Nonisothermal crystallization behavior and molecular dynamics of poly(lactic acid) plasticized with jojoba oil

Abstract

Poly(lactic acid) (PLA) containing different contents of jojoba oil (3 and 7 mass%; namely PLA-3JO and PLA-7JO), as natural plasticizer, was prepared via melt compounding. The nonisothermal crystallization behavior of PLA in the presence of jojoba oil was investigated from the glassy state. The obtained results revealed that the rate of crystallization and degree of crystallinity increased with increasing the content of jojoba. The nonisothermal crystallization kinetics was analyzed by the Avrami–Jeziorny model. Avrami exponent (n) of the PLA, PLA-3JO and PLA-7JO was found to be 4.08, 3.28 and 3.09, respectively, suggesting that the nonisothermal cold crystallizations of the plasticized PLA follow a heterogeneous nucleation and three-dimensional spherulitic growth, as occurring in the neat PLA. Furthermore, the activation energy of nonisothermal crystallization process (ΔE a) was calculated as a function of blend composition based on the Kissinger equation. It was found that the ΔE a of PLA insignificantly changed in the presence of jojoba oil. The dielectric properties of totally amorphous and crystallized plasticized PLA were also investigated for the α-relaxation process as a function of the temperature and frequency. The α-relaxation process was analyzed with Havriliak–Negami and Vogel–Fulcher–Tammann models, and fitting parameters with their evolution were discussed.