Kinetic modelling of thermal degradation and non-isothermal crystallization of silk nano-discs reinforced poly (lactic acid) bionanocomposites

Abstract

The present work investigates the effect of novel biofiller, ‘crystalline silk nano-discs (CSNs)’, on thermal stability and crystallization behaviour of melt-processed poly (lactic acid) (PLA)/CSN nanobiocomposites which are very much important for polymer processing. The PLA/CSN nanobiocomposites are obtained through melt extrusion technique. Thermogravimetric (TGA) data revealed that incorporation of ~ 1 wt.% CSNs in PLA enhanced onset degradation temperature (Tonset) ~ 10 °C, and this improvement in thermal stability is due to the formation of network-like structures. Activation energies (Ea) of nanobiocomposites, determined from model-free (Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose methods) and model fitting (Coats–Redfern method) approaches, increased in comparison with PLA, indicating that CSNs impede thermal degradation process. Possible mechanism is proposed for thermal degradation process of nanobiocomposites using Criado’s method. Hyphenated TGA-Fourier transform infrared is utilized to identify evolved gaseous products during degradation of silk, CSNs, PLA and nanobiocomposites. Differential calorimetry data was analysed by Jeziorny, Liu-Mo and Tobin models. It was found that CSNs act as heterogeneous nucleating agents, hence improve non-isothermal crystallization kinetics of PLA.