Improved thermal stability of poly (l-lactide) with the incorporation of zeolite ZSM-5

Abstract

Thermogravimetric (TG) analysis and differential thermal analysis (DTA) measurements were conducted on ZSM-5 zeolite/poly (l-lactide) (PLLA) composites with two different zeolite loadings. The experimental data were collected under nitrogen atmosphere with heating rates of 5–30 K min−1 and the thermal features were examined from resultant TG and DTA curves. The results show that one-stage thermal decomposition mainly occurs in the temperature range 580–690 K, and the incorporation of ZSM-5 zeolite has substantially boosted the thermal stability of PLLA. Kinetic analysis of the mass loss versus temperature data was performed with different temperature-integral methods, the Flynn-Wall-Ozawa, Coats-Redfern and Madhusudanan–Krishnan– Ninan methods. With the first order reaction assumption, the activation energy and pre-exponential factor values can be readily obtained over the entire conversion range, and they are both much higher than those of pure PLLA. The ZSM-5 zeolite-filled composites required higher Ea values for thermal decomposition than pure PLLA, possibly resulting from enhanced thermal stability. With kinetic parameters thus obtained, the thermal conversion curves have been reconstructed over the entire conversion range by using three kinetic analysis methods, resulting in excellent agreement.