MEAM Seminar: “Nanocellulose Fibers as Reinforcement to Improve Strength and Toughness in Structural Materials”

Cellulose nanofibrils (CNFs) are a naturally abundant polymer and have superior mechanical properties, high aspect ratios, are transparent and biodegradable, which make them attractive to be used in structural materials. As a reinforcing phase, CNFs have the potential to improve the mechanical properties of polymer materials. While there are active research efforts aimed at incorporating CNFs into polymers for use as structural materials, the field is still in its infancy due to the challenge of achieving good compatibility and the challenge of maintaining strength while trying to enhance fracture toughness and crack growth resistance.

In the first part of this study, one dimensional composite fibers are fabricated using TEMPO-CNF to increase the strength and toughness of the common polymer PMMA, a hydrophobic and challenging material to bond with CNFs. The composite fibers were prepared via solvent exchange, melt-spinning and drawing to obtain fibers of diameters around 200 microns. Tensile testing, image correlation to measure the strains, and fracture test with flat faced edge crack demonstrated the enhancement of modulus, strength, and fracture toughness through the addition of CNFs to PMMA. Specifically, an enhancement of 35% in Modulus, 19% in Strength and 100% in fracture toughness were observed at 1% by wt. CNF content.

The second part is a distinct but interrelated research thrust to the traditional polymer integration. Composite pure cellulose sheets consisting of micro- and nanocellulose are fabricated. This study uses printing and subsequent drying processes to infuse nanocellulose into the paper matrix in various patterns to increase the strength and toughness of the network. Tensile tests and single edge notch tension (SENT) tests are performed on the specimens to evaluate their tensile and fracture behavior. Linear elastic finite element modeling is used to help guide the experimental work. This work has potential applications in using nanocellulose fibers to realize fully degradable alternatives to thin plastic sheets.