The Study Of Triploid Populus Tomentosa Carr. CMP's Ultrasonic Pretreatment And H₂O₂ Displacement Bleaching

To improve H2O2 bleaching efficiency and shorten bleaching time, displacement bleaching of Triploid Populus Tomentosa Carr. CMP with modified apparatus was carried out in this dissertation. The effects of displacement chelation and ultrasonic pretreatment on H2O2 bleaching were also studied and all the processes were collaborated with each other, main conculsions were as follows:The optimum conditions of H2O2 displacement bleaching were:dynamic bleaching pulp consistency 10%, static bleaching pulp consistency 10%, speed of displacement was 0.8mL/s, static bleaching time after displacement was 30-60min, temperature 80℃, pH12, MgSO40.1 g/L,Na2Si03 3.6g/L,NaOH 3g/L,H2O25g/L. The bleaching time was shortened by half and and the bleaching efficiency was increased greatly as well as the brightness. The filtrate can be recycled and no adverse effect on the brightness and the color reversion value will be caused.Because the relative movement between the fiber and bleaching liquor break the consistency balance of water surface on fiber, and make the H2O2 consistency in the cell wall higher than traditional methods. The wider range difference accelerated the bleaching and improved the brightness and efficiency.Displacement chelation by EDTA,DTPA and H2SO4 could be similar to or have better result than traditional pretreatment, during which H2SO4 got the best result,1% ISO higher than ordinary H2SO4 treatment.. And the filtrate also can be recycled.The optimum conditions of ultrasonic pretreatment were confirmed:at 1.5% pulp consistency and 50℃for 20min with 90% amplitude and 20s pulse.These conditions showed the most favorable effect of a 3.5%ISO increase of brightness, reaching a final value of 80.2%ISO. With SEM,AFM,FT-IR and XRD, the surface structure, morphology and chemical composition were investigated.It is found that no new linkages or bonds were produced and the whole structure of cellulose was also not transformed. However, the cell wall was destroyed(cracks,grooves,damage,layered),P and S1 layer were mildly damaged and took off, with the S2 layer esposed.The defibrillation accelerated by ultrasound released larger reactive area, and consequently improved the accessibility of bleaching agents and the bleaching efficiency.If the pulp was only treated by ultrasonic irradiation, there was a decrease in crystallinity. But if the pulp is treated by ultrasound and then bleached by hydrogen peroxide, the crystallinity will go up. The whole trend of the difference is consistent with the curve of brightness increase.The effect of displacement pretreatment and ultrasonic pretreatment on H2O2 displacement bleaching was also favorable.The final brightness value of bleached pulp could reach 80%ISO, 1-3%ISO higher than each was employed.