The Effect And Mechanism Of Modification Of Lacase/Glutamic Acid On Recycled Fiber Properties

This paper use laccase glutamic acid to modified fibers, in order to improve the physical properties of fibers. Experiments showed that laccase/glutamic acid can improve the physical properties of recycled fiber, alleviate fiber decay, which are of great significance to slove the papermaking industry resource shortage and environment pollution.Firstly,the paper studied the optimum conditions that modified the OCC fiber, including dosage of enzyme dosage, medium dosage, reaction time, pH and so on.Experiments showed that laccase/histidine system optimum reaction conditions for OCC pulp is: dosage of enzyme1U·g-1, 8 h reaction time, pH value of 4.5, histidine dosage of 1%.Laccase/glutamic acid treatment of OCC pulp optimum reaction condition is: the dosage of laccase 1.5U·g-1, 8 h reaction time, pH 5, glutamic acid dosage of 2%.For a various process conditions the infrared crystalline indexs of fiber also has carried on the contrast, confirmed the optimum process conditions of modified fiber. Experimental data show that under the optimum reaction conditions, laccase/histidine is 10% higher than that of laccase/glutamate in tensile index, tear index by 9%, and laccase/glutamic acidis 21% higher than that of blank sample in tensile index, tear index increased by 18%.Starting from the economic benefits, laccase/glutamic acid is more suitable than laccase/histidine for used to improve the performance of the secondary fiber.Secondly, after modified the laccase/glutamic and laccase/histidine,Fourier infrared spectrum, XRD diffraction spectroscopy, nuclear magnetic resonance(NMR), SEM, fiber pore structure were used to analysis the fiber, the results show that after modification,the fiber molecular structure, crystallinity, morphology and pore structure has changed.FT-IR results show that, compared with the control sample, new molecula structure emerged in the fiber. The relative contents of intermolecular hydrogen bond and intramolecular hydrogen bond changes, from the side confirmed that the intermolecular hydrogen bond plays a main role link stability of fiber, and intramolecular hydrogen bonding assistant position.XRD spectra results show that the crystal size and crystallinity changes in the different modification process, and there are some new crystal shapeformation.After modification of the fiber,BET specific surface increases, laccase/histidine and laccase/glutamic average volume, respectively, were increased by 2.21 x 10-1 cm3 /g, 1.02 x 10-2 cm3 /g.SEM results showthatcompared with control sample,the fiber modified with laccase/glutamicacid and laccase/histidine is more mellower.NMR analysis results show that, after the laccase/glutamic and laccase/histidine modification, different crystal type of cellulose content reduce, polymerization fibrillar size decreases.After the study of reaction condition and the change of the molecular structure of modified fiber, thus explorethe impact of laccase/glutamic acid modified on the quality of fiber recycling.From properties, molecular hydrogen bonds, water retention value, the infrared crystalline index, whiteness and brightness, XRD spectrum, SEM and fines content and fiber length width to analyze the recycled fiber.The study found that tensile index, burst index and tear index decreased with the increase of recycled times.after the first recycle,tensile degradation, fell by about 47.3%, starting from the fourth recycle, modified and unmodified fiber performance is almost the same. It suggests that, in the process of fiber recyclemodified by laccase/glutamic acid, have an advantage before the third time recycle,afterthere is no obvious advantages. Modified and unmodified fiber whiteness and brightness decrease as the recycle number increases, but the modified fiber is lower than the unmodified fibers. Fiber water retention value falls after the recycling, but the modified fiber is slower than the unmodified fiber in falling, and the infrared crystalline index increase with recycling.The experimental results show that the modified and unmodified fiber XRD diffraction spectra did not appear the new diffraction peaks, the crystallinity of modified fiber is smaller than unmodified fiber crystallinity of about 5%, the cross-sectional area of the fiber crystallinity and crystal increase.Modified and unmodified fiber quality changes. After comprehensive comparison and analysis, found that after secondary recycling laccase/glutamic acid modification for improving the quality of the fiber advantage.Finally,the paper discusses mechanism of laccase/glutamic acid react with fiber, the reasoning mechanism is:the ether key or side chain of carbon carbon single bond fracture under the action of laccase produce free radicals, the glutamic acid molecules react with lignin free radicals generated at the first step, so increase the carboxyl content, and the physical properties of fiber increased.From themass spectrogram of glutamic acid it can be seen that, a new material generated, but it can’t prove whether was the reaction of free radicals, and what the role laccase play in the reaction.