A novel approach for intensification of enzymatic depolymerization of carboxymethyl cellulose using ultrasonic and ultraviolet irradiations

• Intensified depolymerization of CMC using US/UV assisted enzymatic approach.
• Detailed investigation of the effect of different operating parameters.
• Comparison of different approaches in terms of intrinsic viscosity reduction.
• Combined ultrasonic–ultraviolet enzymatic method was found as best approach.

The present work investigates the application of ultrasonic (US) and ultraviolet (UV) irradiations operated individually or in combination for intensification of enzymatic depolymerization of aqueous solution of carboxymethyl cellulose (CMC) present as sodium salt. The effect of different operating parameters such as reaction temperature, enzyme loading, UV and US power dissipation on the extent of depolymerization have been studied. The effectiveness of treatment approach has been analyzed on the basis of kinetic rate constant, limiting intrinsic viscosity and the time required for the desired extent of intrinsic viscosity reduction. The kinetic rate constant has been found to increase with an increase in the temperature and cellulase loading. The extent of depolymerization increased from 20% to 58.5% with an increase in the operating power of UV from 8 W to 32 W (irradiation time as 180 min) whereas the increase was from 74% to 87% for an increase in ultrasonic power from 60 W to 120 W (irradiation time of 120 min). In the presence of US (60 W) + UV (16 W) + enzyme (0.05%), the maximum extent of depolymerization of CMC has been observed as 99% with treatment time of 18 min. The effect of ultrasonic irradiation on viscosity reduction was established to be more pronounced than the ultraviolet irradiations. The obtained results from FTIR spectra clearly established that no changes in the chemical structure were observed for the treated CMC using combined ultrasound, ultraviolet irradiations with enzyme and native CMC. The work has conclusively established, for the first time, that the combination of ultraviolet and ultrasonic irradiation in presence of cellulase enzyme gives maximum viscosity reduction in CMC polysaccharides as compared to individual approaches.