| With the development of society,in recent years,people’s awareness of environmental protection is gradually increased.Requirements for high-quality paper or paper-board are increasing day by day.More and more manufacturers begin to focus on the dissolved liquid of COD of pulp,which not only can influence the performance of the succeeding paper making,but also can be used as an indicator of environmental performance.This paper tests the dissolved liquid of COD of pulp board from two different factory lines,and compares the raw material components of the pulp boards to study the influence of raw materials on pulp cleanliness.For further study,we analyzed the structural differences of the black liquid alkali lignin of each raw materials by simulating cooking and the gradient washing experiments were carried out to explore the impact of the pulp washing process on the dissolved liquid of COD and paper making property.Firstly,the dissolved liquid of COD of each pulp samples from PD1 and PD2 plant were tested.We found that the pulp of Australian Eucalyptus(AE)have the lowest COD 36.8mg/L,and the pulp of Vietnam Acacia(VA)have the highest COD 78.3 mg/L.We tested the salt cake loss and DCM extractives simultaneously and found that both them are highest in the pulp of VA 0.48 Kg/ADT and 0.54% respectively and lowest in AE 0.06Kg/ADT and 0.08% respectively.The dissolved liquid of COD of each pulp sample of PD1 plant is higher than that of PD2 plant,so we think the vacuum washer on PD1 plant is better.By comparing the surface tension of the water extraction liquid and COD,we found that the higher the COD the smaller the surface tension,and vice versa.So the COD and the surface tension is a certain linear relationship.Meanwhile,with the increase of the content of tiny fibers,the conductivity increased gradually,and vice versa.So the content of tiny fibers also influence the conductivity.Comparing the fiber morphology and chemical composition of VA,AE and Indonesia Acacia(IA),we found that the fiber quality of AE is best,and that of VA is the worst.Secondly,cooking the three raw materials by Kraft process.The lignin was extracted from the obtained black liquor using acid precipitation method.Analyzing the structure of the three alkali lignin,we found that VA and IA have a similar structure;the content of hydroxyl,methoxy,and ether bond is highest in AE;the molecular mass and polydispersity of AE is smaller than VA and IA;the results of infrared spectrum and NMR indicate that AE contains more S unit,hydroxyl and C-C,C-O,C=O bonds.Finally,by gradient washing the post-coking pulps,we found that AE has the lowest dissolved liquid of COD 75mg/L.This result is consistent with the factory pulp board testing result.Considered the chemical composition of AE,it is clear that the dissolved liquid of COD of pulp has a direct relationship with the raw materials.The COD,kappa number and yield of pulp decreased gradually along with the washing,with a strong dropping trend at the initial stage and then slowed down.Along with washing process,the content of tiny fibers reduced gradually,and the fiber length increased slightly.Gradient washing has some influence on the properties of paper making.Due to the influence from fiber length and the binding force between fibers,the tear ability and bursting strength increasing during the washing process,while the tensile strength,under the influence of the content of tiny fibers,increased earlier and followed by a decline. |
