Development and characterization of sulfur-modified neatsfoot oil derived from cattle leg waste as a bio-based fatliquor for leather processing

Cattle leg waste offers a potential lipid feedstock for leather-processing auxiliaries. This study developed a bio-based fatliquor through wet rendering, purification, extraction-process modelling, sulfur-based modification and leather application. Wet rendering recovered 7.25% neatsfoot oil from prepared bone material. A quadratic response surface model (p < 0.0001; R² = 0.9991) predicted a maximum yield of 7.494%, which requires independent experimental confirmation. The purified oil had an acid value of 3.27 mg KOH g⁻¹ , a saponification value of 208.69 mg KOH g⁻¹ and an iodine value of 71.06 g I₂ 100 g⁻¹ . Spectroscopic and mass-spectrometric analyses indicated that the purified oil retained a triglyceride-rich lipid fraction. Following sulfuric-acid treatment, organically combined SO₃ measurements and infrared spectroscopy supported sulfur incorporation. The formulated fatliquor contained 62.50 wt% active ingredients and 5.458% organically combined SO₃, with a pH of 6.93. Upper leather treated with 6% developed fatliquor and 4% synthetic co-fatliquor exhibited tensile strength of 238 ± 4 kg cm⁻², elongation at break of 54 ± 2%, tear strength of 64 ± 2 kg cm⁻¹ , grain crack load of 22 ± 1 kg and grain crack distension of 8.5 ± 0.1 mm (mean ± standard deviation; n = 3 specimens per property). Mean organoleptic scores ranged from 8.0 to 9.0 on a ten-point scale. The findings demonstrate the technical feasibility of incorporating cattle leg-derived neatsfoot oil into an upper-leather fatliquoring blend. Independent product performance, storage stability and environmental benefits remain to be established.