Particle Size Evolution of Chrome Tanning Agent on Tanning Effect

In a traditional method of chrome tanning, the particle size (PS) of tanning agent is critical for its penetration and the performance of resultant leather. The temperature, pH value and concentration of chrome solution are the important parameters to influence the size scale of the chromium complex. In present study, the PS evolution of chrome tanning agent (CTA) with pH value and temperature changes was investigated firstly, then the influence of the evolution of PS on the tanning process and hydrothermal stability of crust leather was also investigated. The results indicated that with the temperature varied from 25 degrees C to 30 degrees C and 35 degrees C, the pH of the chrome solution increased from 2.5 to 3.8, the PS of CTA increased from 982 nm to 2899 nm, 1265 nm to 3384 nm and 1289 nm to 3630 nm, respectively, showing a rapid increasing tendency. Correspondingly, due to the PS of CTA increased, the chromium absorption rate increased from 31.0% to 53.6% at 25 degrees C, 33.8% to 55.9% at 30 degrees C and 34.5% to 56.4% at 35 degrees C, whilst the uniformity of the chromium distribution in crust leather was gradually reduced. At the same initial tanning temperature, the shrinkage temperature (T) of wet blue tend to increase first and then decrease with the increase of the CTA's PS, and reached above 100 degrees C when the PS was in a range from 2000 nm-2700 nm. As the PS continues to increase, the inner layer was insufficient tanned due to excessive tanning of surface, leading to a decrease in hydrothermal stability of crust leather.