Non-Isothermal Crystallization and Thermal Degradation Kinetics of Biodegradable Poly(butylene adipate-co-terephthalate)/Starch Blends

Abstract

The non-isothermal crystallization behavior of biodegradable poly (butylene adipate-coterephthalate)/starch (PBAT/S) blends was studied using differential scanning calorimetry under a nitrogen atmosphere from 25 to 225 °C at four constant cooling rates of 5, 10, 15 and 20 °C.min-1. There was only one crystallization peak in the exothermic curve which shifted to a lower temperature as the cooling rate was increased. The crystallization temperature decreased from 98 to 84 °C, but the crystallization enthalpy increased from 11 to 12 J.g-1 as the heating rate was increased. The thermal degradation(TG) of the PBAT/S blends was studied using thermogravimetric analysis under a nitrogen atmosphere from 100 to 800 °C at five constant heating rates of 1, 2, 5, 10, and 15 °C.min-1. The TG curves showed two degradation stages occurring at 309–342 °C and 375–420 °C, which were the degradation of corn starch and PBAT, respectively. The thermal degradation kinetics of the PBAT/S were analyzed using the isoconversion FlynnWall-Ozawa model-free method. The results showed that both the apparent activation energy and the logarithm pre-exponent factor increased with increasing conversion α. The average apparent activation energy and the average logarithm apparent pre-exponent factor for α = 0.1 – 0.9 were 266 kJ.mol-1 and 37 min-1, respectively. The reaction model g(α) determined from the master plot method for PBAT/S was a phase-boundary controlled reaction, where g(α) = [1– (1– α)1/2] .