A Novel Nano-SiO2 Tannage for Making Chrome-Free Leather

A novel pickle less combination tannage based on nano-SiO2 and oxazolidine as a substitute for chrome tanning has been developed. The size and distribution of nano-SiO2 in protein, the hydrothermal stability, the mechanical properties and the antifungal effect of final leather as well as the evaluation of eco-friendly characteristics of combination tannage were investigated. Scanning Electric Microscope (SEM) analysis indicates that the distribution of nano-SiO2 in protein is even when the SiO2 concentration is lower than 5 wt% (on bated pelt weight), and the size of SiO2 particles can be controlled to a range from 60 to 150 nm. But when the SiO2 concentration is higher than 7 wt%, most of particles conglomerate together and the size of the SiO2 particles is larger than 400 nm. Differential Scanning Calorimeter (DSC) study shows that the shrinkage temperature of final leather which is related to the content of nano-SiO2 is more than 95°C. Compared to the chrome tannage, leather tanned with oxazolidine-nano-SiO2 demonstrates a higher resistance to mould than conventional wet blue. The later incubated for 3 days began to grow mildew, whilst the oxazolidine-nano-SiO2 tanned leather which was incubated for 6 days had no mildew, showing fine antifungal effect. Environmental impact assessment shows that the developed process exhibits significant reduction in total solids (TS) and better biodegradability of organic compound in the effluent when compared to chrome tanning.