High-value conversion of leather waste: An enhanced protein-based retarder for gypsum construction

Effective management of leather waste is essential for the sustainable advancement of the leather industry. Leather scraps, which represent a valuable biomass resource, are primarily composed of protein-rich collagen fibers. This study presents the development of a novel protein retarding material (PRM) derived from leather scraps through high-pressure hydrothermal treatment. Citric acid (CA) was incorporated into the PRM molecular chain using ethylene glycol diglycidyl ether, resulting in a highly efficient protein-based retarder (C-PRM) optimized for use in building gypsum. C-PRM demonstrated outstanding performance in extending gypsum setting time, with its retarding effect closely linked to its dosage. The CA modification significantly enhanced the delay in hemihydrate hydration and the formation of dihydrate. Additionally, the introduction of carboxyl groups through CA modification improved the calcium-binding capacity of C-PRM by 14.73 % compared to PRM. By promoting calcium-peptide chelation, C-PRM more effectively inhibited the involvement of free Ca 2+ in the hydration reaction, thus delaying the conversion of hemihydrate to dihydrate and providing superior gypsum retardation. This advanced protein-based retarder, derived from leather waste, offers a promising solution for gypsum retarder development and introduces a novel approach to the high-value utilization of leather waste.