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Research Abstracts Online
January - December 2011

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University of Minnesota Twin Cities
College of Food, Agricultural, and Natural Resource Sciences
College of Science and Engineering
Department of Bioproducts and Biosystems Engineering

PI: Shri Ramaswamy, Associate Fellow

Visualization and Characterization of Three-Dimensional Bulk Structure of Porous Materials and Their Relationship to Transport Properties

This research is an attempt to visualize and characterize the three-dimensional bulk structure of paper and board using non-intrusive techniques. These researchers use x-ray micro computed tomography (x-ray CT) to visualize the structure of porous materials. The images are binarized in black and white and analyzed for pore structure characterization using MSI resources. Structural parameters of interest include pore size distribution, average pore diameter, porosity distribution and average porosity, tortuosity, available transfer surface area, and fiber-fiber bonded area. The group also uses MSI resources to sharpen the images as well as to obtain better characterizations of the structure. Results so far indicate an immense potential for this approach.

The group has developed a model to simulate the physics of simultaneous permeation and absorption of liquid in porous media. The results indicate that, in addition to inherent absorption characteristics of cellulose fibers, the rate of permeation through the pore space has a strong influence on the overall absorption by porous media. They are in the process of developing an MRI technique to visualize and characterize the transient three-dimensional structure of porous media during liquid penetration. Brownian motion random walk simulations to estimate transport properties of porous media using actual three-dimensional structures are underway.

In addition, modeling of mechanical behavior to obtain tensile properties from the binarized image data have provided comparisons of bulk elastic modulus distributions within the samples for different aspect ratios (thin sheet, block) assuming full connectivity of the sample block and elasticity. A correlation between material solid fraction and bulk stiffness were obtained for a geometry having regular sides. For thinner (sheet) sub-volumes, the elastic modulus was found to have reduced stiffness. Further work assuming viscoelastic or elastic-plastic properties with large volume samples is planned.

Group Members

Jeffrey A. Chambers, Undergraduate Student
Yves Defrenne, Graduate Student
Huanjiang Huang, Research Associate
Justin Kaffenberger, Graduate Student
Trevor Peterson, Undergraduate Student
Sho Takagaki, Research Associate
Huigang Zuo, Graduate Student