Kinetic and thermodynamic characterization of cellulosic materials using Coats-Redfern method

Abstract

This study presents a comprehensive kinetic and thermodynamic analysis of cellulose components extracted from waste leaves of Butia monosperma using thermogravimetric analysis (TGA). The crude cellulose was then fractionated into α-cellulose and β-cellulose, with α-cellulose being the predominant fraction. The major pyrolytic zone for crude cellulose was observed between 240 and 510 °C, for α-cellulose between 210 and 465 °C, and for β-cellulose between 240 and 451 °C. To determine the kinetic parameters and thermodynamic properties, the Coats-Redfern method was applied, considering 21 different reaction mechanism models. The analysis revealed that the DM 6 model (Zhuravlev equation) provided the best fit for crude cellulose and β-cellulose. In contrast, the NM 4 model (Avrami-Erofeev equation with n = 2) was found most suitable for α-cellulose, also showing superior R² values. These models showed activation energies of 76.84 × 10³ J/mol for crude cellulose, 60.10 × 10³ J/mol for α-cellulose, and 139.78 × 10³ J/mol for β-cellulose. The positive data for ΔH suggest the obligation of external energy to instigate the pyrolysis process. All ΔG values emerged as positive, indicating the non-spontaneous process of pyrolysis. The revealed negative values of entropy suggest a less significant alteration in product structure upon bond breaking compared to the original reactant. Cellulose backbones carried functional groups, and their morphology is evaluated by using FTIR spectra and SEM images, respectively. This research highlights the potential of utilizing Butia monosperma waste leaves in high-value applications, particularly in thermochemical conversion processes and the fabrication of advanced composite materials.