Depolymerization of carboxymethylcellulose in a hydro-alcoholic medium by a mono-component endocellulase

Abstract

Carboxymethylcellulose (CMC) is a cellulose ether with a wide range of applications and markets. In order to tailor the molecular weight and the rheological profile of CMC, the industrial production process often implies a difficult to control depolymerization step with high concentrations of hydrogen peroxide or other oxidizing agents at alkaline pH. Because CMC dissolved in an aqueous buffer at concentrations above 3–4% (w/w) generates extremely high and unmanageable viscosities, we have developed an alternative process of enzymatic depolymerization with a selected, recombinant mono-component endocellulase for the preparation of a highly concentrated aqueous solution of low molecular weight CMC, from a 240–300 kDa CMC dispersed as a slurry in a hydro-alcoholic reaction medium, followed by solvent recovery. Wood cellulose from different tree sources and a few commercially available cellulases, either of natural origin or recombinant, were screened. The recombinant, mono-component endoglucanase Cel12A from T. reesei was selected for CMC hydrolysis carried out in isopropanol. At the end of the reaction, the enzyme is thermally inactivated and the solvent recovered by distillation. This novel industrial process yields a stable aqueous solution of a low viscosity, ready-to-use 35% (w/w) CMC, which is finding increasing new practical applications.