| Waste paper is an important raw material for papermaking in China.Improving the recycling utilization ratio of waste paper plays essential role in saving resources,protecting the environment and reducing energy consumption.The degradation of waste paper properties and whiteness decrease during the process of recycling and deinking will lead to falling off in quality of papermaking inevitably.Using laccase can effectively restrain the degradation of fiber properties and improve the whiteness of waste paper,which has a great importance to improve the recycling of waste paper fiber and promote the sustainable development of China's paper industry.However,the natural laccase has poor stability,easy inactivation and poor tolerance to organic solvents,which has restricted its application in the paper industry.In order to improve the activity and stability of laccase,laccase amino acid carboxyl and amino terminal was modified respectively by using L-phenylalanine methyl ester hydrochloride and thiourea dioxide.then,waste paper fiber is treated by modified laccase/glutamic acid system to improve the performance of fiber.The optimum conditions for the treatment of OCC pulp by modified laccase / glutamic acid system were studied,including dosage of laccase,dosage of glutamic,pH,reaction temperature and time.The results showed that the optimum conditions for L-phenylalanine methyl ester hydrochloride modified laccase/glutamic treatment of OCC fiber were:the dosage of laccase 4% dry pulp,the dosage of glutamic 2%,pH 7,reaction temperature 30?,reaction time 3h;the optimum conditions for thiourea dioxide modified laccase/glutamic treatment of OCC fiber were: the dosage of laccase 4% dry pulp,the dosage of glutamic 1.5%,pH 7,reaction temperature 40?,reaction time 3h.At optimum reaction conditions,the ring crush index,tensile index of the OCC pulp treated by L-phenylalanine methyl ester hydrochloride modified laccase/glutamic acid separately improved 16% and 20.7% compared to OCC pulp treated by the unmodified laccase/glutamic acid;The ring crush index,tensile index of the OCC pulp treated by thiourea dioxide modified laccase/glutamic acid separately improved 11.5% and 12.8% compared to OCC pulp treated by the unmodified laccase/glutamic acid.The effects of modified laccase/glutamic acid system on the microstructure of OCC pulp were studied by analyzing the carboxyl content,cell wall pore structure,hydrogen bond mode and fiber microstructure of OCC pulp.The results show that,compared with unmodified laccase/glutamic acid system,the content of carboxyl group increased further and the roughness increased significantly after the treatment modified laccase/glutamic acid system.The fiber hydrogen bond pattern has changed.Compared with the control sample,after unmodified laccase/glutamic acid,L-phenylalanine methyl ester hydrochloride modified laccase/glutamic and thiourea dioxide modified laccase/glutamic,the intermolecular hydrogen bond O(6)H…O(3')content increased 5.9%,8.0% and 8.8% respectively.Compared with unmodified laccase/glutamic acid system,after the treatment modified laccase/glutamic acid system,the fiber become adhesive stepped construction.And BET specific surface area and average pore size also further increased.The changes of fiber properties,carboxyl content and hydrogen bond pattern in the process of recycling were studied.The results show that the modified laccase/glutamic acid system had advantage of restraining the degradation of fiber properties than unmodified laccase/glutamic acid after three times of recycling.After five times of recycling,there is little difference between the tensile index and the breaking index in terms of modified laccase/glutamic acid system and the control sample.In addition,the fiber bonding pattern also changed during recycling.After three times of recycling,intermolecular hydrogen bonding of the treated fiber by modified laccase/glutamic system was significantly higher than that of the unmodified laccase/glutamic treatment.After five times of recycling,the intermolecular hydrogen bond O(6)H…O(3')content are not difference.Waste paper pulp were pretreated by modified laccase/glutamic system,then hydrogen peroxide bleaching were carried out.And the effect of pretreatment on the bleaching property of the waste paper pulp were studied.The results showed that the optimum conditions for L-phenylalanine methyl ester hydrochloride modified laccase/glutamic pretreatment of waste paper pulp were:the dosage of laccase 0.6% dry pulp,the dosage of glutamic 0.8%,pH 7,reaction temperature 30?,reaction time 90min;the optimum conditions for thiourea dioxide modified laccase/glutamic treatment of waste paper pulp were: the dosage of laccase 0.6% dry pulp,the dosage of glutamic 0.6%,pH 7,reaction temperature 30?,reaction time 120 min.At optimum reaction conditions,the whiteness,tensile index of the waste paper pulp treated by L-phenylalanine methyl ester hydrochloride modified laccase/glutamic acid separately improved 2.3% and 6.0% compared to waste paper pulp treated by the unmodified laccase/glutamic acid;The whiteness,tensile index of the waste paper pulp treated by thiourea dioxide modified laccase/glutamic acid separately improved 1.1% and 2.8% compared to waste paper pulp treated by the unmodified laccase/glutamic acid.Compared with unmodified laccase/glutamic acid system,fiber length and width are not difference.And coarseness and the content of carboxyl group increased further after the treatment modified laccase/glutamic acid system.The surface of fiber becomes coarser and the cross-linking of microfiber becomes closer.The BET specific surface area and average pore size also further increased,which can promote the penetration of the liquid effectively in the bleaching of waste pulp. |
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