Carbon fiber composites are high-performance materials commonly used in advanced applications and their performance is highly dependent on the fiber-matrix interfacial interaction. The non-polar carbon fiber surface may be modified via different techniques to improve adhesion with the polymer matrix. In this work, non-covalent surface modification of carbon fiber has been carried out using two different imidazolium ionic liquids, 1-n-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide (hydrophobic) and 1-n-butyl-3-methylimidazolium chloride (hydrophilic). The treatment was performed by immersing the fiber into 10 wt. % methanolic ionic liquid solution for 10 min. Treated fibers were characterized using Fourier-transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of ionic liquid on the carbon fiber surface. Surface morphology of treated fibers analyzed by scanning electron microscopy showed ionic liquid moieties. Wettability of the treated carbon fiber with epoxy resin significantly increased, with a decrease in contact angle greater than 15°. Interfacial shear strength between the modified carbon fiber and epoxy increased up to 56.5% with respect to the unsized carbon fiber, being comparable with epoxy-sized fibers. Thus, the proposed surface modification has the potential to improve the interfacial performance of carbon fiber polymer composites. Graphical Abstract

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.

Hybrid composite laminates with nanofillers are high performance materials for thermal and structural applications. In this work, multiwall carbon nanotubes (MWCNT) were non-covalently modified by treating them with 1 wt% or 5 wt% of ionic liquid (IL), 1-butyl-3-methylimidazolium chloride. The treated MWCNT were dispersed in epoxy resin (weight content: 0.2–2 wt% or 1 to 3 wt%, respectively) and used to obtain hybrid composite laminates based on carbon fibers (CF) molded by hand layup and vacuum bagging techniques. The hybrid composite laminate containing 1 wt% of MWCNT modified with 1 wt% of IL showed the best mechanical and thermomechanical properties, including an increase of 210% and 151% in flexural strength and modulus, and an increase of 101%, 116% and 29.3% in storage modulus, loss modulus and damping, respectively. Scanning and transmission electron micrographs showed the enhanced MWCNT dispersion and network at low IL content, justifying its improved mechanical properties. The application of a low amount of IL dispersant was found a promising approach to prepare MWCNT/CF/epoxy composites with enhanced properties.

The present study introduces four novel compound binders CB1, CB2, CB3 and CB4, incorporated in cold-bonded briquettes (CBBs), by varying 3–6 wt.% and briquetted at briquetting pressures ranging from 200 to 400 MPa. Experimental analyses show that a minimum of 4 wt.% compound binder is required to fulfil blast furnace application requirements. CBBs with 4 wt.% CB1 and CB2 compound binders, briquetted at 200 MPa, achieved compressive loads of 3411 N and 2728 N. Reduction disintegration index (RDI) analysis revealed that CBBs prepared with 4 wt.% CB1 require 250 MPa briquetting pressure and those with 4 wt.% CB2 requires only 200 MPa. Reduction swelling index (RSI) analysis indicated that 4 wt.% of CB1 and CB2 performed well at 200 MPa briquetting pressure, resulting in 16.7% and 18.8% swelling, respectively. Economic assessments showed a reduction of 12% per ton as compared to conventional sinter and 17% per ton for pellet production, attributed to lower energy requirements.