A cleaner approach to tanning process of cattle hide upper suede leather: chrome-less polycarboxylate/montmorillonite nanocomposites as tanning agent

In this study, a cleaner approach to a ‘sandwich’ chrome-less tanning for cattle hide upper suede leather based on polycarboxylate/montmorillonite nanocomposite (PCM) has been developed. The chromium was reduced both in tanning process and retanning process. Hydrothermal stability, mechanical strength, and organoleptic properties of the leather were closed to traditional chrome tanning. The important advantage of the cleaner tanning approach is that the chromium load in wastewater decreased from 2302 mg/L in tanning process and 2919 mg/L in retanning process to 131 and 257 mg/L, respectively. Moreover, SEM analyses demonstrated that the leather tanned by PCM achieved loose fiber structure and flaky montmorillonite deposition both in intra-triple and inter-triple helix. XRD results suggested that basic chromium sulfate and PCM may form more complexation with the helix chain of collagen fiber, resulting in structural distortion of collagen molecules without destroying the triple helical structure. EDS liner scanning indicated the distribution of chromium on the cross section of the leather. Trypsin degradation curves revealed the cleaner approach might increase the degradation of leather, and the economic analysis results showed that the tanning costs could be reduced and increased the economic benefits.