Tunable Interfaces in Fiber Reinforced-polymer Composites Using Plasma Surface Treatments

Fibers incorporated into polymer matrices suffer from poor adhesion at the fiber-resin interface. In ballistic materials such as body armor, it is imperative that the fiber-resin interface is strengthened for superior energy absorbing capabilities. To address this need, fibers are typically subjected to surface modifications. The overall aim of this work is to establish a methodology of controlling the interfacial adhesion by controlling the degree of chemical bonding between the fiber and the resin. In this study, plasma surface treatments were applied to ultra high molecular weight polyethylene (UHMW-PE) fibers to introduce chemical functionalities to promote covalent bonding. Nitrogen and oxygen plasmas were used and changes imposed by the plasma were characterized using surface analytical techniques. The adhesional strength and energy absorption of the plasma-modified fibers/epoxy interface were assessed using a single-fiber microdroplet shear test. FTIR and XPS reveal the existence of four main chemical groups – hydroxyl, carboxylic, carbonyl and amine groups. Characterization of the interface showed that a six-fold increase of the interfacial shear strength (IFSS) can be attained from plasma treating the fibers.