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.
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.
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.
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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