Lightweight Composites through Imidazolium Ionic Liquid Enhanced Aramid–Epoxy Resin Interactions

Poly­(p-phenylene terephthalamide) (PPTA) is mostly used as a low-density polymeric fiber with high specific stiffness, strength, and thermal and chemical stability. The fiber is used as a reinforcement in composite materials in the aerospace and automobile industries, as well as in ballistic and stab-resistant articles. However, its use in composite materials is hampered by its low interfacial affinity with polymeric matrices due to its smooth and inert surface. To overcome such low interfacial interaction, various treatments have been applied to modify the aramid surface. However, it is still challenging to identify an industrially feasible process that does not negatively impact mechanical properties of the aramid fibers. The objective of this study was to investigate different ionic liquids (ILs) with suitable chemical structures as alternative compatibilizers for aramid fibers and epoxy resin. Kevlar fibers were treated with ethanolic solutions of imidazolium IL (1-n-butyl-3-methylimidazolium chloride, 1-carboxymethyl-3-methylimidazolium chloride, 1-triethyleneglycol monomethyl ether-3-methylimidazolium methanesulfonate, or 1-n-butyl-3-methylimidazolium methanesulfonate) and then analyzed by infrared spectroscopy, thermogravimetry, scanning electron microscopy, and X-ray photoelectron spectroscopy. Fiber tensile tests, pull-out tests, and contact angle measurements were used to characterize the fiber and its interface with the epoxy resin. Treatment with all IL, except 1-carboxymethyl-3-methylimidazolium chloride, enhanced the wettability and adhesion of the fibers without imparing mechanical properties. Epoxy resin-based composites were produced using commercial fabrics before and after 1-triethyleneglycol monomethyl ether-3-methylimidazolium methanesulfonate treatment and characterized via tensile and short-beam tests. The composite produced with treated fabrics presented slightly higher tensile strength, modulus, and interfacial shear strength. This improvement can be of interest to the composite sector.