Effect of annealing on the thermal properties of poly (lactic acid)/starch blends.

A comparative study of the thermal behavior of PLA/starch blends annealed at different temperatures has been conducted. Annealing was found to be beneficial to weaken and even eliminate the enthalpy relaxation near Tg. The degree of crystallinity was evaluated by means of DSC, and the results showed that the crystallinity of the samples increased as the annealing temperatures were increased. It was observed that, during the annealing process, the disorder α (α') crystal modification tended to transform into the order α crystal modification. All of the PLA/starch blends showed a double melting behavior. With the increase of annealing temperatures, the lower Tm1 increased, while the Tm2 showed no evident change. The XRD patterns also showed that annealing was beneficial to the samples to form higher crystallinity. The TGA results indicated that the annealed samples did not show any higher thermal stability than the virgin samples. The activation energy calculated by the Flynn-Wall-Ozawa method at lower conversion degrees confirmed that the annealing slightly slowed the degradation. The activation energy did not show any dependence on the conversion degree, which indicated that there existed a complex degradation process of the PLA/starch blends. The average activation energy did not show obvious differences, indicating that the annealing treatment had little influence on the degradation activation energy.