Development of hyperbranched poly-(amine-ester) based aldehyde/chrome-free tanning agents for sustainable leather resource recycling

Abstract

Leather manufacturing is the main recycling technology used for nature skin biomass resources. However, leather-based products are made by the conventional chrome tanning method, in which the discharge of chrome-containing wastes poses potential threats to the environment and public health. By comparison, the aldehyde/chrome-free tanning strategy is ecologically advantageous for the manufacturing of leather. Therefore, a series of epoxy-terminated hyperbranched poly-(amine-ester) materials (abbreviated as EHBPs) were synthesized in this study using epichlorohydrin modified hydroxyl-terminated hyperbranched poly-(amine-esters) (HHBPs). The characterization and testing of the as-obtained EHBP tanning agent showed significantly improved hydrothermal stability of the treated leather with the shrinkage temperature (T_s) exceeding 75 °C, good physical properties, and a relevant thickening ratio (>50%). Besides, the EHBP tanning approach ensured a high dispersity of collagen fibers with substantially enhanced porosity (control 41% and EHBP-tanned leather > 51%). The environmental impact assessment revealed the preferable biodegradability of EHBPs (BOD₅/COD > 0.3). In sum, the proposed EHBP-based tanning approach looks promising for the realization of environmentally benign leather manufacturing for next-generation green chrome-free tanning.