The Use of Collagen Hydrolysate from Chromium Waste in the Optimization of Leather Retanning

Leather tanning generates substantial amounts of solid waste and effluents, posing significant environmental challenges due to the presence of hazardous chromium compounds. The aim of this study was to develop and optimize a method for recycling chromium-tanned leather waste by utilizing it as a raw material in the retanning process. Collagen hydrolysate was extracted from chrome-tanned leather shavings through acid hydrolysis and subsequently incorporated, together with melamine, into novel retanning compositions. The experimental design, based on the Kleeman method, involved varying the hydrolysate content (25%, 30%, 35%) and melamine concentration (2.5%, 3.0%, 3.5%, 4.0%) to assess their impact on the physicochemical properties of retanned wet-blue leathers. An innovative aspect of the study was the integration of the Kateskór computer program, employing the Kleeman experimental planning method, to optimize the formulation of retanning compositions. This computational approach enabled the precise determination of hydrolysate and melamine quantities required to achieve leather properties that meet both producer and consumer expectations. The optimized formulation identified the hydrolysate content in the range of 28.78–29.63% and melamine in the range of 3.61–3.68% as optimal for obtaining leathers with the desired mechanical strength, shrinkage temperature, and water vapor permeability. The study presents a practical model of a circular economy within the leather industry, aligning with the European Green Deal Strategy by promoting resource efficiency and minimizing hazardous waste. The proposed methodology provides a viable pathway for sustainable leather production through waste valorization and process optimization.