Evolution of phase morphology and ‘network‐like’ structure of multiwall carbon nanotubes in binary polymer blends during melt‐mixing

Polyamide6 (PA6)/acrylonitrile butadiene styrene copolymer (ABS) blends with unmodified multiwall carbon nanotubes (MWNTs) were prepared via melt‐blending in a conical twin‐screw micro‐compounder with varying melt‐mixing time. To improve the state of dispersion of MWNTs, non‐covalent organic modifiers for MWNTs have been utilized: sodium salt of 6‐amino hexanoic acid (Na‐AHA) and 1‐pyrene‐carboxaldehyde (PyCHO). PA6/ABS blends with MWNTs have shown a phase morphology transition from ‘matrix‐dispersed droplet’ type to ‘co‐continuous’ type as a function of melt‐mixing time with the exception of 40/60 PA6/ABS blend with PyCHO‐modified MWNTs. Non‐isothermal crystallization studies revealed the heterogeneous nucleating action of MWNTs through the presence of double crystallization exothermic peaks (at ～192^°C and >200^°C) while pure PA6 shows bulk crystallization peak at ～192°C. 40/60 and 60/40 (wt/wt) PA6/ABS blends with 5 wt% unmodified MWNTs exhibited electrical conductivity values of ～3.9 × 10^?11 S/cm and ～4.36 × 10^?6 S/cm, respectively. A significant enhancement in electrical conductivity was observed with Na‐AHA and PyCHO‐modified MWNTs (order of ～10^?6 and ～10^?4 S/cm, respectively). POLYM. ENG. SCI., 55:429–442, 2015. © 2014 Society of Plastics Engineers     

Synthesis and properties of the amino‐functionalized multiple‐walled carbon nanotubes/polyimide nanocomposites

The 1,6‐hexanediamine‐functionalized multi‐walled carbon nanotubes(a‐MWNTs)/polyimide(PI) nanocomposite films were prepared through in‐situ polymerization followed by mixture casting, evaporation, and thermal imidization. To increase the compatibility of carbon nanotubes with the matrix polyimide, a‐MWNTs was used as the filler. According to the results, a‐MWNTs were homogeneously dispersed in the nanocomposite films. With the incorporation of a‐MWNTs, the mechanical properties of the resultant films were improved due to the strong chemical bonding and interfacial interaction between a‐MWNTs and 4,4′‐oxydiphthalic anhydride(ODPA)/4,4′‐Oxydianiline(ODA) polyimide matrix. The thermal stability of the a‐MWNTs/polyimide nanocomposite was also improved by the addition of a‐MWNTs. The electrical tests showed a percolation threshold at about 0.85 vol% and the electrical properties were increased sharply. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Dispersion,migration, and ‘network‐like’ structure formation of multiwall carbon nanotubes in co‐continuous,binary immiscible blends of polyamide 6 and acrylonitrile–butadiene–styrene copolymer during simultaneous melt‐mixing

Multiwall carbon nanotubes (MWNTs) were melt‐mixed in polyamide 6 (PA6) and acrylonitrile–butadiene–styrene (ABS) copolymer blends using a simultaneous mixing protocol in order to investigate the state of dispersion of MWNTs in PA6/ABS blends. The blend composition was varied from 40/60 (wt/wt) to 60/40 (wt/wt) in PA6/ABS blends, which showed ‘co‐continuous’ morphology in the presence of MWNTs. State of dispersion of MWNTs in these blends was assessed through bulk electrical conductivity measurements, morphological analysis, solution experiments, and UV‐vis spectroscopic analysis. MWNTs were subsequently modified with a novel organic modifier, sodium salt of 6‐aminohexanoic acid (Na‐AHA), to improve the state of dispersion of MWNTs. Blends with unmodified MWNTs exhibited the DC electrical conductivity in the range ～10^?11 to ～10^?5 S/cm, whereas blends with Na‐AHA‐modified MWNTs exhibited DC electrical conductivity in the range ～10^?7 to ～10^?5 S/cm. The reduction in MWNTs ‘agglomerate’ size (～73.7 μm for 40/60 blend with unmodified MWNTs to ～59.9 μm in the corresponding blend with Na‐AHA‐modified MWNTs) was observed through morphological analysis. The rheological studies showed increased complex viscosity and storage moduli in lower frequency region in case of blends with Na‐AHA‐modified MWNTs confirming a refined ‘network‐like’ structure of MWNTs. POLYM. ENG. SCI., 55:443–456, 2015. © 2014 Society of Plastics Engineers     

Preparation and properties of novel epoxy composites containing electrospun PA6/F‐MWNTs fibers

The Nylon 6 (PA6)/the functionalized multiwalled carbon nanotubes (F‐MWNTs) fibrous membranes were fabricated by electrospinning, and then incorporated into an epoxy matrix. Their morphology, thermal stability, mechanical properties, thermal conductivities, and electrical resistivity were investigated. The electrospun PA6/F‐MWNTs fibers performed as a skeleton in the epoxy matrix, and the well interfacial adhesion between the epoxy matrix and the PA6/F‐MWNTs fibers leads to high mechanical properties of composites. The PA6 serves as an intermediate layer and alleviates the modulus mismatch between the stiff MWNTs and the soft epoxy matrix. The thermal conductivities of the epoxy composites increase by 27.3, 35.0, and 36.1%, respectively, with 0.5, 1 and 1.5 wt% F‐MWNTs loading in the PA6/F‐MWNTs fibers. At the same time, the PA6 simultaneously retains the high electrical resistivity of these epoxy composites. POLYM. ENG. SCI., 56:1259–1266, 2016. © 2016 Society of Plastics Engineers     

Stability of electrical properties of carbon black‐filled rubbers

Conducting composites were prepared by melt mixing of ethylene–propylene–diene terpolymer (EPDM) or styrene‐butadiene rubber (SBR) and 35 wt % of carbon black (CB). Stability of electrical properties of rubber/CB composites during cyclic thermal treatment was examined and electrical conductivity was measured in situ. Significant increase of the conductivity was observed already after the first heating–cooling cycle to 85°C for both composites. The increase of conductivity of EPDM/35% CB and SBR/35% CB composites continued when cyclic heating‐cooling was extended to 105°C and 125°C. This effect can be explained by reorganization of conducting paths during the thermal treatment to the more conducting network. EPDM/35% CB and SBR/35% CB composites exhibited very good stability of electrical conductivity during storage at ambient conditions. The electrical conductivity of fresh prepared EPDM/35% CB composite was 1.7 × 10⁻² S cm⁻¹, and slightly lower conductivity value 1.1 × 10⁻² S cm⁻¹ was measured for SBR/35% CB. The values did not significantly change after three years storage. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

MWNT‐filled PC/ABS blends: Correlation of morphology with rheological and electrical response

A systematic study was done on morphological, electrical and rheological behavior of co‐continuous or dispersed‐type polycarbonate (PC)/acrylonitrile‐styrene‐butadiene (ABS) blends, containing different amounts of multiwalled carbon nanotubes (MWNT). The MWNTs gave substantial electrical conductivities to these nanocomposites at very low concentrations, owing to the effective melt processing method. Because of selective localization of MWNTs in the PC phase, along with double percolation phenomenon, the blend with co‐continuous morphology showed a lower electrical and rheological percolation threshold, higher melt viscosity and elasticity, as compared to the system with dispersed morphology. The morphology of both the blend systems was refined as a result of MWNTs incorporation but the morphology type remained unchanged. A typical role of compatibilizer in refining blend morphology was observed in both the systems. The electrical conductivity of the system filled with MWNTs in presence of compatibilizer, was lower than the systems filled with MWNTs only, which was attributed to role of compatibilizer in directing a part of MWNTs from PC matrix toward ABS phase. With increasing compatibilizer/MWNTs ratio, the influence of compatibilizer on morphology refinement and conductivity reduction was intensified. By comparing TEM micrograph of PC/SAN/MWNTs with that of PC/ABS/MWNTs, it was revealed that small portion of MWNTs was also located on polybutadiene rubber fraction of ABS. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 739‐748, 2013     

The morphology and thermal properties of multi‐walled carbon nanotube and poly(hydroxybutyrate‐co‐hydroxyvalerate) composite

Nanocomposites based on poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) and multi‐walled carbon nanotubes (MWNTs) were prepared by solution processing. Ultrasonic energy was used to uniformly disperse MWNTs in solutions and to incorporate them into composites. Microscopic observation reveals that polymer‐coated MWNTs dispersed homogenously in the PHBV matrix. The thermal properties and the crystallization behavior of the composites were characterized by thermogravimetric analysis, differential scanning calorimetry and wide‐angle X‐ray diffraction, the nucleant effect of MWNTs on the crystallization of PHBV was confirmed, and carbon nanotubes were found to enhanced the thermal stability of PHBV in nitrogen. Copyright © 2004 Society of Chemical Industry     

Doped polyaniline/multiwalled carbon nanotube composites: Preparation and characterization

Polyaniline (PANI)/multiwalled carbon nanotube (MWNT) composites with a uniform tubular structure were prepared from in situ polymerization by dissolving amino‐functionalized MWNT (a‐MWNT) in aniline monomer. For this the oxidized multiwalled nanotube was functionalized with ethylenediamine, which provided ethylenediamine functional group on the MWNT surface confirmed by Fourier‐transform infrared spectra (FT‐IR). The a‐MWNT was dissolved in aniline monomer, and the in situ polymerization of aniline in the presence of these well dispersed nanotubes yielded a novel tubular composite of carbon nanotube having an ordered uniform encapsulation of doped polyaniline. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that the nanotubes were coated with a PANI layer. The thermal stability and electrical conductivity of the PANI /MWNTs composites were characterized by thermogravimetric analysis (TGA) and conventional four‐probe method respectively. Compared with pure PANI, the electrical conductivity and the decomposition temperature of the MWNTs/PANI composites increased with the enhancement of MWNT content in PANI matrix. POLYM. COMPOS., 34:1119–1125, 2013. © 2013 Society of Plastics Engineers     

Improvement of dispersion of carbon nanotubes in epoxy resin through pyrogallol functionalization

Multiwalled carbon nanotubes (MWNTs) were functionalized with pyrogallol. The functionalized MWNTs were well‐dispersed in the epoxy/curing agent/ethanol solution, as demonstrated by UV‐vis spectra and optical micrographs. Epoxy resin/MWNTs composites were prepared via solution mixing method. The cure behavior was characterized using differential scanning calorimetry. Pyrogallol‐functionalized carbon nanotubes (CNTs) reacted with the epoxy through the mediation reaction of pyrogallol with the curing agent, leading to the interfacial bonding between the functionalized carbon nanotubes (CNTs) and the resin matrix. Due to the excellent dispersion and interfacial bonding, the mechanical strength and electrical conductivity of the epoxy resin/CNTs composites have been improved. POLYM. ENG. SCI. 56:1079–1085, 2016. © 2016 Society of Plastics Engineers     

High thermal conductive m‐xylylenediamine functionalized multiwall carbon nanotubes/epoxy resin composites

In this study, multiwall carbon nanotubes (MWNTs) functionalized by m‐xylylenediamine is used as thermal conductive fillers to improve their dispersibility in epoxy resin and the thermal conductivity of the MWNTs/bisphenol‐A glycidol ether epoxy resin composites. Functionalization with amine groups of MWNTs is achieved after such steps as carboxylation, acylation and amidation. The thermal conductivity, impact strength, flexural strength, and fracture surfaces of MWNTs/epoxy composites are investigated with different MWNTs. The results show that m‐xylylenediamine is successfully grafted onto the surface of the MWNTs and the mass fraction of the organic molecules grafted onto MWNTs is about 20 wt %. The thermal conductivity of MWNTs/epoxy composites is further enhanced to 1.236 W/mK with 2 wt % m‐MWNTs. When the content of m‐MWNTs is 1.5 wt %, the impact strength and flexural strength of the composites are 25.85 KJ/m², 128.1 MPa, respectively. Scanning electron microscope (SEM) results show that the fracture pattern of composites is changed from brittle fracture to ductile fracture. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41255.     

Use of MWNTs‐COOH to improve thermal energy storage and release rates of capric–palmitic–stearic acid ternary eutectic/polyacrylonitrile form‐stable phase change composite fibrous membranes

A series of novel capric–palmitic–stearic acid ternary eutectic/polyacrylonitrile/carboxyl purified multi‐walled carbon nanotubes (CA–PA–SA/PAN/MWNTs‐COOH) form‐stable phase change composite fibrous membranes (PCCFMs) were fabricated by electrospinning and physical absorption methods. In these form‐stable PCCFMs, the CA–PA–SA ternary eutectic was served as phase change material for thermal energy storage, and the loaded MWNTs‐COOH was acted as thermal conductivity enhancement filler to improve heat transfer rates, as well as electrospun PAN/MWNTs‐COOH fibrous membranes with different weight fractions of MWNTs‐COOH (i.e., 5, 10, and 20 wt%) were used as supporting materials to provide structural strength and prevent liquid leakage of melted CA–PA–SA ternary eutectic. The morphological structure and thermal performances were investigated and analyzed. The images of scanning electron microscopy showed that the CA–PA–SA ternary eutectic was uniformly embedded and dispersed into the three‐dimensional porous network structure of electrospun PAN/MWNTs‐COOH fibrous membranes. Thermal performance tests suggested that the melting and freezing times of the CA–PA–SA/PAN/MWNTs‐COOH form‐stable PCCFMs with the addition of 10 wt% MWNTs‐COOH were significantly shorten by about 52% and 56% in comparison with those of the CA–PA–SA/PAN form‐stable PCCFMs. Their phase change temperatures and enthalpies were about 7°C–32°C and 130–138 kJ/kg, respectively. POLYM. ENG. SCI., 59:E403–E411, 2019. © 2018 Society of Plastics Engineers     

Coupled thermal‐electrical analysis of carbon nanotube/epoxy composites

The electrical and thermal behavior of epoxy composites reinforced with different contents of multi‐walled carbon nanotubes (from 0.1 to 0.4 wt% CNT) is studied when they are subjected to relatively high DC voltages (from 1 to 100 V). These materials obey Ohm's law, reaching values of electrical conductivity in the range of 0.01–0.5 S/m. The transported electric current leads to a significant increase of temperature, which is a result of the Joule heating effect. The temperature increases to 40ºC in CNT/epoxy composites when applying 100 V. The study of heating due to Joule's effect gives information about the electrical transport mechanisms implied. It is also confirmed that both, electrical conductivity and Joule's heating effect depend on the morphological features of the composites. The functionalization of CNTs decreases the electrical conductivity of composites but increases their corresponding Joule heating, due to the strong interface between the nanotubes and matrix, which hinders the formation of pathways in CNT in direct contact. The technique of CNT dispersion applied also affects to the increase of temperature induced by the electrical current. POLYM. ENG. SCI., 54:1976–1982, 2014. © 2013 Society of Plastics Engineers     

Investigation of multi‐walled carbon nanotube‐reinforced high‐density polyethylene/carbon black nanocomposites using electrical,DSC and positron lifetime spectroscopy techniques

BACKGROUND: The positive temperature coefficient (PTC) effect on material properties has attracted much attention in recent years due to the prospects of many applications like temperature sensors, thermistors, self‐regulating heaters, etc. It has been suggested that incorporation of multi‐walled carbon nanotubes (MWNTs) into carbon black (CB)‐filled polymers could improve the electrical properties of composites due to high conductivity and network structure and significantly reduce the required CB loading. RESULTS: We observed no change in melting temperature and crystalline transition temperature on addition of MWNTs. However, the heat of fusion decreases as the amount of conducting carboxylated MWNT (c‐MWNT) filler increases and the resistivity of the composite decreases. The free volume shows an increase up to 1.5 wt% of c‐MWNT content and then decreases. CONCLUSION: Well‐developed crystals could not be formed due to restricted chain mobility as filler content increases. This results in minimum intermolecular interactions, and thus a decreased heat of fusion. A composite with c‐MWNT content of 0.5 wt% showed the highest PTC and higher resistivity at 150 °C possibly due to the formation of flocculated structures at elevated temperature. For filler content greater than 1.5 wt%, the decrease in free volume may be due to restricted chain mobility. Copyright © 2009 Society of Chemical Industry     

Electrical conductivity and major mechanical and thermal properties of carbon nanotube‐filled polyurethane foams

The carbon nanotubes (CNTs)/rigid polyurethane (PU) foam composites with a low percolation threshold of ～ 1.2 wt % were prepared by constructing effective conductive paths with homogeneous dispersion of the CNTs in both the cell walls and struts of the PU foam. The conductive foam presented excellent electrical stability under various temperature fields, highlighting the potential applications for a long‐term use over a wide temperature range from 20 to 180°C. Compression measurements and dynamical mechanical analysis indicated 31% improvement in compression properties and 50% increase in storage modulus at room temperature in the presence of CNTs (2.0 wt %). Additionally, the incorporation of only 0.5 wt % CNTs induced remarkable thermal stabilization of the matrix, with the degradation temperature increasing from 450 to 499°C at the 50% weight loss. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of polydiphenylamine/multi‐walled carbon nanotube composites

We describe the synthesis of methane sulfonic acid (MeSA)‐doped poly(diphenylamine) (PDPA) with carboxylic groups containing multi‐walled carbon nanotubes (c‐MWNTs) via in situ polymerization. Diphenylamine monomers were adsorbed on to the surface of c‐MWNTs and polymerized to form PDPA/c‐MWNT composites. SEM and TEM images indicated two different types of materials: the thinner fibrous phase and the larger globular phase. The individual fibrous phase had a diameter around 100–130 nm, which should be the carbon nanotubes (diameter 20–30 nm) coated with a PDPA layer. The structure of PDPA/c‐MWNT composites was characterized by FTIR, UV‐visible spectroscopy and X‐ray diffraction patterns. The electrical conductivities of PDPA/c‐MWNT composites were much higher than that of PDPA without c‐MWNTs. Copyright © 2006 Society of Chemical Industry     

Characterizing composite of multiwalled carbon nanotubes and POE‐g‐AA prepared via melting method

Multiwalled carbon nanotubes (MWNTs) with acyl chloride functional groups and a metallocene polyethylene–octene elastomer (POE) or an acrylic acid‐grafted metallocene polyethylene–octene elastomer (POE‐g‐AA) were used to prepare hybrids (POE/MWNTs or POE‐g‐AA/MWNTs) using a melting method, with a view to identify a hybrid with improved thermal properties. Hybrids were characterized using Fourier transform infrared spectroscopy, ¹³C solid‐state nuclear magnetic resonance, X‐ray diffraction, thermogravimetry analysis, and scanning electron microscopy. MWNTs were purified using acid treatment, and results showed that ? COOH of MWNTs increased with acid treatment time and leveled off after 24‐h treatment. Much better dispersion and homogeneity of MWNTs was obtained with POE‐g‐AA in place of POE as the matrix. As a result, tensile strength at break of POE‐g‐AA/MWNTs was significantly improved even at 5 wt % MWNT content. Moreover, temperature of thermal decomposition for POE‐g‐AA/MWNTs was about 40–50°C higher than that for POE‐g‐AA, indicating higher thermal stability. This was because the carboxylic acid groups in POE‐g‐AA and the acyl chloride functional sites in MWNTs allow the formation of stronger chemical bonds. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1328–1337, 2007     

The Thermal Conductivity of Polymer‐Derived Amorphous Si–O–C Compounds and Nano‐Composites

Silicon oxycarbide glasses can be produced over a range of Si–O–C compositions by the controlled pyrolysis of polymer precursors. We present measurements of the thermal conductivity of a silicon oxycarbide glass after two different heat treatments and two Si–O–C nano‐composites, hot‐pressed at 1600°C, up to 1000°C and compare them to fused silica, amorphous carbon, and SiC. The temperature dependence of their thermal conductivities is similar to other amorphous materials. The presence of low volume fractions of nanoparticles of hafnia (4.5 v/o) or zirconia (7.4 v/o) dispersed within the amorphous matrix only modifies the conductivity slightly, consistent with a simple Maxwell model, and does not affect the temperature dependence of the thermal conductivity above room temperature.     

Carbon nanotube/graphene oxide‐added CaO‐B2O3‐SiO2 glass/Al2O3 composite as substrate for chip‐type supercapacitor

A CaO‐B₂O₃‐SiO₂ (CBS) glass/40 wt% Al₂O₃ composite sintered at 900°C exhibited a dense microstructure with a low porosity of 0.21%. This composite contained Al₂O₃ and anorthite phases, but pure glass sintered at 900°C has small quantities of wollastonite and diopside phases. This composite was measured to have a high bending strength of 323 MPa and thermal conductivity of 3.75 W/(mK). The thermal conductivity increased when the composite was annealed at 850°C after sintering at 900°C, because of the increase in the amount of the anorthite phase. 0.25 wt% graphene oxide and 0.75 wt% multi‐wall carbon nanotubes were added to the CBS/40 wt% Al₂O₃ composite to further enhance the thermal conductivity and bending strength. The specimen sintered at 900°C and subsequently annealed at 850°C exhibited a large bending strength of 420 MPa and thermal conductivity of 5.51 W/(mK), indicating that it would be a highly effective substrate for a chip‐type supercapacitor.     

Reinforcement of rigid PVC/wood‐flour composites with multi‐walled carbon nanotubes

Multi‐walled carbon nanotubes (CNT) were compounded with PVC by a melt blending process based on fusion behaviors of PVC. The effects of CNT content on the flexural and tensile properies of the PVC/CNT composites were evaluated in order to optimize the CNT content. The optimized CNT‐reinforced PVC was used as a matrix in the manufacture of wood‐plastic composites. Flexural, electrical, and thermal properties of the PVC/wood‐flour composites were evaluated as a function of matrix type (nonreinforced vs. CNT‐reinforced). The experimental results indicated that rigid PVC/wood‐flour composites with properties similar to those of solid wood can be made by using CNT‐reinforced PVC as a matrix. The CNT‐reinforced PVC did not influence the electrical and thermal conductivity of the PVC/wood‐flour composites. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Electrical conductivity of carbon‐filled polypropylene‐based resins

Adding conductive carbon fillers to insulating thermoplastic resins increases composite electrical conductivity. Often, as much of a single type of carbon filler is added to achieve the desired conductivity and still allow the material to be molded into a bipolar plate for a fuel cell. In this study, various amounts of three different carbons (carbon black, synthetic graphite particles, and carbon nanotubes) were added to polypropylene resin. The resulting single‐filler composites were tested for electrical resistivity (1/electrical conductivity). The effects of single fillers and combinations of the different carbon fillers were studied via a factorial design. The percolation threshold was 1.4 vol % for the composites containing only carbon black, 2.1 vol % for those containing only carbon nanotubes, and 13 vol % for those containing only synthetic graphite particles. The factorial results indicate that the composites containing only single fillers (synthetic graphite followed closely by carbon nanotubes and then carbon black) caused a statistically significant decrease in composite electrical resistivity. All of the composites containing combinations of different fillers had a statistically significant effect that increased the electrical resistivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009