Aramid Nanofiber Interphase for Enhanced Interfacial Shear Strength in Ultra-High Molecular Weight Polyethylene/Epoxy Composites

Ultra-high molecular weight polyethylene (UHMWPE) fibers are used in ballistic composites due to their high tenacity; unfortunately, their use in structural composites remains limited due to their poor adhesion with polymer matrix materials. Interphase design to the fiber surface is a promising approach to improve the interfacial properties of composite materials. This work describes the use of an aramid nanofiber (ANF) dip-coating treatment of plasma-treated UHMWPE fibers that increases surface roughness and enhances mechanical interlocking with the matrix. The ANFs also populate the fibers with polar functional groups, specifically hydroxyl, amide, ketone, and carboxyl, allowing for chemical bonding opportunities between the fiber and the epoxy matrix. The UHMWPE fiber surface chemical structure and composition is characterized using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The ANF dip-coating treatment yielded up to a 267% increase in fiber surface roughness, measured using atomic force microscopy. Using single fiber pullout testing, a maximum increase of 173% in interfacial shear strength is measured due to the ANF interphase, while completely maintaining the tensile strength of the fibers measured through single fiber tensile testing. These results demonstrate a simple and cost-efficient technique to improve the interfacial properties of UHMWPE composites through an ANF surface reinforcement.