A salt-free pickling chrome tanning technology: Pretreatment with the collective polyoxyethylene diepoxy ether and urotropine

Overview of the Leather Industry and Pollution Impact

“…Nevertheless, considering the salt-free pickling processes without eradicating the chromium, most of the studies improved the values obtained on leather properties characterization. Denaturation temperatures between 111ºC (Jia et al 2020) and 125.1ºC (Zhang et al 2017a), tear strength increases of 3.1% (Jia et al 2020) to 25% (Zhang et al 2016), and percentages of tensile strength above the conventional process values, between 1.2% (Zhang et al 2017a) and 46.2% (Zhang et al 2016) were achieved. However, the combination of urotropine and PODEE presented the worst results in these studies, especially for the tensile strength, which values stayed below the standard (Jia et al 2020).…”

“…Denaturation temperatures between 111ºC (Jia et al 2020) and 125.1ºC (Zhang et al 2017a), tear strength increases of 3.1% (Jia et al 2020) to 25% (Zhang et al 2016), and percentages of tensile strength above the conventional process values, between 1.2% (Zhang et al 2017a) and 46.2% (Zhang et al 2016) were achieved. However, the combination of urotropine and PODEE presented the worst results in these studies, especially for the tensile strength, which values stayed below the standard (Jia et al 2020). Furthermore, when compared with all the researches, the implementation of aromatic sulfonic acids associated with chromium exhaustion by its recycling showed the highest stability for all the evaluated parameters (Zhang et al 2016;Zhang et al 2017a).…”

“…To overcome the sodium chloride environmental problem, in the pickling effluents, different mechanisms were explored to ensure that no ecological disturbance occurs. Recycling of pickling liquor (Sivakumar et al 2005) and salt-free pickling process (Li et al 2009;Zhang et al 2016;Sundar and Muralidharan 2017;Zhang et al 2017a;Zhang et al 2017b;Jia et al 2020) are the answers presented so far.…”

“…From the pilot-scale trials, emission reductions of 15% of COD and 42% of TDS were observed. Near 280 mg/L of residual chromium was determined in the effluent with an offer of 0.89 wt% and an uptake of 91.3% (Jia et al 2020). Researchers also explored chromium recovery systems and its reintroduction in the tanning process.…”

A salt-free pickling and chrome-free tanning technology: a sustainable approach for cleaner leather manufacturing

“…As mentioned earlier, sulfonic acid groups mainly form ionic bonds with amino groups of collagen (–SO 3− – + NH 3 –), whereas other materials containing epoxy or isocyanate groups and oxazolidines mainly react with free amines on collagen fibers forming covalent bonds and blocking amino groups, which is actually a pre-tanning process. 10 For instance, Jia et al 16 used urotropine as a catalyst to pretreat the bated hide with polyoxyethylene diepoxy ether (PODEE) in order to realize pickling and chrome tanning under salt-free conditions. However, PODEE has some limitations in terms of fullness and increase in the number of active sites to promote coordination and binding with metal tanning agents.…”