| Laccase is a kind of multi-phenol oxidase, copperion involved. As a lignin degradation enzyme, it can degrade the lignin of organism. The potential of oxidation and reduction of laccase is very low, about 300-800mV (normal hydrogen electrode). Laccase can oxidate phenolic units in lignin, but it can not react with nonphenolic units which account for ninty percent of lignin. If a low-mass compound is introduced as a mediator of oxidation and reduction reaction, laccase can also oxidate nonphenolic units. For example, ABTS(2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonate), HBT(1- hydroxybenzotriazole), VIO(Violuric acid), MS(Methyl Syringate), PTC(Promethazine hydrochloride), PPT(Phenothiazine-10-propionic acid), PT(Phenothiazine) etc.As all known, the characteristics of Masson Pine Stone Ground Wood Pulp (SGW) are low-cost, high yield and friendly to environment. However, the disadvantages of low-strength and brightness instability restrict seriously its application to top grade paper. So it was necessary to modify the properties of SGW. Modification of SGW with laccase/mediator was studied, with its mechanism explored in this paper.At present, there are plenty of low-molecular weight matters in nature, which are applied to the modification of SGW. Most of them were synthesized by scientific researchers. It is indispensable to optimize the very mediator to modify SGW, according to the effect of modification.Optimum reaction conditions about modifying properties by laccase/mediator treatment were studied. The optimal reaction conditions were: presence of oxygen, laccase dosage 5 LAMU/g pulp, 1% violuric acid (o.d.), temperature of 55℃, pulp consistency 2.5% and reaction time 60 min. Under this condition, the brightness decreased slightly, but the strength of pulp increased apparently. Both the brightness and the strength of pulp increased after hydrogen peroxide bleaching compared with control sample, which indicated that the bleachablity of pulp was improved after laccase/mediator treatment.The oxygen concentration during the process of laccase/mediator treating SGW was measured by oxygen electrode in order to study different reactivity of laccase/mediator towards lignin under different conditions and kinetics of oxidation reaction. It was found that violuric acid (VIO) among different mediators showed the highest rate of oxygen consumption. When laccase treated pulp only, the oxygen concentration decreased rapidly in initial and then kept at the steady level. In addition, oxygen concentration did not change obvisously when mediator (VIO) treated pulp only. For laccase/VIO treating system, oxygen in sealed vessel was exhausted in 20 minutes. The reactivity of laccase/mediator towards lignin model substance was similar to pulp, but speed differed. It was found that the oxygen consumption follow a single exponential decay in laccase/VIO treatment system over time.The pulp treated with laccase /mediator was investigated by SEM and FQA. It showed that the surface was rough and fuzzy, and the length and coarseness of fiber in pulp became shorter compared with control pulp. The filtrate from pulp treated with laccase /mediator was studied by FI-IR and GC-MS. The results indicated that there were a lot of guaiacol units, carbonylation and some low-molecular weight matters in the treated water. It illuminated that the lignin was degraded, which exposed many hydrogen bonds and strengthened the binding force among fibers. Consequently, the strength of paper treated with laccase/mediator was improved.
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