| With the development of science and technology and the progress of biological technology, more and more enzymes were found and applied. The effective utilization of enzymes not only brings convenience for human, but also brings high economic, social and environmental benefits. In recent years, more and more attention has been paide to the studies of the redox enzymes secreted by microorganisms, particularly the laccase with adaptability to diversified substrates. In this work, pulp fibers were modified by the laccase/TEMPO mediator system, the functional groups of pulp were tested, the change of the physicochemical properties of pulp was analyzed, and the biodegradability of the modified pulp fibers was investigated.The laccase/TEMPO mediator system involved the use of a commercial laccase secreted by aspergillus oryzae as a bio catalyst and TEMPO as electron transfer medium. The conditions for the the reaction of laccase/TEMPO mediator system with pulp fibers were optimized. The optimum conditions for maximum aldehyde content were:reaction time of12h, TEMPO dosage of0.2g/g o.d. pulp, laccase dosage of0.5ml/g o.d. pulp, pH4.5, and reaction temperature of30℃; the optimum conditions for maximum carboxyl content were:reaction time of24h, TEMPO dosage of0.33g/g o.d. pulp, laccase dosage of0.67ml/g o.d. pulp, pH4.5. and reaction temperature of30℃. The aldehyde and carboxyl contents of pulp fibers oxidized by laccase/TEMPO mediator system were increased by225%and360%, respectively. The modified pulp fibers were analyzed by FT-IR and XPS, and the presence of carbonyl group on the surface of pulp fibers was identified. Also, the pulp fiber surfaces were observed and analyzed by optical microscope and scanning electron microscope (SEM). and the occurrence of pulp surface nicking was identified. At the same time, bleached hardwood sulfate pulp was oxidized by laccase/TEMPO mediator system, and carboxyl content of hardwood pulp increased by246%.The physicochemical properties of laccase/TEMPO modified pulp fibers were tested. It was found that all the indices were changed to various degrees. The pulp fiber copper value increased by almost4times. The DP of laccase/TEMPO treated pulp fibers was lower than that of untreated pulp fibers, the polymerization degree was reduced to1/3of that of control sample. The water retention value was increased by nearly20%. The zero tensile strength was reduced by nearly40%. The tensile strength of handsheets prepared from the treated pulp was twice that of untreated pulp, and the bursting strength did not increase significantly. The brightness of handsheets was practically unchanged.Upon modification with laccase/TEMPO, the adsorption of silver ions by the pulp fibers was significantly improved, and the adsorbed amount increased with the increase of carboxyl content. The maximum adsorbed amount of silver ions was2times higher than that of the control sample. The silver ion adsorbed pulp fibers were treated at high temperature, and the color was changed strikinigly. After fiber modification, the antibacterial property of the pulp fibers increased significantly, and the diameter of the inhibition zone became bigger than that of untreated pulp fibers. Scanning electron microscope (SEM) observation revealed that there were silver particles on the pulp fiber surface.The optimum conditions for the degradation of laccase/TEMPO treated pulp and the control sample (treated by cellulose) were investigated. The optimum conditions for the the degradation of the control sample by cellulase were:pH of4.5, temperature of40℃, enzymolysis time of12h, and cellulase dosage of12.5ml; the optimum conditions for the degradation of laccase/TEMPO treated pulp by cellulase were:pH of4.5, temperature of40℃, enzymolysis time of8hours, and cellulase dosage of10ml. To reach the maximum sugar yield, the laccase/TEMPO treated pulp required less reaction time and lower cellulase dosage in comparison with the control sample. Therefore, laccase/TEMPO treated pulp fibers was easier to be degraded by cellulase in comparison with the original pulp.In summary, the functional groups of pulp fibers were changed by laccase/TEMPO oxidation. Such a treatment not only changed the mechanical properties of pulp, but also changed the characteristics of chemical reaction and the sensitivity to cellulase. As a new concept to produce high strength paper, especially high wet-strength paper, it would open up a new way of manufacturing antibacterial paper provide and provide a novel idea for the enzymolysis of cellulose by cellulase as well as the development of bio-ethanol. |
PDF Full Text Request