Leather wastes into high-value chemicals: Keratin-based retanning agents via UV-initiated polymerization

Eco-friendly keratin-based retanning agents have aroused widespread interest in leather manufacturing, because they recycle the biomass wastes for sustainable industry. However, the poor filling effect and binding strength of hydrolyzed keratin from bovine hair wastes limit its application for leather retanning. Here we reported a series of polyacrylate-modified keratin (PMK) retanning agents synthesized from vinyl monomers and bovine hairs via a surfactant-free and UV-initiated polymerization. The obtained spherical PMK retanning agents exhibited ideal characteristics, such as appropriate molecular weight (13–22 kDa) and particle size (86–110 nm), and good colloidal stability in the tanning bath (pH 5.5). We further validated these agents for retanning bovine shoe upper leather. Compared with FB (i.e., a commercial retanning agent), leather retanned with PMK75 showed increased thickness (∼50%) and reduced Δb* (∼80%), suggesting excellent filling properties and yellowing resistance. Moreover, the retanning agent afforded the products improved physical properties (e.g., tensile strength ∼17.3 N/mm2, tear strength ∼72.7 N/mm and elongation at break ∼75.4%) and sensory properties (e.g., compression thickness ∼0.25 mm and resilience thickness ∼0.21 mm). This work not only offered a robust method for preparing low-cost retanning agents in sustainable industry, but also provided more opportunities for recycling biomass-based wastes aiming to closed-loop economy.