Combustion Characteristics of Briquette Fuels from Neem Sawdust and Ayurvedic Waste Using Cassava Starch Binder

The escalating demand for clean, renewable solid fuels and the need to valorize industrial biomass waste streams have motivated this study, which presents the first systematic investigation of briquette fuels produced from neem (Azadirachta indica) sawdust combined with ayurvedic processing residues Tinospora cordifolia and Trichosanthes cucumerina bonded with cassava starch. While biomass briquetting is well established, the utilization of medicinal plant waste as a co-feedstock remains largely unexplored. Six formulations (S1–S6) with neem-to-ayurvedic ratios ranging from 100:0 to 0:100 were characterized through proximate analysis, SEM – EDX, thermogravimetric analysis (TGA), compressive strength, shatter resistance, density, and water absorption testing following ASTM standards. Increasing the ayurvedic fraction progressively improved fuel quality: moisture content declined from 24.5% (S1) to 6.2% (S6), volatile matter increased from 64.7% to 83.6%, and calorific value peaked at 4478 kcal/kg (18.7 MJ/kg) for the optimal blend S4 (40% neem: 60% ayurvedic), which combines adequate-fixed carbon for sustained combustion with high volatiles for rapid ignition and low ash (4.5%) for reduced slagging. This calorific value exceeds that of conventional rice husk and bagasse briquettes (14–17 MJ/kg), demonstrating the energy advantage of incorporating herbal residues. Mechanical testing confirmed a high compressive strength (62.84–67.93 kN), superior shatter resistance (>97%), and water absorption below 5% for ayurvedic-rich samples, validating structural integrity for storage and transport. TGA confirmed sequential thermal decomposition of moisture evaporation (<150°C), devolatilization (200–400°C), and char oxidation (>400°C) with herbal-rich blends exhibiting earlier and more complete volatile release. This study establishes the S4 formulation as a cost-effective, high-performance solid biofuel suitable for domestic cooking and small-scale industrial heating, demonstrating a novel waste-to-energy pathway for the herbal pharmaceutical industry.