Surfactant-Assisted Dispersion of MWCNTs in Epoxy Resin Used in CFRP Strengthening Systems

The epoxy resin used as the bonding agent in carbon fiber-reinforced polymer (CFRP) strengthening systems was modified by the infusion of multiwalled carbon nanotubes (MWCNTs). Two types of surfactants, Triton X-100 and C₁₂E₈, were used to disperse the nanotubes in the epoxy resin employing ultrasonic mixing. Dynamic mechanical analysis and tensile tests were conducted to study the effect of the surfactant-assisted dispersion of nanotubes on the thermal and mechanical properties of epoxy composites. The morphology of the epoxy composites was interpreted using scanning electron microscopy (SEM). Moreover, the effect of surfactant treatment on the structure of nanotubes was investigated by Fourier transform infrared (FT-IR). Based on the experimental results, the tensile strength and the storage modulus of the epoxy resin were increased by 32% and 26%, respectively, by the addition of MWCNTs. This was attributed to the homogeneous dispersion of nanotubes in the epoxy resin according to the SEM images. Another reason for the enhancement in the tensile properties was the reinforced nanotube/epoxy interaction as a result of the surfactant anchoring effect which was proved by FT-IR. A moderate improvement in the glass transition temperature (T _g) was recorded for the composite fabricated using Triton X-100, which was due to the restricted molecular motions in the epoxy matrix. To characterize the temperature-dependent tensile behavior of the modified epoxy composites, tensile tests were conducted at elevated temperatures. It was revealed that the MWCNT modification using surfactant substantially improves the tensile performance of the epoxy adhesive at temperatures above the T _g of the neat epoxy.     

Effect of graphene and CNT reinforcement on mechanical and thermomechanical behavior of epoxy—A comparative study

Graphene‐nanoplateles (Gr) and multiwalled carbon nanotubes (CNTs) reinforced epoxy based composites were fabricated using ultrasonication, a strong tool for effective dispersion of Gr/CNTs in epoxy. The effect of individual addition of two different nanofillers (Gr and CNT) in epoxy matrix, for a range of nanofiller content (0.1–1 wt %), has been investigated in this study. This study compares mechanical and thermomechanical behavior of Gr and CNT reinforced epoxy. Gr reinforcement offers higher improvement in strength, Young's modulus, and hardness than CNT, at ≤0.2 wt %. However, mode‐I fracture toughness shows different trend. The maximum improvement in fracture toughness observed for epoxy‐Gr composite was 102% (with 0.3 wt % loading of Gr) and the same for epoxy‐CNT composite was 152% (with 0.5 wt % loading of CNT). Thorough microstructural studies are performed to evaluate dispersion, strengthening, and toughening mechanisms, active with different nanofillers. The results obtained from all the studies are thoroughly analyzed to comprehend the effect of nanofillers, individually, on the performance of the composites in structural applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46101.     

Nanostructured thermosetting epoxy systems modified with poly(isoprene‐b‐methyl metacrylate) diblock copolymer and polyisoprene‐grafted carbon nanotubes

Nanostructured thermosetting composites based on an epoxy matrix modified with poly(isoprene‐b‐methyl methacrylate) (PI‐b‐PMMA) block copolymer were prepared through PI block segregation. Morphological structures were examined by means of atomic microscopy force microscopy. As epoxy/pristine multi‐walled carbon nanotubes (MWCNT) systems were found to present big agglomerations, with a very poor dispersion of the nanofiller, epoxy/PI‐b‐PMMA/MWCNT systems were prepared by using polyisoprene‐grafted carbon nanotubes (PI‐g‐CNT) to enhance compatibility with the matrix and improve dispersion. It was found that the functionalization of MWCNT with grafted polyisoprene was not enough to totally disperse them into the epoxy matrix but an improvement of the dispersion of carbon nanotubes was achieved by nanostructuring epoxy matrix with PI‐b‐PMMA when compared with epoxy/MWCNT composites without nanostructuring. Nevertheless, some agglomerates were still present and the complete dispersion or confinement of nanotubes into desired domains was not achieved. Thermomechanical properties slightly increase with PI‐g‐CNT content for nanostructured samples, whereas for nonnanostructured epoxy/PI‐g‐CNT composites they appeared almost constant and even decreased for the highest nanofiller amount due to the presence of agglomerates. Compression properties slightly decreased with block copolymer content, while remained almost constant with nanofiller amount. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A comparative study on the properties of the different amino‐functionalized multiwall carbon nanotubes reinforced epoxy resin composites

Multiwall carbon nanotubes (MWCNTs) were amino‐functionalized by 1,2‐ethylenediamine (EDA)' triethylenetetramine (TETA), and dodecylamine (DDA), and investigated by fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (TGA). The dispersion of the DDA functionalized MWCNT in DMF is better than that of the MWCNT functionalized by the EDA and the TETA. Carbon nanotubes reinforced epoxy resin composites were prepared, and the effect of the amino‐functionalization on the properties of the composites was investigated by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), and TGA. The composites reinforced by the MWCNTs demonstrate improvement in various mechanical properties. The increase of T_g of the composites with the addition of amino‐functionalized MWCNT compared to the T_g of the composites with the addition of unfunctionalized MWCNT was due to the chemical combination and the physical entanglements between amino group from modified MWNTs and epoxy group from the epoxy resin. The interfacial bonding between the epoxy and the amino group of the EDA and the TETA‐modified MWCNT is more important than the well dispersion of DDA‐modified MWCNT in the composites for the improvement of the mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of dispersion conditions on the mechanical properties of multi-walled carbon nanotubes based epoxy resin composites

A suitable dispersion technique and quantitative evaluation of degree of dispersion of carbon nanotubes (CNT) in any solvent and matrix system has been one of the key issues for achieving enhanced performance of CNT reinforced composites. We report the use of UV–vis spectroscopy as a useful technique to ascertain the degree of dispersion of multiwalled carbon nanotubes (MWCNT) in the epoxy resin. The study has enabled to maximize dispersion of MWCNT in the epoxy resin using two different routes. As a result the composite samples prepared with only 0.3 wt.% amine functionalized MWCNT showed flexural strength of 140 MPa over the neat resin value of 55 MPa, an improvement of ~155% which is maximum reported so far for CNT-epoxy isotropic composites.     

Effect of deposited carbon nanotubes on interlaminar properties of carbon fiber‐reinforced epoxy composites using a developed spraying processing

Carbon fiber‐reinforced epoxy composites, with incorporated carboxylic multiwall carbon nanotubes (CNTs), were prepared using vacuum‐assisted resin infusion (VARI) molding, and the in‐plane and out‐of‐plane properties, including mode‐I (G_Ic) and mode‐II (G_IIc) interlaminar fracture toughness, interlaminar shear strength (ILSS), tensile, and flexural properties were measured. A novel spraying technique, which sprays a kind of epoxy resin E20 with high viscosity after spraying the CNTs, was adopted to deposit the CNTs on the surface of carbon fiber fabric. The E20 was used to anchor CNTs on the fabric surface, avoiding that the deposited CNTs were removed by the infusing resin during VARI process. The spraying processing, including spraying amount and spraying sequence, was optimized based on the distribution of CNTs on the fibers. After that, three composite specimen groups were fabricated using different carbon fiber fabrics, including as‐received, CNT‐deposited with E20, and CNT‐deposited without E20. The effects of CNTs on the processing quality and mechanical properties of carbon fiber‐reinforced polymer composites were studied. The experimental results show that all studied laminates have uniform thickness with designed values and no obvious defects form inside the laminates. Compared with the composite without CNTs, depositing CNTs with E20 increases by 24% in the average propagation G_Ic, by 11% in the propagation G_IIc and by 12% in the ILSS, while it preserves the in‐plane mechanical properties, However, depositing CNTs without E20 reduces interlaminar fracture toughness. These phenomena are attributed to the differences in the distribution of CNTs and the fiber/matrix interfacial bonding for different spraying processing. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Improved tensile properties of carbon nanotube modified epoxy and its continuous carbon fiber reinforced composites

Carbon nanotubes (CNTs) were used to improve the tensile properties of an epoxy resin and its continuous carbon fiber (CF) reinforced composites. Micrography picture showed that CNTs has been well incorporated into the composites, and made the fracture cross section more rougher through sharing the stress. For the CNT/epoxy composite, the tensile strength and modulus both increased upon the CNT addition, and at a CNT volume concentration of 2.0%, the maximum enhancements in the tensile strength and modulus were achieved as 26.7% and 21.5%, respectively. For the CNT‐CF/epoxy composite, the maximum enhancement in tensile strength was achieved as 11.6% at a CNT volume concentration of 1.0% and then decreased with the further increase of the CNT addition, but the tensile modulus increased monotonically upon the CNT addition. POLYM. COMPOS., 36:1664–1668, 2015. © 2014 Society of Plastics Engineers     

Synthesis of carbon nanotube/epoxy composite films with a high nanotube loading by a mixed-curing-agent assisted layer-by-layer method and their electrical conductivity

A mixed-curing-agent assisted layer-by-layer method is reported to synthesize carbon nanotube (CNT)/epoxy composite films with a high CNT loading from ∼15 to ∼36 wt.%. The mixed-curing-agent consists of two types of agents, one of which is responsible for the partial initial curing at room temperature to avoid agglomeration of the CNTs, and the other for complete curing of epoxy resin at high temperature to synthesize epoxy composite films with good CNT dispersion. The electrical conductivity of the composites shows a value up to ∼12 S/m, which is much higher than that for CNT/epoxy composites with a low CNT loading prepared using conventional methods.     

Resin film infusion: Toward structural composites with nanofillers

Resin Film Infusion (RFI) has been used to fabricate composites with continuous unidirectional E‐glass and epoxy with low weight fractions of carbon nanotubes (CNTs) in matrix. An ultrasound‐assisted dissolution‐evaporation method with thermoplastics or block copolymers as dispersing agents for nanoparticles enabled uniform dispersion of CNTs in the resin. Rheological characterization of CNT‐filled epoxy revealed that viscosity, and hence processing of the resin remains unaffected as compared to pristine resin at elevated temperatures of subsequent composite manufacturing. Local flow of the modified resin through the sandwiched fabric plies in RFI process as against the global flow in traditional liquid composite molding processes, made sure that uniform distribution of nanoparticles is accomplished throughout the composite. Compressive properties of hybrid composites improved considerably with CNTs at loading fractions as low as 0.2 wt %. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Multiwalled carbon nanotube/polysulfone composites: Using the Hildebrand solubility parameter to predict dispersion

Polysulfone composites were prepared by solution casting, using various types of treated carbon nanotubes (CNTs) at loadings of up to 5 wt%. The CNT types tested were: as‐received, acid treated, OCA surfactant, OCA functionalized and Poly(methyl methacrylate) functionalized nanotubes prepared using both as‐received and acid treated CNT. The treatment types investigated were selected based upon their solubility parameters and on the results of previous studies. The treated CNTs, CNT/solvent dispersions and the final composite samples were characterised using Fourier Transform Infrared Spectroscopy (FTIR), thermal analysis, Transmission Electron Microscopy (TEM), Ultraviolet‐Visible (UV‐vis) spectroscopy, optical microscopy, electrical conductivity and tensile testing. It was observed that the all the treatments studied improved the stability of CNT in the solvent. Of the CNT types studied, composites containing OCA functionalised CNT displayed the lowest percolation threshold (3 wt%) and highest mechanical performance. While the use of Hildebrand solubility parameters is useful in indentifying promising CNT treatments, their use can not fully predict CNT dispersion behaviour and composite performance. It is also critical to consider the influence of any treatments on CNT length and residual solvent levels. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Effect of Dodecyal Amine Functionalized Graphene on the Mechanical and Thermal Properties of Epoxy‐Based Composites

Simultaneous surface functionalization and reduction of graphene oxide (GO) was achieved by using dodecyl amine (DA) as surface modifying agent. The DA modified reduced GO (DA‐G) was used for subsequent preparation of DA‐G/epoxy composites by solution mixing. Fourier transform infrared spectroscopy analysis, X‐ray diffraction (XRD) and electrical conductivity measurements were conducted to establish the concurrent functionalization and reduction of GO. The effect of DA‐G on the epoxy composites at 0 to 0.75 wt% loadings was studied by investigating its static and dynamical mechanical properties. XRD study was performed to verify the dispersion of DA‐G in the epoxy polymer. Field emission scanning electron microscopy was used to investigate the fracture surface morphology of the composites and Transmission electron microscopy was employed to further confirm the dispersion of DA‐G in the matrix. It was found that the tensile strength of the composite was increased by 38.8% with the addition of 0.5 wt% of DA‐G. The good adhesion/interaction between DA‐G and epoxy resulted in the increase of storage modulus; however, glass transition temperature (T_g) value of the composites shifted to lower temperature in comparison to the neat epoxy. Thermogravimetric analysis showed small decrease in onset degradation temperature for the composites as compared to neat epoxy except for the composites containing 0.75 wt% of DA‐G. POLYM. ENG. SCI., 56:1221–1228, 2016. © 2016 Society of Plastics Engineers     

Epoxy shape‐memory polymer reinforced by thermally reduced graphite oxide: Influence of processing techniques

In this article, epoxy shape‐memory polymer (ESMP) reinforced with 1 wt % thermally reduced graphite oxide (TrGO) was fabricated by solution blending and three‐roll mill (TRM) mixing, respectively. Both blending techniques allowed a uniform TrGO dispersion in ESMP matrix, and the TRM mixing lead to an exfoliation of the TrGO worms. Compared with pristine ESMP, the TrGO/ESMP composites showed 36.4–41.1% increase in Young's modulus and 38.1–44.1% improvement in tensile strength. The TrGO/ESMP composite fabricated by TRM mixing had a T_5% (the temperature where the material lost 5% of its initial weight) 16.4°C higher than pure ESMP. Compared with pure ESMP, a significant improvement of recovery force by 84.4% and 311.1% was obtained by TrGO/ESMP composite fabricated by solution blending and TRM mixing, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42502.     

Effect of phenol functionalization of carbon nanotubes on properties of natural rubber nanocomposites

This paper reports the results of studies on the effect of phenol functionalization of carbon nanotubes (CNTs) on the mechanical and dynamic mechanical properties of natural rubber (NR) composites. Fourier transform infrared spectrometry (FTIR) indicates characteristic peaks for ether and aromatic rings in the case of phenol functionalized CNT. Although differential scanning calorimetric (DSC) studies show no changes in the glass‐rubber transition temperature (T_g) of NR in the nanocomposites due to surface modification of CNT, dynamic mechanical studies show marginal shifting of T_g to higher temperature, the effect being pronounced in the case of functionalized CNT. Stress‐strain plots suggest an optimum loading of 5 phr CNT in NR formulations and the phenolic functionalization of CNT does not affect significantly the stress‐strain properties of the NR nanocomposites. The storage moduli register an increase in the presence of CNT and this increase is greater in the case of functionalized CNT. Loss tangent showed a decrease in the presence of CNT, and the effect is more pronounced in the case of phenol functionalized CNT. Transmission electron microscopy (TEM) reveals that phenol functionalization causes improvement in dispersion of CNT in NR matrix. This is corroborated by the increase in electrical resistivity in the case of phenol functionalized CNT/NR composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Carbon nanotube film/epoxy composites with high strength and toughness

A strong and tough carbon nanotube (CNT)/epoxy composite was fabricated by resin solution impregnation process based on floating catalyst chemical vapor deposition (CVD)–growth CNT films, which had a tensile strength and toughness of 405 MPa and 122 J/g, respectively, and good damping properties as well. Evolution of the composite structure revealed that the CNTs aligned along the tension direction with decreasing orientation angle, and the CNT bundle size enlarged during the tensile test process, which contributed to efficient load transfer among the composite network. Results showed that the proper resin content could bring benefit for strong connections and dense packing of CNTs/bundles, but excessive resin content was unfavorable for improving mechanical properties and conductivities of the nanocomposite. In addition, the resin in CNT film/epoxy composites had a lower crosslink density than that in a neat epoxy system, which endowed the CNT composites with large deformation capability. POLYM. COMPOS., 38:588–596, 2017. © 2015 Society of Plastics Engineers     

Simultaneous ultrasonication‐assisted internal mixing to prepare MWCNTs‐filled epoxy composites with increased strength and thermal conductivity

The uniform dispersion of carbon nanotubes in epoxy resin is one of the key factors to achieve the composites with desirable mechanical and physical property enforcement. However, the widely used dispersion methods have their own respective limitations in pursuing satisfactory nanotube dispersion. Herein, a new dispersion approach, based on the synergetic effect of combining high speed internal mixing with running simultaneously continuous ultrasonication treatment, has been proposed. The dispersion of nanotubes was carried out in a high speed internal mixer, consisting of twin kneading block structured rotors and an integrated ultrasonic horn, which was intercalated into the central position between the twin rotors. At first, the FEM simulation was conducted to optimize the kneading element assembly and illuminate the geometry influence of the ultrasonic horn intercalation on the mixing flow. Afterwards, to confirm the feasibility of the approach, pristine MWCNTs (P‐CNTs), oxidation modified MWCNTs (M‐CNTs) and M‐CNTs/multilayer graphene nanoplatelets (MGPs) hybrid are dispersed into epoxy resin. The dispersion of each sample in its liquid epoxy state is investigated under transparent optical microscopy. More characterizations, including SEM, TG/DTA, tensile test, and thermal conductivity measurements, were conducted on the cured composites. Competitive reinforcements on mechanical tensile property and thermal conductivity were observed. Especially, at a 1.5 wt% M‐CNTs/MGPs hybrid content, the composite mechanical tensile strength and thermal conductivity were 47% and 30% higher than those of neat epoxy. This preliminary study demonstrates the feasibility and practicability of the proposed approach to achieving good MWCNTs dispersion and distribution in epoxy resin. POLYM. COMPOS., 37:870–880, 2016. © 2014 Society of Plastics Engineers     

Effect of epoxidized soybean oil on mechanical properties of woven jute fabric reinforced aromatic and aliphatic epoxy resin composites

A systematic study was performed to describe the effect of epoxidized soybean oil (ESO) on storage modulus, glass transition temperature (T _g) and mechanical properties in epoxy resin composites reinforced by jute fabric. In addition to aromatic diglycidylether of bisphenol‐A (DGEBA) resin, a glycerol (GER)‐and a pentaerythritol (PER)‐based aliphatic resin was applied as base resin, which can be also synthesized from renewable feedstock. Based on strip tensile test results, the usual alkali treatment of jute fabric was avoided. By increasing the ESO‐content in aliphatic composites the T _g increases, whereas in case of DGEBA, it decreases. The results indicate that although ESO has a significant softening effect, the jute fiber‐reinforced DGEBA composite can be replaced without significant compromise in mechanical properties by a potentially fully bio‐based composite consisting of 25 mass% ESO‐containing aliphatic PER‐reinforced by jute fibers. POLYM. COMPOS., 38:884–892, 2017. © 2015 Society of Plastics Engineers     

Effect of processing technique on the dispersion of carbon nanotubes within polypropylene carbon nanotube‐composites and its effect on their mechanical properties

Carbon nanotube‐reinforced polymer composites are being investigated as promising new materials having enhanced physical and mechanical properties. With regards to mechanical behavior, the enhancements reported thus far by researchers are lower than the theoretical predictions. One of the key requirements to attaining enhanced behavior is a uniform dispersion of the nanotubes within the polymer matrix. Although solvent mixing has been used extensively, there are concerns that any remaining solvent within the composite may degrade its mechanical properties. In this work, a comparison is carried out between solvent and “solvent‐free” dry mixing for dispersing multiwall carbon nanotubes in polypropylene before further melt mixing by extrusion. Various weight fractions of carbon nanotubes (CNTs) are added to the polymer and their effect on the mechanical properties of the resulting composites is investigated. Enhancements in yield strength, hardness, and Young's modulus when compared with the neat polymer, processed under similar conditions, are observed. Differences in mechanical properties and strain as a function of the processing technique (solvent or dry) are also clearly noted. In addition, different trends of enhancement of mechanical properties for the solvent and dry‐mixed extrudates are observed. Dry mixing produces composites with the highest yield strength, hardness, and modulus at 0.5 wt% CNT, whereas solvent mixing produces the highest mechanical properties at CNT contents of 1 wt%. It is believed that this difference is primarily dependent on the dispersion of CNTs within the polymer matrix which is influenced by the processing technique. Field emission scanning electron microscopy analysis shows the presence of clusters in large wt% CNT samples produced by dry mixing. Samples produced by solvent mixing are found to contain homogeneously distributed CNTs at all CNT wt fractions. CNT pull‐out is observed and may explain the limited enhancement in mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Characterization and thermal degradation of poly(d,l‐lactide‐co‐glycolide) composites with nanofillers

Chemical and thermal characterization of poly(d ,l ‐lactide‐co‐glycolide) (PLGA) composites filled with hydroxyapatite (HA) or carbon nanotubes (CNT) were evaluated by infrared spectroscopy, differential scanning calorimetry, thermogravimetry, and dynamic–mechanical–thermal analysis. The morphology and distribution of the nanoparticles were studied by transmission electron microscopy. The composites were prepared by solvent casting using 30% HA or 1, 3, and 5% of pristine and functionalized CNT as nanoparticles and PLGA 75:25 and PLGA 50:50 as copolymer matrix. The Coats–Redfern and E₂ function methodologies were used to calculate the reaction order and the activation energy (E_a) of the thermal degradation process. It was found that the addition of nanoparticles increased the glass transition temperature (T_g) of the composites. Also, higher degradation temperatures and E_a values were obtained for PLGA–HA composites and compared with the neat copolymer, and the opposite behavior was exhibited by PLGA–CNT composites. The thermal and mechanical properties were highly dependent on the morphology and dispersion of the filler. The functionalization process of CNT promoted, to some extent, a better distribution and dispersion of CNT into the matrix, and these composites exhibited a slight enhancement on storage modulus. On the other hand, PLGA–HA composites showed a good dispersion but no improvement on the storage modulus below T_g. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Mechanical properties of hybrid structural composites reinforced with nanosilica

Epoxy‐based hybrid structural composites reinforced with 14 nm spherical silica particles were investigated for mechanical properties as a function of nanosilica loading fractions. Composites were fabricated using continuous glass or carbon fiber of unidirectional architecture and nanosilica dispersed epoxy, through resin film infusion process. Uniform dispersion of nanoparticles in resin matrix was ensured by an optimized ultrasound‐assisted process. Although resin viscosity marginally reduces in the presence of nanosilica enabling a better control in composite manufacturing process, glass transition temperature of epoxy remained unaffected at low weight fractions. Compressive strength of hybrid glass or carbon fiber/epoxy composites showed more than 30–35% increase with nanosilica at a concentration as low as 0.2 wt%. Tensile and compressive properties of hybrid composites in transverse direction to the reinforcement remained unaffected. POLYM. COMPOS. 37:1216–1222, 2016. © 2014 Society of Plastics Engineers     

Processing and failure behavior of carbon‐nanotube composites in sheet forms

In their original forms, carbon nanotubes (CNT) are spatially entangled. To make CNT papers (CNTPs), the CNT agglomerates must be dispersed and re‐entangled into a planar sheet. The processing characteristics are very different from those of traditional buck‐form nanocomposites. This article examines the processing, micro‐structures, and failure behavior of the CNTP composites. The CNTPs were first made by a dispersion and filtering process. Then, an epoxy resin was added into the CNTP by using a vacuum bag method. Different CNT weights were employed to make the CNTPs with different thicknesses and areal weights. The CNTP allows direct resin impregnation along the thickness direction and avoids the difficulty of dispersing CNTs in the viscous resin. The CNT content can be much higher than that attainable in traditional bulk CNT composites. Both tensile and tearing tests were conducted, and the fracture behaviors were examined. POLYM. COMPOS., 37:1564–1571, 2016. © 2014 Society of Plastics Engineers