An Effective and Harmless Recycling Technology for Hazardous Chrome-Tanned Leather Wastes: Re-utilization of dechromed collagen fibres as filler in leather making processing

Utilizing leather production waste to create raw materials for leather chemicals, and reintroducing it into the leather making processing, represents an ideal approach to achieving an "internal circular economy" within the leather industry. This study focuses on the re-utilization of dechromed collagen fibres, obtained from chromium shavings, to generate a retanning filling. The effects of hydrolysis conditions on the viscosity, and gel strength of the dechromed collagen hydrolysates were investigated. The application effectiveness of the collagen hydrolysates with different particle sizes in the leather retanning filling process was also compared. The findings indicate that alkali hydrolysis is more conducive to producing collagen hydrolysates with a relatively higher proportion of medium and low molecular weight components, while acid hydrolysis favours the production of collagen hydrolysates rich in high molecular weight components. Additionally, collagen hydrolysates with an average particle size of 162.8 nm exhibit the best filling efficacy, imparting favorable organoleptic and physical properties to the leather. Herein, a method for preparing protein fillers, using chrome shavings as raw materials, was established, i.e., the dechromed collagen fibres (with a chromium content of approximately 33.6 mg/kg) were mixed with 2000% of water and adjusted to pH 3.0 with a small amount of sulfuric acid, and heated at 60 degrees C with continuous stirring for 11 hours. After hydrolysis, the pH was adjusted appropriately to reuse it in the wet blue retanning filling process. The research outcomes have significant guiding implications for promoting the "internal circular economy" and sustainable development within the leather industry.