Preparation of high solid content oxidized starch by acid pretreatment-HO oxidation and its performance as the ligand in zirconium tanning.

Highly-oxidized starch (HOS) is an excellent ligand for zirconium tanning in leather making. However, oxidation reaction can only be undertaken in diluted solution due to the high viscosity of starch, which leads to high oxidant consumption and low solid content of HOS, and therefore greatly limits its industrial application. Starch was predegraded by using HCl followed by HO oxidation for preparing a practical oxidized starch (OST) ligand with high solid content. HCl (5%) remarkably reduced the viscosity of starch and simplified the subsequent oxidation, resulting in a decrease in HO dosage from 60% to 40% and an increase in solid content from 10% to 38%. HCl broke the α-(1-4) glycosidic bond between glucose units, and HO oxidation led to the generation of abundant carboxyl groups in OST. The OST with moderate molecular weight (Mw 5609 g/mol) and carboxyl content (6.48 mmol/g) made the tanning performance of OST-Zr comparable to those of HOS-Zr and chrome tanning agents. Therefore, this work gives new insights into the crop-polysaccharides based ligands application and exhibits huge potential for promoting industrial applications of zirconium tanning.