High strength fiber reinforced composites with surface fibrilized aramid fibers

Debonding of the fiber-matrix interface is a common issue in composites, especially for aramid fiber reinforced composites due to their smooth and inert surface. Here, a novel surface treatment is developed for aramid fibers in order to enhance the interfacial properties in composites while preserving the fiber's tensile strength. The fibrilization approach follows the recent work on the aramid nanofibers and uses a solution of potassium hydroxide and dimethyl sulfoxide at room temperature. This process is performed to exfoliate the surface fibrils such that a pseudo-wiskerized fiber is prepared, which provides mechanical interlocking with the matrix. The surface bound fibrils also contain increased polar functional groups, which additionally provides improved wetting due to the enhanced compatibility of the fiber with the matrix as well as offering reactive sites to allow covalent bonding with the reactive thermosets such as epoxy. It is shown that the surface fibrilized fibers possess an 128% improved interfacial shear strength with an epoxy matrix, as well as a 62% increased short beam strength, compared with untreated fiber reinforced composites. The tensile strength of the treated fibers is demonstrated to be preserved, ensuring a significant improvement in the common failure modes without a degradation of in-plane properties. The results indicate the potential of this treatment as a simple, fast, and cost-effective method to improve not only the interface in the aramid fiber reinforced polymer matrix composites but also the bulk laminated composite.