Two types of physisorbed imidazolium ionic liquids (IL), 1-n-butyl-3-methylimidazolium chloride (C 4 MImCl) or 1-n-butyl-3-methylimidazolium acetate (C 4 MImAc), were used for the surface treatment of polyaramid pulp (AP), aiming to enhance the interaction with an epoxy matrix. The treatments promoted a greater defibrillation of AP, which was most likely due to an interference of IL in the hydrogen bonding network of polyaramid. Composites of AP/epoxy (0.2, 0.4 or 0.6 parts per hundred of resin (phr)) were prepared, and those with 0.4 phr of IL-treated AP presented enhanced mechanical properties, compared to the neat or the untreated AP composites. Better homogeneity and stronger bonding between AP and the epoxy matrix were also observed, especially in the case of AP treated with C 4 MImCl. Moreover, the AP surface treatment increased the glass transition temperature and the storage moduli in both glassy and rubbery regions. The fracture toughness improvement of the composites was also achieved with the addition of the IL-treated AP.

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This article reports an aramid pulp (AP) treated with two ionic liquids (IL), namely 1-n-butyl-3-methylimidazolium chloride (C 4 .Cl) and 1-carboxymethyl-3-methylimidazolium chloride (HO 2 C), and its use as a filler in reinforced rigid polyurethane foams (RPUF). The RPUF were incorporated with the treated AP at three weight fractions (c.a. 0.1, 0.5, and 1.0 wt%) and were produced by the free rising method. The results showed that the studied IL promoted a better interaction between the AP and the RPUF system, which increased the overall reactivity, imparting a higher cell anisotropy. This also yielded a positive effect in mechanical properties and thermal stability of the RPUF. Compared to the neat RPUF, outstanding increases of approximately 50 and 20% were achieved in compressive modulus and strength, respectively. In all, the use of IL promoted increased compatibility between matrix and reinforcement, especially that HO 2 C IL.

Although carbon black is an effective reinforcement for most rubbers, its replacement by other fillers would be beneficial. Aramid fibers are used in a range of applications in the rubber industry, providing dimensional stability prior to vulcanization and improving the mechanical properties of the elastomeric product. Nevertheless, their relatively inert surface is an obstacle in the exploitation of their full potential. In this work, two ionic liquids were investigated as compatibilizers in the preparation of hydrogenated nitrile butadiene rubber composites with aramid pulp and carbon black fillers. The materials were characterized using swelling, hardness and tensile tests, differential scanning calorimetry, thermal gravimetric analysis, and infrared spectroscopy. The carbon black‐free composite prepared from aramid pulp treated with 1.0 wt% of 1‐carboxymethyl‐3‐methylimidazolium chloride outperformed all other studied materials, presenting a higher modulus at 100% strain (7.31 MPa), while maintaining high strain at break. Thus, ionic liquids were found to potentialize the aramid reinforcement effect in these rubber composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48702.

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.

Poly‐p‐phenyleneterephthalamide is a broadly used aramid for the strengthening of materials. Nevertheless, its relatively inert surface is an obstacle for obtaining composites with enhanced properties. In this work, three ionic liquids (IL) were investigated as compatibilizers in the preparation of styrene‐butadiene rubber (SBR)‐aramid pulp composites. The composites were characterized using hardness and tensile tests, swelling, differential scanning calorimetry, and thermal gravimetric analysis, and also scanning electron microscopy. Aramid pulp treated with IL showed more fibrillation than the untreated pulp. The best characteristics were found for the composite with 5 phr of aramid pulp‐1 wt % of physisorbed IL, which showed the lowest swelling degree compared to the IL‐free SBR‐aramid composite (341% and 410%, respectively) and the highest tensile strength (2.48 MPa), 340% superior to that of SBR (0.73 MPa), and 25% superior to the IL‐free SBR‐aramid composite (2.05 MPa). Confirming the potential of imidazolium IL to be used as compatibilizers in SBR‐aramid composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46693.

This study investigates creep and viscoelastic behavior of the diglycidyl ether of bisphenol A (DGEBA) epoxy resin and triethylenetetramine (TETA) system containing an imidazolium ionic liquid (IL), the 1-n-butyl-3-methylimidazolium chloride (C 4 MImCl). Different time-dependent analysis methods are studied using data from tensile creep, tensile creep/recovery, and three-point and fourpoint flexural creep tests of epoxy with 1.0 or 4.0 phr of IL. From the results, the composition containing 1.0 phr of C 4 MImCl, cured at 60 C, presented greater viscoelasticity and crosslink density compared to compositions cured at 30 and 40 C, which was attributed to higher free volume and higher molecular mobility induced by the presence of the IL. In tensile creep tests using the stepped isostress method (SSM), no important degrading effects were found after the addition of 1.0 phr of IL over long time periods. This composition also showed the best overall performance in flexural SSM creep tests.

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