Improvement of tensile strength and toughness in aramid/epoxy composites by sequential air plasma and (3-glycidyloxypropyl) trimethoxysilane treatments

This work explores sequential surface treatments involving atmospheric-air plasma and (3-glycidyloxypropyl) trimethoxysilane (GLYMO) to enhance the tensile properties of aramid/epoxy composites. To prove the technical advantages of this approach, aramid fibers received individual (atmospheric-air plasma or GLYMO) or sequential (plasma followed by GLYMO, and vice versa) surface treatments. Single fiber tensile tests (SFT) and X-ray photoelectron spectroscopy (XPS) were employed to characterize changes in aramid fibers upon the surface modifications. SFT revealed that none of the surface treatments compromised their tensile strength (σmax). Applying GLYMO, whether individually or in sequence (GLYMO followed by plasma and plasma followed by GLYMO), led to a significant enhancement in the fibers' elastic modulus (E). Composites with plasma-treated fibers displayed a 5% increase in E and an 8.5% increase in σmax, with no changes in toughness. However, the most notable improvements were achieved through sequential plasma followed by GLYMO treatments, resulting in a ~ 10% increase in σmax and a remarkable ~ 40% improvement in toughness. Plasma introduces oxygen-containing groups to the fiber surface, facilitating GLYMO grafting. Subsequent crosslinking of GLYMO with the epoxy resin strengthens the fiber-matrix interface. This sequential surface modification offers an alternative pathway for fabricating composites with superior toughness and σmax.