Silk nanocrystals stabilized melt extruded poly (lactic acid) nanocomposite films: Effect of recycling on thermal degradation kinetics and optimization studies

In this work highly crystalline β sheets of silk nanocrystals (SNCs) have been studied for their effect on the thermal stability of poly (lactic acid) (PLA) during multiple reprocessing. Stable onset degradation temperature was obtained for PLA-SNC nanocomposite (T5% ∼334 °C), and compared to neat poly (lactic acid) (NPLA), which drastically reduces from 336 °C (first cycle) to 322 °C (fifth cycle). The activation energies were estimated using isoconversional Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa methods. Stable activation energy values (∼130 kJ/mol) were obtained for SNC-PLA at three consecutive extrusion cycle. Whereas in the case of NPLA, it significantly reduces from ∼150 kJ/mol (first cycle) to ∼110 kJ/mol (second cycle). Nelder-Mead simplex method was used to optimize the kinetic parameters of nucleation and growth model (A2); which was observed to be the best fit of the experimental thermogravimetric analysis (TGA) data. Decomposition products were analyzed by Thermogravimetry coupled Fourier transform infrared spectroscopy.