Eco-friendly titanium tanning for the manufacture of bovine upper leathers: Pilot-scale studies

Conventional chrome-tanning process is constantly under pressure from increasingly stringent environmental regulations on discharges of chromium-containing effluents and wastes. For this reason, in the past years alternative chrome-free tanning processes have been developed. Among these, titanium tanning is one of the most promising substitutes for chromium tanning in today's leather industry. In this study the use of titanyl sulfate masked with citrate was investigated as tanning agent for the production of high-quality bovine upper leather on pilot scale. Preliminary experimental activities were performed to individuate the minimum citrate/titanium mole ratio to ensure a good titanium sulfate solution stability and minimum quantity of salt (sodium chloride) in pickling solution sufficient to depress acidic swelling of the skins. Ti-tanned leathers produced by the developed Ti-tanning process showed comparable physical-mechanical properties to those of traditionally Cr-tanned leathers, used as control, but a lower hydrothermal stability although acceptable. The Ti-tanned leathers complied with the standards for high-quality upper leather exhibiting better dyeability, due to their higher affinity to anionic dyestuffs, and similar softness, fullness, roundness, and hand compared to the control leathers.