A series of equimolar blends of poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) were prepared by melt mixing and the blends were investigated by means of differential scanning calorimetry (DSC)

nuclear magnetic resonance (13C-NMR)

wide angle X-ray diffraction (WAXD)

etc.It was found that when the blending temperature was 210 ℃

the stereocomplex (sc) formed from equimolar PLLA/PDLA blends exhibited a high melting temperature at 229 ℃ and showed 98.1% crystallinity degree.As for the sample after isothermal annealing up to 120 ℃

the Vicat softening temperature approached to 126.4 ℃.It was indicated that double melting endotherms were characteristic for the sc crystals in the DSC thermograms

where formation of the stereoblock (sb) occured at high processing temperatures.The high-temperature-side (230 ℃) endotherm and the low-temperature-side (210 ℃) endotherm resulted from the melting of sc and sb crystals respectively.As the blending temperature increased

the high-temperature-side endotherm was reduced and the low-temperature-side endotherm was emphasized.The relative amounts and crystallinity degree of sc crystals decreased significantly with the increase of blending temperature.The sc-PLA had good processing stability.The melting temperature of sc crystals stayed constantly after second blending.Moreover

the relative amounts of sc crystals increased slightly.The PLLA/PDLA blends composed of networks of sc might be applicable to the heat-resistant materials

and this paper provided a new method of improving thermal stability and processing property of PLA.