Formaldehyde formation during the preparation of dialdehyde carboxymethyl cellulose tanning agent

Formaldehyde was detected in dialdehyde carboxymethyl cellulose (DCMC) tanning agent prepared through periodate oxidation of sodium carboxymethyl cellulose (CMC). Formaldehyde was then introduced into leather through DCMC tanning, which poses a potential risk to human health. The formation mechanism of formaldehyde in DCMC was investigated by composition analysis and intermediate identification of DCMC with different polymerization degrees and sugar unit structures. Formaldehyde was derived from the overoxidation of C-6 on the reducing glucose residue of CMC. Moreover, glucose was produced from the concomitant degradation of CMC during oxidation, and then oxidized to liberate formaldehyde. The low degradation degree and high degree of substitution of CMC reduced the possibility of the formation of reducing glucose residue and glucose during oxidation, thereby resulting in low formaldehyde content in DCMC and DCMC-tanned leather. These findings serve as a foundation for the minimization of formaldehyde in DCMC and the development of ecological tanning approach.