Electrically conductive multi‐walled carbon nanotube‐reinforced amorphous polyamide nanocomposites

Nanocomposites (NCs) based on an amorphous polyamide (aPA) and multi‐walled carbon nanotubes (MWCNTs) were obtained by melt‐mixing. As individual nanotubes were mostly observed, dispersion of the carbon nanotubes was deemed good. The electrical percolation threshold (p_c) occurred at 2.97 wt% MWCNTs and as a result, electrical conductivity improved by nine orders of magnitude upon addition of 6 wt% MWCNTs. The 6 wt% MWCNTs also led to an increase in both thermal stability (measured by the degradation temperature) and Young's modulus (19%) for the NCs, and ductility remained the same. POLYM. COMPOS., 35:587–595, 2014. © 2013 Society of Plastics Engineers     

Electrical and rheological percolation in poly(vinylidene fluoride)/multi‐walled carbon nanotube nanocomposites

Nanocomposites of poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWCNTs) were prepared through melt blending in a batch mixer (torque rheometer equipped with a mixing chamber). The morphology, rheological behavior and electrical conductivity were investigated through transmission electron microscopy, dynamic oscillatory rheometry and the two‐probe method. The nanocomposite with 0.5 wt% MWCNT content presented a uniform dispersion through the PVDF matrix, whereas that with 1 wt% started to present a percolated network. For the nanocomposites with 2 and 5 wt% MWCNTs the formation of this nanotube network was clearly evident. The electrical percolation threshold at room temperature found for this system was about 1.2 wt% MWCNTs. The rheological percolation threshold fitted from viscosity was about 1 wt%, while the threshold fitted from storage modulus was 0.9 wt%. Thus fewer nanotubes are needed to approach the rheological percolation threshold than the electrical percolation threshold. Copyright © 2010 Society of Chemical Industry     

Investigation of electrical,mechanical, and thermal properties of functionalized multiwalled carbon nanotubes‐reduced graphene Oxide/PMMA hybrid nanocomposites

Electrical, mechanical, and thermal properties of the poly(methyl methacrylate) (PMMA) composites containing functionalized multiwalled carbon nanotubes (f‐MWCNTs) and reduced graphene oxide (rGO) hybrid nanofillers have been investigated. The observed electrical percolation threshold of FHC is 0.8 wt% with maximum conductivity of 1.21 × 10^?3 S/cm at 4 wt% of f‐MWCNTs. The electrical transport mechanism and magneto resistance studied of hybrid composites have also been investigated. Progressive addition of f‐MWCNTs in rGO/PMMA composite results increase in mechanical (tensile strength and Young's modulus) and thermal (thermal stability) properties of f‐MWCNTs‐rGO/PMMA hybrid nanocomposites (FHC). The increased mechanical properties are due to the efficient load transfer from PMMA matrix to f‐MWCNTs and rGO through better chemical interaction. The strong interaction between PMMA and f‐MWCNTs‐rGO in FHC is the main cause for improved thermal stability. POLYM. ENG. SCI., 59:1075–1083, 2019. © 2019 Society of Plastics Engineers     

Enhancing electrical properties of MWCNTs in immiscible blends of poly(methyl methacrylate) and styrene‐acrylonitrile copolymer by selective localization

Multiwalled carbon nanotubes (MWCNTs) were introduced into poly(methyl methacrylate) (PMMA) and styrene‐acrylonitrile copolymer (SAN) blends by melt mixing in an asymmetric miniature mixer (APAM). A composition of 70 wt% of PMMA and 30 wt% of SAN was mixed to create a co‐continuous morphology. Transmission electron microscopy images of ultra‐microtomed samples (70 nm in thickness) showed selective localization of MWCNTs inside the percolated SAN phase. The occurrence of the double percolation phenomenon resulted in lower electrical percolation thresholds of PMMA/SAN/MWCNT blends molded at high temperatures. Dielectric spectroscopy indicated a higher electrical permittivity for samples that were compression molded at 260°C. Due to the higher affinity of MWCNTs to SAN, there was a migration of MWCNTs into the SAN phase during the melt processing. Conductivity measurements revealed a significant decrease in electrical percolation threshold (0.4 wt%) for PMMA70/SAN30 blends compared with MWCNT‐filled SAN and MWCNT‐filled PMMA (ca. 0.8 wt%). POLYM. COMPOS., 37:1523–1530, 2016. © 2014 Society of Plastics Engineers     

Conductivity and mechanical properties of composites based on MWCNTs and styrene‐butadiene‐styrene block™ copolymers

Composites based on multiwall carbon nanotubes (MWCNTs) and the block copolymer styrene‐butadiene‐styrene with two different contents of styrene have been investigated and their electrical conductivity and mechanical properties have been evaluated. The composites were prepared by a solution casting procedure, using a dispersant agent for the MWCNTs. Conductivity values of 10^?4 and 1.6 S cm^?1 have been obtained for samples containing 1 and 12 wt % of MWCNTs, respectively. The percolation threshold achieved for these systems was ～0.25 wt %. According to dynamic mechanical analysis, the MWCNTs interact with both phases of the copolymers, acting as a reinforcement filler, whereas the dispersant agent acts as a plasticizer. However, it was shown that the reinforcing effect of the MWCNTs overcomes the latter, resulting in an overall improvement of mechanical properties of the composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication and dielectric properties of poly(ether ether ketone)/polyimide blends with selectively distributed multi‐walled carbon nanotubes

The distribution and contents of conductive fillers have a decisive influence on the dielectric properties of polymer/conductive filler composites. Herein, we clarified how the phase morphology and filler contents affect the dielectric properties of poly(ether ether ketone) (PEEK)/polyimide (TPI)/multi‐walled carbon nanotubes (MWCNTs) composites, in which MWCNTs were selectively located in the TPI phase. Firstly, PEEK/TPI/MWCNTs composites with identical MWCNTs content but different PEEK/TPI ratios were prepared. The composites with co‐continuous phase structure exhibited much better dielectric properties than those with sea–island structure. Then, PEEK/TPI/MWCNTs composites with the same PEEK/TPI ratio but various MWCNTs contents were prepared. The dielectric constant of the composite with 2 wt% MWCNTs reached 11306, which is because the formation of a co‐continuous phase structure benefited the mini‐capacitor network. Our results provide an effective method to develop high‐dielectric‐constant composites using the concept of double percolation. © 2015 Society of Chemical Industry     

Integration of PDA Chemistry and Surface‐Initiated ATRP to Prepare Poly(methyl methacrylate)‐Grafted Carbon Nanotubes and Its Effect on Poly(vinylidene fluoride)–Carbon Nanotube Composite Properties

Poly(methyl methacrylate)‐grafted carbon nanotubes (PMMA@MWCNTs) are nondestructively prepared via the integration of mussel‐inspired polydopamine (PDA) chemistry and the surface‐initiated atom transfer radical polymerization (ATRP) method. The structures and properties of the poly(vinylidene fluoride)‐based (PVDF‐based) nanocomposites filled with pristine MWCNTs and PMMA@MWCNTs are investigated. The results show that the encapsulation of PMMA on the MWCNTs surface not only improves the dispersibility of MWCNTs in the PVDF matrix but also enhances the interfacial interaction between MWCNTs and PVDF. The addition of PMMA@MWCNTs nanofillers to PVDF can effectively induce the crystal structure of PVDF to transform from the α‐phase to the β/γ ‐phase, and nearly 100% β/γ ‐phase PVDF formed when the nanofiller loading is higher than 5 wt%. Compared with the MWCNTs/PVDF composites, the PMMA@MWCNTs/PVDF composites exhibit obvious improvement in the percolation threshold because the PMMA shells hinder the direct contact of the MWCNTs. Moreover, the loss tangent of the PMMA@MWCNTs/PVDF composites is effectively suppressed due to the reduced leakage current in the composites and the enhanced interfacial strength between the nanofiller and the matrix.     

High dispersion ability of fluorene‐based polyester as a polymer matrix for carbon nanotubes

The high compatibility of fluorene‐based polyester (FBP‐HX) as a polymer matrix for multiwalled carbon nanotubes (MWCNTs) is discussed. A low surface resistivity due to the fine dispersion of MWCNTs in FBP‐HX and polycarbonate (PC) is reported. With a solution‐casting method, a percolation threshold with the addition of between 0.5 and 1.0 wt % MWCNTs was observed in the MWCNT/PC and MWCNT/FBP‐HX composites. Because of the coverage of FBP‐HX on the MWCNTs, a higher surface resistivity and a higher percolation ratio of the MWCNT/FBP‐HX composites were achieved compared with the values for the MWCNT/PC composites. In the MWCNT/FBP‐HX composites, MWCNTs covered with FBP‐HX were observed by scanning electronic microscopy. Because of the coverage of FBP‐HX on the MWCNTs, FBP‐HX interfered with the electrical pathway between the MWCNTs. The MWCNTs in FBP‐HX were covered with a 5‐nm layer of FBP‐HX, but the MWCNTs in the MWCNT/PC composites were in their naked state. MWCNT/PC sheets demonstrated the specific Raman absorption of the MWCNTs only with the addition of MWCNTs of 1 wt % or above because of the coverage of the surface of the composite sheet by naked MWCNTs. In contrast, MWCNT/FBP‐HX retained the behavior of the matrix resin until a 3 wt % addition of MWCNTs was reached because of the coverage of MWCNTs by the FBP‐HX resin, induced by its high wettability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comparative analysis of electric,magnetic, and mechanical properties of epoxy matrix composites with different contents of multiple walled carbon nanotubes

Epoxy composites based on aligned chemical vapor deposition–grown multiwall carbon nanotubes (MWCNTs), containing trapped iron nanoparticles, with weight fractions ranging from 0.03 to 1 wt%, were produced following a well‐known processing way. Electrical and mechanical properties as well as their densities were measured. The results are compared with previous studies investigating the magnetic percolation behavior in the same samples of composites. A percolation threshold at 0.4 wt% of MWCNTs was determined by the electrical property and it agrees with the threshold observed in the magnetic properties. A hop in the porosity and a depression of the bulk mechanical properties were also found at the threshold value. These results point out that there is an efficiency threshold related to the sonication stage of the fabrication process and the weight fraction of MWCNTs, and after this threshold, the initial nanotubes pans were not separated into individual MWCNTs or into small ropes. An optimized sonication stage is proposed and the improvement in the dispersion of the filler is shown. POLYM. COMPOS., 28:612–617, 2007. © 2007 Society of Plastics Engineers     

Effects of multi‐walled carbon nanotubes and conductive carbon black on electrical,dielectric, and mechanical properties of epoxidized natural rubber composites

The influence of multi‐walled carbon nanotubes (MWCNTs) and conductive carbon black (CCB) on cure, electrical, dielectric, and mechanical properties of epoxidized natural rubber (ENR) composites was investigated. It was found that short MWCNTs (S‐MWCNTs) with low loading significantly affected the cure characteristics in a way similar to high loading of CCB. Moreover, the ENR/S‐MWCNTs composites exhibited high AC conductivity, dielectric constant, and dielectric loss tangent (tan δ ) compared to the ENR/CCB and ENR/L‐MWCNTs (long MWCNTs) composites. In addition, the S‐MWCNTs composites showed the lowest percolation threshold concentration, defined as the lowest loading to form conductive paths in the insulating ENR matrix. This might be attributed to the comparatively high interfacial polarization, with good dispersion and distribution, of the S‐MWCNTs in ENR matrix. These characteristics were confirmed by TEM imaging and by a high bound rubber content, corroborating strong filler–rubber interactions in the ENR/S‐MWCNTs composites. However, the L‐MWCNTs composites showed the lowest electrical and other related properties, despite the highest aspect ratio and specific surface area of this filler. This might be because of the flocculation of nanotubes by mutual entanglement, leading to a poor uneven distribution in the ENR matrix. POLYM. COMPOS., 38:1031–1042, 2017. © 2015 Society of Plastics Engineers     

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     

Hot‐melt adhesives based on co‐polyamide and multiwalled carbon nanotubes

Composites of two hot melt adhesives based on co‐polyamides, one high viscosity (coPA_A), the other low viscosity (coPA_B), and multiwalled carbon nanotubes (MWCNTs) were prepared using twin‐screw extrusion via dilution of masterbatches. Examination of these composites across the length scales confirmed that the MWCNTs were uniformly dispersed and distributed in the polymer matrices, although some micron size agglomerations were also observed. A rheological percolation was determined from oscillatory rheology measurements at a mass fraction of MWCNTs below 0.01 for coPA_B and, between 0.01 and 0.02 for coPA_A. Significant increases in complex viscosity and storage modulus confirmed the “pseudo‐solid” like behavior of the composite materials. Electrical percolation, determined from dielectric spectroscopy was, found to be at 0.03 and 0.01 MWCNT mass fraction for coPA_A and coPA_B based composites, respectively. Addition of MWCNTs resulted in heterogeneous nucleation and altered the crystallization kinetics of both copolymers. Indirect evidence from contact angle measurements and surface energy calculations confirmed that MWCNT addition enhanced the adhesive properties of coPA_B to a level similar to coPA_A. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45999.     

Preparation and characterization of poly(trimethylene terephthalate)‐poly(ethylene oxide terephthalate) segmented copolymer/multiwalled carbon nanotubes composites by in situ polymerization

Poly(trimethylene terephthalate)‐poly(ethylene oxide terephthalate) block copolymer (PTG)/multiwalled carbon nanotubes (MWCNTs) composites were prepared via in situ polymerization. To improve the dispersion of MWCNTs in the PTG matrix, the poly(ethylene glycol)‐grafted multiwalled carbon nanotubes (MWCNT‐PEG) were produced by the “graft to” method. The transmission electron microscopy observation demonstrated that a homogeneous dispersion of MWCNT‐PEG was obtained. As a consequence, the percolation threshold for the rheology was around 0.5 wt% and the conductivity was ～1 wt%, respectively. Differential scanning calorimetry and polarized optical microscopy results confirmed that MWCNT‐PEG can act as an effective heterogeneous nucleating agent. Interestingly, the effects of MWCNT‐PEG on crystallization and melting of the poly(ethylene oxide terephthalate) blocks were more pronounced than on those of the PTT blocks. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Electrical conductivity and thermal properties of acrylonitrile‐butadiene‐styrene filled with multiwall carbon nanotubes

Composites of Acrylonitrile‐butadiene‐styrene (ABS) and multiwall carbon nanotubes (MWNTs) have been prepared via solution‐blending. The electrical conductivity of these composites is analyzed. The MWNT‐filled ABS shows percolation point of the electrical conductivity at low filler loadings (1–2 wt%). The micro‐structure of the composites is also analyzed by scanning electron microscopy showing that the nanotubes are dispersed quite homogeneously in the polymer‐matrix. The thermogravimetric analysis is used to study the thermal degradation of ABS/MWNTs composites in nitrogen. MWNTs tend to destabilize the ABS matrix in the 220–450°C degradation regions but improve the thermal stability in the 425–850°C regions. With further addition of MWNTs, the features of the destabilization in the 220–450°C degradation region did not change much but in the 425–850°C degradation process, the MWNTs reinforced stabilization and the quality of the char residue of amorphous carbon deposition was improved. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

The electrical properties and crystallization of stereocomplex poly(lactic acid) filled with carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) filled poly(l-lactic acid) (PLLA) and PLLA/poly(d-lactic acid) (PDLA) composites were prepared through a directly melt mixing process. A special crystalline structure of stereocomplex was formed by PLLA and PDLA, which was easily found when mixing two polymers with identical chemical composition but different steric structures. The electrical conductivities were greatly improved by the formation of stereocomplex compared to that of PLLA/MWCNT composites at same MWCNT content. The percolation threshold of the PLLA/PDLA/MWCNT composite at a PLLA/PDLA weight ratio of 50/50 was 0.35 wt%, while being 1.43 wt% of PLLA/MWCNT composites. The X-ray diffraction, non-isothermal and isothermal crystallization results showed that the formation of stereocomplex greatly increased the crystallinity of the composites, meanwhile MWCNTs acted as heterogeneous nucleating agent, which significantly accelerated the nucleation and spherulite growth. Therefore, the PLLA/PDLA/MWCNT composites have a very low percolation threshold due to the volume exclusion effect.     

Lignin‐based polyurethane doped with carbon nanotubes for sensor applications

Modified eucalyptus kraft lignin doped with multiwall carbon nanotubes (MWCNTs) was used as a macromonomer in step‐growth polymerization with tolylene 2,4‐diisocyanate terminated poly(propylene glycol) with the aim of producing a conductive copolymer for all‐solid‐state potentiometric chemical sensor applications. The crosslinked elastomeric polyurethane obtained was characterized by Fourier transform infrared attenuated total reflection spectroscopy, scanning electron microscopy, tunnelling electron microscopy and atomic force microscopy. Doping of lignin‐based polyurethane with MWCNTs produced a significant enhancement of its electrical conductivity without deterioration of thermal and viscoelastic properties. The polymer composite displayed a low percolation threshold at an MWCNT concentration of 0.18% (w/w), which was explained by the oriented distribution of MWCNTs along lignin clusters. All lignin‐based polyurethanes doped with MWCNTs at concentrations above the percolation threshold are suitable for sensor applications. Copyright © 2012 Society of Chemical Industry     

Mechanical,rheological, and electrical properties of multiwalled carbon nanotube reinforced ASA/Na‐ionomer blend

Varying amounts of multiwalled carbon nanotubes (MWCNTs) was melt‐extruded with the acrylonitrile‐styrene‐acrylate (ASA)/Na‐ionomer blend, and mechanical, rheological, and electrical properties were studied Optical micrographs show good dispersion level at low MWCNT content and network formation at higher nanotubes percentage. DC conductivity model data shows percolation threshold reached at 1% MWCNT content and after percolation, two‐dimensional network structure was formed. The “peak and valley” type surface topology of matrix may be responsible for low percolation threshold limit. The polymer/nanotubes interactions at low MWCNT content increased the mechanical strengths, which were reduced by the network structure and agglomerates of nanotubes at higher nanotubes content. The MWCNTs interacted differently with the architecturally complex polymer chains and controlled chain dynamics accordingly. The Carreau‐Yasuda model was found fit to viscosity data and the model parameters data suggest the zero shear viscosity is function of MWCNTs content but the infinite shear viscosity is independent of nanoparticles content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42516.     

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.     

Electrical and rheological properties of polyamide 6,6/γ-ray irradiated multi-walled carbon nanotube composites

Multi-walled carbon nanotubes (MWCNTs) were treated with γ-ray irradiation to show enhanced interaction with polyamide 6,6. X-ray photoelectron spectroscopy and Raman spectroscopy revealed that oxygen atoms were found on the surface of the MWCNTs, which can enhance the interaction with hydrophilic polymers such as polyamide 6,6. Both morphological investigation and electrical conductivity measurements have demonstrated better dispersion and electrical percolation with a smaller amount of MWCNTs when they were subjected γ-ray irradiation. The electrical percolation thresholds were reduced from 0.934 wt% to 0.401 wt% and 0.332 wt% when MWCNTs were irradiated with 10 and 30 kGy, respectively. Rheological data showed consistent behavior, exhibiting a positive effect of γ-ray treatment on MWCNTs. Allowing large volume treatment in a simple, solvent free process, the proposed γ-ray irradiation based method is potentially suitable for further commercialization.     

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