Kinetic parameters using non-isothermal and model-free methods for wasted disposable bamboo chopsticks in Thailand

This study presents comprehensive thermal analyses of wasted disposable bamboo chopsticks subjected to varying heating rates. The investigation reveals a multi-stage thermal decomposition process occurring between 32 °C and 650 °C. Initial mass loss is attributed to moisture evaporation, succeeded by two distinct stages, designated as A and B, characterized by the release of volatiles and their combustion, as well as char oxidation. The temperature intervals defining the three mass loss phases, along with peak temperatures and maximum mass loss rates, are systematically determined. Notably, the foremost mass reduction occurs during stage A, signifying the formation and ignition of a higher quantity of volatiles. Char combustion, representing around 30 wt% of the mass loss, is assigned to stage B, occurring within peak temperature ranges of 411 °C – 449 °C.

Coats-Redfern method was used to explain the reaction mechanisms, modeled as F1, F2, and F3, representing chemical reaction, diffusion, and phase interfacial reaction, respectively, are employed to scrutinize the oxidation stages A and B. The correlation coefficients between the models and experimental data are particularly high for F1 in stage A and F2 in stage B. The activation energy values for stages A and B are determined, ranging from 80.8 kJ/mol to 88.7 kJ/mol and 26.4 kJ/mol to 28.9 kJ/mol, with the highest values attributed to models F1 and F2, respectively. Furthermore, the pre-exponential factor (A) displays variability between 6 min^-1 and 22.8 min^-1 for stage A (F1 model) and between 1.2 × 10^⁻⁷ min^-1 and 8.8 × 10^⁻⁶ min^-1 for stage B (F2 model).

Employing FWO and KAS methods, correlation coefficients (R²) remain notably high, ranging from 0.836 to 0.977. Activation energy values yielded by FWO and KAS approaches closely approximate average values of 194.2 kJ/mol and 194.1 kJ/mol, respectively. This investigation provides valuable insights into the thermal behavior of bamboo chopsticks, elucidating their decomposition kinetics under diverse heating conditions.