Insights into kinetics, reaction mechanism, thermodynamics, and co-combustion characteristics for Gmelina arborea with polyethylene using thermogravimetric analyzer

The study explores the thermogravimetric and co-combustion behavior of Gmelina arborea , polyethylene and its blend at different GA: PE weight ratios at the heating rates of 3, 5, and 10 °C min − 1 , respectively in air atmosphere. TG and DTG analysis revealed multiple-stage degradation for GA & PE while GA: PE at 70:30 weight ratio demonstrated a broad and overlapping decomposition zone attributed to strong GA with PE interactions with maximum synergistic effect. The maximum synergistic effect was observed with GA: PE of 70:30 whereas GA: PE of 50:50 indicated antagonist effect. Kinetic parameters determined by employing iso-conversional methods (OFW, KAS, and Starink) showed similar nature of degradation. The average activation energy needed for GA & PE degradation lies in the range of 178–179 kJ mol −1 and 137–141 kJ mol −1 respectively, however GA: PE at 50:50 requires much lower activation energy in the range of 94–100 kJ mol −1 whereas at 70:30 the activation energy lies in the range between 170 and 172 kJ mol −1 , as a result of which the synergism effect during co-combustion is significant. Reaction mechanism revealed multi stage degradation where lower conversions utilized diffusion-controlled mechanisms until they transitioned to ordered reaction kinetics and phase-boundary processes at higher conversions. For GA: PE (70:30) blend, the reaction mechanism followed heterogeneous multi-step process with diffusion-controlled at lower conversion & reaction-controlled at intermediate conversion The average ∆H for GA: PE degradation was much lower compared to GA whereas the average change in ∆S for GA: PE degradation was negative signifying that the transition state is more ordered in the case of co-combustion. Combustion index study revealed linear co-relation with the heating rate showing higher combustion index at higher heating rate and the synergy index study revealed blending of GA with PE slowed the degradation process because of deposition of viscous molten layer over GA & its char. These findings provide an important insight the for design and development thermal degradation system to co-combust GA & PE blend for bio-energy generation.