Reduction of percolation threshold through double percolation in melt‐blended polycarbonate/acrylonitrile butadiene styrene/multiwall carbon nanotubes elastomer nanocomposites

We demonstrate a method that involves melt blending of polycarbonate (PC) and melt‐blended acrylonitrile butadiene styrene (ABS) with multiwall carbon nanotubes (MWCNTs) to prepare electrically conducting PC/MWCNT nanocomposites at significantly low MWCNT loading. The partial solubility of ABS in PC led to a selective dispersion of the MWCNTs in the ABS phase after melt‐blending PC and ABS. Thus, a sudden rise in electrical conductivity (∼10⁸ orders of magnitude) of the nanocomposites was found at 0.328 vol% of MWCNT, which was explained in terms of double percolation phenomena. By optimizing the ratio of PC and the ABS–MWCNT mixture, an electrical conductivity of 5.58 × 10⁻⁵ and 7.23 × 10⁻³ S cm⁻¹ was achieved in the nanocomposites with MWCNT loading as low as 0.458 and 1.188 vol%, respectively. Transmission electron microscopy revealed a good dispersion and distribution of the MWCNTs in the ABS phase, leading to the formation of continuous MWCNT network structure throughout the matrix even at very low MWCNT loading. Storage modulus and thermal stability of the PC were also increased by the presence of a small amount of MWCNTs in the nanocomposites.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

A facile route to develop electrical conductivity with minimum possible multi‐wall carbon nanotube (MWCNT) loading in poly(methyl methacrylate)/MWCNT nanocomposites

Today, we stand at the threshold of exploring carbon nanotube (CNT) based conducting polymer nanocomposites as a new paradigm for the next generation multifunctional materials. However, irrespective of the reported methods of composite preparation, the use of CNTs in most polymer matrices to date has been limited by challenges in processing and insufficient dispersability of CNTs without chemical functionalization. Thus, development of an industrially feasible process for preparation of polymer/CNT conducting nanocomposites at very low CNT loading is essential prior to the commercialization of polymer/CNT nanocomposites. Here, we demonstrate a process technology that involves in situ bulk polymerization of methyl methacrylate monomer in the presence of multi‐wall carbon nanotubes (MWCNTs) and commercial poly(methyl methacrylate) (PMMA) beads, for the preparation of PMMA/MWCNT conducting nanocomposites with significantly lower (0.12 wt% MWCNT) percolation threshold than ever reported with unmodified commercial CNTs of similar qualities. Thus, a conductivity of 4.71 × 10^?5 and 2.04 × 10^?3 S cm^?1 was achieved in the PMMA/MWCNT nanocomposites through a homogeneous dispersion of 0.2 and 0.4 wt% CNT, respectively, selectively in the in situ polymerized PMMA region by using 70 wt% PMMA beads during the polymerization. At a constant CNT loading, the conductivity of the composites was increased with increasing weight percentage of PMMA beads, indicating the formation of a more continuous network structure of the CNTs in the PMMA matrix. Scanning and transmission electron microscopy studies revealed the dispersion of MWCNTs selectively in the in situ polymerized PMMA phase of the nanocomposites. Copyright © 2012 Society of Chemical Industry     

High electromagnetic interference shielding with high electrical conductivity through selective dispersion of multiwall carbon nanotube in poly (ε‐caprolactone)/MWCNT composites

This study presents the preparation of electrically conducting poly(ε‐caprolactone) (PCL)/multiwall carbon nanotube (MWCNT) composites with very low percolation threshold (p_c). The method involves solution blending of PCL and MWCNT in the presence of commercial PCL beads. The PCL beads were added into high viscous PCL/MWCNT mixture during evaporation of solvent. Here, the used commercial PCL polymer beads act as an ‘excluded volume’ in the solution blended PCL/MWCNT region. Thus, the effective concentration of the MWCNT dramatically increases in the solution blended region and a strong interconnected continuous conductive network path of CNT−CNT is assumed throughout the matrix phase with the addition of PCL bead which plays a crucial role to improve the electromagnetic interference shielding effectiveness (EMI SE) and electrical conductivity at very low MWCNT loading. Thus, high EMI SE value (∼23.8 dB) was achieved at low MWCNT loading (1.8 wt %) in the presence of 70 wt % PCL bead and the high electrical conductivity of ∼2.49×10⁻² S cm⁻¹ was achieved at very low MWCNT loading (∼0.15 wt %) with 70 wt % PCL bead content in the composites. The electrical conductivity gradually increased with increasing the PCL bead concentration, as well as, MWCNT loading in the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42161.     

Graphene nanoplate and multiwall carbon nanotube–embedded polycarbonate hybrid composites: High electromagnetic interference shielding with low percolation threshold

This study has reported the preparation of polycarbonate (PC)/graphene nanoplate (GNP)/multiwall carbon nanotube (MWCNT) hybrid composite by simple melt mixing method of PC with GNP and MWCNT at 330°C above the processing temperature of the PC (processing temperature is 280°C) followed by compression molding. Through optimizing the ratio of (GNP/MWCNT) in the composites, high electromagnetic interference shielding effectiveness (EMI SE) value (∼21.6 dB) was achieved at low (4 wt%) loading of (GNP/MWCNT) and electrical conductivity of ≈6.84 × 10⁻⁵ S.cm⁻¹ was achieved at 0.3 wt% (GNP/MWCNT) loading with low percolation threshold (≈0.072 wt%). The high temperature melt mixing of PC with nanofillers lowers the melt viscosity of the PC that has helped for better dispersion of the GNPs and MWCNTs in the PC matrix and plays a key factor for achieving high EMI shielding value and high electrical conductivity with low percolation threshold than ever reported in PC/MWCNT or PC/graphene composites. With this method, the formation of continuous conducting interconnected GNP‐CNT‐GNP or CNT‐GNP‐CNT network structure in the matrix polymer and strong π–π interaction between the electron rich phenyl rings and oxygen atom of PC chain, GNP, and MWCNT could be possible throughout the composites. POLYM. COMPOS., 37:2058–2069, 2016. © 2015 Society of Plastics Engineers     

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

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

Morphology and electrical properties of polymethylmethacrylate/poly(styrene‐co‐acrylonitrile)/multi‐walled carbon nanotube nanocomposites

Nanocomposites of blends of polymethylmethacrylate (PMMA) and poly(styrene‐co‐acrylonitrile) (SAN) with multi‐walled carbon nanotubes (MWCNTs) were prepared by melt mixing in a twin‐screw extruder. The dispersion state of MWCNTs in the matrix polymers was investigated using transmission electron microscopy. Interestingly enough, in most of the nanocomposites, the MWCNTs were observed to be mainly located at SAN domains, regardless of the SAN compositions in the PMMA/SAN blend and of the processing method. One possible reason for this morphology may be the π–π interactions between MWCNTs and the phenyl ring of SAN. The shift in G‐band peak observed in the Raman spectroscopy may be the indirect evidence proving these interactions. The percolation threshold for electrical conductivity of PMMA/SAN/MWCNT nanocomposites was observed to be around 1.5 wt %. Nanocomposites with PMMA‐rich composition showed higher electrical conductivity than SAN‐rich nanocomposites at a fixed MWCNT loading. The dielectric constant measurement also showed composition‐dependent behavior. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Low percolation threshold in polycarbonate/multiwalled carbon nanotubes nanocomposites through melt blending with poly(butylene terephthalate)

Here, we demonstrate an easy method for the preparation of highly electrically conductive polycarbonate (PC)/multiwalled carbon nanotubes (MWCNTs) nanocomposites in the presence of poly(butylene terephthalate) (PBT). In the presence of MWCNTs, PC and PBT formed a miscible blend, and the MWCNTs in the PC matrix were uniformly and homogeneously dispersed after the melt mixing of the PC and PBT–MWCNT mixture. Finally, when the proportion of the PC and PBT–MWCNT mixture in the blend/MWCNT nanocomposites was changed, an electrical conductivity of 6.87 × 10^?7 S/cm was obtained in the PC/PBT–MWCNT nanocomposites at an MWCNT loading as low as about 0.35 wt %. Transmission electron microscopy revealed a regular and homogeneous dispersion and distribution of the MWCNTs and formed a continuous conductive network pathway of MWCNTs throughout the matrix phase. The storage modulus and thermal stability of the PC were also enhanced by the presence of a small amount of MWCNTs in the nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrically conductive polycarbonate/ethylene‐propylene copolymer/multi‐walled carbon nanotubes nanocomposites with improved mechanical properties

In this article, the effect of Multi‐walled carbon nanotubes (MWCNTs) on the electrical conductivity and mechanical properties of polycarbonate (PC) toughened with cross‐linked ethylene‐propylene copolymer (EPC) was investigated. The solubility parameters of the PC and EPC were calculated using Hoy methods to clarify the miscibility of the polymer blends. It could be concluded that in the cooled state, the blends form a heterogeneous structure with two separate phases. The tensile, flexural, impact toughness properties of the PC/EPC blend and PC/EPC/MWCNT nanocomposites were carried out to illuminate the optimum concentration of polymer blends and MWCNTs. The 335% increment for the impact strength results appeared with combination of 10% EPC in the PC matrix. The flexural modulus and strength of PC/EPC blend increased by 75.1% and 59.1%, respectively. The Nielsen model was performed to fit the best curve of theoretical simulation to experimental results for elastomeric dispersed in the plastic matrix. Halpin‐Tsai model was applied to estimate the stiffness of nanocomposites blends with different volume fraction and aspect ratio of MWCNTs in the PC/EPC blends. Finally, in the presence of MWCNTs, all nanocomposite samples were semi‐conducting and the percolation threshold of the PC/EPC (10%) blends was between 0.5% and 1.0% MWCNTs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44661.     

Matrix tacticity controlled tuning of microstructure,constitutive behavior and rheological percolation effect of melt‐mixed amino‐functionalized MWCNT/PP nanocomposites

Amino‐functionalized multi walled nanotube (MWCNT‐NH₂) filled isotactic PP and isotactic‐syndiotactic (70:30) mixed PP based melt‐mixed nanocomposites have been comparatively evaluated with regard to morphological, rheological and thermo‐mechanical properties. The ratio of mean free space lengths (L_f) to infiltrated mean free space lengths (L_inf) between nanotubes in isotactic‐syndiotactic (70:30) blended matrix based nanocomposites increased relatively indicating a dispersed‐morphology. The rheological percolation threshold increased up to a higher extent of MWCNT‐NH₂ loading (from ø_c ～ 2.3 × 10^?4 in isotactic to ø_c ～ 11 × 10^?4 in iso‐syndio blend) accompanied with the formation of a mechanically responsive network structure. van‐GurpPalmen plot showed a transition in the rheological response as a consequence of network morphology getting shifted to higher concentration of MWCNT‐NH₂ in the isotactic‐syndiotactic mixed PP based nanocomposites than in the isotactic based one. Constitutive modeling of complex viscosity response of the nanocomposites led to functional correlation between the percolation and relaxation dynamics of polymer chains. POLYM. ENG. SCI., 58:1115–1126, 2018. © 2017 Society of Plastics Engineers     

High‐performance electromagnetic interference shielding material based on an effective mixing protocol

A facile and economic method is developed for the fabrication of new lightweight materials with high electromagnetic interference (EMI) shielding performance, good mechanical properties and low electrical percolation threshold through melt mixing. Electrical properties, DC conductivity, EMI shielding performance and mechanical properties of poly(trimethylene terephthalate) (PTT)/multiwalled carbon nanotube (MWCNT) nanocomposites with varying filler loading of MWCNTs were investigated. High‐resolution transmission electron microscopy was used to determine the distribution of MWCNTs in the PTT matrix. The newly developed nanocomposites show excellent dielectric and EMI shielding properties. Theoretical electrical percolation threshold was achieved at 0.21 wt% loading of MWCNTs, due to the high aspect ratio and the three‐dimensional network formation of MWCNTs. Experimental DC conductivity values were compared with those of theoretical models such as the Voet, Bueche and Scarisbrick models, which showed good agreement. The PTT/3% MWCNT composite showed an EMI shielding value of ～38 dB (99.99% attenuation) with a sample thickness of 2 mm. Power balance was used to determine the actual contribution of reflection, absorption and transmission loss to the total EMI shielding value. The nanocomposites showed good tensile and impact properties and the composite with 2% MWCNTs exhibited an improvement in tensile strength of as much as 96%. © 2018 Society of Chemical Industry     

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     

Electrical properties of FeII‐terpyridine‐Modified cellulose nanocrystals and polycaprolactone/FeII‐CTP nanocomposites

Supramolecular crosslinked Fe^II‐terpyridine cellulose nanocrystals (Fe‐CTP) were prepared by surface modification of cellulose nanocrystals with 4′‐chloro‐2,2′:6′,2″‐terpyridine and subsequent reaction with Fe(II)SO₄. The prepared complex was characterized using transmission electron microscopy (TEM), ultraviolet spectroscopy (UV), thermogravimetric analysis (TGA), and measuring its electrical properties at temperatures from 25 to 70°C. Use of Fe‐CTP at loadings from 1% to 10% (wt. ratio) in nanocomposites with polycaprolactone polymer was investigated; the nanocomposites were characterized regarding their electrical properties, which studied using broadband AC‐relaxation spectroscopy in the frequency range between 0.1 Hz and 1 MHz. The results were compared to that of PCL nanocomposites containing multiwalled carbon nanotubes (CNT). Variation in real and imaginary parts of permittivity has been explained on the basis of interfacial polarization of fillers in the polymer medium. The percolation limit of the conductive CNT and Fe‐CTP as studied by ac conductivity measurements has also been reported. Fe‐CTP showed conductivity values in the range of semiconductors. PCL/Fe‐CTP nanocomposites showed conductivity values from 1.98 × 10⁻¹¹ to 3.76 × 10⁻⁶ while PCL/CNT nanocomposites showed conductivity values from 1.4 × 10⁻¹⁰ to 3.67 × 10⁻⁴ S/m for 1–10 wt% CNT content. POLYM. COMPOS., 37:2734–2743, 2016. © 2015 Society of Plastics Engineers     

Polyethylene multiwalled carbon nanotube composites

Polyethylene (PE) multiwalled carbon nanotubes (MWCNTs) with weight fractions ranging from 0.1 to 10 wt% were prepared by melt blending using a mini-twin screw extruder. The morphology and degree of dispersion of the MWCNTs in the PE matrix at different length scales was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and wide-angle X-ray diffraction (WAXD). Both individual and agglomerations of MWCNTs were evident. An up-shift of 17 cm⁻¹ for the G band and the evolution of a shoulder to this peak were obtained in the Raman spectra of the nanocomposites, probably due to compressive forces exerted on the MWCNTs by PE chains and indicating intercalation of PE into the MWCNT bundles. The electrical conductivity and linear viscoelastic behaviour of these nanocomposites were investigated. A percolation threshold of about 7.5 wt% was obtained and the electrical conductivity of PE was increased significantly, by 16 orders of magnitude, from 10⁻²⁰ to 10⁻⁴ S/cm. The storage modulus (G′) versus frequency curves approached a plateau above the percolation threshold with the formation of an interconnected nanotube structure, indicative of ‘pseudo-solid-like’ behaviour. The ultimate tensile strength and elongation at break of the nanocomposites decreased with addition of MWCNTs. The diminution of mechanical properties of the nanocomposites, though concomitant with a significant increase in electrical conductivity, implies the mechanism for mechanical reinforcement for PE/MWCNT composites is filler-matrix interfacial interactions and not filler percolation. The temperature of crystallisation (T_c) and fraction of PE that was crystalline (F_c) were modified by incorporating MWCNTs. The thermal decomposition temperature of PE was enhanced by 20 K on addition of 10 wt% MWCNT.     

Electrical conductivity behavior of epoxy matrix nanocomposites with simultaneous dispersion of carbon nanotubes and clays

In this work, nanocomposites with simultaneous dispersion of multiwalled carbon nanotubes (MWCNT) and montmorillonite clays in an epoxy matrix were prepared by in situ polymerization. A high energy sonication was employed as the dispersion method, without the aid of solvents in the process. The simultaneous dispersion of clays with carbon nanotubes (CNT) in different polymeric matrices has shown a synergic potential of increasing mechanical properties and electrical conductivity. Two different montmorillonite clays were used: a natural (MMT‐Na⁺) and an organoclay (MMT‐30B). The nanocomposites had their electrical conductivity (σ) and dielectric constant (ε_r) measured by impedance spectroscopy. The sharp increase in electrical conductivity was found between 0.10 and 0.25 wt% of the MWCNTs. Transmission electron microscopy (TEM) of the samples showed a lower tendency of MWCNT segregation on the MMT‐30B clay surface, which is connected to intercalation/exfoliation in the matrix, that generates less free volume available for MWCNTs in the epoxy matrix. Data from electrical measurement showed that simultaneously adding organoclay reduces the electrical conduction in the nanocomposite. Moreover, conductivity and permittivity dispersion in low frequency suggest agglomeration of nanotubes surrounding the natural clay (MMT‐Na⁺) particles, which is confirmed by TEM. POLYM. COMPOS., 37:1603–1611, 2016. © 2014 Society of Plastics Engineers     

Electrical and mechanical properties of acrylonitrile‐butadiene‐styrene/multiwall carbon nanotube nanocomposites prepared by melt‐blending

The electrical properties in polymer/carbon nanotube (CNT) nanocomposites are governed not only by the degree of dispersion but also to a greater extent on the aspect ratio of the CNTs in the final composites. Melt‐mixing of polymer and CNTs at high shear rate usually breaks the CNTS that lowers the aspect ratio of the nanotubes. Thus, homogeneous dispersion of CNTs while retaining the aspect ratio is a major challenge in melt‐mixing. Here, we demonstrate a novel method that involves melt‐blending of acrylonitrile‐butadiene‐styrene (ABS) and in situ polymerized polystyrene (PS)/multiwalled CNT (MWCNT) nanocomposites, to prepare electrically conducting ABS/MWCNT nanocomposites with very low CNT loading than reported. The rationale behind choosing PS/MWCNT as blending component was that ABS is reported to form miscible blend with the PS. Thus, (80/20 w/w) ABS/(PS/MWCNT) nanocomposites obtained by melt‐blending showed electrical conductivity value ≈1.27 × 10^?6 S cm^?1 at MWCNT loading close to 0.64 wt %, which is quite lower than previously reported value for ABS/MWCNT system prepared via solution blending. Scanning electron microscopy and differential scanning calorimetry analysis indicated the formation of homogenous and miscible blend of ABS and PS. The high temperature (100°C) storage modulus of ABS (1298 MPa) in the nanocomposites was increased to 1696 MPa in presence of 0.64 wt % of the MWCNT. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

The effect of multiwalled carbon nanotube dimensions on the morphology,mechanical, and electrical properties of melt mixed polypropylene‐based composites

The effect of multiwalled carbon nanotube (MWCNT) dimensions and surface modification on the morphology, mechanical reinforcement, and electrical properties of PP‐based composites, prepared by melt mixing, has been studied. The MWCNTs of small (d < 10 nm) and large (d = 40–60 nm) diameters with various intrinsic aspect ratios (L/d) have been used as filler. Transmission electron microscopy and very cold neutrons (VCN) scattering showed that both as‐received and surface modified small diameter MWCNT(1)s exhibit a strong tendency to bundle or cluster together in melt compared to both long MWCNT(3)s and short MWCNT(2)s large diameter nanotubes. The fractions of isolated nanotubes are higher and the mass‐fractal dimensions are lower for thick MWCNT‐based nanocomposites. The nanotubes of all types are heterogeneous nucleation sites for PP crystallization. The tensile and DMA testing results revealed that both long thick MWCNT(3)s with L/d ≈ 300 and thin MWCNT(1)s with highest intrinsic L/d > 1000 exhibit similar reinforcing effects, because drastically decreasing the effective aspect ratio (L/d)_eff of the thin flexibly nanotubes within polymer matrix. The nanocomposites based on the long large diameter MWCNT(3)s demonstrated the lowest percolation threshold equal to 1.5 vol % loading, highest dielectric and electromagnetic waves shielding properties. It was concluded that the choice of optimal diameter and length of MWCNTs is right approach to the improvement in the dispersion state and straightness of multiwelled carbon nanotubes in polymer melt as well as to enhancement of their efficiency as reinforcing and conductive nanosized filler. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Microwave‐assisted synthesis and characterization of polyimide/functionalized MWCNT nanocomposites containing quinolyl moiety

Polyimide‐MWCNT nanocomposites were prepared by the reaction of a heterocyclic diamine monomer of bis(4‐amino‐3,5‐dimethylphenyl)‐2‐chloro‐3‐quinolylmethane (BACQM), pyromellitic dianhydride (PMDA) with unmodified MWCNT (MWCNT), acid‐functionalized MWCNT (acid‐MWCNT) or amine‐functionalized MWCNT (amine‐MWCNT) using microwave irradiation as well as by the conventional method. The structure of the monomer was confirmed by FTIR, ¹H‐NMR, and ¹³C‐NMR spectral techniques. The glass transition temperature (T_g) of the MWCNTs/polyimide nanocomposite was found to be higher than that of the unfilled polyimide system. The T_g's of both systems were higher when prepared with the microwave method than the conventional synthesis. The T_g's of the nanocomposites using acid and amine functionalized MWCNTs are greater than 300°C, in both methods. This is attributed to the presence of hydrogen bond and strong covalent bond in both the acid‐MWCNT/polyimide and amine‐MWCNT/polyimide systems. The morphological studies of the nanocomposites synthesized using microwave irradiation show that a distinct MWCNT nanofibrillar network is formed in the matrix when MWCNT or acid‐MWCNT is used. A homogeneous morphology, without distinct nanotube domains is seen when the amine‐MWCNT is covalently linked to the polymer. POLYM. COMPOS., 37:2417–2424, 2016. © 2015 Society of Plastics Engineers     

Improving the electrical conductivity of ethylene 1‐octene copolymer/cyclic olefin copolymer immiscible blends by interfacial localization of MWCNTs

The localization of multiwall carbon nanotubes (MWCNTs) in the immiscible blends of ethylene–1‐octene copolymer (EOC) and cyclic olefin copolymer (COC) with the sea–island morphology and electrical conductivity of resulting nanocomposites were investigated. Depending on the feeding orders, as the MWCNTs were located in the COC droplet, the electrical conductivity was obtained as high as 5.71 × 10^?7 S/cm, while the MWCNTs were located in EOC/COC interface, the electrical conductivity increased significantly up to 1.72 × 10^?2 S/cm. The improved electrical conductivity in EOE/COC/MWCNTs nanocomposite is attributed to the interfacial localization of MWCNTs which is resulted from thermodynamic affinity of MWCNTs to COC, as well as an interconnected structure via deformed and swelled COC droplets. Thermodynamic affinity of MWCNTs to COC and established interconnected structure are confirmed by rheological characterization, microscopic observations, dynamic mechanical analysis, and electrical conductivity measurements. Therefore, as a result of selective localization of MWCNTs and well‐designed phase morphology, lower rheological and especially electrical percolation thresholds could be obtained in the ternary nanocomposites compared to the binary systems. POLYM. ENG. SCI., 59:447–456, 2019. © 2018 Society of Plastics Engineers     

Effects of filler geometry on internal structure and physical properties of polycarbonate composites prepared with various carbon fillers

BACKGROUND: The effects of filler geometry are important for understanding the internal structure and physical properties of polymer composites. To investigate the effects of filler geometry on electrical conductivity as well as morphological and rheological properties, three types of polycarbonate (PC) composites were prepared by melt compounding with a twin‐screw extruder. RESULTS: The electrical conductivity of PC/carbon black (CB) and PC/graphite (carbon) nanofibre (CNF) composites did not show a percolation threshold through the entire filler loading ranges. However, PC‐blend‐carbon nanotube (CNT) composites showed a percolation electrical threshold for a filler loading of 1.0 to 3.0 wt% and their maximum electrical conductivity approached 10^?3 S m^?1. PC‐blend‐CB and PC‐blend‐CNF composites showed Newtonian behaviour like pure PC matrix, but PC‐blend‐CNT composites showed yield stress as well as increased storage modulus and strong shear thinning behaviour at low angular frequency and shear rate due to strong interactions generated between CNT–CNT particles as well as PC molecules and CNT particles on the nanometre scale. CONCLUSIONS: The electrical conductivity of the PC composites with different carbon constituents was well explained by the continuous network structure formed between filler particles. The network structure was confirmed by the good dispersion of fillers as well as by the yield stress and solid‐like behaviour observed in steady and dynamic shear flows. Copyright © 2009 Society of Chemical Industry