Keratin hydrolysate as a chrome exhaust aid and keratin filler in leather processing: A cleaner technology approach for tannery solid waste management and leather manufacturing

Hair burning unhairing and dampening of tannery wastes during the hair-saving unhairing process are becoming significant problems in the tanning industry. Therefore, this research article focuses on the extraction of keratin hydrolysate (KH) and its application as a chrome exhaust aid and keratin filler in leather manufacturing process. The structure, morphology and functional groups of the extract were examined using X-Ray Diffractometer (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FTIR), respectively. To study and contrast the degree of improvement in chromium uptake, the KH solution was applied both before tanning on the pickled pelt and after tanning during basification. The thermal stability, physical strength characteristics and organoleptic properties of the leathers obtained were characterized. Furthermore, the environmental impact of the tanning system was assessed through a comparative analysis of the spent liquors. Finally, experimental retanning process was conducted to replace the commercial protein filler (Celatan F: 50, 75, and 100 %) with KH solution, with concurrent processing of control leather using conventional chrome tanning agent at 6 % dosage of chromium. The FTIR analysis of the extract confirmed the presence of alkyl side chains of amino acids as well as carboxylic, amide, carboxyl group and aldehyde functional groups at 1400-1700 cm^-1,3,303.46 cm^-1,3270 cm^-1 and 2752 cm^-1, respectively. XRD spectrum showed two diffraction peaks at 2 theta values of 9.36° and 21.16°, respectively. Leathers with improved mechanical strength, organoleptic properties and thermal stability were obtained with 100 % substitution of Celatan F at pH 6 and 10 % chromium dosage. It was also discovered that the shrinkage temperature of the experimental leather was enhanced to more than 105 °C. Environmental impact evaluation on the spent liquor showed that the complete replacement of Celatan F with KH solution brought about a notable decrease in COD and TDS in the spent liquor. The extraction and application of tannery hair waste-based keratin hydrolysate as an efficient, environmentally friendly chrome exhaust aid and keratin filler has been attempted and established in this research article.