Isothermal crystallization kinetics and crystal structure of poly(lactic acid): Effect of triphenyl phosphate and talc

In this article, kinetics of neat poly(lactic acid) (PLA) and its blends with triphenyl phosphate (TPP) and/or talc crystallized isothermally in the temperature range of 113-128°C was analyzed by differential scanning calorimetry (DSC) and described by the Avrami equation. The results showed that the average value of Avrami exponents n is around 2.0 for neat PLA and the PLA/15TPP blend, and around 3.0 for the PLA/1.2Talc blend and the PLA/15TPP/1.2Talc blend. The crystallization rate constants k for neat PLA and its blends were increased in the following order: the PLA/15TPP blend, neat PLA, the PLA/15TPP/1.2Talc blend, and PLA/1.2Talc blend. The half-time of crystallization t₁/₂ was increased with an increase of crystallization temperature Tc and the presence of TPP, and was decreased sharply with the incorporation of talc. Further investigation into crystallization activation energy ΔEa of neat PLA and its blends with 15 wt % TPP and/or 1.2 wt % talc showed that the values of ΔEa were increased with the incorporation of TPP and/or talc compared to that of neat PLA. It was verified by wide angle X-ray diffraction (WAXD) that neat PLA and its blends with TPP and/or talc crystallized isothermally in the temperature range of 113-128°C, and all formed the α-form crystal after enough annealing time.