Effect of Dialdehyde Carboxymethyl Cellulose Cross-Linking on the Porous Structure of the Collagen Matrix.

Porous structures are essential for some collagen-based biomaterials and can be regulated by crosslinkers. Herein, dialdehyde carboxymethyl cellulose (DCMC) crosslinkers with similar size but different aldehyde group contents were prepared through periodate oxidation of sodium carboxymethyl cellulose with varying degrees of substitution (DS). They can penetrate into the hierarchy of fibril and form inter-molecular and intra-fibril cross-linking within the collagen matrix due to their nanoscale sizes and reactive aldehyde groups. The collagen matrices possessed higher porosity, significantly greater proportion of large pores (Φ > 10 µm), and shorter D-periodicity after cross-linking, showing greater potential for biomedical applications. In addition, the crosslinked collagen matrices showed satisfactory biocompatibility and biodegradation. The decreased DS of carboxymethyl cellulose, which led to the increased aldehyde content of corresponding DCMC, brought about an enhanced cross-linking degree, porosity, and proportion of large pores of the crosslinked collagen matrix. DCMC dosage of 6% was sufficient for cross-linking and pore formation. Excess DCMC would physically deposit in the matrix and decrease the porosity instead. Therefore, the desired pore properties of the collagen matrix could be obtained by regulating the structure of DCMC and thereby achieving the required functions of the biomaterial.

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.

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 Mw 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.