Study On The Strengthen TCF Bleaching Technology Of Non-wood Fibers

At present, the brightness of non-wood fibers TCF (Total Chlorite Free) bleached pulp was limited. Silicate was a widely used peroxide bleaching stabilizing agent in the pulp and paper industry. Though efficient stabilizer, silicate caused problems in papermaking by contributing to silicate deposit formation, decreased retention and sheet strength, increased anionicity leading to higher consumption of wet end chemicals, and at times scaling in the system. Peroxide bleaching required NaOH as the alkaline source, which caused an increase of the effluent COD. To solve these problems above, this paper studied the strengthen TCF bleaching technology of wheat straw pulp and bagasse pulp, application non-silicate stabilizer into peroxide bleaching, bleached the wheat straw and bagasse TCF pulp to high brightness. The aim of this study was to offer technological and theoretical support for TCF bleaching technology of non-wood fibers in medium consistency pulp bleaching system.Hydrogen peroxide was applied to strengthen the oxygen delignification of wheat straw pulp and the influencing factors were studied. We also investigated the TCF bleaching of wheat straw pulp using an OpQP sequence. The results showed that adding hydrogen peroxide into pulp had a notable effect on oxygen bleaching process. The efficiency and selectivity of oxygen delignification were improved. The OpQP bleaching indicated that the pulp reinforced with H₂O₂ could improve the bleaching efficiency and stability,but reduced slightly the strength of paper .The feasibility of non-silicate stabilizers PP-1, PP-2 applied into wheat straw pulp hydrogen peroxide bleaching was investigated and the optimization of the bleaching chemicals was carried out. The results showed that the substitution of sodium silicate with PP-1,PP-2 as the stabilizer in hydrogen peroxide bleaching for wheat straw pulp was technically feasible. PP-1 contained the scale inhibiton composition, so there was no fouling phenomenon as it caused by sodium silicate.The TCF bleaching of bagasse pulp was carried out, and the possibility of non-silicate stabilizer in hydrogen peroxide bleaching was investigated. The results indicated that non-silicate stabilizers PP-1, PP-2 in place of sodium silicate as the stabilizers in pressured hydrogen peroxide bleaching was technically feasible. The brightness of bagasse pulp with OpQPo bleaching can be achieved to 85%ISO. The pollutant loads of OpQPo sequence were much lower. The fiber morphology, physical strength properties and the charge characteristcs between the (PP-1+PP-2) process and Na₂SiO₃ process were compared. The fiber morphology and length distribution of (PP-1+PP-2) process was silimar to those of Na₂SiO₃ process. The tensile index and tearing index, as well the charge characteristcs were higher than those of Na₂SiO₃ process. The FTIR spectra indicated that (PP-1+PP-2) could increase the crystal area of fiber, so increased the tensile index. And the absorbtion strength of lignin was higher than Na₂SiO₃ bleached pulp, so the (PP-1+PP-2) had stronger delignification.Low kappa number of wheat straw oxygen delignification chelated (OQ) pulp, bleached with two conventional hydrogen peroxide bleaching(PP), the highest brightness was achieved to 85.7%ISO, viscosity was 775 mL.g^-1, and total H₂O₂ consumption was 1.55%. To meet the required brightness of North American Pulp and Papermaking Industry, the wheat straw OQ pulp bleached with two pressurized hygrogen peroxide bleaching stage (PoPo). The highest brightness was achieved to 90.1%ISO, viscosity was 479mL.g^-1, and total H₂O₂ consumption was 6.31%. And the strength propersities and fiber morphology was favorable. Pressurized hydrogen peroxide bleaching method increased the bleached pulp brightness. FTIR spectra indicated that wheat straw pulp after oxygen delignification, the lignin cleavaged, produced more hydroxy. And the chelation and hydrogen peroxide bleaching stage decreased the carbonyl of lignin.Mg(OH)₂ substitution of NaOH as the alkaline source in the peroxide bleaching of wheat straw pulp was investigated. The results showed that for the high kappa number, high metal ions of wheat straw pulp, under the same conditions, the bleached pulp brightness, viscosity and yield increased obviously with the increase of substitution degree of Mg(OH)₂, and the residual hydrogen peroxide charge decreased obviously. The bleached pulp of Mg(OH)₂ peoxide bleaching process had higher tensile intex, bursting index, and teraing index, but lower freeness. And Mg(OH)₂ can reduce the COD of effluents, 25% of Mg(OH)₂ substitution of NaOH decreased 22% of the effluent COD.