Biocompatible Thermally Responsive Vinyl Sulfone Silica Nanocapsules as Stabilizing and Softening Agents for Metal-Free Leather Production

Developing nanomaterial-based leather chemicals with multifunctional smart properties and biocompatibility for crafting high-quality leather products poses a significant challenge. The double layer formation of silica with an amine and vinyl sulfone terminal created metal-free robust oil deliverable silica nanocapsules (Si–O and Si-OVS). The hydroamination of vinyl sulfone and amine terminal silica yielded a distinctive flower-like structure within a core–shell model. This model encompasses a silica–oil core surrounded by a silica shell incorporating vinyl sulfone. This intricate synthesis results in the encapsulation of a larger quantity of oil, making it suitable to serve as a softening agent for leather applications. Two silica capsule types were developed: one with low oil content and amine terminals for collagen stabilization and another with high oil content and vinyl sulfone terminals for lubrication. The efficacy of Si–O nanocapsules as a stabilization agent and Si-OVS as a softening agent has been demonstrated through their application in leather processing, revealing noteworthy improvements over conventional organic (conventional silica tanning) and metal-based tanning agents. The leather treated with Si–O and Si-OVS exhibits enhanced tensile strength, tear resistance, and softness. This enhancement is attributed to the formation of chemical bonds between the vinyl sulfone terminals and the amine and carboxyl groups present in collagen fibers instead of conventional electrostatic interactions. Additionally, the cytotoxicity of Si–O and Si-OVS were evaluated, revealing no toxicity toward a fibroblast cell line and confirming the biocompatible nature of the prepared nanocapsules. The multifunctional oil-deliverable silica nanocapsules address the challenges of a metal-free tanning process, enabling the smart delivery of oil into the three-dimensional leather matrix, thereby contributing to the production of high-quality leather.