Degradation of TEMPO-oxidized cellulose fibers and nanofibrils by crude cellulase

Abstract

The biodegradation behavior of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose fibers (TOCs) suspended in water and TEMPO-oxidized cellulose nanofibrils (TOCNs) dispersed in water by a commercial crude cellulase was studied. Products crude cellulase-treated for 0–7 days were separated into water/ethanol-insoluble and -soluble fractions. Weight recovery ratios and viscosity-average degrees of polymerization of the water/ethanol-insoluble fractions clearly decreased with crude cellulase-treatment time, showing that both TOCs and TOCNs have biodegradability. Water/ethanol-soluble fractions were subjected to size-exclusion chromatography (SEC) with photodiode array (PDA) detection to obtain SEC elution patterns detected by reflective index and UV spectra of each SEC pattern elution slice. SEC–PDA and 13C-NMR analyses showed that glucuronosyl unit-containing molecules present on microfibril surfaces in TOCs and TOCNs were primarily cleaved by hydrolyzing enzymes present as contaminants in the crude cellulase to form glucuronic acid as one of the major water-soluble degradation compounds. After the glucuronosyl units in TOCs and TOCNs were degraded and removed from microfibril surfaces by the hydrolyzing enzymes, cellulose chains newly exposed on the microfibril surfaces were rapidly hydrolyzed by cellulases predominantly present in the crude cellulase to form cellobiose. Both TOCs and TOCNs having sodium carboxyl groups are thus biodegradable, but TOCN having free carboxyl groups had clearly low biodegradability by the crude cellulase. Thus, biodegradation behavior may be controllable by controlling the structure of carboxyl group counter ions in TOCs and TOCNs.