A multifunctional designing approach is of great importance for advanced composite applications. This study assessed the use of ionic liquids (ILs) to modify the surface of carbon fiber (CF) and ...impart multifunctional characteristics to it. For that, ethanolic solutions of different ILs, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium chloride and 1-(2-hydroxyethyl)-3-methylimidazolium chloride, at different concentrations, were used to treat the CF. Fourier-transform infrared spectroscopy confirmed the presence of IL on the CF surface. The contact angle for 1% w/v IL-treated CF and DGEBA epoxy decreased by up to 35%, corresponding to an increase in surface energy of fiber, accompanied by an increase of 91% in interfacial shear strength. These enhancements were achieved with the hydroxy-functionalized IL, showing the tunability of CF properties through the N-imidazolium substituent. An increase in crystallite size along the basal plane was also found due to the ordering of the graphitic structure on the surface. Moreover, there was a decrease in electrical resistivity of 77%. In all, the imidazolium ILs were considered a promising approach to induce multifunctional characteristics, namely enhanced interfacial strength and electrical conductivity, to unsized CF, which can also be beneficial for recycled fibers without deteriorating their inherent surface properties.
Several high‐performance reinforcements may be used in epoxy‐based composites. These commonly undergo chemical and/or physical treatments to enhance their interfacial interactions with polymer ...matrices. One recent technology comprises the use of ionic liquids (IL) as compatibilizers. This strategy may result in the development of composite materials with greater performance or multifunctional characteristics. Herein, an overview in the area of IL‐modified reinforcements and their effect on epoxy‐based composites is presented. The PRISMA protocol was followed for the review, and the focus of these studies was on the modification of carbon nanotubes, followed by graphene/graphite nanoplatelets and bio‐fillers. The most used IL were those based on imidazolium cation, especially 1‐butyl‐3‐methylimidazolium chloride. In most cases, when IL are used, the reinforcement displays stronger interactions with the epoxy matrix, depending the treatment route employed. Improved interfacial interactions are cited as the main reason for the improvement in the composite mechanical and thermal performances. It was also found that strategies for using low IL content, or routes that enable recovery of the salts after fiber/particle treatment, are still required, as well as the study of the influence of different amounts/types of IL on the structure of fillers and their relationships with the composite properties.
Main differences for the composites' microstructure, when IL is used for improvements on the interface.
Microcrystalline cellulose (MCC) has unique properties and its use as reinforcement for polymer composites has been increasing. However, the intrinsic incompatibility with most polymers requires ...surface modification to improve chemical compatibility prior to its incorporation into a polymer. In this paper, a grafting amount and structural characteristics of MCC functionalized with 3-aminopropyltriethoxysilane (APTES) (MCC-Si) at different contents was performed. We reported a comparison of three different methods for quantifying the APTES grafting amount: from TGA curves, nitrogen content, and silicon content. Supplementary analyses were performed: solid-state
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C and
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Si nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy with energy dispersive X-ray (SEM-EDX). A deep study of structural properties by X-ray diffraction was also conducted. A better correlation for grafting amount of APTES onto MCC was observed for nitrogen content method than residual mass according to the Pearson’s correlation.
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C NMR revealed all the carbon structures from cellulose and side bands for MCC-Si samples and from APTES molecules and
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Si NMR revealed T structures. The silane treatment did not alter the shape of MCC and all treated samples showed Si characteristic peak at ~ 1.75 kEv. The exposure to APTES in an acidic medium caused several effects on the MCC, splitting larger I
β
crystallites in half and along the more reactive hydrophilic sides. The diameter of the smaller IV
I
crystallites was largely reduced by the treatment, especially when the silane concentration was 1:5 (m/v), above which the diameter increases again.
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This article reports an aramid pulp (AP) treated with two ionic liquids (IL), namely 1‐n‐butyl‐3‐methylimidazolium chloride (C4.Cl) and 1‐carboxymethyl‐3‐methylimidazolium chloride (HO2C), 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 HO2C IL.
The mechanical behaviour of strain-rate-dependent materials varies when they are exposed to dynamic conditions (compared with static ones), and material parameters like modulus, strength, and failure ...strain may depend on the loading rate. Simulation of the ballistic impact effect on composite materials may be strongly dependant on the suitable calibration of the strain rate effect on their constitutive law. Indeed, knowledge of the strain rate-dependent properties is of great interest but still lacks comprehensive studies (i.e., the effect on the mechanical parameters, besides strength, is commonly ignored). In the present work, three meso-heterogeneous models for 2D woven glass-fibre composites under impact loading were built considering strain rate-dependent strength, modulus and failure strain, coupled with macro-homogeneous models with and without the strain rate effect on strength. All the numerical predictions were compared with actual ballistic test results. It was found that the accuracy in residual velocity and damage morphology predictions can be improved by considering the strain rate effect on modulus and failure strain.
The thermal degradation behavior of six different vegetal fibers was studied using thermogravimetry under nitrogen atmosphere at four different heating rates (5, 10, 20 and 40 °C min⁻¹). The ...degradation models Kissinger, Friedman and Flynn–Wall–Ozawa methods were used to determine the apparent activation energy and the frequency factor of these fibers. Furthermore, the solid state degradation mechanisms were determined using Criado’s method. Additionally, X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy were analyzed to corroborate the obtained results. The results indicated that the apparent calculated activation energies can be more closely related to the exponential dependence of the rate of heterogeneous reactions than to the, necessary “energy”, which is commonly used. The Criado’s master curves indicated two different degradation mechanisms for the fibers: diffusion followed by random nucleation. The results also indicated that the crystallinity index as calculated by X-ray diffraction and determinated by FTIR does not necessarily represent higher thermal stability as noted by the thermogravimetric analysis curves. The thermal behavior and the degradation mechanism did not show to be influenced by the lignocellulosic components of the fibers, exception for buriti and sisal. This behavior was attributed to higher extractive content.
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•Silanized microcristallyne cellulose were study in this paper.•The best APTES/MCC ratios was determined.•Samples showed an independence of activation energy (Ea) from conversion ...degree (α).•The degradation model proposed in this paper were: A→B→C.•The degradation mechanism was modified from 5 silane ratio.
Microcrystalline cellulose (MCC) can be a reinforcement in composites, especially after surface modification. In this paper, MCC was modified using 3-aminopropyltriethoxysilane (APTES) in the following ratios (MCC/APTES): 1:3, 1:4, 1:5, 1:10). The MCC morphologies did not change with the treatment even though the distribution of APTES over the MCC surface varied. FTIR analysis showed MCC and APTES characteristic peaks for all samples. The crystallinity index (CI) decreased with the APTES ratio. The non-isothermal kinetic degradation by thermogravimetric analysis in different heating rates was studiedin order to evaluate the kinetic triplet: activation energy Ea, exponential factor (A), and reaction order (f(α)). The Ea dependence on conversion degree was not affected, but two degradation steps were observed for all samples. Ratios up to 1:4 suggested two consecutive autocatalytic degradation mechanisms. The 1:5 and 1:10 ratios caused a change in the most probable degradation mechanism for nucleation followed by autocatalytic degradation mechanism.
Abstract Three ethanolic solutions containing different imidazolium ionic liquids (IL), namely 1‐butyl‐3‐methylimidazolium chloride, 1‐carboxymethyl‐3‐methylimidazolium chloride or ...1,3‐dicarboxymethylimidazolium chloride), were used for the surface modification of aramid pulp (AP) (5 wt.% of IL in relation to AP mass) to improve its interfacial interaction with triethylene tetramine‐cured epoxy resin. Composites were prepared by casting with 0.4 phr of AP. Scanning electron microscopy, mechanical tests, isothermal dynamic mechanical analysis (at 1, 10 and 100 Hz), and conventional non‐isothermal analysis were performed. The IL‐modified AP (AP‐IL) presented greater defibrillation and strengthened interaction with the polymeric matrix, minimizing fiber pullout in the mechanical tests. The AP distribution in the epoxy matrix was assessed, and morphological changes were partly responsible for the improvement in the mechanical and dynamical mechanical response of the AP‐IL/epoxy composites. The AP/epoxy composite compatibilized with IL 1‐butyl‐3‐methylimidazolium chloride presented the lowest activation energy and, in turn, the strongest interaction with the epoxy matrix. Normalized DMA curves provided more detailed information on the differences between neat epoxy and the studied composites.
Recently, considerable effort has been made to study cellulose/epoxy composites. However, there is a gap when it comes to understanding the post‐conditioning anomalous effect of moisture uptake on ...their mechanical and dynamic‐mechanical properties, and on their creep behavior. In this work, up to 10.0 wt% microcrystalline cellulose (MCC) was incorporated into epoxy resin by simple mixing and sonication. Epoxy/MCC composites were fabricated by casting in rubber silicone molds, and rectangular and dog‐bone test specimens were produced. The moisture uptake, dynamic mechanical, chemical, tensile, and creep behavior were evaluated. The incorporation of MCC increased the water diffusion coefficient. The changes in storage modulus and glass transition temperature, combined with Fourier‐transform infrared spectroscopy analysis, evidenced that water sorption in epoxies causes both plasticization and additional resin crosslinking, although the latter is prevented by the addition of MCC. The creep strain of the composites increased by 60% after conditioning, indicating that plasticization induced by water sorption plays an important role in the long‐term properties of the composites.
Epoxy resin and microcrystalline cellulose (MCC) composites were submitted to water uptake experiments. Water uptake caused plasticization and additional crosslinking of epoxy resins, the latter being prevented by the addition of MCC fillers.
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