Thermal degradation kinetics of polylactic acid/acid fabricated cellulose nanocrystal based bionanocomposites

Cellulose nanocrystals (CNC) are fabricated from filter paper (as cellulosic source) by acid hydrolysis using different acids such as sulphuric (H₂SO₄), phosphoric (H₃PO₄), hydrochloric (HCl) and nitric (HNO₃) acid. The resulting acid derived CNC are melt mixed with Polylactic acid (PLA) using extruder at 180°C. Thermogravimetric (TGA) result shows that increase in 10% and 50% weight loss (T₁₀, T₅₀) temperature for PLA-CNC film fabricated with HNO₃, H₃PO₄ and HCl derived CNC have improved thermal stability in comparison to H₂SO₄-CNC. Nonisothermal kinetic studies are carried out with modified-Coats-Redfern (C-R), Ozawa-Flynn-Wall (OFW) and Kissinger method to predict the kinetic and thermodynamic parameters. Subsequently prediction of these parameter leads to the proposal of thermal induced degradation mechanism of nanocomposites using Criado method. The distribution of E_a calculated from OFW model are (PLA-H₃PO₄-CNC: 125-139 kJmol^-1), (PLA-HNO₃-CNC: 126-145 kJmol^-1), (PLA-H₂SO₄-CNC: 102-123 kJmol^-1) and (PLA-HCl-CNC: 140-182 kJmol^-1). This difference among E_a for the decomposition of PLA-CNC bionanocomposite is probably due to various acids used in this study. The E_a calculated by these two methods are found in consonance with that observed from Kissinger method. Further, hyphenated TG-Fourier transform infrared spectroscopy (FTIR) result shows that gaseous products such as CO₂, CO, lactide, aldehydes and other compounds are given off during the thermal degradation of PLA-CNC nanocomposite.