Bridging-induced densification strategy based on biomass-derived aldehyde tanning integrated with terminal Al(III) crosslinking towards high-performance chrome-free leather production.

Chrome-free leather manufacturing has been acknowledged as a desirable option to eliminate potential environmental and human health risks of conventional chrome tanning. This work applied a sequential bridging-induced densification strategy to produce high-performance chrome-free leather with high crosslinking density derived from the biomass-derived aldehyde (BAT) crosslinking (BAT tanning of leather), followed by terminal Al(III) crosslinking (TAC). The TAC conditions for BAT tanned leather were optimized and the results suggested that the optimized conditions were as follows: the fixation pH was 4.2, the pre-penetration time was 180 min, the fixation temperature was 40 °C, and the dosage of the aluminum tanning agent (ATA) was 0.5% (based on Al2O3). Under the optimized conditions, the resultant BAT-TAC crust leather exhibited favorable overall performances compared with BAT crust leather in terms of higher hydrothermal stability, mechanical strengths, more pleasant uniform color, and comparable smooth grain surface. The obtained high-performance chrome-free leather is scalable, providing an avenue for designing and rationalizing other engineering technology towards high-performance eco-leather production.

Discarded enoki mushroom root-derived multifunctional chrome-free chitosan-based tanning agent for eco-leathers manufacturing: Tanning-dyeing, non-acid soaking, and non-basifying.

The aim of this study was to develop new discarded enoki mushroom root-derived multifunctional chrome-free chitosan-based tanning agents that can be used for eco-leather manufacturing. In this study, oligochitosan (OCS) was prepared from chitosan extracted from the enoki mushrooms and chemically modified using reactive dye R19 and epichlorohydrin (ECH) to prepare chromium-free tanning agent (OCS-R19-ECH) with both tanning and dyeing functions. FT-IR, XRD, and NMR (1H) confirmed the successful synthesis of the product. The molecular weight of OCS-R19-ECH is 6355 g/mol, with an average particle size of 1249.37 nm and an epoxy value of 0.276 mol/100 g. OCS-R19-ECH was used for tanning experiments on bated sheepskin, and the results showed that the leather tanned with OCS-R19-ECH not only exhibited excellent wet-heat stability (shrinkage temperature = 81 °C), but also superior dyeing uniformity, resistance to dry and wet abrasion, mechanical strength (tensile strength = 12.4 MPa, tear strength = 57.3 N/mm), and outstanding antimicrobial properties. Most importantly, compared with traditional tanning agents, OCS-R19-ECH has a higher pH (9.0), tanning-dyeing integration, non-acid soaking, and non-basifying can be achieved in leather making, which can greatly simplify the tanning processes. This new multifunctional chrome-free chitosan-based tanning agent facilitates high-value utilization of waste resources.