| Eucalypt woodchips have taken an important role on raw material supply for China’s pulping industry. In the field of mechanical pulping, there are several challenges, for mechanical pulping lines using Eucalypt woodchips, such as high electricity consumption, high chemical usage and unstable pulp quality as well as high pollutant discharge, due to variety of wood properties from different Eucalyptus spp. It is necessary to initiate fundamental investigations on influencing relationships between mechanical pulping properties and Eucalypt woodchips qualities. Thus, the comprehensive study on wood properties to find out their influence on chemimechanical pulping properties and understand the related mechanisms are necessary for pulp quality improvement, specific refining energy reduction and clean production.Investigations on wood properties of 5 species of Eucalypt woodchips, including E. urograndis, E. grandis × urophylla, E. urophylla, E. globules, and E. tereticonis were conducted. The results show that the selected five wood specimens of Eucalypt woodchips are featured with medium-density in the range from the lowest 469 kg/m3 of E. tereticon to the highest 515 kg/m3 of E. grandis × urophylla wood; The average fiber length of these five Eucalyptus varied from 755μm to 785μm without significant difference; While the ratio of fiber wall thickness to lumen diameter and holocellulose content and lignin present significant difference. A conventional P-RC APMP pulping process was used to evaluate pulp properties of these five wood specimens, under the impregnation conditions with H2O2 dosage of 5.0 % and, Na OH of 4.5%. The results show that, E. tereticonis woodchips provided the highest pulping yield, up to 86.7 %, while, E. grandis × urophylla woodchips had the lowest pulping yield of 84.2 %. In addition, at the same level of Canadian Standard Freeness, 300 m L, specific refining energy consumption for E. globules woodchips pulping is the lowest, 1188 k Wh/t, and pulp from E. globules woodchips has optimal tensile strength and excellent optical properties; by the contrast, E. grandis × urophylla pulp shows the worst pulp properties and requires the highest refining energy.For P-RC APMP pulping process using stored eucalyptus chips for a period, regardless of the moisture of chips, the refining energy consumption increased with longer storing time; however, the pulp yield and pulp physical strength and optical properties decreased to some extent.The dosage of alkali in the impregnation stage of P-RC APMP process has a significant impact on the properties of the pulp. The yield and bulk properties of pulps was decreased with alkali dosage increasing; In particular, with higher H2O2 dosage, the refining energy consumption reduced and the pulp strength improved; plus, when the ratio of Na OH and H2O2 dosages was less than 1, the pulp brightness declined slightly with the increment of alkali dosage; while the ratio was over 1, the brightness decreased significantly with alkali dosage increasing. In addition, it is found that certain penetrating agent can improve pulping performance. At the freeness level of 300 m L CSF, with addition of 0.4 % sodium diethylhexyl sulfosuccinate at the impregnation stage, it was shown that the refining energy consumption and shives content in pulp were reduced by over 10 % and 46 %, respectively, compared to the control pulp sample; and the tensile strength, burst strength and tear strength increased by 11.4 %, 14.3 % and 15.6 %, respectively without losing brightness.Under the impregnation condition with H2O2 dosage of 5.0 % and Na OH of 4.5 % in the P-RC APMP pulping of E. tereticonis woodchips, the impact on refining energy consumption by different refiner disc speed was investigated. The results show that, for the given pulp freeness of 670 m LCSF, the increment of the refiner disc speed from 3000 r/min to 3500 r/min in the first refining stage, from 3000 r/min to 4000 r/min, the specific refining energy consumption can be reduced by 16 % and the shives contents in pulps decreased by 20 %; when the refiner disc speed increased further to 4000 r/min, the specific refining energy consumption could be lowered by 27% while the shives content being decreased by 35%. With a given energy input of 1000 k Wh/t during the secondary refining stage following the primary refining stage with different speed of 3500 r/min and 4000 r/min, the tensile strength of screened pulp improved by 15.6 % and 22.4 %, respectively.The refining consistency in the secondary refining stage has significant impact on specific refining energy consumption and pulp properties. The results show that with comparison to refining at a high consistency,the refining at low consistency consumed less energy to achieve the given freeness and could produce the pulp with lower shives content; However, with the same total energy input of 1000 k Wh/t, low consistency refining produced the pulp having lower tensile strength without significantly losing brightness compared to high consistency refining.The fibers morphology of E. tereticornis during the refining was observed by SEM. It was shown that most cell pits and vessels in woodchips became closed after long time storing. More fissures in chips and more opening in cell pits could be achieved by mechanical compression, which could facilitate the impregnation of chemical liquor into chips. The impregnation of eucalypt woodchips during chemi-mechanical pulping was affected by many factors. The order of importance of various factors from high to low is listed as following: the degree of wood compression, impregnation time, impregnation temperature, refining consistency and chemical usage.The chemi-mechanical pulp made from E. tereticornis woodchips were examined by UV-Vis spectroscopy and IR spectroscopy. The results show that the bleaching operation by alkaline H2O2 in P-RC APMP process could be attributed to the effects of H2O2 on the aldehyde group, carbonyl and quinoid structure in lignin. The ultraviolet irradiation or high temperature and humidity could induce the yellowness of this pulp. The main reason could be related to structure change of lignin chromophoric group causedby heat, moisture or UV irradiation, particularly UV irradiation having strongest effect. |
PDF Full Text Request