Study of flame retardancy effect on the thermal degradation of a new green biocomposite and estimation of lower flammability limits of the gaseous emissions

Green biocomposites (GBCs) decompose and release significant amount of gases under high temperature that poses self-ignition risk and contribute to the growth of fire. Thermal characterisation of green biocomposite is therefore an essential task to assess the characteristics of the material to approve its use at the industrial scale. In this context, research work has been carried out to evaluate thermal decomposition patterns of the material, to record the volatile emissions and to estimate the self-ignition risk so that the newly developed green biocomposite can be standardised based on the fire safety standards of marine, automotive and aeronautical industry. This research endeavour focuses on the thermal characterisation of a newly developed green biocomposite for the evaluation of thermal stability, identification of gaseous emission and calculation of lower flammability limit (LFL). Intumescent fire-retardant coating composed of ammonium polyphosphate–tris(2-hydroxyethyl)isocyanurate (APP-THEIC) and boric acid (BA) was coated on a GBC that is composed of 38% bioepoxy and flax fibre to improve thermal profile of the material. The thermal stability of the newly developed material was evaluated using thermogravimetric analysis (TGA). An analytical pyrolyser coupled with gas chromatograph and mass spectrometer (Py-GC–MS) was used at four selected temperatures, i.e. 350, 550, 750 and 900 °C, to record the gaseous emissions from GBC. The evolved species during pyrolysis were identified on the pyrograms, and their lower flammability limit was determined using quantitative structure–property relationship (QSPR). The hazards of the new materials for emergency response were identification using NFPA 704. In this study, the GBC developed was characterised based on its thermal decomposition profile, degradation temperature, gaseous emissions and lower flammability limit. It was observed on the TG curves that the green biocomposite fully degrades at approximately 600 °C. The application of intumescent fire-retardant (IFR) coating improves the fire retardancy of the material, and final degradation temperature of the material reaches approximately 800 °C. The newly developed green biocomposite needs to be tested under medium-scale tests to reach a conclusion about its thermal degradation profile. The QSPR study of the gaseous emissions evolved from the pyrolysis of green biocomposite reveals that the LFL decreases as the temperature is increased up to 750 °C. Based on the toxicity analysis of the gaseous emission, the material releases high amount of phenol above 350 °C, which is hazardous for health if inhaled.