| In order to clarify and understand the mechanisms of enzyme，the cellullase, xylanase and laccase were used to modify the ultrastructure and fiber properties of P-RC APMP. A large number of modern analytical equipment, such as X-ray diffraction (XRD), atomic force microscopy (AFM), X diffraction-photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) etc. were applied to investigate the fiber structural changes after treated with enzymes.Firstly, the P-RC APMP were modified by using cellulase, xylanase and laccase, and the changes in the structure of the fiber surface after enzyme treatment were thoroughly analyzed. The experimental results shown that: with the cellulase treatment, the degree of crystallinity increased from51.82%to56.09%, the structure of the fiber surface becomes porous, the separation between intercellular layer and S1layer become more pronounced and the texture of fiber surface becomes clearer. With the xylanase treatment, the degree of crystallinity increased from53.07%to51.82%, the porous structure of fiber surface increased significantly, while the particulate matter of the surface reduced. With the laccase treatment, the degree of crystallinity increased from51.82%to52.29%, and the proportional change of the amorphous region and crystalline region is not obvious. As the fibers filler, lignin and particulate matter on fiber surface were significantly reduced and the surface structure became loose.Secondly, the elementary composition and molecular structure of the P-RC APMP before and after enzyme modification were investigated. The experimental results show that: with the cellulase treatment, the content of the cellulose on fiber surface is reduced, while the lignin content is relatively increased. The CH2, C-O-C, O-H and C=O groups were destroyed by cellulases, resulting in degradation of cellulose. Xylanase can degrade most of the hemicellulose and a small amount of lignin. It can be seen from FTIR analysis, the absorption peaks at1425cm–1,1317-1319cm-1and1235cm–1were reduced. The results indicated that xylanase can promote degradation of the hemicellulose, while played limited role on lignin. With the laccase treatment, the functions of laccase-mediator primarily in lignin, and there is no damage to the cellulose and hemicellulose, so that the most of the lignin in intercellular layer is removed and S1layer is exposed. By infrared spectral analysis, in1161cm-1,1163cm-1,1111cm-1,1056cm-1and896cm-1band, the relative strength of absorption peak has not changed much. These shown that the laccase can selectively degrade lignin, while it difficult to play a degradation role to cellulose and hemicellulose.Finally, the fiber morphology and physical properties of P-RC APMP before and after enzyme treatment were analyzed and compared. The experimental results show that: with the cellulase treatment, fines content decreases with the increasing of the fiber length and width. Beating at the same revolution number, it can be increased up to5-7。SR, and the fiber itself strength increase, the influence of fiber length to fiber strength and the bonding strength between fibers are all increased. With the xylanase treatment, the fiber flexibility, fiber length and width were all increased. Under the same beating revolutions, it can be increased up to4-5。SR, and the hemicellulose of LCC structures can be degraded, fiber becomes swelling soft, enhance the strength of the fiber itself. With the laccase treatment, the specific surface area increases, the fiber is easy to curl, the average fiber length of pulp fibers and the crimp index are higher than the pulp without the enzyme treatment, but no significant effect on the fines content. Beating at the same revolution number, the degree of beating can be increased up to3-4。SR. Laccase degrade lignin on the surface of the fiber and fiber surface appear empty and osteoporosis, the fiber itself strength increase, the influence of fiber length to fiber strength and the bonding strength between fibers are all increased. |
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