Wet Strength Improvement of Unbleached Kraft Pulp with Laccase in Presence of Methyl Syringate

摘要

In this paper,the unbleached kraft pulp was treated by laccase in presence of methyl syringate (laccase/MS).The tensile strengths of handsheets made by the treated unbleached kraft pulp were determined,and the treated fibers were investigated by electron paramagnetic resonance spectroscopy(EPR)and scanning electron microscope (SEM).The laccase catalytic reaction with pulp was studied by monitoring the oxygen consumption in a pulp suspension.The results showed that using combination of laccase and MS could significantly increase the wet tensile strength of pulp compared with using laccase alone,whereas it had little effect on the dry tensile strength and led to a loss of brightness.The EPR measurement demonstrated that the radical concentration in the iaccase/MS-treated fibers was much higher than that in the fibers treated by laccase alone.The SEM photographs showed that in laccase/MS-treated fibers an intense agglutination phenomenon of fibers occurred in wide areas.During the laccase treatment of pulp,the oxygen concentration decreased in initial in a few minutes and then kept at a higher level.For the laccase treatment on the pulp in presence of MS,oxygen in sealed vessel decreased rapidly and was exhausted after 20 min.It was suggested that the participation of MS accelerated the activation of fiber and an intense adhesion of fibers occurred via the extensive cross-linking of radicals,which caused the significant improvement of the wet strength of pulp.