Hydrogen bond containing multiwalled carbon nanotubes in polyurethane composites

Introduction of hydrogen bonding sites onto multi‐walled carbon nanotubes (MWCNTs) included carboxylic acid, amide‐amine, and novel amide‐urea MWCNTs for the formation of homogenous polyurethane composites. Acid oxidation and subsequent derivatization introduced hydrogen bonding functionality onto MWCNTs to reveal the effect of surface functionalization on mechanical properties in a 45 wt% hard segment polyurethane matrix. Raman spectroscopy showed an increase in the D/G peak ratio, which indicated successful oxidation, and X‐ray photoelectron spectroscopy also revealed elemental compositions that supported each step of the functionalization strategy. Thermogravimetric analysis supported functionalization with an increase in percent weight loss for each functionalization, and the MWCNT surface functionalization determined pH‐dependent dispersibility. The nonfunctionalized MWCNT composites showed poor dispersion with transmission electron microscopy, and in sharp contrast, the functionalized composites displayed homogenous dispersions. Tensile testing revealed improved stress at break in the functionalized MWCNT composites at low loadings due to homogenous dispersion. POLYM. COMPOS., 37:1425–1434, 2016. © 2014 Society of Plastics Engineers     

Polystyrene composites containing crosslinked polystyrene‐multiwalled carbon nanotube balls

Crosslinked polystyrene‐multiwalled carbon nanotube (PS‐MWCNT) balls, which act as conductive microfillers, were prepared by the in situ suspension polymerization of styrene with MWCNTs and divinyl benzene (DVB) as a crosslinking agent. The diameters of the synthesized crosslinked PS‐MWCNT balls ranged from 10 to 100 μm and their electrical conductivity was about 7.7 × 10^?3 S/cm. The morphology of the crosslinked PS‐MWCNT balls was observed by scanning electron microscopy and transmission electron microscopy. The change in the chemical structure of the MWCNTs was confirmed by Raman spectroscopy and Fourier transform infrared spectroscopy. The mechanical and electrical properties of the PS/crosslinked PS‐MWCNT ball composites were investigated. It was found that the tensile strength, ultimate strain, Young's modulus, and impact strength of the PS matrix were enhanced by the incorporation of the crosslinked PS‐MWCNT balls. In addition, the mechanical properties of the PS/crosslinked PS‐MWCNT ball composites were better than those of the PS/pristine MWCNT composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Modified carbon nanotube composites with high dielectric constant, low dielectric loss and large energy density

Flexible dielectric polystyrene based composites containing multi-walled carbon nanotubes (MWCNTs) were reported. The MWCNTs were coated with polypyrrole (PPy) by an inverse microemulsion polymerization. Transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy indicated that the MWCNTs were coated with PPy. Our composites presented a stable high dielectric constant (∼44), rather low loss (<0.07), and large energy density (up to 4.95 J cm⁻³). The largely-enhanced dielectric performance originates from the organic shell PPy, which not only ensure good dispersion of MWCNTs in the polymer matrix but also screen charge movement to shut off leakage current. Such MWCNT composites can be used to store charge and electrical energy and play a key role in modern electronics and electric power systems.     

Synthesis and characterization of polypyrrole‐au coated SiO2@poly(4‐vinylpyridine) composites

Microspheres with silica as core and poly(4‐vinylpyridine) (P4VP) as shell were synthesized. AuCl ions were bound by P4VP chains to form the complex, which acted both as an oxidant of pyrrole monomers and as a source of Au atoms. By vapor phase polymerization, the PPy and Au nanoparticles were simultaneously formed on the surfaces of SiO₂@P4VP microspheres. The core‐shell structure was confirmed by transmission electron microscopy. The surface morphologies of the composites were observed by scanning electron microscopy. The molecular structures of composites were characterized in detail by Raman spectra, X‐ray diffraction, and X‐ray photoelectron spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

5‐Sulfoisophthalic acid monolithium salt doped polypyrrole/multiwalled carbon nanotubes composites for EMI shielding application in X‐band (8.2–12.4 GHz)

This article describes the synthesis and characterization of highly conductive polypyrrole (PPy)/multiwalled carbon nanotube (MWCNT) composites prepared by in situ polymerization of pyrrole using 5‐sulfoisophthalic acid monolithium salt [lithio sulfoisophthalic acid (LiSiPA)] as dopant and ferric chloride as oxidant. Several samples were prepared by varying the amounts of MWCNTs ranging from 1 to 5 wt %. Scanning electron microscope and transmission electron microscope images clearly show a thick coating of PPy on surface of MWCNTs. The electrical conductivity of PPy increased with increasing amount of MWCNTs and maximum conductivity observed was 52 S/cm at a loading of 5 wt % of MWCNTs. Pure PPy prepared under similar conditions had a conductivity of 25 S/cm. Electromagnetic interference (EMI) shielding effectiveness (SE) also showed a similar trend and average EMI shielding of ?108 dB (3 mm) was observed for sample having 5 wt % MWCNT in the frequency range of 8.2–12.4 GHz (X‐band). The light weight and absorption dominated total SE of ?93 to ?108 dB of these composites indicate the usefulness of these materials for microwave shielding. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45370.     

Microstructural characterization of corn starch‐based porous thermoplastic composites filled with multiwalled carbon nanotubes

Microstructural characterization of corn starch‐based porous thermoplastic (TPS) composites containing various contents (0.1, 0.5, and 1 wt %) of multiwalled carbon nanotubes (MWCNTs) was performed. Corn starch was plasticized with a proper combination of glycerol and stearic acid. TPS composites with MWCNT were prepared conducting melt extrusion followed by injection molding. TPS containing 1 wt % of MWCNTs exhibited higher tensile strength and elastic modulus values than neat TPS. Moreover, TPS electrical conductivity was determined to increase with increasing content of MWCNTs. X‐ray diffraction measurements revealed that incorporation of MWCNTs increased the degree of TPS crsystallinity to some extent. Scanning electron microscopy examination revealed that MWCNT altered TPS surface morphology and tensile failure modes, significantly. Transmission electron microscopy investigation showed that dispersion characteristics of MWCNTs within TPS were in the form of tiny clusters around micro pores of TPS, which is considered influential on electrical conductivity of the resulting composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

Synthesis and characterization of LiFePO4–carbon nanofiber–carbon nanotube composites prepared by electrospinning and thermal treatment as a cathode material for lithium‐ion batteries

Binder‐free LiFePO₄–carbon nanofiber (CNF)–multiwalled carbon nanotube (MWCNT) composites were prepared by electrospinning and thermal treatment to form a freestanding conductive web that could be used directly as a battery cathode without addition of a conductive material and polymer binder. The thermal decomposition behavior of the electrospun LiFePO₄ precursor–polyacrylonitrile (PAN) and LiFePO₄ precursor–PAN–MWCNT composites before and after stabilization were studied with thermogravimetric analysis (TGA)/differential scanning calorimetry and TGA/differential thermal analysis, respectively. The structure, morphology, and carbon content of the LiFePO₄–CNF and LiFePO₄–CNF–MWCNT composites were determined by X‐ray diffraction, high‐resolution transmission electron microscopy, Raman spectroscopy, scanning electron microscopy, and elemental analysis. The electrochemical properties of the LiFePO₄–CNF and LiFePO₄–CNF–MWCNT composite cathodes were measured by charge–discharge tests and electrochemical impedance spectroscopy. The synthesized composites with MWCNTs exhibited better rate performances and more stable cycle performances than the LiFePO₄–CNF composites; this was due to the increase in electron transfer and lithium‐ion diffusion within the composites loaded with MWCNTs. The composites containing 0.15 wt % MWCNTs delivered a proper initial discharge capacity of 156.7 mA h g^?1 at 0.5 C rate and a stable cycle ability on the basis of the weight of the active material, LiFePO₄. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43001.     

Functionalization of multi-walled carbon nanotubes with non-reactive polymers through an ozone-mediated process for the preparation of a wide range of high performance polymer/carbon nanotube composites

Polymer chains are chemically bonded to multi-walled carbon nanotubes (MWCNTs) through an ozone-mediated process. Four polymers, poly(vinylidene fluoride) (PVDF), polysulfone (PSF), poly(2,6-dimethylphenylene oxide), and poly(phthalazinone ether ketone) are used to demonstrate this MWCNT functionalization. MWCNT-polymer hybrids are characterized by Fourier transform infrared spectroscopy, Raman spectrometry, X-ray photoelectron spectrometry, and high-resolution transmission electron microscopy. This approach provides a general method of preparation of matrix-polymer-modified MWCNTs to be used in the preparation of polymer/MWCNT composites. Compared to pristine MWCNTs and PSF-modified MWCNTs, PVDF-modified MWCNTs are more efficient additives to enhance the mechanical strength and electrical conductivity of PVDF. Therefore, matrix-polymer-modified MWCNTs are relatively attractive in the preparation of high performance polymer/MWCNT composites.     

Improved dispersibility of multi‐wall carbon nanotubes with reversible addition–fragmentation chain transfer polymer modification

A non‐covalent approach is used to modify multi‐wall carbon nanotubes (MWCNTs) via a block polymer that can be synthesized in aqueous solvent through reversible addition–fragmentation chain transfer polymerization. The block polymer consists of oligo(ethylene glycol) methyl ether acrylate and acrylic acid. The hydrophobic backbone is significantly adsorbed on hydrophobic MWCNT surfaces, which is verified using transmission electron microscopy, thermogravimetric analysis and X‐ray photoelectron spectroscopy. The coated block polymer can prevent the aggregation of MWCNTs and improve their dispersibility in water. The MWCNTs after modification are stable in water even after standing in a long‐term test. © 2015 Society of Chemical Industry     

Amino functionalization of multiwalled carbon nanotubes by gamma ray irradiation and its epoxy composites

In this paper, γ‐ray radiation technique was utilized to simply functionalize multi‐walled carbon nanotube (MWCNT) with amino groups. The successful amino functionalization of MWCNTs (MWCNTs‐Am) was proven and the physicochemical properties of MWCNTs before and after radiation grafting modifications were characterized using FT‐IR, X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results indicated that the γ‐ray radiation had the visible effects on the surface properties of MWCNTs. The effects of various functionalized MWCNTs on morphological, thermal, and mechanical properties of an epoxy‐based nanocomposite system were investigated. Utilizing in situ polymerization, 1 wt% loading of MWCNT was used to prepare epoxy‐based nanocomposites. Compared to the neat epoxy system, nanocomposites prepared with MWCNT‐Am showed 13.0% increase in tensile strength, 20.0% increase in tensile modulus, and 24.1% increase in thermal decomposition temperature. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Magnetic and electrical properties of polypyrrole nanocomposites with iron nanoparticles attached to 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid

Polypyrrole (PPy) nanocomposites with iron nanoparticles attached to 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMP) were chemically prepared by varying the concentration of AMP using ammonium persulfate as an oxidant. The synthesized composites were characterized by using Fourier transform infrared (FTIR) spectroscopy, and their surface morphology and amended crystallinity were determined by using the transmission electron microscopy (TEM) and X‐ray diffraction (XRD), respectively. The electrical and magnetic properties of PPy–Fe–AMP composites were investigated at room temperature. The increase of AMP has brought out a significant increase of DC conductivity and magnetic saturation moment of the composites, which might have been caused by the increased mobility of charge carriers due to the hydrophilic AMP components. POLYM. COMPOS., 35:364–371, 2014. © 2013 Society of Plastics Engineers     

Fabrication and characterization of multilayer SiO2/polymethacrylic acid/polypyrrole composites and hollow polypyrrole microspheres

Methacrylic acid was polymerized on the 3‐(methacryloxy)propyl trimethoxysilane‐modified silica core. The carboxylic acid groups of polymethacrylic acid (PMAA) not only provide the “active‐sites” for growth of the pyrrole monomers but also act as doping acids for polypyrrole (PPy). By in situ polymerization route, SiO₂/PMAA/PPy multilayer composites and hollow PPy microspheres with controllable shell thickness were fabricated. The morphologies, sizes, and structures of the nanocomposites were investigated in detail by transmission electron microscopy, scanning electron microscopy, Fourier‐transform infrared spectra, X‐ray photoelectron spectroscopy, and thermogravimetric analysis. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of proton irradiation on mechanical properties of low‐density polyethylene/multiwalled carbon nanotubes composites

The mechanical properties of low‐density polyethylene/multiwalled carbon nanotubes (LDPE/MWCNTs) composites without and with 170 keV proton irradiation were studied by tensile tests. Mechanisms of changes of mechanical properties were examined by means of small angle X‐ray scattering (SAXS), wide angle X‐ray diffraction (WAXD), Raman spectroscopy, and scanning electron microscopy (SEM). The tensile curve of LDPE exhibits three characteristic regions, while those for LDPE/MWCNTs composites only give the first and the second ones. The tensile curves of all samples with 170 keV proton irradiation have no obvious yield phenomenon. The addition of MWCNTs increases the ultimate tensile strength and decreases the elongation at break. Moreover, the ultimate tensile strengths of both LDPE and LDPE/MWCNTs composites with 170 keV proton irradiation are enhanced, and the elongations at break for them are decreased. Based on the analyses of SAXS, WAXD, Raman spectroscopy, and SEM, both the loading of MWCNTs and the proton irradiation can change the mechanical properties of LDPE/MWCNTs composites by a number of factors including the homogeneous distribution of MWCNTs in LDPE matrix, the aberrance zone between MWCNTs, and LDPE matrix, the interaction between MWCNTs and LDPE matrix, and the crystallinities of samples. POLYM. COMPOS., 36:278–286, 2015. © 2014 Society of Plastics Engineers     

Synthesizing multi‐walled carbon nanotube‐polymethyl methacrylate conductive composites and poly(lactic acid) based composites

Multi‐walled carbon nanotube was modified with polymethyl methacrylate (MWCNT‐PMMA) by in situ solution radical polymerization in the presence of 2,2′‐Azobis (isobutyronitrile) as an initiator. The products with different addition of methyl methacrylate (MMA) were pressed into slices to prepare specimens for electrical conductivity testing. It was found that the MWCNT‐PMMA nanocomposites demonstrate excellent electrical conductivity. To investigate the microsphere morphology and the colloidal surfactant of MWCNTs in MWCNT‐PMMA composites, samples were submitted to scanning electron microscopy and transmission electron microscopy. The thermogravimetric analysis of the prepared composites confirmed that MWCNTs as a thermal stabilizer for PMMA, which could have a wide range of potential applications, such as in catalysts, sensors, environmental remediation, and energy storage. Two series of poly(lactic acid) (PLA) based biocomposites with different MMA additions and MWCNT‐PMMA composites contents were prepared with twin‐screw extruding and injection molding. The results show the mechanical properties changed a little with the MMA and MWCNT‐PMMA composites contents increasing, which suggested the well compatibility between MWCNT‐PMMA composites and PLA. POLYM. COMPOS., 37:503–511, 2016. © 2014 Society of Plastics Engineers     

In situ polymerization and photophysical properties of poly(p‐phenylene benzobisoxazole)/multiwalled carbon nanotubes composites

Poly(p‐phenylene benzobisoxazole)/multiwalled carbon nanotubes (PBO‐MWCNT) composites with different MWCNT compositions were prepared through in situ polymerization of PBO in the presence of carboxylated MWCNTs. The nanocomposite's structure, thermal and photophysical properties were investigated and compared with their blend counterparts (PBO/MWCNT) using Fourier transform infrared spectra, Raman spectra, Wide‐angle X‐ray diffraction, thermogravimetric analysis, UV‐vis absorption, and photoluminescence. The results showed that MWCNTs had a strong interaction with PBO through covalent bonding. The incorporation of MWCNTs increased the distance between two neighboring PBO chains and also improved the thermal resistance of PBO. The investigation of UV‐vis absorption and fluorescence emission spectra exhibited that in situ PBO‐MWCNT composites had a stronger absorbance and obvious trend of red‐shift compared with blend PBO/MWCNT composites for all compositions. This behavior can be attributed to the efficient energy transfer through forming conjugated bonding interactions in the PBO‐MWCNT composites. © 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     

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     

Microwave assisted functionalization of carboxylated‐multiwalled carbon nanotubes with 5‐aminoisophthalic acid and its application for the preparation of chiral poly(ester‐imide)/CNT nanocomposites

This article presents the results of investigation into surface modification of carboxylated‐multiwalled carbon nanotubes (MWCNT)s by 5‐aminoisophthalic acid under microwave irradiation as a fast, safe, and simple method. The different contents of functionalized MWCNTs (5, 10, 15 wt%) were effectively dispersed in an aromatic polymer through ultrasonic irradiation to prepare MWCNT reinforced polymer nanocomposites (NC)s. The chiral poly(ester‐imide) (PEI) was prepared by a direct polycondensation of chiral diacid with 4,4′‐thiobis(2‐tert‐butyl‐5‐methylphenol). The effect of the presence of MWCNTs on morphological and thermal properties of the NCs was investigated by X‐ray diffraction, FT‐IR spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy, and field emission scanning electron microscopy. According to TGA data, the PEI/MWCNT NCs showed a much better thermal stability than pristine polymer. The microstructure study of the NCs indicated the compatibility of functionalized MWCNTs with PEI and uniform distribution of them in the polymer matrices. POLYM. COMPOS., 37:835–843, 2016. © 2014 Society of Plastics Engineers     

Dispersion of multiwalled carbon nanotubes in polyacrylonitrile‐co‐starch copolymer matrix for enhancement of electrical,thermal, and gas barrier properties

Nanomaterials gained great importance on account of their wide range of applications in many areas. Carbon nanotubes (CNTs) exhibit exceptional electrical, thermal, gas barrier, and tensile properties and can therefore be used for the development of a new generation of composite materials. Functionalized multiwalled carbon nanotubes (MWCNTs) reinforced Polyacrylonitrile‐co‐starch nanocomposites were prepared by in situ polymerization technique. The structural property of PAN‐co‐starch/MWCNT nanocomposites was studied by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The conductivity, tensile strength, and thermal properties of nanocomposites were measured as a function of MWCNT concentrations. The thermal stability, conductivity, and tensile strength of PAN‐co‐starch/MWCNT nanocomposites were improved with increasing concentration of MWCNTs. Oxygen barrier property of PAN‐co‐starch/MWCNT nanocomposites was calculated and it was found that, the property was reduced substantially with increase of MWCNTs proportion. The synthesized PAN‐co‐starch/MWCNT nanocomposites may used for electrostatically dissipative materials, aerospace or sporting goods, and electronic materials. © 2013 Society of Plastics Engineers