Effect of organoclay content on the mechanical properties of ethylene‐vinyl acetate copolymer/ multi‐walled carbon nanotube/organoclay foams

The main objective of this study is to obtain ethylene‐vinyl acetate copolymer (EVA)/multi‐walled carbon nanotube (MWCNT)/organoclay foams with improved mechanical properties without increase of their density, compared with EVA/MWCNT foams. MWCNT content was fixed at 5 phr in this study. To achieve the objective, EVA was melt‐mixed with MWCNTs and organoclays in a bench kneader. And the obtained EVA/MWCNT/organoclay mixtures were mixed with chemical blowing agent and cross‐linking agent in a two roll‐mill. After being mixed in a two roll‐mill, the mixtures were put in a mold and the foams were obtained by compression‐molding. The effect of organoclay content on the mechanical properties and surface resistivity of EVA/MWCNT (5 phr)/organoclay foams was investigated. The addition of 1 phr organoclays to the EVA/MWCNT (5 phr) foams resulted in the improvement of tensile strength, 100% tensile modulus, tear strength, and compression set without increase of the density. However, further increase in content of organoclay (3 phr) leaded to a deterioration of mechanical properties. Therefore, determining the optimal content of organoclay was very important in order to achieve the main objective of this study. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Effect of processing parameters on the surface resistivity of ethylene–vinyl acetate copolymer/multiwalled carbon nanotube nanocomposites

In this study, ethylene–vinyl acetate (EVA) copolymer was melt‐mixed with multiwalled carbon nanotube (MWCNT). To realize full‐scale application of MWCNT to the polymer industries, the effect of melt‐processing parameters on the surface resistivity in the polymer/MWCNT nanocomposites should be well‐understood. The effect of mixing time, rotor speed, compression molding time, and temperature on the surface resistivity was investigated. Increasing the rotor speed and longer mixing time lead to an improvement of dispersion of MWCNT in polymer matrix, resulting in a decrease of surface resistivity. The surface resistivity of EVA/MWCNT nanocomposites is also sensitive to the press temperature and time. However, the dominant processing parameters to affect surface resistivity depend on the amount of MWCNT. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal and flame retardant properties of ethylene‐vinyl acetate copolymer/modified multiwalled carbon nanotube composites

The synthesized flame retardant 9,10‐dihydro‐9‐oxa‐10‐phosphaphanthrene‐10‐oxide/vinyl methyl dimethoxysilane (DV) was used to modify multiwalled carbon nanotubes (MWNTs). The results of FTIR, ¹H‐NMR, and TGA measurements show that DV has been covalently grafted onto the surfaces of MWNTs, and the MWNTs‐g‐DV is obtained successfully. Transmission electron microscopy images show that a core‐shell nanostructure appears with MWNTs as the core and the DV thin layers as the shell, and the modified MWNTs with DV can achieve better dispersion than unmodified MWNTs in EVM matrix. Thermogravimetric analysis and cone calorimeter tests indicate that the thermal stability and flame retardant are improved for the presence of the MWNTs in EVM matrix. Moreover, the improvement is more evident for EVM/MWNTs‐g‐DV composite compared to unmodified MWNTs‐based composite, which can be attributed to the better dispersion of the DV‐modified MWNTs and to the chemical structure of the combustion residue. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ethylene vinyl acetate copolymer (EVA)/multiwalled carbon nanotube (MWCNT) nanocomposite foams

In this study, multiwalled carbon nanotube (MWCNT) and ethylene vinyl acetate copolymer (EVA) nanocomposite bulk foams were prepared for static dissipative applications by using melt compounding method, the most compatible with current industrial applications. Closed‐cell structure was verified with Scanning Electron Microscope. All the mechanical properties investigated improved with increasing content of MWCNT except elongation at break. At 5 phr of MWCNT, significant improvement of mechanical properties and compression set were observed. Also, the surface resistivity begins to decrease at 5 phr of MWCNT. Interestingly, the increase of surface resistivity of nanocomposite foams with 8 and 10 phr MWCNT were observed with increasing thickness of removed surface layers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of electron beam irradiation on the properties of ethylene‐(vinyl acetate) copolymer/natural rubber/organoclay nanocomposites

The effects of electron beam (EB) irradiation on the morphology, crosslink density, and tensile properties of EVA/SMR L (Standard Malaysian Rubber)/organoclay nanocomposites prepared by a melt‐blending technique were investigated. All the samples were irradiated by using a 3.0‐MeV EB apparatus with doses ranging from 50 to 200 kGy. Organoclay loading was varied from 0 to 10 phr (parts by weight per hundred parts of resin). X‐ray diffraction results and transmission electron microscopy images proved that the dispersion of organoclay in the nanocomposites was slightly improved by EB irradiation. The gel fraction yield for the nanocomposites increased with irradiation dose but decreased with organoclay loading. However, at 200 kGy, the gel fraction yield was almost the same at all organoclay loadings. Tensile strength and stress at 100% elongation increased proportionally with the irradiation dose. Elongation at break of the nanocomposites increased up to 100 kGy but then decreased at higher irradiation doses. The intercalation and exfoliation of the organoclay, the barrier effect, and the Hofmann degradation of the modification agent are the three major factors leading to the improvement of the properties of the irradiated nanocomposites. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Rheological and mechanical characteristics of low density polyethylene/ethylene‐vinyl acetate/organoclay nanocomposites

Attempts were made to trace the effect of organoclay (OC) on the rheological and mechanical behaviors of the low density polyethylene (LDPE)/ethylene‐vinyl acetate (EVA) blends. To do this effectively, in addition to LDPE/EVA/OC system, pure LDPE and LDPE/EVA blends were also examined as model systems. The rheological behavior was determined by the capillary rheometer. Morphological characterization was also carried out using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and theoretical approach based on interfacial energies. Shear viscosity, tensile strength and elastic modulus of LDPE/EVA were found to decrease by increasing the EVA content, while for LDPE/EVA/OC ternary nanocomposites, such properties showed an increase by increasing the content of EVA. Such behavior was explained by the morphological characteristic of the system in which OC was mainly intercalated/exfoliated in the EVA phase. This morphological characteristic was corroborated by the XRD, TEM and interfacial energies data. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Improvement of compression set property of ethylene vinyl acetate copolymer/ethylene‐1‐butene copolymer/organoclay nanocomposite foams

To chemically bond polymer and organoclay, low molecular weight trimethoxysilyl‐modified polybutadiene (Silane) was used in this study. When Silane was added, ethylene‐vinyl acetate copolymer (EVA)/ethylene‐1‐butene copolymer (EtBC)/methyl tallow bis‐2‐hydroxyethyl quaternary ammonium‐modified montmorillonite (OH‐MMT)/Silane foams with and without maleic anhydride grafted EtBC (EtBC‐g‐MAH) display lower compression set than EVA/EtBC foams. According to the compression set result, OH‐MMT is more effective in improvement of compression set than dimethyl dihydrogenated tallow quaternary ammonium‐modified montmorillonite (DM‐MMT) because in addition of OH groups in the organoclay surface, the OH groups of the alkylammonium ion existed in interlayer of OH‐MMT may react with silanol group of Silane. The possible chemical reactions between Silanol groups of Silane and the hydroxyl groups of OH‐MMT and DM‐MMT were proved by ATR‐FTIR experiments. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Thermal and mechanical behavior of poly(vinyl butyral)‐modified novolac epoxy/multiwalled carbon nanotube nanocomposites

The effects of poly(vinyl butyral) (PVB) and acid‐functionalized multiwalled carbon nanotube modification on the thermal and mechanical properties of novolac epoxy nanocomposites were investigated. The nanocomposite containing 1.5 wt % PVB and 0.1 wt % functionalized carbon nanotubes showed an increment of about 15°C in the peak degradation temperature compared to the neat novolac epoxy. The glass‐transition temperature of the novolac epoxy decreased with increasing PVB content but increased with an increase in the functionalized carbon nanotube concentration. The nanocomposites showed a lower tensile strength compared to the neat novolac epoxy; however, the elongation at break improved gradually with increasing PVB content. Maximum elongation and impact strength values of 7.4% and 17.0 kJ/m² were achieved in the nanocomposite containing 1.5 wt % PVB and 0.25 wt % functionalized carbon nanotubes. The fractured surface morphology was examined with field emission scanning electron microscopy, and correlated with the mechanical properties. The functionalized carbon nanotubes showed preferential accumulation in the PVB phase beyond 0.25 wt % loading. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43333.     

A liquid‐like multiwalled carbon nanotube derivative and its epoxy nanocomposites

Multiwall carbon nanotubes (MWCNTs) with liquid‐like behavior at room temperature were prepared with sulfonic acid terminated organosilanes as corona and tertiary amine as canopy. The liquid‐like MWCNT derivative had low viscosity at room temperature (3.89 Pa s at 20°C) and exhibited non‐Newtonian shear‐thinning behavior. The weight fraction of MWCNT in the derivative was 16.72%. The MWCNT derivative showed very good dispersion in organic solvents, such as ethanol and acetone. The liquid‐like MWCNT derivative was incorporated into epoxy matrix to investigate the mechanical performance of the nanocomposites and the distribution of MWCNTs in the matrix. When the liquid‐like MWCNT derivative content was up to 1 wt %, the flexural strength and impact toughness of composites were 12.1 and 124% higher than the pure epoxy matrix, respectively. Transmission electron microscope (TEM) confirmed the very good dispersion of the liquid‐like MWCNT derivative in epoxy matrix. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2217–2224, 2013     

Preparation and properties of multiwalled carbon nanotube/polycaprolactone nanocomposites

Multiwalled carbon nanotube/polycaprolactone nanocomposites (MWNT/PCL) were prepared by in situ polymerization, whereby as‐received MWNTs (P‐MWNTs) and purified MWNTs (A‐MWNTs) were used as reinforcing materials. The A‐MWNTs were purified by nitric acid treatment, which introduced the carboxyl groups (COOH) on the MWNT. The micrographs of the fractured surfaces of the nanocomposites showed that the A‐MWNTs in A‐MWNT/PCL were better dispersed than P‐MWNTs in PCL matrix (P‐MWNT/PCL). Percolation thresholds of the P‐MWNT/PCL and A‐MWNT/PCL, which were studied by rheological properties, were found at ～2 wt % of the MWNT. The conductivity of the P‐MWNT/PCL was between 10^?1 and 10^?2 S/cm by loading of 2 wt % of MWNT although that of the A‐MWNT/PCL reached ～10^?2 S/cm by loading of 7 wt % of MWNT. The conductivity of the P‐MWNT/PCL was higher than that of the A‐MWNT/PCL at the entire range of the studied MWNT loading, which might be due to the destruction of π‐network of the MWNT by acid treatment, although the A‐MWNT/PCL was better dispersed than the P‐MWNT/PCL. The amount of the MWNT at which the conductivity of the nanocomposite started to increase was strongly correlated with the percolation threshold. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1957–1963, 2007     

Cellulose acetate/multiwalled carbon nanotube nanocomposites with improved mechanical,thermal, and electrical properties

Cellulose acetate (CA)‐based nanocomposites with various contents of neat multiwalled carbon nanotube (MWCNT) or acid‐treated one (MWCNT‐COOH) are prepared via melt‐compounding method and investigated their morphology, thermal stability, mechanical, and electrical properties. SEM microphotographs reveal that MWCNT‐COOHs are dispersed uniformly in the CA matrix, compared with neat MWCNTs. FTIR spectra support that there exists a specific interaction between carboxyl groups of MWCNT‐COOHs and ester groups of CA, indicating good interfacial adhesion between MWCNT‐COOHs and CA matrix. Accordingly, thermal stability and dynamic mechanical properties of CA/MWCNT‐COOH nanocomposites were higher than those of CA/MWCNT composites. On the contrary, electrical volume resistivities of CA/MWCNT‐COOH nanocomposites are found to be somewhat higher than those of CA/MWCNT composites, which is because of the deterioration of graphene structures for MWCNT‐COOHs and the good dispersion of MWCNT‐COOHs in the CA matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Improved dielectric performance of polypropylene/multiwalled carbon nanotube nanocomposites by solid‐phase orientation

By means of a die‐drawing technique in the rubbery state, the effect of the orientation of the microstructure on the dielectric properties of polypropylene (PP)/multiwalled carbon nanotube (MWCNT) nanocomposites was examined in this study. The viscoelastic behavior of the PP/MWCNT nanocomposites with MWCNT weight loadings ranging from 0.25 to 5 wt % and the dielectric performance of the stretched PP/MWCNT nanocomposites at different drawing speeds and drawing ratios were studied to obtain insight into the influences of the dispersion and orientation state of the MWCNTs and matrix molecular chains. A viscosity decrease (ca. 30%) of the PP/MWCNT‐0.25 wt % (weight loading) melt was obviously due to the free volume effect. Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction were adopted to detect the orientation structure and the variation of crystal morphology of the PP/MWCNTs. Melting plateau regions, which indicated the mixed crystallization morphology for the stretched samples, were found in the DSC patterns instead of a single‐peak for the unstretched samples. We found that the uniaxial stretching process broke the conductive MWCNT networks and consequently increased the orientation of MWCNTs and molecular chains along the tensile force direction; this led to an improvement in the dielectric performance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42893.     

Microstructure and thermal properties of ethylene‐(vinyl acetate) copolymer/rectorite nanocomposites

Ethylene‐(vinyl acetate) copolymer (EVA)/rectorite nanocomposites were prepared by direct melt extrusion of EVA and organo‐rectorite. The microstructures and thermal properties of EVA nanocomposites were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), solid‐state nuclear magnetic spectroscopy, positron annihilation spectroscopy, thermal gravimetric analysis (TGA) and dynamic mechanical analysis techniques. XRD pattern and SEM images show that the intercalated structure is formed and rectorite is finely dispersed in EVA matrix. When organoclay content of the hybrid increases to 7.5 wt%, or pristine rectorite was used instead of organoclay, the crystallization behavior of EVA nanocomposite changes greatly and the ratio of the monoclinic to orthorhombic crystal increases significantly. The relative fractional free volume of the nanocomposite decreases with the increasing organo‐rectorite content, and the values of damping factor (tan δ) for all nanocomposites are lower than that of pure EVA. These facts illuminate that intercalated structure restricts the segment motion and mobilization of polymer chain. TGA results of EVA nanocomposites in air indicate that deacylation of EVA is accelerated because of the catalytic effect and the thermal degradation of the main chain is delayed owing to the barrier effect of silicate layers. Copyright © 2005 Society of Chemical Industry     

Shape‐memory polyurethane/multiwalled carbon nanotube fibers

Shape‐memory polyurethane/multiwalled carbon nanotube (SMP–MWNT) composites with various multiwalled carbon nanotube (MWNT) contents were synthesized, and the corresponding SMP–MWNT fibers were prepared by melt spinning. The influence of the MWNT content on the spinnability, fracture morphology, thermal and mechanical properties, and shape‐memory behavior of the shape‐memory polymer was studied. The spinning ability of SMP–MWNTs decreased significantly with increasing MWNT content. When the MWNT content reached 8.0 wt %, the fibers could not be produced because of the poor rheological properties of the composites. The melt‐blending, extrusion, and melt‐spinning processes for the shape‐memory fiber (SMF), particularly at low MWNT contents, caused the nanotubes to distribute homogeneously and preferentially align along the drawing direction of the SMF. The crystallization in the SMF was promoted at low MWNT contents because it acted as a nucleation agent. At high MWNT contents, however, the crystallization was hindered because the movement of the polyurethane chains was restricted. The homogeneously distributed and aligned MWNTs preserved the SMF with high tenacity and initial modulus. The recovery ratio and recovery force were also improved because the MWNTs helped to store the internal elastic energy during stretching and fixing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Investigation of cure kinetics in epoxy/multiwalled carbon nanotube nanocomposites

With the increased interest in thermoset resin nanocomposites, it is important to understand the effects of the material on nanoscale characteristics. In this study, a curing reaction of an epoxy resin, which contained 0.25, 0.50, or 1.00 wt % of multiwalled carbon nanotubes (MWCNTs), at different heating rates was monitored by differential scanning calorimetry; cure kinetics were also evaluated to establish a relationship between crosslinking (network formation) and mechanical properties. MWCNT concentrations above 0.25 wt % favored crosslinking formation and decreased the activation energy (E_a) in the curing reaction. Examination of the kinetic mechanism suggests that the MWCNT locally restricted the spatial volume and favored the formation of nodular morphology in the resin, especially for high MWCNT concentrations. The MWCNT exhibited some entanglement in the matrix, which hindered a more pronounced effect on the mechanical properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39857.     

Preparation and thermal properties of multiwalled carbon nanotube/polybenzoxazine nanocomposites

In this study, we prepared nanocomposites comprising multiwalled carbon nanotubes (MWCNTs) and polybenzoxazine (PBZ). The MWCNTs were purified through microwave digestion to remove most of the amorphous carbon and metal impurities. After purification, MWCNTs were treated with H₂SO₄/HNO₃ (3 : 1) to introduce hydroxyl and carboxyl groups onto their surfaces. Raman spectroscopy revealed the percentage of nanotube content improved after prolonged microwave treatment, as evidenced by the decrease in the ratio of the D (1328 cm^?1) and G (1583 cm^?1) bands. For the untreated MWCNTs, the I_D/I_G ratio was 0.56. After microwave treatment for 40 min, the value decreased to 0.29, indicating that the percentage of nanotube content improved. Dynamic mechanical analyses (DMAs) revealed that the storage moduli and the T_gs of the MWCNTs/PBZ nanocomposites were higher than that of the pristine PBZ. This is due to the nanometer‐scale MWCNTs restricting the motion of the macromolecular chains in the nanocomposites. Transmission electron microscopy (TEM) image revealed that the MWCNTs were well dispersed within the PBZ matrix on the nanoscale when the MWCNT content was less than 2.0 phr. The coefficient of thermal expansion (CTE) of the nanocomposites decreased on increasing the MWCNTs content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Isothermal crystallization behavior of polyamide 6,6/multiwalled carbon nanotube nanocomposites

The good dispersion of functionalized multiwalled carbon nanotube (f‐MWCNT) in polyamide 6,6 (PA 6,6) matrix was prepared by solution mixing techniques. The crystalline structure and crystallization behaviors of PA 6,6 and PA 6,6/f‐MWCNT nanocomposites were studied by X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and polarized optical microscopy (POM) analysis. DSC isothermal results revealed that the overall isothermal crystallization rates of PA 6,6 increased as well as the activation energy of PA 6,6 extensively decreased by adding f‐MWCNT into PA 6,6, suggesting that the addition of f‐MWCNT probably induces the heterogeneous nucleation. The effect of f‐MWCNT on the chain arrangement for the crystallization of PA 6,6/f‐MWCNT nanocomposites was also discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effect of dispersion state of organoclay on cellular foam structure and mechanical properties of ethylene vinyl acetate copolymer/ethylene‐1‐butenecopolymer/organoclay nanocomposite foams

In this study, our goal is to obtain lower density of ethylene‐vinyl acetate copolymer (EVA)/ethylene‐1‐butene copolymer (EtBC) foams without sacrificing mechanical properties. For this purpose EVA/EtBC/organoclay (Cloisite 15A, Closite 30B) nanocomposite foams were prepared. To investigate the effect of compatibilizer on the dispersion state of organoclay in cellular foam structure and mechanical properties of the EVA/EtBC/organoclay foams composites were prepared with and without maleic anhydride grafted EtBC (EtBC‐g‐MAH). The dispersion of organoclay in EVA/EtBC/organocaly foams was investigated by X‐ray diffraction and transmission electron microscopy. The EVA/EtBC nanocomposite foamswith the compatibilzer, especially EVA/EtBC/Cloisite 15A/EtBC‐g‐MAH foams displayed more uniform dispersion of organoclay than EVA/EtBC nanocomposite foams without the compatibilzer. As a result, EVA/EtBC/Cloisite 15A/EtBC‐g‐MAH foams have the smallest average cell size and highest 100% tensile modulus followed by EVA/EtBC/Cloisite 30B/EtBC‐g‐MAH foams. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3879–3885, 2007     

Electrical,mechanical, and crystallization properties of ethylene‐tetrafluoroethylene copolymer/multiwalled carbon nanotube composites

Multiwalled carbon nanotubes (MWCNTs) were melt‐mixed in a conical twin‐screw extruder with a random copolymer of ethylene and tetrafluoroethylene. Surprisingly, the electrical percolation threshold of the resultant composites was quite low; ～0.9 wt %. In fact, this value is as low or lower than the value for most MWCNT/semicrystalline polymer composites made with roughly equivalent aspect ratio tubes mixed in a similar manner, for example, melt mixing. This low percolation threshold, suggestive of good dispersion, occurred even though the polymer surface energy is quite low which should make tubes more difficult to disperse. Dynamic mechanical measurements confirmed the rather low percolation threshold. The effect of nanotubes on crystallization kinetics was quite small; suggesting perhaps that a lack of nucleation which in turn reduces/eliminates an insulating crystalline polymer layer around the nanotubes might explain the low percolation threshold. Finally, the modulus increased with the addition of nanotubes and the strain at break decreased. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41052.     

Rheology and dispersion behavior of high‐impact polystyrene/ethylene–vinyl acetate copolymer/TiO2 nanocomposites

TiO₂ nanoparticles were introduced into high‐impact polystyrene (HIPS) in the form of a master batch in which TiO₂ was predispersed in composites of HIPS and ethylene–vinyl acetate copolymer (EVA) by melt compounding. The resulting materials were analyzed with a Rosand Precision rheometer, transmission electron microscopy, atomic force microscopy, and ultraviolet–visible light spectrophotometry. The results showed that the introduction of TiO₂ nanoparticles into HIPS influenced the apparent viscosity of the composites to a rather small extent. The addition of EVA could regulate the rheological behavior of the HIPS/TiO₂ master batch greatly. EVA helped the dispersions of the agglomerates of TiO₂ nanoparticles in the flow; this was featured by the distinct yielding in the flow after the introduction of EVA, as well as the large change in the non‐Newtonian indices. The dispersions of the HIPS/TiO₂ master batch in the HIPS matrix were improved greatly by the addition of EVA. TiO₂ nanoparticles were dispersed randomly in HIPS/EVA/TiO₂ nanocomposites. The dispersion improvement of the HIPS/EVA/TiO₂ master batch was also proved by atomic force microscopy and ultraviolet–visible spectroscopy investigations. The mechanical properties of HIPS/EVA/TiO₂ nanocomposites with low TiO₂ contents were slightly higher than those of pure HIPS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4434–4438, 2006