Thermal degradation behavior and kinetic analysis of chemically modified cucumber vine biomass for sustainable thermal applications

Investigation of biomass pyrolysis is of particular interest for the production and use of biofuels, composite and building materials with broad applications. Cucumber vine, an agricultural waste from cucumber harvesting, holds potential as biopolymer fiber for composites. Understanding its pyrolysis behavior is key to elucidate thermal stability and complex pyrolysis process. This study aims to explore pyrolysis characteristics for primordial and chemically treated cucumber vine by experiment and the combined kinetic analysis. A synergistic treatment of 5% sodium hydroxide, 20% acetic acid + 5% sodium hypochlorite and 5% silane coupling agent was applied, and its impact was evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Based on inert thermogravimetric analysis, kinetic triplets were determined using both model-free and model-fitting approaches, and thereby the optimal reaction mechanisms were reconstructed by considering kinetic compensation effect. Results indicated that chemical treatment effectively isolated cellulose from raw samples with reduction of amorphous components, like hemicellulose, and slight promotion of crystallinity by FTIR and XRD analysis. Thermogravimetric analysis found the lessened water absorption with a narrower region and the more distinct characteristics of three reaction stages for treated samples. The initial pyrolysis temperature and average activation energy increased from 216.93 to 233.80 °C and from 88.54 to 103.16 kJ/mol, respectively. F n reaction model best described the pyrolysis of both raw and treated samples with further refinement via Sestak-Berggren model. Thermodynamic analysis confirmed an increase of 15.73 kJ/mol in average enthalpy, supporting the reaction’s non-spontaneous and endothermic nature.