The Research On Pre-biobleaching Of Eucalyptus Pellita Chemical Pulps By The Extracellular Enzymes From Saccharomonospora Viridis

The research use the extracellular enzymes from Saccharomonospora viridis to pretreat the chemical pulps of Eucalyptus Pellita, discussed the optimum condition of biobleaching, the promoting function of enzymes and the mechanism of biobleaching, etc..The eucalyptus pulps biobleached by the extracellular enzymes from Saccharomonospora viridis, the optimal technical condition of biobleaching was achieved as follows:the optimal dosage of enzymes was 3U/g (according to the lignin peroxidase activities), pH 7.0, treatment duration 120min, pulp density 10%, H2O2 O.lmmol·L-1. The brightness exceeded 82% ISO for both KP and AS-AQ while the amount of total chlorine is only 2.8% with DED sequence. The brightness remained unchanged until the total chlorine of DED decreased sharply 30%. While the SS, CU and CODCr of effluent reduced above 20% on average. The extracellular enzymes play a great role on subsequent chemical bleaching, with more obvious effect for the assistant bleachability. For pulp properties, the effect of kraft pulp is better than alkalinesulfite-anthraquinone. However, for the depressed effluent load, the alkaline sulfite-anthraquinone was more effective than kraft pulp.The extracellular enzymes degraded the pulp obviously and made the fiber structure become loose and the fiber surface appear breakage, voids and groove. The exposed lignin structure promoted the process of subsequent chemical bleaching. Meanwhile, the amorphous region was partly damaged by enzymes.The extracellular enzymes not only degraded the xylan but also attacked the lignin directly, and reduced the chromophoric group of pulp. In the process of biobleaching, more hydroxyl groups in pulp were produced and lignin reactions of subsequent chemical bleaching were enhanced. Besides, in the process of degradation, the structure of lilac was degraded easily and more guaiacyl type lignin can be preserved.