Effective utilization of tannery hair waste to develop a high-performing re-tanning agent for cleaner leather manufacturing.

Accumulation of hair waste is a major burden to the leather industry, causing a negative impact on the industry's sustainable development. The industry is already bogged down by the usage of synthetic re-tanning agents that are not only extremely challenging for biodegradation but also release free-form of formaldehyde in the final leather stage. This research work focuses on developing a formaldehyde-free bio-based re-tanning agent from hair waste. In order to do so, hair waste is subjected to alkali hydrolysis and subsequently graft-copolymerized with methacrylic acid (MAA). These treatments were optimal using 20 % (w/w) sodium hydroxide and thermal activity at 90 °C. This resulted in effective hydrolysis of red sheep hair, which was the ideal candidate in this study. The hydrolysate was subjected to monomer in situ polymerization (using MAA) with potassium per sulfate/sodium meta-bisulphite redox system, leading to the development of keratin hydrolysate-g-methacrylic acid (KH-g-MA) copolymer (this was noted both at a laboratory level and pilot scale). The obtained KH-g-MA copolymer exhibited ideal characteristics such as increased protein content (78.3 ± 1.2), appropriate particle size (1516 nm), suitable pH (5) and required viscosity of 512 cP. The developed KH-g-MA copolymer was then applied as a re-tanning agent in the leather manufacturing process. Significant improvement in leather's mechanical strength characteristics was observed. In addition, the organoleptic properties of leather such as fullness, softness and grain tightness showed much improvement. Scanning electron microscopy (SEM) showed an enhanced surface smoothness and filling of the voids in experimental leather in comparison to the control leather. This recycle and reuse strategy of hair waste not only helps resolve issues with handling of hair solid waste but also results in producing an eco-friendly re-tanning agent in leather manufacturing, thereby paving the way for cyclic economic utilization and cleaner environment.

Leather solid waste: An eco-benign raw material for leather chemical preparation - A circular economy example.

One of the long lasting problems associated with leather industry is to meet environmental standards for both liquid and solid wastes. Statistics show that one tonne of wet-salted hides/skins yields around 650 kg of solid waste. Among various wastes generated, trimmings for the most part have been underutilized. Collagen presents in trimmings waste are effectively used but hair goes unutilized or at the most as feed for boilers during gelatin manufacturing. Hence, newer technology is needed for complete and effective utilization of raw trimmings. In leather manufacture, formaldehyde condensates polymers are used as re-tanning agent to enhance the compaction of leather. However, these products are hard for biodegradation and also cause the release of free formaldehyde in leather, which is a known carcinogen. Here, there is a need for development of formaldehyde free re-tanning agent for eco-benign leather processing. In this work an attempt had been made to develop formaldehyde free biodegradable eco-benign re-tanning agent from raw trimming of tannery solid waste as a circular economy model. Alkaline (7.5%w/w NaOH) - hydrogen peroxide (10%w/w) pre-treatment followed by thermal hydrolysis at 100 °C for 5 h was an optimized method for effective hydrolysis of trimmings and the process of preparation of product results in the holistic utilization of raw trimmings. The developed product was characterized using Dynamic light scattering and FTIR techniques. The product prepared was further used in leather manufacture as a re-tanning agent and was found to impart multifunctional properties to leathers such as fullness, grain tightness and shade of dye brilliance. Product improves the mechanical strength characteristics of leather and also the exhaustion of post-tanning chemicals. SEM analysis shows that the experimental leather is more compact and flat than control. This novel strategy had not only solved the issue of solid waste but also resulted in a greener leather auxiliary leading to greener environment.