Study On The Improvement Of The Quality Of Fiber By Modified Laccase

Using small molecular substances to improve the laccase activity and stability is an important way. The carboxyl and amino groups of the end of laccase amino acide residues were modified by L-phenylalanine methyl ester hydrochloride(L-PEM) and thiourea dioxide(TDO), respectively. The two reagents were grafted to the laccase with the auxiliary agents. Firstly, the process conditions of laccase modification were studied, including modified reagent dosage, temperature, p H. The study found that the activity and stability of modified laccase were improved greatly. The best conditions of modified experiment were determined by the indicators of laccase activity and stability. The optimum conditions of L-PEM modified laccase were as follows: the ratio of laccase(10mg/m L) and L-PEM(1mg/m L) 10:4, reaction time 8h, reaction p H 6, reaction temperature 30℃. The optimum conditions of TDO modified laccase were as follows: the ratio of laccase(10mg/m L) and TDO(1 mg/m L) 10:4.5, reaction time 13 h, reaction p H 9, reaction temperature 30℃. The half-life of L-PEM modified laccase was 16.05 min under 72℃, increased by 56.9% compared to the unmodified laccase. While the half-life of TDO modified laccase was 7.6min, increased by 1.3% compared to the unmodified laccase.Secondly, the modified laccase and unmodified laccase were analyed by fourier transform infrared spectrum(FT-IR), fluorescence spectrum and nuclear magnetic resonance. The results showed that the natural structure of modified laccase changed compared with the unmodified laccase. When the L-PEM was grafted on laccase, the laccase secondary structure of β-sheet content and random coil were reduced, the α-helix content was increased, the content of β-turn was unchanged. When the TDO was grafted on laccase, the laccase secondary structure of random coil was reduced, the α-helix content and β-angle were increased, the content of β-turn was unchanged. These changes made the structure of the modified laccase more compact, but still maintained the close hydrophobic structure of unmodified laccase.Then, the original eucalyptus pulp fibers were pretreated by the laccase/histidine system. The factors of reaction time, laccase dosage, dosage of histidine, reaction p H and effects of recycling times on the modification effect were studied. These studies found that, the optimum conditions of the original eucalyptus pulp fibers pretreated by the unmodifiedlaccase/histidine system were as follows: the reaction time 3h, the dosage of laccase 8U/g(o.d.), the dosage of histidine 1%(o.d.), the optimum reaction p H 7. The optimum conditions of the original eucalyptus pulp fibers pretreated by the L-PEM modified-laccase/histidine system were as follows: the reaction time 2h, the dosage of laccase 8U/g(o.d.), the dosage of histidine 1%(o.d.), the optimum reaction p H 7. The optimum conditions of the TDO modified laccase/histidine system pretreated the original eucalyptus pulp fibers were as follows: the reaction time 1.5h, the dosage of laccase 8U/g(o.d.), the dosage of histidine 1%(o.d.), the optimum reaction p H 6. Using the modified laccase/histidine system pretreated the original eucalyptus pulp, founded that the paper physical strength was better than that of the unmodified/histidine system. After recycled five times, the physical properties of original eucalyptus pulp fiber pretreated by the modified-laccase /histidine system were higher than that of the unmodified laccase/histidine systemr.Finally, compared with the blank sample, the average length, weight length, the double weight length and coarseness of paper fiber were decreased after laccase/histidine pretreatment. The surface of the blank sample was relatively smooth by the SEM, fiber morphology of the native eucalyptus pulp samples after laccase/histidine pretreatment had no obvious change. But the fiber surface became rough and had collapsed, and the fiber surface had tiny fiber or holes. Compared with the blank sample, after the unmodified laccase/histidine, L-PEM modified laccase/histidine and TDO modified laccase/histidine pretreated the fiber, their cellulose molecules hydrogen content were increased 14.90%, 6.57% and 3.88% respectively. While the total intramolecular hydrogen bond of O(3)H…O(5) and O(2)H…O(6) were decreased by 33.35%, 14.70% and 8.68% respectively. Analysed the XRD diffraction of the paper fiber after pretreatment, the cellulose crystal type did not affected, but the characteristic peaks of 101, 101- diffraction position overlapped and the intensity of diffraction peaks changed.