Preparation and Application of a High Exhaustion Chrome Tanning Auxiliary from Limed Fleshings

The recycling of leather solid waste has become a key issue aimed at realising the sustainable development of the leather industry. Recently, more and more attention has been paid on the recycling of limed fleshings. In this paper, a new recycling method for limed fleshings is reported. First, collagen protein hydrolysate (CH) was obtained by hydrolysing limed fleshings under alkaline conditions, and then the CHwas modified with cyanuric chloride (TCT) to obtain a high exhaustion chrome auxiliary (HECA). The coordination of HECA with chromium salts was investigated by ultraviolet-visible (UV-Vis) spectrum. HECA was applied in the chrome tanning process as an additive. The chrome concentration in effluent, the shrinkage temperature and mechanical properties of the resultant wet-blue were determined. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyse the properties of the obtained leather. The results show that HECA could coordinate with chromium salts and significantly improved the absorption and fixation of chrome salt into leather. When the amount of chrome tanning agent was 5% and the amount of HECA was 3%, the uptake of chrome tanning agent could be increased to 92.42%, the shrinkage temperature (Ts) of wet-blue leather could reach 102.8 degrees C, the relative increases being 27.26% and 7.3 degrees C, respectively, compared with the conventional tanning process. The obtained wet-blue leather demonstrated uniform grain, good fullness and improved mechanical properties. This recycling method provides a valuable insight of developing high exhaustion chrome tanning aid from limed fleshings, and consequently increases the economic and environmental benefits in leather production.