Constructing a robust chrome-free leather tanned by biomass-derived polyaldehyde via crosslinking with chitosan derivatives

Tanning leather using green biomass-derived polyaldehyde (BPA) is a promising approach to eliminate the widespread Cr pollution in leather industry, but unsatisfactory thermal stability and mechanical strength of the correlated resultant leather limited its industrial application. Herein, we report a green methodology to strengthen BPA tanned leather via introducing chitosan derivatives to crosslink with free aldehyde groups on dialdehyde carboxymethylcellulose (DCMC) tanned leather. H₂O₂ was employed for purposely modifying chitosan to prepare low-molecular chitosan (LMC) with lower positive charge. The interactions between chitosan/LMC and DCMC were investigated to elucidate the strengthening mechanism. Owing to the weakened hydrogen bonding network and higher accessibility of amino groups on LMC, LMC could react much easier with aldehyde groups on DCMC. Moreover, LMC could efficiently penetrate into the internal fiber networks of leather for further interlocking, which enhanced the thermal stability and the lubricating degree of crust leather and, as a result, the tensile and tear strengths were significantly improved by 79.3% and 25.3%, respectively. Therefore, the use of LMC can promote the widespread application of BPA tanned leather, benefiting to the complete elimination of hazardous Cr pollution.

Peroxide-periodate co-modification of carboxymethylcellulose to prepare polysaccharide-based tanning agent with high solid content

Dialdehyde carboxymethylcellulose (DCMC) solution generally has quite low solid content, which inevitably limits its industrial application. In this work, carboxymethylcellulose sodium (Na-CMC) was pre-degraded using H₂O₂ followed by periodate oxidation for preparing DCMC with high solid content as practical tanning agent. Pre-degradation conditions optimization showed that H₂O₂ dosage most impacted the tanning effect of DCMC, and the M_w and viscosity of Na-CMC underwent remarkable reduction. FT-IR and ¹H NMR illustrated that aldehyde group was successfully introduced into DCMC after periodate oxidation. Under the optimized conditions, the solid content of DCMC could be improved to around 30%. This DCMC could endow tanned leather with high shrinkage temperature and satisfactory fiber dispersion. Besides, DCMC tanned leather had comparable physical and organoleptic properties to those of leathers tanned by chrome tanning agent and commercial polyaldehyde tanning agent TWT. This suggests the prospect of DCMC with high solid content as useful tanning agent.