Date of Award

Spring 5-9-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

First Committee Advisor

Douglas W. Bousfield

Second Committee Member

Andre Khalil

Third Committee Member

Daniel H. Varney

Abstract

Current estimates anticipate doubling the value of sustainable paper packaging in the next ten years. As the use of sustainable paper packaging continues to increase, understanding how to use those fibers efficiently will be important. For example, there is a push to light-weight boxes to increase sustainability through weight reduction of shipping and decreased fiber demand. The paper that makes up the box material starts out as wood pulp and we desire to better understand the interactions of the individual pulp fibers. There is a need to link fiber properties and fiber bond strength to macroscopic mechanical properties. Understanding the effects of fiber dimension, orientation, and bonding on tension, compression and folding in such applications can help meet that objective. A Discrete Element Method (DEM) model was developed to model the deformation of paper. A theoretical wood fiber made up of three hundred spheres. The fiber was 2 spheres thick, 3 spheres wide and 50 spheres long. Additional fibers were made the identical size and all of the fibers were placed into a fiber web, also referred to as a fiber network, randomly to simulate how fibers lay in a sheet of paper. The spheres of adjacent fibers that were laying against each other would form bonds if they were within a defined distance. The strength of the interactions between those spheres was differentiated from the spheres that were in the same fiber in terms of strength. The length and internal strength of an individual fiber in the model was adjusted to match the properties of a typical pulp fiber. Tension and compression forces were then applied to the network to collect data on the interactions. The fiber-fiber interactions can be modified by adjusting the parameters in the model to change strain to failure, modulus and maximum stress. By packing the same number of modeled fibers into different areas gives some insight into the effect of increasing the number of bonds in a fiber network. Changing the strength of how tightly bonded fibers are within the structure gives additional information and is done with a factor termed adhesive force fraction (ff). The adhesive force fraction is defined as the ratio of the fiber-fiber bond strength to the internal strength of the fiber. The results of the model give reasonable results that lead to the conclusion that this DEM model could be used to closely match paper characteristics. The results from the model were compared to published handsheet test data and provide maximum stress, strain at failure and modulus values comparable to that data. An unrefined bleached softwood kraft handsheet exhibited tensile failure at 2% strain with 13 MPa of stress. The finite element model within the same published work predicted 6% strain and only 5 MPa of stress at failure. Our DEM model with 100 0.5 mm fibers packed into a 500 x 500 area with the adhesive force fraction set to 0.5 predicted 5% strain and 14 MPa stress at failure.

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