figure 2).From the nonisothermal crystallization results,we conclude that shear at 175℃ increases the content of SC and the final crystallinity of PLLA/PDLA,while the content of PLA homo-crystals is decreased(Figure 3).A deep understanding of shear effect on the crystallization behavior of PLA stereocomplex and the following alpha crystals can provide a theoretical basis for the preparation of high performance PLA-based materials.Further studies are now in progress.