| Waste paper is an important raw material for papermaking industry in China.With the implementation of China's "zero import" policy for waste paper,the main obstacle to sustainable development facing the papermaking industry is how to make full use of domestic and foreign waste paper.Waste paper fiber will decay in fiber performance during repeated recycling,which is mainly manifested in the decline of physical properties and whiteness.And the decay of waste paper fiber performance limits paper quality and reuse times.Looking for an environmentally friendly methods to inhibit fiber performance decay is plays essential role in saving resources and protecting the environment.In this paper,the waste paper fiber were used as the main raw material,and waste paper fiber were treated by using xylanase and modified laccase/glutamate acid system(X-MLac/Glu)to improve the recycling properties of the waste paper fiber.Firstly,the strength properties of obsolescence corrugated cardboard(OCC)pulp were studied treated with X-MLac/Glu from the dosage of xylanase,dosage of modified laccase,dosage of glutamic acid,reaction time and reaction temperature.The results showed that the strength properties of X-MLac/Glu treated pulp was increased significantly.The optimum conditions for X-MLac/Glu treatment OCC pulp were:20U/g of modified laccase,20U/g xylanase,1.8%glutamate acid(based on the oven dried weight of the pulp),temperature 45?,and reaction time 120 min.At optimum enzymatic system,the ring crush index,tensile index and burst index were increased by 29.53%,35.96%and 38.39%,compared with control pulp.And its strength properties were better than that of OCC pulp just treated with xylanase or with modified laccase/glutamate.By fitting peaks of the FTIR,it is found that the enzymatic system is beneficial to the binding between adjacent fibers.Compared with the control pulp,after xylanase,modified laccase/glutamate and X-MLac/Glu treated pulp,the intermolecular hydrogen bond O(6)H…O(3')were increased by 5.36%,14.52%and 20.50%.Secondly,the bleaching performance of old newsprint pulp(ONP)were studied treated with X-MLac/Glu from the dosage of xylanase,dosage of modified laccase,dosage of glutamic acid,reaction time and reaction temperature.The optimum conditions for X-MLac/Glu treatment ONP pulp were:10U/g of modified laccase,20U/g xylanase,1%glutamate acid(based on the oven dried weight of the pulp),temperature 45 ?,and reaction time 120 min.At optimum enzymatic system,the weightiness and lightness(L*)were increased by 6.86ISO%and 3.58%,the handsheets tensile index,tear index and burst index were increased by 8.67%,13.81%and 19.20%.XPS data and SEM analysis showed that after the enzymatic system treatment,the content of lignin and extracts on the fiber surface decreased significantly.Thirdly,the mechanism of X-MLac/Glu treatment waste paper fiber was investigated by means of fiber quality analysis(FQA),Fourier infrared spectroscopy(ATR-IR),X-ray diffraction(XRD),low temperature nitrogen adsorption,headspace image chromatography(HSGC)and scanning electron microscopy(SEM).The results showed that the pretreatment of X-MLac/Glu can increase the fiber coarseness and the content of fine fibers.At the same time,it can effectively remove the lignin and xylan in the fiber,reducing the chromophoric group in the fiber.In addition,complex enzyme system treatment can increase the content of carboxyl groups in waste paper pulp,improve the fiber's ability to re-moisturize and swell,and decrease the relative proportion of cellulose crystallization area.SEM and fiber pore size analysis showed that the fiber specific surface area and average pore size were increased by 30.31%and 16.62%compared with the control pulp after the enzyme system treatment.In particular,more changes in fiber surface morphology,such as cracks,flaking,filaments and peeling,were observed in the pulp treated with X-MLac/Glu.Xylanase acts on the xylan and LCC structure on the surface of the fiber,and it is beneficial for the modified laccase/glutamic acid to better react with the lignin in the fiber,the synergistic effect is obvious.Finally,the effects of three amino acid mediators,glutamic acid,glycine and histidine,on improving the recycling performance of waste paper fibers were discussed.Under the same experimental conditions,the optimal dosages of glutamic acid,glycine and histidine as mediators for the strength properties of paper tensile index,bursting index and tearing index were 2%,2%and 1.5%,respectively.The best dosages for whiteness were 1%,2%and 1.5%respectively.The analysis of fiber carboxyl group content shows that different amino acids have different abilities to introduce carboxyl groups into the pulp.When glutamic acid,glycine and histidine were used as mediators,compared with unpretreated bleached pulp,the carboxyl content in the fiber were increased by 22.22%,13.33%and 6.67%,respectively. |
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