Study On The Characteristics Of Fibers And Its Mechanism In Recycling And Chemical Behavior

With the demand of protecting forest resources and developing low-carbon economy, thewaste has become one of the most important raw materials for papermaking industry. Butdecay phenomenon has happened to the recycled fiber, resulting in lower quality, andaffecting the utilization of waste paper. Therefore, it is conducive to the efficient recycling ofwaste paper to explore the decayed law of recycling of fiber and study the refrainedmechanism of the fiber decaying, and it has a great significance for the sustainabledevelopment of papermaking industry. In this research, the changes of microstructure duringrecycling and chemical behavior were studied firstly. The physical properties and morphologyof recycled fiber and paper properties were studied in order to investigate the relationshipwith the microstructure. In the meaning time, the resolution of hornification was discussed,from which mechanisms and reasons of it were observed.The results showed that fiber length and fines contents did not change significantlyduring the recycling process. Crystallinity calculated by XRD and FTIR increased with theincrease of recycling times, as well as the average width in002plane and the cross sectionalarea of microcrystallinity, resulting in decay phenomenon. The results suggest thatcocrystallization might provide a mechanism for quality decay of recycled fibers. FT-IRanalysis showed the strength of hydrogen bond increased, forming a dense network structure,which promote the decay of fiber properties. The pulps had very different recyclingcharacteristics, which may be explained by the changes observed at cellulose fiber structurelevel. From the beginning to the fifth reuse, Water retention value, tensile index, tear indexand Burst index were decreased by22.0%,54.71%,9.35%and37.41%, respectively.The changes of fiber properties are different in different deinking methods. The resultsshowed that fiber length and fines content decreased after the alkaline deinking, neutraldeinking and enzymatic deinking treatment, indicating that the fiber was damaged duringdeinking processes. The sequence is alkaline deinking pulp＞neutral deinking pulp＞lipaseenzymatic deinking pulp, at the same time we can easily find that fiber morphology havechanged after deinking from the SEM images. The results also show that the crystallinity from63.56%decreased to55.31%、58.98%and61.29%, and the relative content of intermolecularhydrogen bond decreased, which indicated that the stability of crystallization was destroysdduring all the deinking processes and further indicated that alkali deinking have the mostinjury to the fiber. The different in WRV and paper properties which may be explained by thechanges observed at cellulose fiber structure level. The changes of fiber properties are also different in different ble`aching methods. Theresults showed that fiber lenghth changed little after hydrogen peroxide bleaching, sodiumdithionite bleaching and laccase bleaching treatment. But the fines content increased,whichwas caused by the “peel off” phenomenon. The SEM images showed that the fiber surfacewas smooth after bleaching treatment. After peroxide bleaching treatment, the crystallinitydecreased and the average width in002plane decreased from4.2nm to4.7nm, while aftersodium dithionite bleaching and laccase bleaching treatment, the crystallinity increased andthe average width in002plane increased to5.0nm,5.3nm. The energy and relative content ofintermolecular hydrogen bond had the same trends with the crystalline structure, indicatingthat hydrogen peroxide bleaching can damage the stability and orderliness of crystallization.And the other two bleaching methods had the the contrary effects. After bleaching, WRV ofhydrogen peroxide bleached pulp increased, WRV of dithionite bleaching pulp basicallyunchanged, and laccase bleached pulp changed little in WRV.Based on the studies above, the resolution of hornification was discussed further.Studies showed that optimized deinking and bleaching process was suitable for old newsprintand mixed office waste deinking and bleaching. Compared the optimization process with thetraditional process, the paper physical properties increased significantly. At the same time, thesmall pollution load was also an advantage of optimized deinking process.