Study On The Magmesium-based Alkaline Peroxide Mechanical Pulping And Its Mechanism Of Poplar

In conventional Alkaline Peroxide Mechanical Pulping, sodium hydroxide is usually used as the alkali source. Due to its strong alkalinity, NaOH can cause the dissolution of carbohydrates into the bleach effluent, decrease pulp yield, and increase BOD and COD of the bleach effluent. Magnesium hydroxide (Mg(OH)2), a much weaker alkali source than sodium hydroxide, can replace sodium hydroxide as the alkali source during the Alkaline Peroxide Mechanical Pulping process, and it has received much attention recently.A partial and total substitution of sodium hydroxide (NaOH) by magnesium hydroxide (Mg(OH)2) as the alkali source in Alkaline Peroxide Mechanical Pulping and its Mechanism of Poplar were studied, including the APMP processes with one-stage or two-stage pretreatment of poplar and its influence factors were investigated when the Mg(OH)2 was used as alkali source. Some analysis methods, such as FQA, ESEM and XPS were used to investigate the pulp properties of magnesium-based APMP and its mechanism.Firstly, the optimal pretreatment conditions of one-stage magnesium-based APMP process are: H2O2: 5.0-6.0%,Mg(OH)2: 6.0%,Na2SiO3: 4.0%,EDTA: 0.5%, liquid ratio: 4:1, temperature: 70-80℃,time: 90 min. When the beating degree is 45 0SR, the pulp gives the following properties: brightness: 67.5-68.4%ISO, breaking length: 1.32 km, bursting index: 1.63, opacity: 91.1%, light scattering coefficient: 47.65 m2·kg-1.Secondly, pulp properties were used to investigate the effects of partially and totally substituting Mg(OH)2 for NaOH on poplar APMP process. The results showed that when increasing the substitution levels of Mg(OH)2 for NaOH, the pulp physical strength and brightness reduced, but the bulk and the light scattering coefficient of handsheets improved. The optimal conditions of one-stage partial substitution of NaOH by Mg(OH)2 as the alkili source in poplar APMP process are: Mg(OH)2 substitution: 50%, H2O2: 5.0%, Na2SiO3: 4.0%, EDTA: 0.5%, liquid ratio: 4:1, time: 90min; The better conditions for two-stage poplar APMP process are: NaOH was used as the alkili source in the first pretreatment stage, the Mg(OH)2 substitution for NaOH is 50% in the second pretreatment stage. And the pulp has better physical strength, at the same time, the pulp has higher opacity and light scattering coefficient. brightness: 71.9%ISO, breaking length: 3.76 km, bursting index: 4.53 , opacity: 83.3%, light scattering coefficient: 42.52 m2·kg-1, meanwhile, the COD in the pulp effluent reduced with increasing the substitution levels of Mg(OH)2 for NaOH, which can decrease the cost of production, yield good economic returns and make the clean production come true easierly. And increasing the substitution levels of Mg(OH)2 for NaOH can reduce dissolving of organic solvent extraction, lignin, holocellulose, and pentosan.Thirdly, the results from fiber quality analysis and SEM observation illustrated that with increasing the substitution levels of Mg(OH)2 for NaOH the fiber average length, kinking and curl of pulp reduced, while fines content increased.Finally, the XPS analysis of pulps from different substitution levels of Mg(OH)2 for NaOH showed that with the increasing substitution levels of Mg(OH)2 for NaOH, the binding energy of C1 decrease, the peak area of C1 increase and the peak area of O1 decrease, so the O/C ratio on the fiber surface decrease, which illustrates that the lignin concentration on the fiber surface increases and carbohydrate concentration decreases. The O/C ratio of pulp after acetone extraction increases, which means the carbohydrate concentration in fiber surface increases, compared with that of the pulp before acetone extraction.When the Mg(OH)2 is used as the alkilily, the strength properties of APMP are poor. And the reasons can be concluded as follows: (1) The alkalescent of Mg(OH)2 and the adsorption of Mg2+ ions onto fibers surface, may decrease the swelling and softness of fibers, so when refining, lots of the fibers are cutted of, the length of fibers is short and fines content are higher; (2) The alkalescent of Mg(OH)2 makes less lignin dissolving from fiber, and increasing hydrophobic material reduces interfiber bonding.