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

[Display omitted] •Re-tanning agent has been prepared from tannery trimmings waste.•Effective hydrolysis with 7.5% NaOH and 10% H2O2 pre-treatment.•Improvement in grain crack resistance about 26%.•Improvement in colour intensity about 17%.•The developed product is free from toxic and harmful substances. 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.