Comparison of enzymes for converting eucalyptus Kraft pulp to dissolving pulp for hydrogel production
摘要
Cellulosic paper-grade pulp can be upgraded by chemical treatments to dissolving-grade pulp for the production of textiles and other cellulose derivatives. Environmentally friendly processes may include the use of enzymes to replace chemicals for the upgrade of Kraft pulps. In this work, the effect of enzymatic treatments on eucalyptus bleached Kraft pulp was evaluated using commercial Cellic enzyme cocktails CTec2 (CCT2) and CTec3 (CCT3) for the conversion of paper-grade pulp into dissolving pulp, comparing their performance with a single-component endo-glucanase from Trichoderma reesei (EGTr). Pulps were treated at two enzyme doses (10 and 100 IU/g), followed by acid hydrolysis, dissolution in NMMO solvent, and regeneration as hydrogels for cationic dye adsorption. Chemical analysis of the treated Eucalyptus pulps revealed an increase in carboxyl group content from 0.080 to 0.139 mmol/g after the application of 10 IU/g EGTr. However, at a higher enzyme dosage of 100 IU/g of EGTr, the carboxyl groups decreased to 0.103 mmol/g likely due to the partial reduction in xylans content in the treated pulps. The initial intrinsic viscosity of the bleached kraft pulp (642 mL/g), was reduced by 17.61% and 33.96% after treatments with 10 and 100 IU/g of EGTr, respectively. Among the treatments, hydrogels derived from 10 IU/g EGTr-treated pulps showed lower density (0.0437 g/cm3), higher porosity (96.92%) and a maximum methylene blue (MB) adsorption capacity of 22.9 mg/g. These values were similar to or higher than those obtained with the 100 IU/g treatments. In comparison, hydrogels derived from pulp treated with 10 IU/g of CCT2 and CCT3 cocktails showed bulk density of 0.0503 and 0.0505 g/cm3, a porosity of 96.49 and 96.45%, and maximum MB adsorption capacities of 20.4 and 19.9 mg/g, respectively. Control pulps that were only treated with alkaline extraction and acid hydrolysis exhibited the lowest adsorption capacity (17.1 mg/g). The superior performance of EGTr-treated hydrogels was positively correlated with increased carboxyl group content, which may reflect a secondary oxidative activity associated with the enzyme. The monocomponent EG from T. reesei proved to be the most effective alternative for pulp modification to develop lightweight hydrogels with hight porosity suitable for environmental applications.