Improved impact strength of epoxy by the addition of functionalized multiwalled carbon nanotubes and reactive diluent

Multiwalled carbon nanotubes (MWCNTs), both oxidized and amine functionalized (triethylenetetramine—TETA), have been used to improve the mechanical properties of nanocomposites based on epoxy resin. The TGA and XPS analysis allowed the evaluation of the degree of chemical modification on MWCNTs. Nanocomposites were manufactured by a three‐roll milling process with 0.1, 0.5, and 1.0 wt % of MWCNT–COOH and MWCNT–COTETA. A series of nanocomposites with 5.0 wt % of reactive diluent was also prepared. Tensile and impact tests were conducted to evaluate the effects of the nanofillers and diluent on the mechanical properties of the nanocomposites. The results showed higher gains (258% increase) in the impact strength for nanocomposites manufactured with aminated MWCNTs. Optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to investigate the overall filler distribution, the dispersion of individual nanotubes, and the interface adhesion on the nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42587.     

Study of alternating current impedance analysis and dielectric properties of carbon nanotube‐based polysulfone nanocomposites

Polysulfone (PSU)/multiwalled carbon nanotubes (MWCNTs) nanocomposites containing 0.5–3 wt% of MWCNTs were prepared by solution casting technique. To understand the dispersion behavior of MWCNTs inPSU matrix, high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) were used. Electrical properties of nanocomposites were investigated by analyzing alternating current (AC) impedance spectra. The real part of complex impedance was decreased with increasing carbon nanotubes loading in the PSU matrix, which may be due to increase in conductive networks in the nanocomposite. The complex impedance Nyquist plots for PSU/MWCNTs nanocomposites were characterized by the appearance of a single semicircular arc, whose radii of curvature decreases with increasing MWCNTs loading. The polarization mechanism and the AC conduction mechanism were studied by designing equivalent circuit from impedance data. The dielectric response of PSU/MWCNTs nanocomposite was investigated over a wide range of frequency from 10 Hz to 10⁻⁶ Hz. Dielectric constant of PSU/MWCNTs nanocomposite was enhanced significantly from 2 to 6 × 10¹⁰ at 10 Hz when the addition of MWCNTs was increased from 0 to 3 wt%. The enhancement of dielectric property might be due to the interfacial polarization between carbon nanotubes and polysulfone. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Synthesis and processing of PMMA carbon nanotube nanocomposite foams

Poly(methyl methacrylate) (PMMA) multi-walled carbon nanotubes (MWCNTs) nanocomposites were synthesized by several methods using both pristine and surface functionalized carbon nanotubes (CNTs). Fourier transform infrared (FTIR) spectroscopy was used to characterize the presence and types of functional groups in functionalized MWCNTs, while the dispersion of MWCNTs in PMMA was characterized using scanning electron microscopy (SEM). The prepared nanocomposites were foamed using carbon dioxide (CO₂) as the foaming agent. The cell morphology was observed by SEM, and the cell size and cell density were calculated via image analysis. It was found that both the synthesis methods and CNTs surface functionalization affect the MWCNTs dispersion in the polymer matrix, which in turn profoundly influences the cell nucleation mechanism and cell morphology. The MWCNTs are efficient heterogeneous nucleation agents leading to increased cell density at low particle concentrations. A mixed mode of nucleation mechanism was observed in nanocomposite foams in which polymer rich and particle rich region co-exist due to insufficient particle dispersion. This leads to a bimodal cell size distribution. Uniform dispersion of MWCNTs can be achieved via synergistic combination of improving synthesis methodology and CNTs surface functionalization. Foams from these nanocomposites exhibit single modal cell size distribution and remarkably increased cell density and reduced cell size. An increase in cell density of ∼70 times and reduction of cell size of ∼80% was observed in nanocomposite foam with 1% MWCNTs.     

Effects of multiwall carbon nanotubes on the thermal and mechanical properties of medium density polyethylene matrix nanocomposites produced by a mechanical milling method

Medium‐density polyethylene/multiwall carbon nanotube (MDPE/MWCNT) nanocomposites were produced by a mechanical milling method using a high‐energy ball mill. The MDPE and MWCNTs were added to the ball mill at a constant 20:1 weight ratio of ball/powders and milled for 10 h to obtain polyethylene matrix nanocomposites reinforced with 0.5, 1, 2.5, and 5 weight percent of MWCNTs. To clarify the role of both MWCNT content and milling time on the morphology of MDPE, some nanocomposite samples were investigated by using a scanning electron microscope. To evaluate the role of milling on the microstructure of the nanocomposites, very thin films of MDPE/MWCNTs were prepared and studied by transmission electron microscopy. Thermal behavior of these nanocomposites was investigated by using differential scanning calorimetry (DSC). Standard tensile samples were produced by compression molding. The dependence of the tensile properties of MDPE on both milling time and MWCNT content was studied by using a tensile test. The results of the microscopic evaluations showed that the milling process could be a suitable method for producing MDPE/MWCNT nanocomposites. The addition of carbon nanotubes to MDPE caused a change in its morphology at constant milling parameters. The results of the DSC tests showed that the crystallization temperature of MDPE increased as MWCNTs were added, although no dependency was observed as milling time increased. Crystallization index changed from 50 to 55% as MWCNT content increased from 0 to 5%. The results of the tensile tests showed that both the Young's modulus and the yield strength of MDPE increased as MWCNTs were added. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

Improvement in properties of multiwalled carbon nanotube/polypropylene nanocomposites through homogeneous dispersion with the aid of surfactants

The effects of different surfactants on the properties of multiwalled carbon nanotubes/polypropylene (MWCNT/PP) nanocomposites prepared by a melt mixing method have been investigated. Sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (NaDDBS) were used as a means of noncovalent functionalization of MWCNTs to help them to be dispersed uniformly into the PP matrix. The effects of these surfactant‐treated MWCNTs on morphological, rheological, thermal, crystalline, mechanical, and electrical properties of MWCNT/PP composites were studied using field emission scanning electron microscopy, optical microscopy, rheometry, tensile, and electrical conductivity tests. It was found that the surfactant‐treatment and micromixing resulted in a great improvement in the state of dispersion of MWCNTs in the polymer matrix, leading to a significant enhancement of Young's modulus and tensile strength of the composites. For example, with the addition of only 2 wt % of SDS‐treated and NaDDBS‐treated MWCNTs, the Young's modulus of PP increased by 61.1 and 86.1%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of carbon nanotubes functionalization on properties of their nanocomposites with polycarbonate/poly(acrylonitrile-butadiene-styrene) matrix

In this work, a comparative study evaluating the influence of different functionalization of carbon nanotubes on the properties of nanocomposites with polymeric matrix was performed. A 50/50 wt% polycarbonate (PC)/poly(acrylonitrile-butadiene-styrene) (ABS) blend was used as polymeric matrix of the nanocomposites. The comparison was made between nanocomposites reinforced with covalently functionalized multiwall carbon nanotubes (MWCNTf) and MWCNTf/nanoclay hybrid functionalization. The effect on the mechanical and morphological properties of the nanocomposites was evaluated through tensile and Izod impact tests and scanning electron microscopy and transmission electron microscopy (TEM) analyses. The thermal characterization of PC/ABS blends and nanocomposites was performed by differential scanning calorimetry (DSC). Results showed that both methods of functionalization of MWCNTs increased the stiffness and impact resistance of the nanocomposites. TEM micrographs indicated the preferred location of the reinforcements in the SAN phase of ABS. Results from DSC indicated an increase in the thermal resistance of the nanocomposites.     

Rheological and thermal properties of poly(ethylene oxide)/multiwall carbon nanotube composites

Poly(ethylene oxide) (PEO) based nanocomposites were prepared by the dispersion of multiwall carbon nanotubes (MWCNTs) in aqueous solution. MWCNTs were added up to 4 wt % of the PEO matrix. The dynamic viscoelastic behavior of the PEO/MWCNT nanocomposites was assessed with a strain‐controlled parallel‐plate rheometer. Prominent increases in the shear viscosity and storage modulus of the nanocomposites were found with increasing MWCNT content. Dynamic and isothermal differential scanning calorimetry studies indicated a significant decrease in the crystallization temperature as a result of the incorporation of MWCNTs; these composites can find applications as crystallizable switching components for shape‐memory polymer systems with adjustable switching temperatures. The solid‐state, direct‐current conductivity was also enhanced by the incorporation of MWCNTs. The dispersion level of the MWCNTs was investigated with scanning electron microscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High performance polyurethane composites with isocyanate‐functionalized carbon nanotubes: Improvements in tear strength and scratch hardness

A microwave‐assisted functionalization of carbon nanotubes (CNTs) with isocyanate groups allowed a reduction of functionalization time from 24 h to 30 min with no change in the degree of functionalization or in the nanotube characteristics. Polymer nanocomposites with enhanced mechanical properties were obtained because of the tailored interface by the covalent linkage between the surface‐modified multiwalled‐carbon nanotubes (MWCNTs) and an elastomeric polyurethane (PUE) matrix. The mechanical data revealed that the composite containing 0.25 wt % of MWCNT‐NCO showed an increase of 31% in tear strength and 28% in static toughness. A good adhesion between the matrix and individually dispersed nanotubes was observed in the scanning electron microscopy and transmission electron microscopy images. Nanoindentation and nanoscratch experiments were conducted to investigate the properties on the sub‐surface. An increase by a factor of 3 in the scratch hardness was observed for the composite with 0.50 wt % of MWCNT‐NCO with respect to the neat PUE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44394.     

The effect of multiwall carbon nanotubes on the properties of room temperature-vulcanized silicone adhesives

The effects of surface-functionalized and pristine multiwall carbon nanotubes (MWCNT) on the bulk and adhesion properties of silicone nanocomposites were investigated. The MWCNTs surface functionalization was carried out by silanization of methacryloxy or vinyl-based silanes. The nanocomposites were prepared using solvent mixing which enhanced distribution and dispersion of the MWCNTs in the high-viscosity silicone matrix. The quality of dispersion was evaluated using scanning electron microscopy (SEM) indicating good dispersion state. It was found that the optimal concentration of both treated and untreated MWCNTs in the nanocomposites was 1 wt.%. Above this threshold value, the nanocomposites properties were reduced. Furthermore, the silane treatment of the MWCNTs was proven to be an effective process that resulted in a significant increase in the nanocomposites properties compared to the neat polymer, leading to higher storage modulus simultaneously with up to 27% improvement in the tensile strength and elongation, 20–30% reduction in the thermal expansion coefficient, 220–300% enhancement in crystallinity (enthalpy of fusion), and up to 56% improvement in the lap shear strength. SEM analysis indicated that significant changes in the fracture morphologies occurred due to higher energy absorption in the case of silane-treated MWCNTs. It was concluded that incorporation of silane-treated MWCNTs is an effective route to reinforce and increase the toughness of silicone-based adhesives.     

Plasma treatment‐induced fluorine‐functionalized multi‐walled carbon nanotubes to modify poly(ethylene terephthalate) obtained via in situ polymerization

The introduction of carbon nanotubes in a polymer matrix can markedly improve its mechanical properties and electrical conductivity, and much effort has been devoted to achieve homogeneous dispersions of carbon nanotubes in various polymers. Our group previously performed successfully fluorine‐grafted modification on the sidewalls of multi‐walled carbon nanotubes (MWCNTs), using homemade equipment for CF₄ plasma irradiation. As a continuation of our previous work, in the present study CF₄ plasma‐treated MWCNTs (F‐MWCNTs) were used as a nanofiller with poly(ethylene terephthalate) (PET), which is a practical example of the application of such F‐MWCNTs to prepare polyester/MWCNTs nanocomposites with ideal nanoscale structure and excellent properties. As confirmed from scanning electron microscopy observations, the F‐MWCNTs could easily be homogeneously dispersed in the PET matrix during the in situ polymerization preparation process. It was found that a very low content of F‐MWCNTs dramatically altered the crystallization behavior and mechanical properties of the nanocomposites. For example, a 15 °C increase in crystallization temperature was achieved by adding only 0.01 wt% F‐MWCNTs, implying that the well‐dispersed F‐MWCNTs act as highly effective nucleating agents to initiate PET crystallization at high temperature. Meanwhile, an abnormal phenomenon was found in that the melt point of the nanocomposites is lower than that of the pure PET. The mechanism of the tailoring of the properties of PET resin by incorporation of F‐MWCNTs is discussed, based on structure–property relationships. The good dispersion of the F‐MWCNTs and strong interfacial interaction between matrix and nanofiller are responsible for the improvement in mechanical properties and high nucleating efficiency. The abnormal melting behavior is attributed to the recrystallization transition of PET occurring at the early stage of crystal melting being retarded on incorporation of F‐MWCNTs. Copyright © 2009 Society of Chemical Industry     

Preparation and properties of cyclic olefin copolymers multiwalled carbon nanotube nanocomposites

Nanocomposites of cyclic olefin copolymer (COC) and two types of multiwalled carbon nanotubes (MWCNTs) with different aspect ratios were prepared. The morphology, thermal behavior, and electrical conductivity of the nanocomposites were investigated by scanning electron microscopy, differential scanning calorimetry, thermal gravimetric analysis, and the DC conductivity measurement. It was found that the developed nanocomposite preparation method resulted in good nanotubes dispersion in the polymer matrix for both types of MWCNTs. No appreciable differences in glass transition temperatures were observed between the pure COC and nanocomposites. On the other hand, CNTs significantly improved the thermo‐oxidative stability of the COC. The nanocomposites showed significant delay in onset of degradation and the degradation temperature was ～ 40°C higher than that of the pure COC. The nanocomposites also showed substantially higher DC conductivity, which increased with the nanotube concentration and aspect ratio. An increase of DC electrical conductivity over 10⁹ times can be achieved by the addition of 2 wt % CNTs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Properties of PMMA/Carbon nanotubes nanocomposites prepared by “grafting through” method

A number of batch polymerizations were performed to study the effect of multi‐walled carbon nanotubes (MWCNTs) on the properties of PMMA/MWCNTs nanocomposites. To improve the dispersion of nanotubes in PMMA matrix, MWCNTs were functionalized with methacrylate groups via a four‐step modification process and the modified nanoparticles were used to synthesize the nanocomposites. The prepared samples were characterized by Raman spectroscopy, thermogravimetric analysis, dynamic mechanical thermal analysis, differential scanning calorimetry, gel permeation chromatography, UV–visible, and TEM techniques. According to the results, modified nanotubes improved thermal and mechanical properties better than the pristine MWCNTs. The main improvement in the mechanical and thermophysical properties was achieved for the nanocomposite containing 0.5 wt% of MWCNTs. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Preparation and properties of polyurethane/multiwalled carbon nanotube nanocomposites by a spray drying process

A spray drying approach has been used to prepare polyurethane/multiwalled carbon nanotube (PU/MWCNT) composites. By using this method, the MWCNTs can be dispersed homogeneously in the PU matrix in an attempt to improve the mechanical properties of the nanocomposites. The morphology of the resulting PU/MWCNT composites was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observations illustrate that the MWCNTs are dispersed finely and uniformly in the PU matrix. X‐ray diffraction results indicate that the microphase separation structure of the PU is slightly affected by the presence of the MWCNTs. The mechanical properties such as tensile strength, tensile modulus, elongation at break, and hardness of the nanocomposites were studied. The electrical and the thermal conductivity of the nanocomposites were also evaluated. The results show that both the electrical and the thermal conductivity increase with the increase of MWCNT loading. In addition, the percolation threshold value of the PU composites is significantly reduced to about 5 wt % because of the high aspect ratio of carbon nanotubes and exclusive effect of latex particles of PU emulsion in dispersion. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal and electrical properties of carbon nanotubes based polysulfone nanocomposites

Carbon nanotubes (CNTs)-reinforced polysulfone (PSU) nanocomposites were prepared through solution mixing of PSU and different weight percent of multi-walled carbon nanotubes (MWCNTs). Thermal properties of nanocomposites were characterized using thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA studies revealed an increase in thermal stability of the PSU/MWCNTs nanocomposites, which is due to the hindrance of the nanodispered carbon nanotubes to the thermal transfer in nanocomposites and also due to higher thermal stability of CNTs. Morphological properties of nanocomposites were characterized by high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscope (FESEM). The influence of CNTs loading on electrical properties of PSU/MWCNTs nanocomposites was studied by the measurement of AC and DC resistivity. Dielectric study of nanocomposites was carried out at different frequencies (10 Hz–1 MHz) by using LCR meter. An increase in dielectric constant and dielectric loss was observed with increase in CNTs content, which is due to the interfacial polarization between conducting CNTs and PSU.     

Viscoelasticity and thermal stability of poly(arylene ether nitrile) nanocomposites with various functionalized carbon nanotubes

Poly(arylene ether nitrile) (PEN) nanocomposites containing various functionalized multi‐walled carbon nanotubes (MWCNTs) were prepared through a solution‐casting method. The as‐prepared PEN nanocomposites were investigated using parallel‐plate rheometry and thermogravimetric analysis, aimed at examining the effect of surface functionalization on the dispersion of MWCNTs from the viscoelastic and thermal properties. The linear viscoelasticy results indicated that 4‐aminophenoxyphthalonitrile‐grafted MWCNTs presented better dispersion in the PEN matrix than purified and carboxylic MWCNTs because the corresponding composite showed the lowest rheological percolation threshold, which was further confirmed from scanning electron microscopy, dissolution experiments and solution rheological experiments. The thermogravimetric analysis results revealed that the presence of 4‐aminophenoxyphthalonitrile‐grafted and carboxylic MWCNTs retarded the depolymerization compared with purified MWCNTs, showing a marked increase in the temperature corresponding to a loss of 5 wt% (increased by 14–22 °C) and maximum rate of decomposition (increased by 4–8 °C). Both the state of dispersion and the surface functionalization of MWCNTs are very important to the thermal stability of the PEN matrix. Copyright © 2011 Society of Chemical Industry     

On the dispersion of CNTs in polyamide 6 matrix via solution methods: assessment through electrical, rheological, thermal and morphological analyses

In this study, polyamide 6 (PA 6)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by different solution methods based on phase inversion, drop-casting and simple evaporation processes. Optical microscopy and field emission scanning electron microscopy techniques were used to investigate the dispersion states of the nanotubes in PA 6 matrix. The results indicated that the dispersion state of MWCNTs in the nanocomposites prepared by the phase inversion-based method was better than those in the nanocomposites prepared by the other two methods. Electrical, rheological, differential scanning calorimetry and thermo-gravimetric analysis measurements showed that the PA 6/MWCNTs nanocomposites prepared by the phase inversion-based method had higher electrical conductivity, storage modulus, crystallization temperature and thermal stability in comparison with those prepared by the other two methods, attributed to the better dispersion state of MWCNTs. These results confirmed achievement of a good dispersion state of MWCNTs within PA 6 matrix by the phase inversion-based efficient approach.     

Morphology,crystallization, and mechanical properties of poly(ethylene terephthalate)/multiwalled carbon nanotubes composites

Poly(ethylene terephthalate)/multiwalled carbon nanotubes (PET/MWCNTs) with different MWCNTs loadings have been prepared by in situ polymerization of ethylene glycol (EG) containing dispersed MWCNTs and terephthalic acid (TPA). From scanning electronic microscopy images of nanocomposites, it can be clearly seen that the PET/MWCNTs composites with low‐MWCNTs contents (0.2 and 0.4 wt %) get better MWCNTs dispersion than analogous with high‐tube loadings (0.6 and 0.8 wt %). The nonisothermal crystallization kinetics was analyzed by differential scanning calorimetry using Mo kinetics equation, and the results showed that the incorporation of MWCNTs accelerates the crystallization process obviously. Mechanical testing shows that, in comparison with neat PET, the Young's modulus and the yield strength of the PET nanocomposites with incorporating 0.4 wt % MWCNTs are effectively improved by about 25% and 15%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study on the Reusability of Multiwalled Carbon Nanotubes in Biodegradable Chitosan Nanocomposites

The mechanical properties, water absorption, biodegradation, multiwalled carbon nanotubes (MWCNTs) recovery and reusability of chitosan/oxidized MWCNTs nanocomposites were investigated. The highest Young's modulus (E) was obtained by the nanocomposites with 0.1 wt.% MWCNTs, while further increase of MWCNTs loading decreases the tensile strength (TS) and E. The water absorption and degradation rate of the nanocomposites were decreased by the loading of MWCNTs; 89.7% of MWCNTs were recovered by physical base separation. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and tensile test results showed that the recovered MWCNTs displayed properties similar to the oxidized MWCNTs, suggesting the possibility of reuse and recycle.     

Preparation and properties of plasticized starch/multiwalled carbon nanotubes composites

In this work we have studied the utilization of multiwalled carbon nanotubes (MWCNTs) as filler‐reinforcement to improve the performance of plasticized starch (PS). The PS/MWCNTs nanocomposites were successfully prepared by a simple method of solution casting and evaporation. The morphology, thermal behavior, and mechanical properties of the films were investigated by means of scanning electron microscopy, wide‐angle X‐ray diffraction, differential scanning calorimetry, and tensile testing. The results indicated that the MWCNTs dispersed homogeneously in the PS matrix and formed strong hydrogen bonding with PS molecules. Compared with the pure PS, the tensile strength and Young's modulus of the nanocomposites were enhanced significantly from 2.85 to 4.73 MPa and from 20.74 to 39.18 MPa with an increase in MWCNTs content from 0 to 3.0 wt %, respectively. The value of elongation at break of the nanocomposites was higher than that of PS and reached a maximum value as the MWCNTs content was at 1.0 wt %. Besides the improvement of mechanical properties, the incorporation of MWCNTs into the PS matrix also led to a decrease of water sensitivity of the PS‐based materials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Analysis of MWCNT/epoxy composites at microwave frequency: reproducibility investigation

A wide-band microwave characterization of nanocomposites based on commercial multiwalled carbon nanotubes (MWCNTs) and epoxy resin is presented. The sample preparation method is discussed in detail. Field emission scanning electron microscopy is used for morphological sample analysis of nanocomposites and MWCNTs. The complex permittivity is measured in a wide frequency band (3 to 18 GHz) using a commercial dielectric probe (Agilent 85070D) and a network analyzer (E8361A). A statistical analysis based on one-way analysis of variance (ANOVA) technique is performed. The aim of this statistical analysis is to investigate the influence of concentration of nanoparticles inside the polymer matrix on the complex permittivity. This can be significantly different in nanocomposites even if the samples have similar electrical properties.