Studies On The Properties Of Secnodary Fiber In Different Bleaching Methods

In recent years, people are growing shortage of paper raw materials at domestic andabroad, at the same time pulp and paper industry is facing serious environmental and energyconsumption problems, so people pay more attention to the use of secondary fiber. Bleachingas a key technology in secondary fiber reuse, its development will promote the use ofsecondary fiber. In this paper, the influence of fiber properties after different bleachingperformance was studied, so as to provide the basis theory for promote secondary fiberproperties.After the H₂O₂bleaching treatment, the pulp brightness increased7.93%ISO, tear indexdecreased2.03%, tensile index increased9.84%, burst index increased5.75%, fiber lengthdecreased2.48%, the small fiber content increased4.19%and crystallinity index decreased2.31%. And then, amorphous cellulose and dissoluted lignin in the fibers with randomstacking uneven surface, lead to uneven surface topography. Carboxymethylation treatmentcan successfully import the carboxyl to fiber, and in the form of sodium salt. it can improvethe physical strength of paper, reduce the fiber length, increase a small fiber content, lowercrystallinity index of cellulose and increase the amorphous region, to form the fiber surface isnot flat. This will help to enhance the bonding strength between fibers and inhibit the decay ofrecycled fibers.After the Na₂S₂O₄bleaching treatment, the pulp brightness increased5.73%ISO, tearindex increased1.65%, tensile index increased17.19%, burst index decreased4.27%, fiberlength decreased3.47%and the small fiber content increased4.19%. The Na₂S₂O₄bleachingtreatment will increase the crystalline regions, increase crystallization index, which will leadto hornification of fiber.After the laccase/mediator bleaching treatment, the pulp brightness increased8.30%ISO,tear index increased9.03%, tensile index increased8.42%, burst index decreased2.44%.Enzymatic bleaching has little effect on fiber length, but small fiber content increases firstdecreases and then increases with the amount of enzyme rise. Enzymatic bleaching caneffectively improve the swelling performance of pulp, and destroy the crystalline structure ofpulp. Most of the dissoluted of lignin will deposite in the fiber surface, which lead to theformation of ravines on the surface morphology.I have compared the effect of different bleaching methods on the properties of secnodaryfiber. The effect of bleaching on old newsprint deinked pulp, enzymatic bleaching> H₂O₂bleaching> Na₂S₂O₄bleaching, and these three bleaching methods can enhance the physical strength of paper, especially tensile strength. The relative intensity of the hydroxyl absorptionpeak was showed by FT-IR analysis, and the results are as follows, enzymatic bleaching>H₂O₂bleaching> Na₂S₂O₄bleaching, and lignin or colored groups which in the pulp wasremovaled after bleaching. XRD analysis showed that, the fiber crystallite size have changedafter bleaching, and the magnitude of change is as follows,enzymatic bleaching> H₂O₂bleaching> Na₂S₂O₄bleaching. The microcrystalline cross-sectional area increased, soaccessibility of crystalline could be decreased. AFM analysis showed that，the uneven degreeof fiber surface are as follows, enzymatic bleaching> H₂O₂bleaching> Na₂S₂O₄bleaching.