An Experimental Study on Crack Propagation in Green Composites Made from Cellulose Nanofibers and Epoxy

The current examples of natural-fiber based polymer composites, because of their biobased and biodegradable properties, offer an alternative as a ‘green’ material available for automotive and other engineering applications. However such composites suffer from low strength and fatigue properties compared to the carbonor glass-fiber based polymer composites. Cellulose nanofibers (CNFs), a new type of nanofibers made entirely from cellulose molecules, have very high mechanical properties compared to other natural fibers, even approaching that of inorganic reinforcing fibers. The composites made from cellulose nanofiber films are likely to have very good strength compared to other kinds of biocomposites. However such an assertion about the mechanical properties of composites made from CNF films is yet to be investigated through experiments. This paper presents the results from a crack-propagation test conducted using a double cantilever beam made using two types of resins and reinforcements. The resins used were a traditional epoxy and a bio-based epoxy. For reinforcement, cellulose nanofiber (CNF) films were used. The samples were tested against a reference case made from fiberglass to study and compare crack propagation patterns in the composites. Various crack resistance characteristics are observed in the two systems. The study shows the need to investigate methods for improving the fracture toughness of polymer composites fabricated using CNF films.