| The shortage of wood fiber resources restricts the development of paperindustry in China for decades. Bamboo is widely distributed in China. The fibercharacteristics are similar to wood fibers, and the cost of bamboo pulp isrelatively lower than wood pulp, which can be potentially used as raw materialfor paper industry. Among the types of bamboo used as raw materials ofpapermaking, Neosinocalamus is one of the best candidates. The digesterdiagnosis system (DDS) is an energy-efficient and environmentally-friendlypulping method. Therefore, the development of DDS technology ofNeosinocalamus not only helps to alleviate the shortage of raw material in China,but also accords with the trend of green, environment-friendliness and lowcarbon in paper industry.In this work, the technologies of DDS replacement cooking and cleanbleaching were applied in Neosinocalamus pulping. The cooking parameters ofDDS replacement cooking and non-sulfur cooking with chemical aids wereinvestigated systematically, which indicated Neosinocalamus had the feature oflow-pollution. The correlation between DDS displacement cooking and cleanbleaching of Neosinocalamus was established combining the results from oxygendelignification, ECF and TCF bleaching, which helps to enrich the theoreticalsystem of clean pulping of Neosinocalamus.The effect of the parts and the storage period of Neosinocalamus on thechemical composition were studied. Neosinocalamus skin showed the highercontent in ash, alcohol-benzene extract than pole. Based on the results, one totwo months can be spent in the change in colour for Neosinocalamus beforepulping. The effect of pretreatment on the chemical composition of fiber and cooking properties of Neosinocalamus was also investigated. It is found thatsodium hydroxide and sodium sulphide can be used for pretreatment ofNeosinocalamus before cooking, which can reduce the content of lignin andprevent the excessive degradation of holocellulose. As compared to cookingconditions without pretreatment, the yield and the viscosity of bamboo pulp withpretreatment was lower but the Kappa number was decreased more significantly.These all satisfied the requirements of the use of commercial bleached pulp.Design-Expert software was employed to design and optimize theexperiment of DDS displacement cooking. It was found that alkali charge,sulfidity, max temperature and heat preservation time could affect the yield ofscreened pulp and brightness significantly in the stage of hot filling. Additionally,a remarkable impact of alkali charge on viscosity was also observed. For a givenKappa number, the optimal results of yield of screened pulp, viscosity andbrightness of pulp could not be obtained simultaneously. The mathematic modelof DDS displacement cooking built by Design-Expert software showed a goodresult in prediction and optimization.For a given parameters of cooking, the model can be used to predict theresults, including Kappa number, yield of screened pulp, viscosity and brightness.The cooking conditions, including the alkali charge in Initial Cooking（IC）,Initial Middle Cooking（IMC）and Final Middle Cooking（FMC）respectively,sulfidity, max temperature and heat preservation time can also be optimized.Compared to traditional kraft cooking, DDS displacement cooking ofNeosinocalamus had advantages of low Kappa number, high yield and low alkalicharge.The relationship between the conditions of non-sulfur cooking withchemical aids and pulp properties was analyzed and the comparison of greenoxygen and self-made cooking aids during non-sulfur cooking was alsodiscussed. When the usage of green oxygen was fixed at0.06%, the pulp properties from the cooking conditions of18%alkali and max temperature of160was similar to that of19%alkali and max temperature of155. Thecorresponding pulp properties were as follows: Kappa number of22, the yield ofscreened pulp of49%, the viscosity of1200mL/g and the brightness of30%ISO.The self-made cooking aids E, H, I can also achieved the pulp properties inKappa number, yield of screened pulp and brightness with the dosage of0.06%compared to green oxygen.The results of orthogonal experiment showed that when the usage ofcooking aids in IC, IMC and FMC was fixed at0.02%,0.02%,0.03%,respectively, the pulp properties was as follows: Kappa number of23.6, yield ofscreened pulp of50.1%, viscosity of1237mL/g. The pulp properties weresimilar to that of DDS kraft cooking. FT-IR results indicated the difference incooking method resulted in the variations in delignification and the structure ofresidual lignin. Unlike anthraquinone, the self-made cooking aids showed thegood solubility, which helps to improve the pulp properties. However, thechemical structure of self-made cooking aid needs to be analyzed further.During the DDS kraft cooking of Neosinocalamus, the akali charge and themax temperature of cooking had a significant effect on the content of HexA.There was no obvious correlation between the content of HexA and Kappanumber, yield of screened pulp and viscosity of pulp. It is found that low alkalicharge and cooking temperature, and short cooking time can improve the contentof HexA and the yield of screened pulp.The correlation between DDS displacement cooking of Neosinocalamusand ECF and TCF bleaching was investigated. It showed that the good pulpproperties can be obtained by oxygen delignification with high temperature whenthe Kappa number of unbleached pulp was18-20. The viscosity and yield of pulpwas lowest when adopting the bleaching sequence of D0EopD1with the Kappanumber below10. The chlorine demand, reaction time, viscosity and yield of bleached pulp with ECF sequence were increased as Kappa number increasedwhen the Kappa number of unbleached pulp was12-20. The viscosity ofbleached pulp decreased but a small increase of the corresponding pulp yield canbe observed when the Kappa number of unbleached pulp was more than20. Thebrightness of bleached pulp with TCF bleaching sequence (QP1P2) can notachieve85%. The viscosity and yield of bleached pulp with low Kappa number(less than10) of unbleached pulp were580mL/g and37.51%, respectively whenTCF bleaching sequence (QP1P2) was adopted. The bleaching conditions ofabove results were3%H2O2and reaction time of270min, the correspondingbrightness of pulp was83.6%ISO. The demand of H2O2with TCF bleachingincreased with increasing Kappa number from12to19. The brightness ofbleached pulp was in the range of81.3%~77.8%ISO with the dosage of H2O2were3.5%~4.0%, the corresponding viscosity and yield of bleached pulp werealso increased, which can be up to650mL/g and40.98, respectively. When theKappa number of unbleached pulp was more than19, the viscosity of bleachedpulp was in the range of634~588mL/g, and the yield was in the range of42.53%~43.48%. These results can be obtained when the usage of H2O2was4.5%~5.0%and the reaction time of270min, the corresponding brightness was76.1%~71%ISO. These results indicated ECF bleaching had advantages in pulpbrightness, yield and viscosity while the limited improvement in brightness canbe obtained by using TCF bleaching which can be adopted with Kappa numberof less5after oxygen delignification stage.The fiber morphology and fines content of unbleached pulp, bleached pulpand refined pulp of Neosinocalamus were compared by FQA analysis. Theresults showed that the weighted length, crimp index and fines content decreasedwith stages while the kink index of fiber was decreased firstly and then increasedafter bleaching. The weighted length of fiber decreased from1.035mm to0.810mm after refining. The crimp index and kink index decreased while fines content of fiber can be up to21.59%after refining, which is the major differencein bamboo fiber and wood fiber. XRD, SEM and AFM were used to investigatethe change in fiber properties of DDS pulp, ECF bleached pulp and TCFbleached pulp of Neosinocalamus. It is found that the crystallinity of fiber wasincreased with stages. The uneven lignin deposition can be observed on thesurface of fiber from DDS cooked pulp. Oxygen delignification removed thelignin deposited on the surface of fiber, resulting in the smoothed fiber surface.Dislocation and delamination can be observed in the structure of microfiber inS1layer after ECF bleaching. Meanwhile, the increase of the roughness of fibersurface verified fiber was damaged during bleaching. In contrast to EFCbleaching, the structure of microfiber in S1layer was not changed obviouslyafter TCF bleaching, indicating the bleaching condition of TCF bleaching ismilder. The increased degree of the damage of fiber further verified theamorphous region of fiber was damaged, resulting in the increase in crystallinityof pulp, which was accordance with SEM results. |
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