| Paper industry is an important pillar industry in China's national economy.Increasing the recycling rate of plant fiber can save resources and energy,and help alleviate the shortage of raw materials and serious pollution in the paper industry.Due to the irreversible degradation of fiber during the recycling process,the fiber quality and whiteness are reduced,which seriously restricts the development of products to high-grade,high-quality and multi-color.Therefore,plant fiber bleaching technology need to be further researched.As the main bleaching agent of the chlorine-free bleaching pulp process,hydrogen peroxide is the development trend of bleaching technology in the pulp and paper industry.However,hydrogen peroxide bleaching has many problems in practical applications,which restricts the efficiency of hydrogen peroxide bleaching.In this paper,aiming at the problems of hydrogen peroxide bleaching,a new green chelating agent(IDS)and laccase/glycine system(Lac/Gly)were used to pretreat pulp in order to enhance the peroxide bleaching performance of pulp.First,using obsolescence corrugated cardboard as raw materials,the application of IDS as chelating agent in hydrogen peroxide bleaching of pulp was studied.The pH value,IDS dosage,reaction time and temperature of chelating process were evaluated by the primary variables.Under the process conditions obtained in this experiment,the optical properties of hydrogen peroxide bleached OCC pulps using IDS are comparable to traditional chelating agents Ethylenediaminetetraacetic acid(EDTA)and Diethylenetriaminepentaacetic acid(DTPA),and do not compromise the mechanical properties of bleached pulps.At the same time,the mechanism of IDS to enhance the bleaching performance of hydrogen peroxide was discussed by means of Infrared Spectroscopy and Atomic Absorption Spectroscopy.It is found that the ability of IDS to remove transition metal ions has advantages and disadvantages compared with EDTA and DTPA,but the retention effect on alkali metal ions is better.And the lignin content of the bleached pulp after IDS pretreatment is relatively reduced.Second,wood pulp,waste paper pulp and non-wood pulp are the three major components of pulp consumption in China,and also the source of recycled fiber.Using recycled eucalyptus pulp and recycled bagasse pulp as raw materials,the application of IDS as chelating agent in hydrogen peroxide bleaching of pulp was studied.Through the single factor experiment and the orthogonal experiment designed on this basis,the optimum conditions for the use of IDS as the chelating agent for hydrogen peroxide bleaching pretreatment of Eucalyptus Pulp and bagasse pulp were obtained.The results showed the optimum condition of IDS for the recycled eucalyptus pulp bleaching pretreatment section: temperature 60?,time 50 min,IDS dosage 0.3%.As for recycled bagasse pulp the optimum conditions was: IDS dosage 0.8%,time 60 min,temperature 70?.In comparison with EDTA,the chelating effect of IDS is similar to that of EDTA,but IDS is easy to be biodegraded and has no secondary pollution,which has certain advantages in the experiment under the optimum conditions of IDS obtained by this experiment.Third,the performance of laccase/glycine system(Lac/Gly)pretreatment for improving the bleaching performance of recycled fiber hydrogen peroxide was studied.Compared the optical,physical and waste liquor properties of OCC bleached pulp pretreated with laccase system,laccase/mediator system(LMS)and laccase/amino acid system,it was found that Lac/Gly pretreated OCC pulp has better bleaching performance than traditional LMS pretreatment.And compared with the control group,the whiteness of Lac/Gly pretreated bleaching pulp increased by 18.88%,the brightness increased by 5.76%,the tensile index increased by 32.75%,the bursting index increased by 20.67%,and the bleaching efficiency increased by 49.6%.The optimal reaction conditions for Lac/Gly pretreatment OCC pulp were as follows: laccase dosage 10U/g,glycine dosage 0.5%,pretreatment time 60 min,pretreatment temperature 25°C,pulp concentration 3%,pH=5.Under these conditions,compared with the control pulp,whiteness and tensile index and bursting index of Lac/Gly pretreated pulp increased by 19.03%,32.47% and 21.48%,respectively.Finally,the mechanism of old corrugated container bleached pulp with laccase and glycine pretreatment was investigated by means of fourier transform infrared spectroscopy(FTIR),headspace gas chromatography(HGC),fiber quality measurements(FQA),X-ray diffraction method(XRD)and atomic force microscope(AFM).The FQA indicated that the Lac/Gly system treatment increased the fiber weight average length,thickness,crimp index,and fine fiber content.The FTIR analysis showed that Lac/Gly treatment can degrade the lignin and xylan in the slurry,reduce the chromophore group and improve the whiteness of the paper.The XRD analysis showed that Lac/Gly treatment decrease the crystallinity of the fiber,promoted the penetration of the bleaching solution,and increased the contact area between the bleaching liquid and the pulp fiber,thereby improving the bleaching efficiency.The HGC analysis showed that the carboxyl content of the pulp could be increased,and the swelling degree of the fiber was deepened,thereby increasing the contact area and bonding strength between the fibers and improving the paper forming property of the paper.The HGC analysis showed that the Lac/Gly treatment increased the carboxyl content of the pulp,and the swelling degree of the fiber was deepened,thereby increasing the contact area and bonding strength between the fibers and improving the paper-forming property of the paper.The AFM analysis showed that Lac/Gly treatment can reduce the lignin and extract on the surface of pulp fiber,which is beneficial to improve the bleaching efficiency and paper mechanical properties. |
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