Rheological properties and fracture toughness of epoxy resin/multi‐walled carbon nanotube composites

Multi‐walled carbon nanotubes (MWCNTs), surface‐treated via chemical functionalization, i.e., oxidation and amidation, were used to reinforce diglycidylether of bisphenol F (DGEBF) epoxy resin. The effects of the functionalization on the dispersion stability, rheological properties, and fracture toughness of DGEBF/MWCNT composites were investigated. The dispersion homogeneity of the MWCNTs in the epoxy matrix improved after functionalization. In addition, isothermal rheology measurements revealed that the DGEBF/dodecyl amine‐functionalized MWCNT (D‐MWCNT) composite had a longer gel time and higher activation energy of cross‐linking than the DGEBF/acid‐treated MWCNT (A‐MWCNT) composite. The fracture toughness of the former was also significantly higher than that of the latter; this resulted from the relatively high dispersion stability of the D‐MWCNTs in the epoxy matrix, owing to the presence of alkyl groups on the D‐MWCNT surface. POLYM. ENG. SCI., 55:2676–2682, 2015. © 2015 Society of Plastics Engineers     

The preparation of cation-functionalized multi-wall carbon nanotube/sulfonated polyurethane composites

Covalent functionalization of multi-wall carbon nanotubes (MWCNTs) with minimal alteration to the MWCNT surface is important to achieve homogenously dispersed carbon nanotubes while maintaining their unique mechanical and electrical properties. Carboxylic acid derivatized MWCNTs (MWCNT-COOH) were covalently functionalized with 3,3′-iminobis(N,N-dimethylpropylamine) (DMPA). Upon subsequent quaternization of DMPA, dendritic ammonium cation-functionalized MWCNTs (MWCNT-DMPA⁺) were formed, where two ammonium cations were incorporated per amide site. Thermogravimetric analysis and X-ray photoelectron spectroscopy demonstrated successful covalent functionalization and formation of the surface-bound ammonium salt. Raman spectroscopy and atomic force microscopy indicated the absence of an appreciable decrease in the MWCNT aspect ratio. Compared with pristine MWCNTs and MWCNT-COOH, MWCNT-DMPA⁺ exhibited enhanced dispersibility in N,N-dimethylformamide (DMF) as observed with UV–Visible spectroscopy and transmission electron microscopy (TEM). In addition, blending the cation-bound MWCNT-DMPA⁺ with anion-bound sulfonated polyurethane in DMF generated novel composites with a nanotube content ranging from 0.5 to 5 wt.%. Characterization of the composite films using both field emission scanning electron microscopy and TEM revealed that MWCNT-DMPA⁺ exhibited uniform dispersion in sulfonated polyurethane matrices even at 5 wt.%. Tensile analysis showed that the modulus of the sulfonated polyurethane matrix linearly increased with MWCNT-DMPA⁺ content.     

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     

Effects of carbon nanotube functionalization on the mechanical and thermal properties of epoxy composites

Chemically functionalized multi-walled carbon nanotube (MWCNT)/bisphenol-A glycidol ether epoxy resin/2-ethyl-4-methylimidazole composites were prepared. MWCNTs were first treated by a 3:1 (v/v) mixture of concentrated H₂SO₄/HNO₃, and then triethylenetetramine (TETA) grafting was carried out. X-ray photoelectron spectroscopy analysis proved the effectiveness of H₂SO₄/HNO₃ treatment and confirmed the TETA functionalization mechanism. Chemical functionalization decreases the crystalline content of MWCNTs, however, it did not greatly disrupt their structure. Transmission electron microscopy showed that there was a TETA thin layer on the MWCNT surface, which contributes to the homogenous dispersion of MWCNTs in epoxy matrix and the improvement of the MWCNT-epoxy interfacial interaction. Thus the impact strength, bending strength and thermal conductivity of the composites are enhanced.     

Effect of the synthetic strategy on the non-covalent functionalization of multi-walled carbon nanotubes with polymerized ionic liquids

Multiwalled carbon nanotubes (MWCNTs) have been non covalently functionalized with various imidazolium-based polymerized ionic liquids (PILs). Two functionalization methods, starting from ionic liquid (IL) monomers containing a vinyl group, have been explored: a simple solution mixing of MWCNTs and PILs and the in situ polymerization. The resulting hybrid materials have been characterized by infrared and Raman spectroscopy, transmission electron microscopy, zeta potential measurement, thermogravimetric analysis and differential scanning calorimetry, and their dispersibility in various solvents has been evaluated to access the effect of the functionalization. The particle size analysis of MWCNTs/PILs agglomerates in various solvents is also reported. The in situ method allows a homogeneous coating of the MWCNT surface and thus a better dispersion of the nanotubes. The solution mixing method, for which diffusion limitations of the PILs into MWCNT aggregates should exist, does not allow a uniform surface functionalization. Finally, with protic IL monomers showing a tendency for hydrogen bonding, we have produced stable CNT/PIL organo- or hydrogel composites.     

Effect of amino‐functionalization of multi‐walled carbon nanotubes on the dispersion with epoxy resin matrix

Amino‐functionalization of multiwalled carbon nanotubes (MWCNTs) was carried out by grafting triethylenetetramine (TETA) on the surfaces of MWCNTs through the acid–thionyl chloride way. The amino‐functionalized MWCNTs show improved compatibility with epoxy resin and, as a result, more homogenous dispersion in the matrix. The mechanical, optical, and thermal properties of the amino‐functionalized MWCNT/epoxy composites were also investigated. It was found that introducing the amino‐functionalized MWCNTs into epoxy resin greatly increased the charpy impact strength, glass transition temperature, and initial decomposing temperature of cured epoxy resin. In addition, introducing unfunctionalized MWCNTs into epoxy resin was found greatly depressing the light transmission properties, which would affirmatively confine the application of the MWCNTs/epoxy composites in the future, while much higher light transmittance than that of unfunctionalized MWCNTs/epoxy composites was found for amino‐functionalized MWCNTs/epoxy composites. SEM of the impact cross section and TEM of ultrathin film of the amino‐functionalized MWCNTs/epoxy composites showed that the amino‐functionalized MWCNTs were wetted well by epoxy matrix. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 97–104, 2006     

Supramolecular bionanocomposites 3: Effects of surface functionality on electrical and mechanical percolation

Percolation phenomena in bionanocomposites composed of the bioplastic polylactide and surface decorated supramolecular multiwalled carbon nanotubes (MWCNTs) are investigated. MWCNTs with three distinct surface chemistries—a native surface, a hydroxyl functionalized surface, and a short hydrocarbon functionalized surface—are prepared and studied. Two experimental methods are used to determine percolation thresholds; melt rheology provides a measure of the mechanical percolation threshold and electrical impedance spectroscopy provides values of the electrical percolation threshold. The MWCNT‐loading level required to obtain mechanical percolation is systematically found to be lower than the loading level needed to achieve electrical percolation. Hydroxylated MWCNTs have the highest percolation thresholds of 1.8 (mechanical) and 6.7 wt % (electrical), which is attributed to aggregation caused by hydrogen bonding. Alkane‐grafted MWCNTs have lower percolation thresholds of 0.76 (mechanical) and 2.8 wt % (electrical). However, untreated MWCNTs have the lowest thresholds of 0.16 (mechanical) and 1.5 wt % (electrical). The reduced percolation threshold observed upon conversion of the hydroxylated surface to the alkylated surface is attributed to morphological differences—functionalization disrupts hydrogen bonding and leads to better nanotube dispersion. The combination of higher inherent conductivity and more favorable nanotube‐polylactide interactions implies that unmodified MWCNTs are preferred to produce electrically conductive bionanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Efficient functionalization of multi‐walled carbon nanotubes with p‐aminophenol and their application in the fabrication of poly(amide‐imide)‐matrix composites

The ultrasonically assisted preparation and characterization of poly(amide‐imide) (PAI) composites containing functionalized multi‐walled carbon nanotubes (MWCNTs) are reported. To improve the dispersion in and compatibility with the polymer matrix, the MWCNTs were surface‐modified with p‐aminophenol (p‐AP) under microwave irradiation. The process is fast, one‐pot, easy and results in a high degree of functionalization as well as dispersibility in organic solvents. The p‐AP‐functionalized MWCNTs (MWCNTs‐AP) were analysed by means of field emission and transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction and thermogravimetric analysis (TGA). The results consistently confirm the formation of p‐AP functionalities on MWCNTs which are able to undergo additional reactions, while the structure of the MWCNTs remains relatively intact. MWCNTs‐AP/PAI hybrid films were prepared with various MWCNTs‐AP contents (5–15 wt%) using a solution‐casting technique. Microscopic observations show that the dispersion of the MWCNTs‐AP is improved as a result of the organic groups on the MWCNT surface and functional groups in the PAI structure. The properties of the obtained composites were characterized extensively using the aforementioned techniques. TGA results show that the hybrid films exhibit a good thermal stability. Tensile mechanical testing was performed for the prepared composites, the results of which indicate an increase in the elastic modulus and tensile strength with increasing MWCNTs‐AP content. © 2013 Society of Chemical Industry     

Properties and degradation behavior of surface functionalized MWCNT/poly(L‐lactide‐co‐ε‐caprolactone) biodegradable nanocomposites

In this research, poly(L ‐lactide‐co‐ε‐caprolactone) (PLACL) reinforced with well‐dispersed multiwalled carbon nanotubes (MWCNTs) nanocomposites were prepared by oxidization and functionalization of the MWCNT surfaces using oligomeric L ‐lactide (LA) and ε‐caprolactone (CL). It is found that the surface functionalization can effectively improve the dispersion and adhesion of MWCNTs in PLACL. The surface functionalization will have a significant effect on the physical, thermomechanical, and degradation properties of MWCNT/PLACL composites. The tensile modulus, yield stress, tensile strength, and elongation at break of composite increased 49%, 60%, 70%, and 94%, respectively, when the concentration of functionalized MWCNTs in composite is 2 wt %. The in vitro degradation rate of nanocomposites in phosphate buffer solution increased about 100%. The glass transition temperature (T_g) of composites was decreased when the concentration of functionalized MWCNTs is 0.5 wt %. With further increasing the concentration of functionalized MWCNTs, the T_g was increased. The degradation kinetics of nanocomposites can be engineered and functionalized by varying the contents of pristine or functionalized MWCNTs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhancement in mechanical properties of multiwalled carbon nanotube‐reinforced epoxy composites: Crosslinking of the reinforcement with the matrix via diamines

In this study, the effect of diamine molecular structure, attached to the multiwalled carbon nanotubes (MWCNTs), on the interfacial interactions of the MWCNTs and the epoxy matrix was studied. Pristine MWCNTs were successfully functionalized with multiple aliphatic and aromatic diamines. It has been found that, compared to aliphatic molecules, aromatic diamines can yield higher functionalization degree, due to higher activity and longer half‐life of aromatic intermediates. However, at the same functionalization degree, the aliphatic ligands were more successful in reacting with epoxy chains and forming covalent bonds between the MWCNTs and the matrix. Considerable improvements were achieved in the mechanical properties of functionalized MWCNT‐reinforced epoxy composites in comparison with the pristine MWCNT‐reinforced composites. Fractography observations revealed distinct differences in the failure modes of reinforced composites after functionalization of the MWCNTs with diamines. POLYM. ENG. SCI., 59:1905–1910, 2019. © 2019 Society of Plastics Engineers     

Noncovalent compatibilization of polypropylene/MWCNT composites using an amino‐pyridine grafted polypropylene matrix

Polypropylene (PP)/multiwalled carbon nanotube (MWCNT) composites are prepared by implementing noncovalent compatibilization. The compatibilization method involves PP matrix functionalization with pyridine (Py) aromatic moieties, which are capable of π–π interaction with MWCNT sidewalls. Imaging revealed that the addition of 25 wt% of PP‐g‐Py to neat PP is capable of drastically reducing nanotube aggregate size and amount, compared to a matrix containing the equivalent amount of a maleated PP (PP‐g‐MA). Raman spectroscopy confirms improved polymer/nanotube interaction with the PP‐g‐Py matrix. The electrical percolation threshold appears at a MWCNT loading of approximately 1.2 wt%, and the maximum value of the electrical conductivity achieved is 10⁻² S/m, irrespective of the functionalization procedure. The modulus of the composites is improved with the addition of MWCNTs. Furthermore, composites functionalized with Py display significant improvements in composite ductility compared with their maleated counterparts because of the improved filler dispersion. POLYM. COMPOS., 37:2794–2802, 2016. © 2015 Society of Plastics Engineers     

Improving thermal conductivity and shear strength of carbon nanotubes/epoxy composites via thiol‐ene click reaction

This study investigates the effect of the thiol‐ene click reaction on thermal conductivity and shear strength of the epoxy composites reinforced by various silane‐functionalized hybrids of sulfhydryl‐grafted multi‐walled carbon nanotubes (SH‐MWCNTs) and vinyl‐grafted MWCNTs (CC‐MWCNTs). The results of Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermal gravimetric analysis (TGA), and transmission electron microscopy (TEM) show that the sulfhydryl groups and vinyl groups are successfully grafted onto the surface of MWCNTs, after treatment of MWCNT with triethoxyvinylsilane and 3‐mercaptopropyltrimethoxysilane, respectively. Scanning electron microscopy (SEM), HotDisk thermal constant analyzer (HotDisk), optical microscope, and differential scanning calorimetry (DSC) are used to characterize the resultant composites. It is demonstrated that the hybrid of 75 wt % SH‐MWCNTs and 25 wt % CC‐MWCNTs has better dispersion and stability in epoxy matrix, and shows a stronger synergistic effect in improving the thermal conductivity of epoxy composite via the thiol‐ene click reaction with 2,2′‐azobis(2‐methylpropionitrile) as thermal initiator. Furthermore, the tensile shear strength results of MWCNT/epoxy composites and the optical microscopy photographs of shear failure section indicate that the composite with the hybrid MWCNTs has higher shear strength than that with raw MWCNTs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44579.     

Influence of aminosilane‐functionalized carbon nanotubes on the rheometric,mechanical, electrical and thermal degradation properties of epoxidized natural rubber nanocomposites

We describe the preparation, characterization and physical properties of multiwalled carbon nanotube (MWCNT)‐filled epoxidized natural rubber (ENR) composites. To ensure better dispersion in the elastomer matrix, the MWCNTs were initially subjected to aminopropyltriethoxysilane (APS) treatment to bind amine functional groups (?NH₂) on the nanotube surface. Successful grafting of APS on the MWCNT surface through Si–O–C linkages was confirmed using Fourier transform infrared spectroscopy. Grafting of APS on the MWCNT surface was further corroborated using elemental analysis. ENR nanocomposites with various filler loadings were prepared by melt compounding to generate pristine and APS‐modified MWCNT‐filled elastomeric systems. Furthermore, we determined the effects of various filler loadings on the rheometric, mechanical, electrical and thermal degradation properties of the resultant composite materials. Rheometric cure characterization revealed that the torque difference increased with pristine MWCNT loading compared to the gum system, and this effect was more pronounced when silane‐functionalized MWCNTs were loaded, indicating that this effect was due to an increase in polymer–carbon nanotube interactions in the MWCNT‐loaded materials. Loading of silane‐functionalized MWCNTs in the ENR matrix resulted in a significant improvement in the mechanical, electrical and thermal degradation properties of the composite materials, when compared to gum or pristine MWCNT‐loaded materials.© 2013 Society of Chemical Industry     

Properties of surface‐modified multiwalled carbon nanotube filled poly(ethylene terephthalate) composite films

Poly(ethylene terephthalate) (PET)/multiwalled carbon nanotube (MWCNT) composites were prepared by in situ polymerization. To improve the dispersion of MWCNTs in the PET matrix, functionalized MWCNTs having acid groups (acid‐MWCNTs) and acetic groups (acetic‐MWCNTs) on their surfaces were used. The functional groups were confirmed by infrared spectrometry. Scanning electron microscopy showed that acetic‐MWCNTs had a better dispersion in the PET matrix than pristine MWCNTs and acid‐MWCNTs. A reaction between PET and acetic‐MWCNTs was confirmed by a shift of the Raman G band to a higher frequency and an increase of the complex viscosity in the rheological properties. The composites containing functionalized MWCNTs showed a large increase in their tensile strengths and moduli. The values of the strengths and moduli of the PET/acetic‐MWCNT composites were higher than those of the PET/acid‐MWCNT composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Estimation of dispersion stability of UV/ozone treated multi-walled carbon nanotubes and their electrical properties

Chemical functionalization of multi-walled carbon nanotubes (MWCNTs) was carried out by UV/ozone treatment. MWCNTs were characterized by elemental analysis, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) before and after treatment. The dispersion stability was investigated using UV–vis spectroscopy and a dispersion stability analyzer. Results confirmed the presence of oxygen-containing groups on the MWCNT surfaces by UV/ozone treatment resulting in dispersion stability better than for pristine MWCNTs in polar solvents. A simple method described to investigate the solubility behavior of MWCNTs functionalized with UV/ozone treatment in various organic solvents. To illustrate this concept, CNT dispersions were prepared using UV/ozone treatment with controlled times, and their solubility behavior was represented on three-dimensional graphs using Hansen solubility parameters. Based on these solubility data, a MWCNT/PMMA composite was prepared using an appropriate solvent and the sheet resistance was measured using a four-point probe method. As a result, composites made with MWCNTs having undergone UV/ozone treatment showed lower sheet resistance than CNT composites made from pristine or acid-treated MWCNTs.     

Effect of radical grafting of tetramethylpentadecane and polypropylene on carbon nanotubes' dispersibility in various solvents and polypropylene matrix

Multiwalled carbon nanotubes (MWCNTs) have been functionalized by tetramethylpentadecane (TMP), 1-dodecanethiol (DT) and polypropylene (PP) through radical addition onto MWCNTs' surface using dicumyl peroxide as hydrogen abstractor. Surface functionalized MWCNTs were characterized by Raman, IR spectroscopy, elementary analysis (EA) and thermogravimetric analysis (TGA). We studied the effect of temperature, peroxide concentration and solvent on TMP grafting densities and it was found that this surface treatment lead to a fair solubility in various solvents. TMP-functionalized MWCNTs were also imaged by transmission electronic microscopy showing single long functionalized MWCNTs distinct from the starting pristine bundles. For the first time, PP was then grafted onto MWCNTs through a radical grafting reaction. However, scanning electronic microscopy images of PP-functionalized MWCNTs/PP composites did not show a significant improvement in MWCNTs dispersion within the PP matrix.     

Mild functionalization of carbon nanotubes filled epoxy composites: Effect on electromagnetic interferences shielding effectiveness

The effect of nitric acid mild functionalized multiwalled carbon nanotubes (MWCNTs) on electromagnetic interference (EMI) shielding effectiveness (SE) of epoxy composites was examined. MWCNTs were oxidized by concentrated nitric acid under reflux conditions, with different reaction times. The dispersion of MWCNTs after functionalization was improved due to the presence of oxygen functional groups on the nanotubes surface. Functionalization at 2 h exhibits the highest EMI SE and electrical conductivity of MWCNTs filled epoxy composites. However, EMI shielding performance of MWCNTs filled epoxy composite declined when the functionalization reaction time was prolonged. This was due to extensive damage on the MWCNT structure, as verified by a Raman spectroscope. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42557.     

Hyperbranched polyurethane/triethanolamine functionalized multi‐walled carbon nanotube nanocomposites as remote induced smart materials

Triethanolamine functionalized multi‐walled carbon nanotubes (TEA‐f‐MWCNTs)/hyperbranched polyurethane nanocomposites were prepared by the in situ polymerization technique. The functionalization of the MWCNTs was confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy studies. The homogeneous distribution and the strong interfacial interaction of TEA‐f‐MWCNTs with the polyurethane chains were confirmed by transmission electron microscopy and Fourier transform infrared spectroscopy studies, respectively. Significant enhancements of tensile strength (6.5 ? 28.5 MPa) and scratch resistance (3–7 kg) with content of TEA‐f‐MWCNTs (0–2 wt%) were observed. Thermogravimetric analysis showed an increase in thermal stability from 240 to 287 °C by the formation of nanocomposites. X‐ray diffraction and differential scanning calorimetry studies confirmed an increment in the degree of crystallinity of the nanocomposites with increase in TEA‐f‐MWCNT content. The extent of shape recovery as well as recovery speed were enhanced with increase in the output power of the microwave. Thus the studied nanocomposites could be utilized as non‐contact microwave energy tunable shape memory materials. © 2013 Society of Chemical Industry     

Effect of compatibilizer on morphology,thermal, and rheological properties of polypropylene/functionalized multi‐walled carbon nanotubes composite

Multi‐walled carbon nanotubes (MWCNTs) filled polypropylene (PP) composites were prepared by a corotating intermeshing twin screw extruder. To improve the dispersion of MWCNTs, the surface of MWCNT was modified with 1,10‐diaminodecane, and maleic anhydride grafted polypropylene (MA‐g‐PP) was used as a compatibilizer. Micrographs of well dispersed functionalized MWCNTs (diamine‐MWCNT) were observed due to the reaction between MA‐g‐PP and diamine‐MWCNT in PP/MA‐g‐PP/diamine‐MWCNTs composites. The different behaviors in crystallization and melting temperatures of PP/MA‐g‐PP/diamine‐MWCNTs composite were observed compared to PP and PP/neat‐MWCNT. Especially, the decomposition temperature of the composite was increased by 50°C compared to PP. PP/MA‐g‐PP/diamine‐MWCNTs composite showed the highest complex viscosity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of a doubly modified carbon nanotube derivative on the microstructure of epoxy resin

The surface of multi wall carbon nanotubes (MWCNTs) was first covalently functionalized with oleyl amine and then non-covalently wrapped with polycarbosilane (PCS). The hybrid functional groups were chosen to introduce different features in the MWCNTs properties. For covalent functionalization a long chain unsaturated aliphatic amine was used to simultaneously achieve the dissociation of MWCNT bundles along with the dispersion and interaction with the host matrix using the amide functionality and double bond. On the other hand, a thermally stable polymer was selected which can interact with both resin and glass fabric to promote interfacial adhesion. This hybrid doubly modified MWCNT is thus possesses duel advantages in glass fiber based epoxy composite. The pristine, covalent, noncovalent and covalent-noncovalent doubly modified MWCNT systems were used to study the viscoelastic behavior and interactions of functionalized MWCNTs in the matrix above and below the glass transition temperature of the matrix. The PCS coating on the MWCNTs is amorphous and thermally insulating whereas the nanotube is highly graphitized and thermally conducting. This contrasting behavior provides us to insight into the temperature dependant resin microstructure and curing thermodynamics of epoxy resin in the presence of MWCNTs.