Thermal Characterisation of Millet to Develop Sustainable Intumescent Passive Fire Protection Systems

ABSTRACT Intumescent paints, coatings, or sealants are a popular form of passive protection in the fire industry. However, the impact of their toxicity and constituent synthetic chemical ingredients is an important consideration for sustainability. This research experimentally studied an agricultural grain, known as millet, quantifying its unusual intumescent behaviour. It swells to approximately three times its size, forming a low conductivity char layer, making it an ideal base for potential biomass passive protection systems. The grain was analysed through three experimental methods, namely, thermogravimetric analysis (TGA), hot stage analysis (HS), and cone calorimetry (CC), with consideration of the physical characteristics and thermal resistance development. Physical and chemical decomposition phenomena driving the intumescent behaviour were identified. TGA found millet to have four distinct thermal degradation stages, with similar behaviour for both whole and ground millet in air. This signifies that the grains' behaviour can be predicted independent of the implemented form. HS identified the visual decomposition stages of the grain, as well as gases and compounds released which potentially drive intumescence, with accelerated release from 180°C to 350°C, and initial and maximum expansion at 300°C and 330°C, respectively. Both whole and ground millet provided improved thermal resistance to the substrate in the CC, through formation of an expanded lattice‐like structure with micro‐scale openings. This demonstrates good potential for millet to provide protection to structural members in a fire.