Study On The Components And Properties Of Triploid Poplar P-RC Apmp Pulps By Substituting Magnesium Oxide For Sodium Hydroxide

With the development of pulp and paper industry, high yield pulp (HYP) has been gained increasing in recent years. P-RC APMP (Preconditioning followed by Refiner Chemical treatment, Alkaline Peroxide Mechanical Pulp) process is a highly efficient, clean and high-yield pulping process. However, many wood compositions can be dissolved during the P-RC APMP process due to the strong alkalinity of sodium hydroxide (NaOH), resulting in a high content of anionic trash in pulp and of COD in the effluent, and causing the loss of pulp yield. Magnesium oxide (MgO) is a weak alkali, it can be used as a substitution of sodium hydroxide in P-RC APMP process to solve these problems.Triploid poplar P-RC APMP was used in this study. NaOH was substituted with MgO in the second-stage impregnation and high-consistency retention stage of P-RC APMP process.First, MgO was used to substitute for NaOH as the alkali source. The effect on chemical components of the treated wood chips or of the bleaching pulps with different MgO substitution ratios, as well as the characteristics of the resultant P-RC APMP pulp fibers and the physical properties of the pulp handsheets were studied. The results showed that the dissolution of benzene alcohol extractives, lignin and carbohydrates were reduced, while the yield was increased with increasing the substitution ratios of MgO. The bulk and light scattering coefficient of pulp were increased with increasing of MgO substitution. However, the.tensile index, tearing index and bursting index of pulp were decreased. The fines content was increased significantly, the average fiber length and kink index of pulp were decreased while the substitution level was increased. After replacing50%NaOH with MgO, the resultantly yielded P-RC APMP pulp has higher brightness than the others.Then, the reaction courses by substituting MgO for NaOH in the second-stage impregnation and high-consistency retention stage of P-RC APMP process were investigated to explore the potential advantages of the process. The results showed that MgO substitution for50%NaOH, resulted in a lower pH of residual bleaching liquor by0.5-0.9units than those of the NaOH-based process. In addition, the dissolution of chemical components was all decreased, resulting in a higher pulp yield.In the second-stage impregnation, there were about50%of the total benzene alcohol extractives,7%of lignin,9%of pentosan and10%of carbohydrates removing from the treated wood chips. The removal of the lignin and carbohydrates can be divided into three stages:the first15minutes is the initial stage in which less of compositions were dissolved; from15to90minutes is the second stage in which more of compositions were removed; beyond90minutes is the last stage in which a small quantity of compositions were dissolved. In the high-consistency retention stage, benzene alcohol extractives have not be completely removed, instead, the dissolved ones could be adsorbed onto the fibers at the later stage of bleaching. The dissolution of the lignin and carbohydrates can be divided into two stages:before60minutes is the first stage in which compositions were largely removed; beyond60minutes is the second stage in which less of lignin and carbohydrates were dissolved.In a word, replacing NaOH with MgO in the triploid poplar P-RC APMP process can reduce the removal of wood compositions, improve pulp yield, increase bulk, generate lower effluent load and reduce chemical costs.