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

Abstract

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.

Aramid pulp treated with imidazolium ionic liquids as a filler in rigid polyurethane bio‐foams

“…10 Indeed, the π-π stacking between aromatic rings of aramid groups is considered the main responsible for the high stiffness, strength, and elongation of this reinforcement when incorporated into conventional composites. 9 In a previous report, a small content (0.5 phr) of 1-nbutyl-3-methylimidazolium chloride (C 4 .Cl) was enough to increase AP fibrillation, and 5 phr of AP yielded styrene-butadiene rubber (SBR) composites with the highest increase in tensile strength, ca. 42% superior to the IL-free composite.…”

“…2,8 Aramid (poly-p-phenylene-terephthalamide) pulp (AP) is a configuration of AF with some advantages, such as ease of handling and low density, apart from being a common waste from fiber cutting in composites processing labs and industries. 9 Despite these benefits, the use of this material as reinforcement filler presents some obstacles due to the considerably inert surface and the trend to produce aggregates when a high content is incorporated.…”

Epoxy-based composites reinforced with imidazolium ionic liquid-treated aramid pulp

“…Treatment of the AP was performed in an ethanolic solution with 5 wt% of IL in relation to the AP mass, and followed previous reports [15][16][17][18]. The AP-IL mixture was placed in an ultrasonic bath at 50 • C for 30 min, left to evaporate the solvent for 24 h at room temperature and then placed in a vacuum oven for 12 h at 110 • C. The effectiveness of the treatment was assessed using scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR).…”

“…This would break pre-existing hydrogen bonds and π-stacking interactions among adjacent aramid chains [20]. Moreover, when these pulps (treated with 5 wt% of IL) are compared with those treated with lower amount of IL (0.5; 1.0 and 2.0 wt%) the higher defibrillation and rougher surface is evident [15][16][17][18][19]. The AP defibrillation can have beneficial effects related to the increase in mechanical anchoring between AP and the matrix; and a more fibrillated system also has greater surface area, which favors overall adhesion.…”

“…For instance, 1-n-butyl-3-methylimidazolium chloride (C 4 MImCl), 1-n-butyl-3-methylimidazolium methanesulfonate (C 4 MImMeS), 1-carboxymethyl-3-methylimidazolium chloride (HO 2 CC 1 MImCl), 1-triethyleneglycol monomethyl ether-3-methylimidazolium methanesulfonate (C 7 O 3 MImMeS) (Fig. 1) have been used to treat aramid for the preparation of styrene-butadiene rubber (SBR) [15,16], hydrogenated nitrile butadiene rubber (HNBR) [17], laminated epoxy-based composites [18] and also for bio-based rigid polyurethane foams [19]. Due to the contribution of the imidazolium cation π-cloud in π-π interactions and their hydrogen atoms (C 2 -H, C 4 -H, and C 5 -H) in hydrogen bonds with adjacent polymer matrix chains, these IL were considered promising compatibilizers.…”