Modification of collagen with three novel tannages, sulfonated calix[4]arenes

Chromium (III) salts are the most extensively used tanning agents due to the higher quality and stabilization ability to leather collagen. However, chromium (III) salts tanning agent has a strong impact on the environment owing to the pollution of wastewater and the solid waste containing chrome. In order to crosslink the collagen by a cleaner method, three kinds of sulfonated calix[4]arenes {sulfonated calix[4]arene (SC), sulfonated tetraphenyl calix[4]resorcinarene (STCR), and sulfonated tetramethylene tetraphenyl calix[4]resorcinarene(STTCR)} were prepared and utilized for the collagen crosslinking and leather tanning. The collagen crosslinking degree of sulfonated calix[4]arenes was investigated by fourier transform infrared (FTIR), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), scanning electron micrograph (SEM), and X-ray photoelectron spectroscopy (XPS). The results show that the collagen can be crosslinked by phenol hydroxyl groups on sulfonated calix[4]arenes. Moreover, STCR shows better crosslinking effects than others because the number of phenol hydroxyl groups and the position of sulfonic groups on sulfonated calix[4]arenes play important roles in the crosslinking process. These results can be confirmed by sulfonated calix[4]arenes tanning processes, and STCR tanned leather shows the higher shrinkage temperature. This paper provides a promising chrome-free method to reduce the pollution of chromium tanning waste.