Localization Of Multi-walled Carbon Nanotubes Research Articles

Carbon nanotube manipulates crystallization kinetics and viscoelastic behavior of PP/EBC blends

AbstractPolypropylene (PP) offers numerous benefits to industrial applications due to its excellent processability and cost‐effectiveness. However, the widespread utilization of this commodity thermoplastic is constrained by its inherently low‐impact resistance. Herein, we suggest a ternary system with the addition of ethylene‐butene copolymer (EBC) and multiwalled carbon nanotubes (MWCNTs) to improve the overall performance of PP. We unveil the role of MWCNTs on the crystalline behavior of the PP/EBC blends when various ratios are considered. The calculated half‐time crystallization from the Avrami equation indicates that 1.5 wt% MWCNTs accelerate the crystallization of the PP/EBC blend nearly threefold. The formation of a semisolid microstructure is also reported using the rheological measurements. An upturn in complex viscosity, along with a frequency‐independent storage modulus, indicates strong interactions between MWCNTs and polymer chains. We confirm such robust interactions by employing temperature ramp sweep on the prepared nanocomposites as the decomposition temperature of the materials shifts to higher values. The dynamic mechanical analysis further interprets the role of MWCNTs as compatibilizers by bridging the gap between the glassy temperature of PP and EBC components.Highlights Theoretical prediction of the MWCNTs localization in the PP/EBC blends. Depicting the solid‐like behavior and viscosity upturn of PP/EBC/MWCNTs. Decelerating polymer chain relaxation led by nucleation role of MWCNTs. Formation of larger and more imperfect crystals upon the addition of MWCNTs. Faster crystallization kinetics in the PP/EBC/MWCNTs nanocomposites.

Electrically conductive nanocomposites based on poly(lactic acid)/flexible copolyester blends with multiwalled carbon nanotubes

AbstractNanocomposites of poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate) (PBAT) blends with multiwalled carbon nanotubes (MWCNTs) were prepared and their morphology, as well as electrical, mechanical, and thermal properties were investigated. The motivation of this work is to prepare electrically conductive and environmentally benign polymer nanocomposites using biodegradable PLA/PBAT blends. The composites were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning and transmission electron microscopy, tensile and microindentation tests, and thermogravimetric analyses (TGA). Volume resistivity and resistance to tensile deformation were measured for electrical characterization. The nanocomposites films were integrated into an electrical circuit to confirm their electrical conductivity. The FTIR spectra revealed the physical mixing between the polymer matrix and the filler. TEM micrographs suggested selective localization of MWCNTs in the PBAT phase with partial agglomeration forming a co‐continuous morphology. TGA and derivative thermogravimetric curves suggested the overall decreasing thermal stability of composites than pure polymer blends regardless of the effects on individual blend components. A relatively low electrical percolation threshold (around 1 wt% of the fillers) compared to the literature works was achieved. Increasing electrical resistance of nanocomposites upon tensile deformation suggested their possibility of piezoresistive properties. Furthermore, the overall mechanical performance (i.e., elastic modulus, tensile strength, and hardness) of the materials was found to improve with increasing filler content.

Migration induced localization of multiwalled carbon nanotubes in PP phase of PP/ABS blend and their hybrid composites: Influence on mechanical and thermal properties

Carbon black (CB) and multiwalled carbon nanotubes (MWNTs) reinforced 80/20 (wt/wt) polypropylene (PP)/acrylonitrile butadiene styrene (ABS) blends and its composites in presence of dual compatibilizer are processed using twin screw extruder followed by injection moulding. The two-step processing is adopted to disperse the MWNTs and CB in 80/20 (wt/wt) PP/ ABS blends in presence of dual compatibilizer. Initially, MWNTs are dispersed with ABS using melt-mixing followed by addition in PP matrix in presence of CB and dual compatibilizer using melt-mixing. A solution experiments is performed to selectively etch the PP and ABS phase respectively show the migration of MWNTs in the PP phase; and CB is localized in the PP phase. Scanning electron microscope (SEM) observation revel the formation of matrix-droplet morphology for MWNTs and CB in 80/20 (wt/wt) PP/ ABS blends and its composites in presence of dual compatibilizer. The average droplet diameter (Dd) measured using SEM images shows decrease in Dd values with the incorporation of MWNTs and CB in 80/20 (wt/wt) PP/ ABS blends and its composites in presence of dual compatibilizer along with calculated interparticle distance (ID) as compared to pure blend. Differential scanning calorimetry (DSC) studies shows the percent crystallinity (Xc) and lamellae thickness of MWNTs and CB filled 80/20 (wt/wt) PP/ ABS blends and its composites in presence of dual compatibilizer increases as compared to pure blend. The tensile properties increases significantly for MWNTs and CB filled 80/20 (wt/wt) PP/ABS blends and its hybrid composites in presence of dual compatibilizer due to the refined morphology and increase in crystallinity. In addition, the thermal stability is enhanced significantly for the selectively localized MWNTs and CB in PP phase of 80/20 (wt/wt) PP/ABS blends and its composites in the presence of dual compatibilizer as compared to pure blend established using thermogravimetric analysis (TGA). The composition of 2.5 wt% of CB filled 80/20 (wt/wt) PP/ABS blends and its composites in presence of dual compatibilizer and MWNTs is the optimized concentration to achieve the highest enhancement in tensile properties, crystallinity, morphology refinement and thermal stability.

The Localization Behavior of Different CNTs in PC/SAN Blends Containing a Reactive Component.

Co-continuous blend systems of polycarbonate (PC), poly(styrene-co-acrylonitrile) (SAN), commercial non-functionalized multi-walled carbon nanotubes (MWCNTs) or various types of commercial and laboratory functionalized single-walled carbon nanotubes (SWCNTs), and a reactive component (RC, N-phenylmaleimide styrene maleic anhydride copolymer) were melt compounded in one step in a microcompounder. The blend system is immiscible, while the RC is miscible with SAN and contains maleic anhydride groups that have the potential to reactively couple with functional groups on the surface of the nanotubes. The influence of the RC on the localization of MWCNTs and SWCNTs (0.5 wt.%) was investigated by transmission electron microscopy (TEM) and energy-filtered TEM. In PC/SAN blends without RC, MWCNTs are localized in the PC component. In contrast, in PC/SAN-RC, the MWCNTs localize in the SAN-RC component, depending on the RC concentration. By adjusting the MWCNT/RC ratio, the localization of the MWCNTs can be tuned. The SWCNTs behave differently compared to the MWCNTs in PC/SAN-RC blends and their localization occurs either only in the PC or in both blend components, depending on the type of the SWCNTs. CNT defect concentration and surface functionalities seem to be responsible for the localization differences.

Morphology Evolution, Molecular Simulation, Electrical Properties, and Rheology of Carbon Nanotube/Polypropylene/Polystyrene Blend Nanocomposites: Effect of Molecular Interaction between Styrene-Butadiene Block Copolymer and Carbon Nanotube.

This work studied the impact of three types of styrene-butadiene (SB and SBS) block copolymers on the morphology, electrical, and rheological properties of immiscible blends of polypropylene:polystyrene (PP:PS)/multi-walled carbon nanotubes (MWCNT) with a fixed blend ratio of 70:30 vol.%. The addition of block copolymers to PP:PS/MWCNT blend nanocomposites produced a decrease in the droplet size. MWCNTs, known to induce co-continuity in PP:PS blends, did not interfere with the copolymer migration to the interface and, thus, there was morphology refinement upon addition of the copolymers. Interestingly, the addition of the block copolymers decreased the electrical resistivity of the PP:PS/1.0 vol.% MWCNT system by 5 orders of magnitude (i.e., increase in electrical conductivity). This improvement was attributed to PS Droplets-PP-Copolymer-Micelle assemblies, which accumulated MWCNTs, and formed an integrated network for electrical conduction. Molecular simulation and solubility parameters were used to predict the MWCNT localization in the immiscible blend. The simulation results showed that diblock copolymers favorably interact with the nanotubes in comparison to the triblock copolymer, PP, and PS. However, the interaction between the copolymers and PP or PS is stronger than the interaction of the copolymers and MWCNTs. Hence, the addition of copolymer also changed the localization of MWCNT from PS to PS–PP–Micelles–Interface, as observed by TEM images. In addition, in the last step of this work, we investigated the effect of the addition of copolymers on inter- and intra-cycle viscoelastic behavior of the MWCNT incorporated polymer blends. It was found that addition of the copolymers not only affects the linear viscoelasticity (e.g., increase in the value of the storage modulus) but also dramatically impacts the nonlinear viscoelastic behavior under large deformations (e.g., higher distortion of Lissajous–Bowditch plots).]

Reactive melt processing of poly (L-lactide) in the presence of thermoplastic polyurethane and carboxylated carbon nanotubes

In this study, two types of polymeric nanocomposite blends based on poly(l-lactide) (PLLA) and a thermoplastic polyurethane were prepared by reactive and non-reactive melt mixing. Multiwalled carbon nanotubes (MWCNTs) participated in reactive melt mixing and changed in both cases the morphology of blends. Melt rheology was used to study the influence of reactive melt mixing and localization of MWCNTs in terms of melt viscoelastic properties and relaxation time spectrum. Two relaxation times were observed for both types of blends due to reptation and stress release mechanism, although blends prepared by reactive melt mixing showed another relaxation mechanism associated with the generated interphase. Solid-state viscoelasticity determined by dynamical mechanical analysis showed significant influences of both MWCNTs and reactive melt mixing on storage modulus of the blends. Thermogravimetric analysis showed several degradation steps for polymer blends that contrast with the single step determined for both pure PLLA and PLLA nanocomposites.

Excellent electromagnetic shield derived from MWCNT reinforced NR/PP blend nanocomposites with tailored microstructural properties

Blends of polypropylene (PP) and natural rubber (NR) with different loadings (1,3,5 &7 wt%) of multiwalled carbon nanotubes (MWCNTs) were prepared by melt blending process to design a nanocomposite with tunable electromagnetic interference (EMI) shielding performance. Scanning electron microscopy (SEM) studies show that the addition of MWCNTs changes the droplet morphology into quasi co-continuous morphology for PP/NR 80/20 (wt/wt) blend system. However there is a refinement in the co-continuous morphology of PP/NR (50/50) by the addition of MWCNTs. The effects of the blend morphology and selective localization of MWCNTs on the dielectric, electrical properties and EMI shielding performance were systematically investigated. The largely enriched dielectric performance originates from the interfacial polarization of MWCNTs within the polymer. It is understood that the shielding performance significantly enhanced due to the selective localization of MWCNTs in the NR phase that provided high conductivity and heterogeneous dielectric media with multiple interfaces. The blend nanocomposites show a shielding effectiveness of ca.29 dB at 3 GHz for 7 wt% of MWCNT loading.

Electrical self-sensing of strain and damage of thermoplastic hierarchical composites subjected to monotonic and cyclic tensile loading

Electrical monitoring of strain and damage in multiscale hierarchical composites comprising unidirectional aramid fibers modified by multiwall carbon nanotubes and polypropylene as matrix is investigated. The key factor for electrical self-sensing in these thermoplastic composites is the formation of a multiwall carbon nanotube network, which is achieved by using two material architectures. In the first architecture, the multiwall carbon nanotubes are dispersed within the polypropylene matrix, while aramid fibers remain unmodified. The second architecture uses also multiwall carbon nanotube-modified polypropylene matrix, but the aramid fibers are also modified by depositing multiwall carbon nanotubes. Under tensile loading, the electrical response is nonlinear with strain ( ε), and the piezoresistive sensitivity was quantified by gage factors corresponding to low ( ε < 0.25%) and high ( ε > 0.3%) strain regimes. Such gage factors were 4.83 (for ε < 0.25%) and 13.2 (for ε > 0.3%) for composites containing multiwall carbon nanotubes only in the polypropylene matrix. The composites containing multiwall carbon nanotubes in the matrix and fibers presented higher piezoresistive sensitivity, with average gage factors of 9.24 ( ε < 0.25%) and 14.0 ( ε > 0.3%). The higher sensitivity to strain and damage for a specific material architecture was also evident during cyclic and constant strain loading programs and is attributed to the preferential localization of multiwall carbon nanotubes in the hierarchical composite.

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

Selective Localization of MWCNT in Poly (Trimethylene Terephthalate)/Poly Ethylene Blends: Theoretical Analysis, Morphology, and Mechanical Properties

Theoretical analysis is carried out to predict the nature of selective localization of multi‐walled carbon nanotubes (MWCNTs) in poly(trimethylene terephthalate/polyethylene (PTT/PE) blends. In agreement with theoretical data experimental results clearly indicate that MWCNT prefers to get associated with PTT phase than with PE. Molecular interactions responsible for such selective localization of MWCNT to PTT component can be attributed to mutual and collective π–π interactions possible between the aromatic moieties present in PTT and MWCNT. In addition, the reinforcing effect of MWCNT in the PTT/PE system was determined using tensile analysis and the morphological features of blends and blend nanocomposites are studied using scanning electron microscope (SEM). Compared to the PTT/PE blend system MWCNT incorporated blend nanocomposites show better mechanical properties. The elongation at break of the blend system is seen to rise with increasing amount of PE content. Among various blend nanocomposites, we have investigated the nanocomposites with higher PTT content show higher tensile strength and Young's modulus. The blend nanocomposite with 90/10/1 composition shows 12% increment in Young's modulus and as much as 80% increment in tensile strength compared to 90/10 blend system which signifies the role MWCNT plays in the blend system.

Manipulation of thermo-mechanical, morphological and electrical properties of PP/PET polymer blend using MWCNT as nano compatibilizer: A comprehensive study of hybrid nanocomposites

In this paper, the electrical resistivity, morphology and dynamic mechanical properties of in-situ reinforced microfibrillar composites (MFNC-C) based on polypropylene reinforced with polyethylene terephthalate (PET)-multiwalled carbon nanotubes (MWCNT) fibres have been investigated. Influence of various factors such as the effect of the morphology, CNT composition and the nano compatibilizer effect of CNT on the in-situ reinforced microfibrillar nanocomposites, have been analysed. The dynamic mechanical analysis (DMA) showed that the storage modulus microfibrillar composites are precisely related to the fibrils morphology and composition of CNT. It is found that the presence of CNTs on the fibrils surface has improved the storage modulus as well as normalized storage modulus. The results of four probe analysis showed that by increasing CNTs content, the resistivity remarkably decreased with respect to the morphology of the of nanocomposites. Also, scanning electron microscopy images likewise revealed that the preferential localization of MWCNT on to the PET microfibrils enhanced the compatibility between PET fibrils and PP matrix. Hence, The in –situ formation of fibrillar morphology along with MWCNTs is highly useful in terms of mechanical and electrical performance of the resultant nanocomposites. We assume that the optimized results of this work may open an alternative path for the production of commercially important polymer nanocomposite based on the incompatible immiscible blends.

Double percolated MWCNTs loaded PC/SAN nanocomposites as an absorbing electromagnetic shield

This research reports on the preparation and characterization of absorbing electromagnetic (EM) nanocomposite shields based on polycarbonate (PC)/ polystyrene-co-acrylonitrile (SAN) 60/40 blend containing low contents of multi-walled carbon nanotubes (MWCNTs). The nanocomposites were prepared using a melt-compounding process at a temperature of 260 °C. The melt linear viscoelastic results together with scanning electron microscopy (SEM) micrographs implied a co-continuous type morphology, which remained unchanged by the addition of nanoparticles (NPs). The results of dynamic mechanical thermal analysis (DMTA) suggested a preferential localization of MWCNTs in the PC phase, evidenced by the transmission electron microscopy (TEM) micrograph. The direct current (DC) electrical conductivity results showed a low electrical double percolation threshold around 0.32 wt% of MWCNTs. A maximum DC electrical conductivity of 0.0834 S/cm was obtained for 1 wt% MWCNTs-filled nanocomposite. Applying EM theory based on the measured dielectric permittivity and magnetic permeability [over the X-band frequency (8.2–12.4 GHz)] suggested a maximum shielding efficiency of 25–29 dB for the 1 wt% MWCNTs-filled nanocomposite with a thickness of 10 mm. In addition, the contribution of the absorption mechanism below and above the electrical percolation threshold was studied. It was revealed that the shielding performance of the nanocomposites is mainly due to noticeable absorption of EM waves above the percolation threshold, which was attributed to the induced conductance loss as a result of the formation of conductive paths.

The adverse vascular effects of multi-walled carbon nanotubes (MWCNTs) to human vein endothelial cells (HUVECs) in vitro: role of length of MWCNTs

BackgroundIncreasing evidences indicate that exposure to multi-walled carbon nanotubes (MWCNTs) could induce adverse vascular effects, but the role of length of MWCNTs in determining the toxic effects is less studied. This study investigated the adverse effects of two well-characterized MWCNTs to human umbilical vein endothelial cells (HUVECs).MethodsThe internalization and localization of MWCNTs in HUVECs were examined by using transmission electron microscopy (TEM). The cytotoxicity of MWCNTs to HUVECs was assessed by water soluble tetrazolium-8 (WST-8), lactate dehydrogenase (LDH) and neutral red uptake assays. Oxidative stress was indicated by the measurement of intracellular glutathione (GSH) and reactive oxygen species (ROS). ELISA was used to determine the release of inflammatory cytokines. THP-1 monocyte adhesion to HUVECs was also measured. To indicate the activation of endoplasmic reticulum (ER) stress, the expression of ddit3 and xbp-1s was measured by RT-PCR, and BiP protein level was measured by Western blot.ResultsTransmission electron microscopy observation indicates the internalization of MWCNTs into HUVECs, with a localization in nuclei and mitochondria. The longer MWCNTs induced a higher level of cytotoxicity to HUVECs compared with the shorter ones. Neither of MWCNTs significantly promoted intracellular ROS, but the longer MWCNTs caused a higher depletion of GSH. Exposure to both types of MWCNTs significantly promoted THP-1 adhesion to HUVECs, accompanying with a significant increase of release of interleukin-6 (IL-6) but not tumor necrosis factor α (TNFα), soluble ICAM-1 (sICAM-1) or soluble VCAM-1 (sVCAM-1). Moreover, THP-1 adhesion and release of IL-6 and sVCAM-1 induced by the longer MWCNTs were significantly higher compared with the responses induced by the shorter ones. The biomarker of ER stress, ddit3 expression, but not xbp-1s expression or BiP protein level, was significantly induced by the exposure of longer MWCNTs.ConclusionsCombined, these results indicated length dependent toxic effects of MWCNTs to HUVECs in vitro, which might be associated with oxidative stress and activation of ER stress.

Vapor sensing performance as a diagnosis probe to estimate the distribution of multi-walled carbon nanotubes in poly(lactic acid)/polypropylene conductive composites

Abstract Multi-walled carbon nanotubes (MWCNT)/poly (lactic acid) (PLA)/polypropylene (PP) with different polymer blend ratios were fabricated by melt processing method. When fixed the MWCNT content at 1.0 wt.%, A6P4 (PLA/PP 60w/40w) showed the lowest resistivity, which is attributed to the formation of a co-continuous structure. According to the thermodynamics prediction, MWCNT is estimated to be selectively distributed in PLA phase. To further investigate the MWCNT localization behavior in polymer blend, a two-step compounding sequence approach was utilized to fabricate Pre-PLA ( i.e. , MWCNT were firstly mixed with PLA) and Pre-PP composites. Morphology observation and rheology tests were then carried out to demonstrate the MWCNT distribution in the composites. Vapor sensing behaviors of CPCs towards organic vapors with different polarity were investigated in detail. CPCs with higher PLA content showed a higher responsivity to dichloromethane, a ‘good solvent’ to PLA. CPCs containing higher PP content exhibited a higher responsivity towards xylene due to the strong interaction between PP and the xylene vapor. While for cyclohexane, a ‘poor solvent’ to PLA and PP, all the CPCs demonstrate a low responsivity. Interestingly, the vapor sensing feature can be used to testify the MWCNT localization in the polymer blend as a diagnosis probe.

On the phase affinity of multi-walled carbon nanotubes in PMMA:LDPE immiscible polymer blends

The localization of multi-walled carbon nanotubes (MWCNTs) in PMMA/LDPE blends was studied. Theoretical predictions suggested their preferential localization in the PMMA. Conversely, experimental work revealed that non-functionalized MWCNTs located in the LDPE, polymer first to melt. When the extrusion time is not long enough, the MWCNTs do not have the chance to further migrate to the thermodynamically most favourable phase. The evolution of a double percolation determined if the composite became semi-conductive. In that sense, two blends with PMMA to LDPE ratios of 80:20 and 20:80 containing 2 wt.% MWCNTs had electrical resistivity values in the order of 105 and 1012 Ω cm, respectively. Only in the 80:20 blend was the “effective” MWCNT concentration high enough such that electrical percolation was attained. However, bulk rheological properties were controlled by the major phase. Thus, 2 wt.% MWCNTs had a notable effect on the linear viscoelasticity at low frequencies of the 20:80 blend.

Achieving Large Dielectric Property Improvement in Poly(ethylene vinyl acetate)/Thermoplastic Polyurethane/Multiwall Carbon Nanotube Nanocomposites by Tailoring Phase Morphology

In this work, multiwall carbon nanotubes (MWCNTs) were melt compounded with a poly(ethylene vinyl acetate)/thermoplastic polyurethane (EVA/TPU) blend to prepare EVA/TPU/MWCNT blend nanocomposites. The effects of the blend morphology and selective localization of MWCNTs on the dielectric properties including dielectric constant and loss were systematically investigated. The results show that when the blend exhibits sea–island morphology accompanying MWCNT selective localization in island droplets, the dielectric constant was increased to 1200@100 Hz with addition of 5 wt % MWCNTs; in addition, the growth of dielectric loss is suppressed and the values of dielectric loss always remain around 1 with varying the loading of MWCNTs. Furthermore, based on the investigations of rheological percolation testing, morphological observation, and selective localization, the microcapacitor model was evoked to explain the underlying mechanism for the improvement of the dielectric constant for the blend with sea–island mo...

Carbon nanotube induced double percolation in polymer blends: Morphology, rheology and broadband dielectric properties

In this study, we investigate the effect of multi-walled carbon nanotube (MWCNT) on the rheology, morphology and broadband dielectric properties of polypropylene:polystyrene (PP:PS) blends (PP:PS—10:90, 50:50 and 90:10). Transmission electron microscopy showed that MWCNTs were localized at the interface and inside the PS phase, regardless of the polymer blend ratio. Employing scanning electron microscopy, we observed that addition of MWCNT led to a transition from dispersed to interconnected morphology for the blends with PS as minor phase (PP:PS/50:50 and PP:PS/90:10). We propose that the selective localization of MWCNT in PS and at the interface slowed down the breakup mechanisms, increasing the lifetime of PS/MWCNT elongated domains, thus decreasing the amount of PS/MWCNT needed to percolate in PP phase. In addition, it is proposed that MWCNT located at the interface act as bridges between PS/MWCNT domains, favouring the coarsening of PS/MWCNT domains. The dielectric properties of the polymer blends PP:PS/50:50 and PP:PS/90:10 confirmed that double percolation was achieved with increase in MWCNT content. This transition provided the possibility to tune dielectric properties of the PP:PS/MWCNT blends. The double percolated structure offered high imaginary permittivity, while the dispersed morphology presented low imaginary permittivity. In other words, this study reveals that manipulating blend morphology can lead to blends with capacitive or dissipative characteristics.

Design and fabrication of morphologically controlled carbon nanotube/polyamide-6-based composites as electrically insulating materials having enhanced thermal conductivity and elastic modulus

Electrically insulating polymer materials having high thermal conductivity and elastic modulus are in high demand for next-generation electric machines and electronic devices. Carbon nanotubes (CNTs) show extremely high thermal conductivity and elastic modulus; however, even the addition of a few CNTs to polymers leads to them losing their electrically insulating properties. Herein, morphologically controlled multiwalled CNT (MWCNT)/polyamide-6 (PA6)/poly(p-phenylene sulfide) (PPS) composites, having high thermal conductivity, electrical insulation and elastic modulus, were designed and fabricated. First, MWCNT/PA6/PPS/EGMA composites comprising a PA6 matrix and MWCNT-localized PPS domains surrounded by shell-layers formed from poly(ethylene-co-glycidyl methacrylate) (EGMA) were prepared. The thermal conductivity of the composites was improved without losing the volume resistivity. However, these composites showed low elastic modulus, especially at high temperature, due to MWCNT localization and the existence of EGMA. Therefore, MWCNT/PA6/PPS/(3-glycidyloxypropyl)trimethoxysilane (GOPTS) composites having a novel morphology were designed and fabricated using GOPTS as a highly reactive shell-forming agent. In this composite, the MWCNT ends were capped with nano-sized PPS domains (MWCNT-PPS nanodomain-linked structure) to prevent electrically conductive paths forming, and MWCNT-PPS nanodomain-linked structures were uniformly dispersed in the PA6 matrix, leading to much enhanced elastic modulus and heat resistance in addition to improved thermal conductivity and electrically insulating properties. These composites containing CNT-nanodomain-linked structures are promising as electrically insulating materials for various applications including high-performance electric machines and electronic devices.

Improvement of rigidity for rubber-toughened polypropylene via localization of carbon nanotubes

A methodology for controlling the localization of multi-walled carbon nanotubes (MWCNTs) was studied using an immiscible polymer blend composed of isotactic polypropylene (PP) and ethylene-co-propylene rubber (EPR). We found that the MWCNTs were localized in EPR domains within the composite, which was prepared at 280 °C. EPR molecules bonded to the MWCNT surface are responsible for the localization in EPR. Conversely, MWCNTs preferentially resided in the matrix when the composite was prepared at 190 °C along with nitrogen gas purging. Because of the selective localization of the MWCNTs in the matrix, the composite obtained via mixing at the lower temperature exhibited a higher Young's modulus and yield strength. These findings demonstrate that mixing conditions greatly affect the MWCNT distribution and thus the mechanical properties of PP/EPR blends.

Unraveling the localization behavior of MWCNTs in binary polymer blends using thermodynamics and viscoelastic approaches

Using thermodynamics and viscoelastic approaches, the present work evaluated the localization of multiwalled carbon nanotubes (MWCNTs) in binary polymer blends with matrix/dispersed morphologies from pairs of poly(methyl methacrylate) (PMMA), polystyrene (PS), and polypropylene (PP). Thermodynamic predictions suggested that the MWCNTs should preferentially localize at the blend interface for all the nanocomposite samples. However, viscoelastic measurements showed that the MWCNTs localize elsewhere in the binary blend samples, either in the matrix, the droplets, or both; this suggests that the thermodynamic parameters were not the only ones at work. Linear viscoelastic experiments showed that the affinity toward the individual polymers was in the following order: PS ≫ PP > PMMA. Furthermore, it was shown that the dispersive mixing of the MWCNTs in the blend components was mainly controlled by the rheological properties. This was further confirmed by start‐up experiments, electron microscopy, and dynamic mechanical analysis. Therefore, the kinetic parameters needed to be considered in determining where the MWCNTs eventually ended up in the binary polymer blends. POLYM. COMPOS., 39:2356–2367, 2018. © 2016 Society of Plastics Engineers