The Research Focused On Pulp Deligninfication And Bleaching With Laccase

Laccase is a copper-containing polyphenol oxidase, which can oxidize a variety ofphenols and aromatic amines, and simultaneously reduce oxygen moleculers into water.Laccase alone can effectively oxidize phenolic-lignin structure due to its high redox potential.With the addition of some small chemical compounds which are called mediators can extendthe substrate range of enzyme to non-phenolic lignin structures as well.This makes laccasehighly suitable to many industrial applications such as pulp biobleaching, wastewatertreatment, organic dye decolouration, polymer synthese, etc. laccase is considered as the mostpromising enzymes in the pulp and paper industry.Those current available mediators are mostly artificially synthesized. The high pricemade them not conducive to the realization of the enterprises economic benefits. Furthermore,highly toxic by-products are outputted during the bleaching process, which would pollute theenvironment seriously. On the basis of this background, the process of NaOH-AQ corn stalkpulp was treated with laccase/mediator system (LMS) was optimized with Response SurfaceMethodology. With target brightness of85%ISO, reducing the dosage of HBT as the firstgoal, and the second was to shorten the reaction time, the optimized bleaching conditionswere: laccase dosage27.7IU/g, HBT dosage1%odp, treatment time4.2h.A stable complexe with high affinity is produced when laccase reacted with H2O2. Underanaerobic conditions, the laccase could be reduced by hydroquinone becamehydroquinone-enzyme intermediate complexes, then the intermediate complexes transforminto semiquinone and L-Cu(Ⅰ). H2O2can replace O2to oxidize the L-Cu(Ⅰ) into L-Cu(Ⅱ).Synergic action exists between H2O2and laccase in a short time. The catalytic reaction rateincreased by adding a small amount of H2O2, and the catalytic action of H2O2takes placewithin a short time.There is no report about the synergy of laccase/H2O2system on pulp blleaching. Addingsmall amount of H2O2during the laccase treatment process was firstly reported in this study.Whether the H2O2in the laccase/H2O2system(LHPS) was beneficial to the laccase bleachingfor pulp was investigated. The optimized bleaching conditions obtained with single-factorexperiments with Flammulina velutiper to eucalyptus KP pulp were: laccase dosage10IU/g,55℃, pH4,90min. On the basis of this optimal treatment conditions, optimal dosage ofH2O2in the LHPS system was0.4%odp. Compared with laccase from different strains ondifferent bleaching system (laccase, laccase/HBT, laccase/xylanase, laccase/H2O2system),physical properties and yellowing number of paper were determined. Results showed thatbetter strength quality and higher brightness stability were obtained using laccase/H2O2 system.In order to further verify whether the laccase/H2O2system has positive effect in pulpbleaching, two different kinds of laccase(commercial laccase、Panus conchatus)were appliedto the biobleaching of reed pulp. Kappa number, brightness, physical properties andyellowing number of different systems were determined. The results suggested that pulptreated with laccase/H2O2system could get better physical properties and higher brightnessstability and simultaneously get preferable brightness and Kappa number. It also indicatedthat laccase/H2O2system indeed played a positive role in pulp bleaching. Not only effectivefor the specific bacteria laccase and specific pulp. This study laid the foundation for thepractical application of laccase in pulp and paper industry.