Session: 17-01-01: Research Posters

Paper Number: 149838

149838 - Quantifying the Mechanics of Nanofibrillated Cellulose Gels 

Gels made of nanofibrillated cellulose (NFC) are biodegradable and renewable, making them appealing for use in food packaging, 3D printing, and drilling fluids. The behavior of cellulose gels is similar to that of a viscoelastic fluid, as the fibers are an entangled network with van der Waals interactions between them. The different production methods used to create NFC can change the rheology of the system and the characteristics of the fibers, such as the fiber length, thickness, and density. The mechanics of an individual fiber are straightforward, as each fiber acts as a beam that bends, stretches, or buckles when subjected to various forces. Networks of fibers exhibit more complicated mechanics, however, as the bending of multiple connected fibers causes geometric nonlinearities and nonaffine deformations. The mechanics of these materials have been often quantified using shear rheometers, but the results have shown dependence of the measured modulus on sample thickness, which has been proposed to be caused by shear banding. It is unclear how these fibers interact with each other and how the bonds between them break and reform, which may be a cause of the shear banding seen in experiments using rheometers. There is also not a strong understanding of the mechanical behavior of cellulose fibers at large deformations in a gel. Here, we devise an experimental method to quantify the mechanical properties of NFC gels at the length scale of the fibers. NFC gels are thoroughly mixed with fluorescent beads for imaging on a confocal microscope. The gels are placed in a device that can produce uniaxial tension or compression on the gel with a micrometer; the device is mounted to the microscope stage. We take images of the gel before applying deformation and additional images at different applied deformations, with an applied nominal strain of approximately 1% for each step. We intend to apply at least 5% nominal strain to the gels. We then perform Digital Image Correlation on the images to compute displacement and strain fields. Preliminary strain fields show variability of a magnitude of five percent, which may be due to nonaffine displacements in the network. This experimental method gives a novel way to study the mechanics of NFC under large deformations, and how the mechanics depend on the length, thickness, and density of the fibers. In ongoing work, we are adding rigid spheres to the NFC gels, which produces variability in the strain field and will be used to study strain localization, as occurs in shear banding.

Presenting Author: Samir Patel University of Wisconsin-Madison

Presenting Author Biography: 3rd year Engineering Mechanics Ph. D Student at the University of Wisconsin-Madison.
Member of the Notbohm Lab Group.

Authors:

Samir Patel University of Wisconsin-Madison
Jacob Notbohm University of Wisconsin-Madison