The Production Of Low Dirt Count Chemi-Mechnaical Pulp Of Whole Cotton Stalks

As a large cotton producer in the world, China is rich in cotton stalk resource which is agricultural residue producted by cotton. Utilizing the plentiful cotton stalk material reasonably and availably can increase fiber supply for papermaking and enhance economy benefit under the circumstance of low utilization of cotton stalk. The clean pulping and bleaching technology of cotton stalk were investigated in this thesis for the existed problems in material application and the development tendency of pulping technology. The pretreatment and bleaching technology were studied to analysis the effect of high temperature on the brightness, dirt count and strength properties for solving the problem of high dirt count in cotton stalk chemi-mechanical pulp. The bleached cotton stalk chemi-mechanical pulp with low dirt count was expected to obtained and therefor enhance the added value of paper productions.The contents of ash, benzene-alcohol extraction and pectin in cotton stalk bark decreased obviously when was treated by sodium oxalate and sodium hydroxide. Especially, the sodium oxalate pretreatment decreased the ash of19.5%, reduced benzene-alcohol extraction of39.4%and pectin of53.7%. The temperature of the one-stage bleaching should be controlled at80℃-90℃in the production of cotton stalk chemi-mechanical pulp adding sodium oxalate pretreatment, the brightness decreased sharply with the increasing temperature of one-stage bleaching. The crew press stage could be omitted after chemical pretreatment then to high-concentration refining. The brightness and dirt count of final pulp could reach to76.2%and50.1mm2·m-2, satisfied the requirements of design paper, text book, food packing paper and so on.Duuning the screening experiment of pulp, the effect of mesh of screen, screen cut of screen plates and screening concentrations on dirt count were studied. The lowest dirt count of pulp screened by screen was achieved at an concentration of0.20%, screen mesh of40. And the dirt count screened by screen plate of0.20mm-o.25mm at concentration of0.60%was the lowest, the value was120.5mm2·m-2.In the experiment of high temperature hydrogen peroxide bleaching without chelation pretreatment, the yield, brightness, tensile index and tearing of pulp reached the highest value at100℃-110℃. The highest yield of bleached pulp was about95.2%, the highest brightness was66.2%and were achieved at an ratio NaOH/H2O2of1.2. The highest tensile index could reached to26.1N·m·g-1and was achieved when the NaOH/H2O2was1.4. The lowest dirt count of bleached pulp appeared at100℃-110℃. The temperature of high temperature hydrogen peroxide bleaching was not suitable for more than110℃The parameters of pulp bleached by high temperature hydrogen peroxide adding AQ chelation were significantly improved. The brightness, tensile index and tearing index first increased then decreased with the increase in bleaching temperature at different ratio of NaOH/H2O2, and the optimum value appeared in100℃-110℃. The dirt count of pulp bleached adding AQ chelation decreased obviously, the highest decreasing value could reach to39.5mm2·m-2, the tensile index increased16.4N·m·g-1in temperature of110℃and H2O2/NaOH of0.8-1.2.