Study on the selective oxidation of tapioca starch via a two-step method and its application in titanium tanning.

To address the limitations of insufficient collagen fiber cross-linking in titanium-tanned leather and environmental pollution associated with traditional chrome tanning, and presented a bio-based tanning agent modification strategy based on a two-step oxidation method of tapioca starch in this work. Hydrogen peroxide (H₂O₂) was employed to further oxidize aldehyde-functionalized tapioca (DAS), resulting in a novel bio-based tanning agent for synergistic application with titanium tanning agents. The synergistic cross-linking and filling mechanisms of oxidized starch and titanyl sulfate in leather tanning were systematically investigated. By controlling the aldehyde content in DAS, the oxidation process was optimized based on oxidant molar ratios, yielding oxidized tapioca (ROS) with multifunctional groups including aldehydes and high carboxyl content. FT-IR, XRD, and Raman characterization confirmed reduced crystallinity, disrupted internal structure, and generation of new functional groups. Tanning experiments demonstrated that carboxyl groups in oxidized starch form stable coordination bonds with titanium tanning agents (TiO2+), while short-chain starch molecules enhance physical properties through filling collagen fiber gaps. This elevated the shrinkage temperature of tanned leather to 85.0 °C, an increase of 16.7 °C increase compared with single‑titanium tanning. Raman spectroscopy confirmed the formation of ROS-TiO2+ collagen ternary complexes. These findings indicate that combining oxidized tapioca (ROS) with titanium tanning significantly improves leather shrinkage temperature and fiber morphology, providing a sustainable, biodegradable, chromium-free, and formaldehyde-free strategy for clean leather manufacturing.