| The paper sheet is a porous material formed by interweaving fibers.Its microscopic pore structure not only affects the permeability of the paper,but also directly affects the physical and optical properties of the paper.In recent years,three-dimensional（3D）structure visualization and non-destructive testing of materials have become research hotspots.Regarding the correlation between the three-dimensional structure and the performances of the paper sheet,the following three aspects of research work were carried out:First of all,Masson pine pulp,eucalyptus pulp,cotton pulp,bamboo pulp and bagasse pulp were taken as research objects,and fiber characteristics of five kinds of pulps（beating degree:30°SR）were quantitatively characterized.The tensile strength,zero-strength tensile strength,tear strength,bursting strength and air permeability of five kinds of paper sheets were tested,and the contribution factors of different pulp fibers to the performances of paper sheets were analyzed.With the mixing ratio of 8:2,6:4,5:5,4:6,2:8,the five kinds of pulp fibers were mixed in pairs to papermaking,and the effect of mixed fiber on paper performances were analyzed.The results showed that the paper physical properties could be improved by mixing wood fiber and non-wood fiber in a certain proportion.Then,in view of the limitations of current researches of paper performances mainly from mechanism analysis,providing a research basis for analyzing the impact of paper structure on paper performance from a micro perspective.In this paper,the experimental model of paper structure was constructed.The fibers were dyed with safranine-O fluorescent dye and papermaking.Next,the paper was scanned with a laser confocal scanning microscope（CLSM）and the Z-direction sequence diagrams of the paper were obtained under the excitation of X-ray energy.The acquired images were processed with MATLAB,which including grayscale,anisotropic diffusion,minimum error threshold and other image processing,to obtain three-dimensional structures of the paper.The results indicated that the relative error between the calculated value of porosity obtained by CLSM and the experimental value was less than 8%,and feasibility of the method are verified.Subsequently,the image features of the material are digitally recorded by reference to digital core technology.The prediction model of paper structure was established that the 3D structure of paper was predicted by using the two-dimensional（2D）structure characteristics of paper.In this paper,two algorithms of two-point correlation and linear path function and co-occurrence correlation function are used to calculate the 2D pore structure characteristics of paper.The simulated annealing algorithm was used to obtain the 3D pore structure of the paper which satisfies the characteristics of the 2D pore structure.The paper pore structure can be visualized from two to three dimensions.The results demonstrated that the 3D reconstruction effect of paper pores was the best and the calculation speed was the fastest,when the initial temperature is 10-5℃,monte Carlo iterations are 500 times,and the cooling coefficient is 0.90 and the reconstruction time of co-occurrence correlation function was reduced by 30%.Finally,fluid simulation was carried out based on 3D pore structure of paper.The reconstructed 3D structure of the paper was taken as input,the pore-throat model was constructed to obtain the porosity and pore size distribution of the paper sheet by using AVIZO image processing software.On this basis,the pore throat model was used for pore penetration simulation to obtain the absolute permeability of the paper sheet,and to achieve the non-destructive detection of the paper penetration performance.The trend of calculation results of the absolute permeability of the five kinds of paper was consistent with the test results of the air permeability of the paper.The feasibility and accuracy of the structural prediction model and the method of paper penetration simulation are verified. |
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