Crystal structure and morphology influenced by shear effect of poly(l-lactide) and its melting behavior revealed by WAXD, DSC and in-situ POM

Shear effect on crystal structure, morphology and melting behavior of poly(l-lactide) (PLLA) were investigated by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and in-situ polarized optical microscope (POM). Influences of steady shear on PLLA melt was investigated during annealing. The impacts of crystallization temperature (Tc) and shear rate (SR) on crystal structure, crystal growth rate, nucleation, and melting behavior were studied. It could be clarified into the low (<20 s−1) and high shear rate ranges in terms of the crystal structure, growth rate, nucleation and melting behavior. It was found that phase transition and recrystallization during heating completely changed the stack structure. A new stable structure was established after a temperature jump in the melting range. Cylindric morphology arranged with spherulite was also observed in the polymer films at high Tc influenced by shear effect.