Comparative physicochemical study of soaps derived from alkalis produced using corn cobs and groundnut shell ash with coconut oil

This study investigates corn cobs and groundnut shells as alternative alkali sources for soap formulation. The agro-wastes were subjected to high-temperature combustion at 1050 °C in a muffle furnace to generate ash, from which alkali was extracted via aqueous leaching. Eight soap formulations were prepared: two synthetic controls (N: caustic soda + silicate + SLS + palm kernel oil; NC: caustic soda + silicate + SLS + coconut oil); and six agro-waste-derived soaps, all using coconut oil as the fat base, coded as CCN, CGCN, GCN, CC, CGC, and GC. Soaps were evaluated for pH, moisture content, total fatty matter (TFM), foamability, foam stability, and free alkali content after saponification. Results showed CC achieved the highest TFM (80%), exceeding synthetic controls, while GC and CGCN had 60%. Agro-waste-derived soaps showed lower foamability (6–31 cm3) than controls (170–320 cm3), but additive-containing formulations (CCN, CGCN) exhibited improved foam stability (1200–1350 s). Moisture content ranged from 10 to 28%, with groundnut shell formulations (GC, CGCN) exceeding 25%. Free alkali levels (0.5–1.9%) generally met international standards, though only NC (0.22%) satisfied the SON specification of ≤ 0.3%. pH values (7.83–10.18) fell within acceptable limits, with corncob-derived soaps showing higher alkalinity due to elevated K2O (22.88%) in corncob ash. CC (corncob ash + coconut oil) emerged as the optimal bio-based formulation, supporting waste valorization as a sustainable alternative alkali source. Future research should focus on standardizing ash extraction protocols and evaluating long-term storage stability under tropical conditions.