Sustainable leather tanning: Evaluation of Aphanamixis polystachya extract as an eco-friendly alternative to conventional tanning agents

Vegetable tanning agents have emerged as sustainable alternatives to chromium-based tanning, which generates hazardous waste harmful to ecosystems and human health. Although numerous plant-derived tannins have been studied, few meet commercial standards due to limitations in efficiency, quality, and extraction methods. This study investigates the potential of Aphanamixis polystachya bark extract as a novel vegetable tanning agent in comparison with conventional mimosa tannin. Among the solvents tested, methanol yielded the highest extraction efficiency (30.75 ± 1.45 %). The extract showed a pH of 4.02 ± 0.15, moisture content of 4.14 ± 0.12 %, and total tannin content of 115.34 mg/g—comparable to mimosa (114.25 mg/g) and slightly lower than quebracho (129.96 mg/g). Condensed tannin content (23.7 ± 1.92 %) also fell within the reported range of reference tannins. FTIR analysis confirmed functional groups essential for collagen interaction, and UV-Vis spectroscopy revealed a characteristic peak at 280 nm, indicative of catechin and tannic acid-like compounds. Leather tanned with the extract showed a shrinkage temperature of 82.67 ± 0.57 °C, tensile strength of 250.35 ± 0.77 kg/cm², and elongation of 41.67 ± 1.03 %. It also outperformed mimosa in tear resistance, grain distension (8.5 mm), and fracture resistance (22.81 ± 1.39 kg). No surface cracks appeared after 50,000 dry flexing cycles. TGA and SEM analyses confirmed the thermal stability and fiber integrity of the treated leather. Overall, Aphanamixis polystachya extract demonstrated strong tanning performance and eco-friendly characteristics, making it a promising alternative to conventional vegetable tanning agents.