Rheological and electrical properties of polycarbonate/multi-walled carbon nanotube composites

Rheological and electrical properties of the polycarbonate (PC)/multi-walled carbon nanotube (MWNT) were studied. The MWNT was funtoinalized by treating with the hydrogen peroxide (H₂O₂). The H₂O₂ treated MWNT was dried by thermal and freeze drying methods. From the morphological studies, the degree of entanglement of the MWNT was decreased after treating with the H₂O₂. For the H₂O₂ treated MWNT (thermal drying), the length of the MWNT was shortened compared that of the H₂O₂ treated MWNT (freeze drying). The rheological and electrical properties of the PC/MWNT (H₂O₂ treated) composites increased compared that of the PC/MWNT (untreated) composites. Also, the electrical conductivity showed higher value for the PC/MWNT (H₂O₂ treated, freeze drying) composites compared that of the PC/MWNT (H₂O₂ treated, thermal drying) composites. From the results of the morphological, rheological, and electrical properties of the PC/MWNT composites, it is suggested that the electrical and rheological properties of the PC/MWNT composites are affected by the MWNT-MWNT network structure, which is related with the MWNT morphologies such as the degree of aggregation and aspect ratio of the MWNT.     

Dynamic mechanical and morphological properties of polycarbonate/multi-walled carbon nanotube composites

Dynamic mechanical and morphological properties of the polycarbonate (PC)/multi-walled carbon nanotube (MWNT) composites were studied by dynamic mechanical thermal analysis (DMTA) and X-ray diffractometry, respectively. For the without annealed PC/MWNT composites containing the higher content of the MWNT (≥7.0 wt%), double tan δ peaks were observed, which could be explained by the phase separation morphology model. For the annealed PC/MWNT composites, a broad single tan δ peak was observed. From the X-ray diffraction of the annealed PC/MWNT composites, it was observed that more regular structure of the PC was obtained, which was consistent with the result of the thermal analysis of the annealed PC/MWNT composites. From the dynamic mechanical properties, thermal analysis, and X-ray diffraction of the annealed PC/MWNT composites, it is suggested that PC/MWNT composites show a broad single tan δ peak and partially crystalline structure of the PC in the PC/MWNT composites by annealing.     

Rheological and dielectrical characterization of melt mixed polycarbonate-multiwalled carbon nanotube composites

A series of composites of polycarbonate (PC) with 23 different contents of multiwalled carbon nanotubes (MWNT) was produced by melt mixing using the masterbatch dilution method. In dielectric measurements, AC conductivity and complex permittivity data obtained in the frequency range between 10⁻³ and 10⁷ Hz at room temperature indicated the electrical percolation threshold at about 1.0 wt%.

The dynamic mode melt rheological measurements for the same samples at eight temperatures between 170 and 280 °C showed a visible change in the frequency dependence of dynamic moduli and the absolute value of the complex viscosity |η*| particularly at low frequencies. In literature these changes are sometimes related to so called ‘percolation threshold concentration’. Applying this picture to our experimental data we have to assume that the percolation threshold is strongly dependent on the measurement temperature. It changes from about 5 to 0.5 wt% MWNT by increasing the measurement temperature from 170 to 280 °C, respectively. This temperature dependence cannot be explained by a classical liquid-solid transition but may be related to the existence of a combined nanotube-polymer network.     

Impact toughness,viscoelastic behavior,and morphology of polypropylene–jute–viscose hybrid composites

In this investigation, we studied the impact toughness and viscoelastic behavior of polypropylene (PP)–jute composites. In this study, we used viscose fiber as an impact modifier and maleated PP as a compatibilizer. The toughness of the composites was studied with conventional Charpy and instrumental falling‐weight impact tests. The composites’ viscoelastic properties were studied with dynamic mechanical analysis. The results show that the incorporation of viscose fibers improved the impact strength and toughness to 134 and 65% compared to those of the PP–jute composites. The tan δ peak amplitude also increased with the addition of the impact modifier and indicated a greater degree of molecular mobility. The thermal stability of the composites was evaluated with thermogravimetric analysis. The addition of 2 wt % maleated polypropylene (MAPP) to the impact‐modified composite improved the impact strength and toughness to 144 and 93%, respectively. The fiber–matrix morphology of the fracture surface and the Fourier transform infrared spectra were also studied to ascertain the existence of the type of interfacial bonds. Microstructural analysis showed the retention of viscose fibers in the composites compared to the more separated jute fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42981.     

Dielectric spectroscopy on melt processed polycarbonate—multiwalled carbon nanotube composites

Complex permittivity and related AC conductivity measurements in the frequency range between 10⁻⁴ and 10⁷ Hz are presented for composites of polycarbonate (PC) filled with different amounts of multiwalled carbon nanotubes (MWNT) varying in the range between 0.5 and 5 wt%. The composites were obtained by diluting a PC based masterbatch containing 15 wt% MWNT by melt mixing using a Micro Compounder. From DC conductivity measurements it was found that for samples processed at a mixing screw speed of 150 rpm for 5 min, the percolation occurs at a threshold concentration (p_c) between 1.0 and 1.5 wt% MWNT. For concentrations of MWNT near the percolation threshold, the processing conditions (screw speed and mixing time) were varied. The differences in the dispersion of the MWNT in the PC matrix could be detected in the complex permittivity and AC conductivity spectra, and have been explained by changes in p_c. The AC conductivity and permittivity spectra are discussed in terms of charge carrier diffusion on percolation clusters and resistor-capacitor composites.     

Morphology,thermal stability,and dynamic mechanical properties of atactic polypropylene/carbon nanotube composites

Nanocomposites based on atactic polypropylene (aPP) and multiwall carbon nanotubes were prepared by melt blending at 80°C with a Barabender mixer. The morphology, thermal stability, and dynamic mechanical properties of the obtained composites were studied subsequently. SEM observations indicate that the nanotubes are well dispersed in the aPP matrix. Each nanotube is covered by a layer of aPP molecules. Thermal stability of the aPP in nitrogen is found to be enhanced significantly by the addition of nanotubes. Peak temperature of the DTG curve for the nanocomposite with 5 wt % nanotube loading shows about 70°C higher than that of pure aPP. Dynamic mechanical properties of aPP are also influenced by nanotubes, as shown by the increase in the storage modulus as well as significantly broadened loss tanδ peak. These effects of nanotubes on the thermal stability and mechanical properties of aPP are explained by the adsorption effect of the aPP molecules on the nanotube surfaces in this study. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1087–1091, 2005     

Nylon 6/multiwalled carbon nanotube composites: Effect of the melt‐compounding conditions and nanotube content on the morphology,mechanical properties,and rheology

The effect of the melt‐compounding conditions with the use of a corotating intermeshing twin‐screw extruder and of the nanotube content on the morphology and the mechanical and rheological properties of nylon 6/multiwalled carbon nanotube (MWCNT) composites was investigated. The melt‐compounding conditions affected the morphology, but the variations in the morphology did not necessarily result in substantial variations in the mechanical and rheological properties. The mass throughput had the strongest influence on the mechanical properties, whereas the MWCNT feeding substantially affected the rheology. The increase in the MWCNT volume content from 0.0 to 3.5 vol % led to an increase in the Young's modulus, whereas the tensile strength, elongation at break, and notched impact strength exhibited maximum values around 0.5 to 1.0 vol %. With increasing MWCNT volume contents, higher complex viscosities and storage and loss moduli and a lower loss factor compared to neat nylon 6 were observed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40893.     

Comparative study on electrical properties of copper nanowire/polypropylene and carbon nanotube/polypropylene composites

Nanocomposites using copper nanowires (CuNWs) or carbon nanotubes (CNTs) as fillers with polypropylene (PP) as matrix were prepared by miscible solution mixing and precipitation method. Comparative studies on electrical conductivity and electromagnetic interference shielding properties were reported. On the conductivity curve, a plateau was found for both CuNW/PP composite and CNT/PP composite. The plateaus are located at a different concentration range for each composite type: for CuNW/PP composite, it is between 0.8 and 1.7 vol %, while for CNT/PP composite the plateau occurs in a narrower range between 0.4 and 0.6 vol %. The shielding effectiveness (SE) increases with increased concentration of fillers. CNT/PP composite has higher SE at concentrations less than 2 vol %; the two curves cross near 10 dB at this point and at concentrations higher than 2 vol %, CuNW/PP composite has higher SE. © 2014 American Institute of Chemical Engineers AIChE J, 61: 296–303, 2015     

Development of elastic and plastic properties of polyoxymethylene during bending fatigue

The development of the plastic and viscoelastic properties and the corresponding failure limits of the acetal homopolymer polyoxymethylene were studied in unidirectional cyclic fatigue. Samples with molecular weights (MWs) ranging from 90 to 142 kg/kmol were tested in displacement‐controlled conditions, resulting in maximum stress amplitudes between 30 and 59 MPa and strain amplitudes between 35.8 and 92.6 με. The zero‐hour material properties and the cycle‐dependent property development were predominantly dictated by deformations in the crystalline regions and showed a negligible dependence on MW. However, the final failure limits were found to be primarily dependent on the length of the amorphous tie chains that connect the crystallites. As such, fatigue life analysis showed a strong dependence on MW. Results are interpreted in light of the primary mechanical failure mechanisms and the corresponding molecular deformations. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40762.     

Microwave absorbing properties of a radar absorbing structure composed of carbon nanotube papers/glass fabric composites

In this study, carbon nanotube papers were employed in fabricating thin and broadband radar absorbing structures (RAS). Different concentrations of the CNT papers have been made by using a vacuum filtration method, with 20 × 20 cm in size and 21-27 μm in thickness. An epoxy resin was added into the CNT paper and then cured to become a composite with 1-5 wt.% of CNTs and 83-309 μm in thickness. The complex permittivity and permeability (ε′, ε″, μ′, μ″) of the CNT paper composites were measured using the transmission/reflection method in the frequency range of 2-18 GHz. The results reveal that the real (ε′) and imaginary (ε″) parts of the complex permittivity are increased with the CNT concentration. The ε′ of 5 wt.% CNT sample reaches 323 at 2 GHz and then decreases to 49.0 at 18 GHz. The ε″ reaches 321 at 2 GHz and decreases to 26.0 at 18 GHz. The CNT paper composite combined with a glass fabric composite used for a dielectric spacer is fabricated for an innovative RAS and the reflection loss is measured using the arch method in a microwave anechoic chamber. The results show that the 5 wt.% CNT paper composite/glass fabric composite absorbers attain maximum reflection loss of −13.3 dB at 12.0 GHz, −13.8 dB  at 10.0 GHz, and −16.0 dB at 7.5 GHz for spacer thickness of 1.5, 2.0, and 3.0 mm, respectively.     

Morphologies and properties of polycarbonate/polyethylene in situ microfibrillar composites prepared through multistage stretching extrusion

The sheets of polycarbonate (PC)/polyethylene (PE) in situ microfibrillar composites are successfully prepared directly through multistage stretching extrusion with an assembly of laminating‐multiplying elements (LMEs) instead of the secondary processing. The morphological development of the PC dispersed phase in PE matrix with increasing the number of LMEs during multistage stretching extrusion investigated by scanning electron microscope shows that core‐skin structure of the microfibrillar PC/PE composites during multistage stretching extrusion with 4 LMEs is weakened, and the diameter of the PC microfibrils is relatively more uniform, indicating that the shear field in LMEs greatly affects the morphology of PC dispersed phase in PE matrix. The tensile, crystalline, melting, orientation and rheological behavior of the PC/PE microfibrillar composites are also investigated. The results show that the PC microfibrils are helpful to increase complex viscosity and yield stress of the PE/PC composites. In addition, it is found that the glass transition temperature of PC in PE matrix reduced with increasing the number of LMEs during dynamic rheological testing. It is coincided with the results of DSC analysis of the PC/PE composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40108.     

Conductivity spectroscopy on melt processed polypropylene-multiwalled carbon nanotube composites: Recovery after shear and crystallization

Frequency dependent investigations of conductivity and dielectric permittivity have been performed on composites of polypropylene (PP) containing different amounts of 2, 3.5, and 5 wt% of multiwalled carbon nanotubes (MWNTs) in the melt and during crystallization. The experiments were performed in a measurement slit die containing two dielectric sensors in plate-plate geometry, which was flanged to the outlet of a single screw laboratory extruder. AC conductivity and the related complex permittivity were measured in the frequency range from 20 Hz to 10⁶ Hz after stopping the extruder (recovery after shearing) and during cooling (non-isothermal crystallization). For a sample with a MWNT content of 2 wt% the AC conductivity shows a tremendous increase with time after shearing was stopped. This conductivity recovery is explained by the reorganization of the conducting network-like filler structure, which was partially destroyed by the shear. The reformation kinetics of filler clusters is assumed to be due to a cooperative aggregation. For conductive fillers in a thermoplastic matrix the kinetics of cooperative aggregation is coupled to the electrical percolation. The reorganization of the percolation network can be related to reformation of (i) the local contact regions between the nanotubes (separated by polymer chains) and (ii) to the reorientation of nanotubes oriented in the shear flow. The conductivity recovery is less pronounced for samples with MWNT concentrations well above the percolation threshold. During cooling of the melt to temperatures below crystallization a significant decrease in the conductivity and permittivity was detected. This is consistently expressed in the conductivity and permittivity spectra and can be explained by reduction of the amorphous phase (high ion mobility) on expense of the crystalline phase and/or by crystalline regions in the contact region between tubes.     

Role of processing history on the mechanical and electrical behavior of melt‐compounded polycarbonate‐multiwalled carbon nanotube nanocomposites

This work investigates the effects of primary compounding temperature and secondary melt processes on the mechanical response and electrical resistivity of polycarbonate filled with 3 wt % multiwalled carbon nanotubes (CNT). Nanocomposites were melt compounded in an industrial setting at a range of temperatures, and subsequently either injection molded or compression molded to produce specimens for the measurement of electrical resistivity, surface hardness, and uniaxial tensile properties. Secondary melt processing was found to be the dominant process in determining the final properties. The effects observed have been attributed to structural arrangements of the CNT network as suggested by morphological evidence of optical microscopy and resistivity measurements. Properties were found to be relatively insensitive to compounding temperature. The measured elastic moduli were consistent with existing micromechanical models. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42277.     

Mechanical and thermo-mechanical properties of carbon nanotube reinforced composites

A study on the mechanical and thermo-mechanical properties of carbon nanotube (CNT) reinforced nanocomposites is presented in this article. Mori–Tanaka method is used for modeling the effective stiffness and coefficient of thermal expansion. Regression formulas were developed to describe the effects of CNT orientation, aspect ratio, and CNT volume fraction. Given the statistical distributions of CNT orientations and aspect ratios, the effective properties can be conveniently derived by numerical integration using these formulas.     

The mechanical and tribological properties of nitric acid‐treated carbon fiber‐reinforced polyoxymethylene composites

The carbon fibers have been exposed to nitric acid oxidation treatments and introduced into polyoxymethylene composites (POM/CF). The nitric acid treatment increases the number of the flaws, roughness of the surface, and disorder of carbon atoms on fiber, as well as introduces reactive functional groups, which could lead to a better mechanical bonding between fiber and the matrix. It is shown that the impact strength and fiber‐matrix adhesion in composites (POM/mCF) are superior to those for POM/CF composites. Simultaneously, the addition of mCF improves flexural strength and modulus relative to virgin POM significantly. Average friction coefficient values of POM/CF composites are lower than that of POM/mCF composites. As the percentage of fiber increases, the trend of wear ratio of the composites goes down initially and bumps up afterwards. The results indicate that the proper contents of CF and mCF in composites range from 5 wt % to 20 wt %. Scanning electron microscopy of worn surface morphology has revealed that the main wear mechanism of the composites were adhesive wear and ploughing wear. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41812.     

Synthesis and characterization of multiwall carbon nanotube/waterborne polyurethane nanocomposites

The preparation of thermoplastic nanocomposites of waterborne polyurethane (WBPU) and multiwall carbon nanotubes (MWCNTs) via an in situ polymerization approach is presented. The effects of the presence and content of MWCNTs on the morphology and thermal, mechanical and electrical properties of the nanocomposites were investigated. Carbon nanotubes were modified with amide groups in order to enhance their chemical affinity towards WBPU. Thermogravimetric studies show enhanced thermal stability of the nanocomposites. Scanning and transmission electronic microscopy images prove that functionalized carbon nanotubes can be effectively dispersed in WBPU matrix. Mechanical properties reveal that Young's modulus and tensile strength tend to increase when appropriate amounts of MWCNTs are loaded due to the reinforcing effect of the functionalized carbon nanotubes. Thermal properties show an increase in the glass transition temperature and storage modulus with an increase in MWCNT content. X‐ray diffraction reveals better crystallization of the WBPU in the presence of MWCNTs. The WBPU/MWCNT nanocomposite film containing 1 wt% of MWCNTs exhibits a conductivity nearly five orders of magnitude higher than that of WBPU film. © 2017 Society of Chemical Industry     

Synthesis and properties of new polyamide/multiwalled carbon nanotube nanocomposites containing a pyridine group

The effects of multiwalled carbon nanotubes (MWCNTs) on the thermal properties and flame retardancy of a new polyamide (PA) derived from glutaric acid and aromatic diamine were investigated in this work. The synthesized PA containing pyridine and trialkylamine groups was characterized by ¹H NMR and SEC. The PA unit structure was geometrically optimized at the B₃LYP/6‐311⁺⁺G(d, p) level of theory. PA showed a glass transition temperature of 151 ºC. PA nanocomposites containing two different amounts of MWCNTs were prepared via the solution intercalation technique with the solvent N,N‐dimethylacetamide. Transmission electron microscopy showed that MWCNTs were exfoliated in the polymer matrix, resulting in well‐dispersed morphologies at 3 wt% MWCNT content. The redox behaviors of PA and the nanocomposites were examined using cyclic voltammetry (CV). PA showed a reversible oxidation process in the CV scan. Thermal and flammability properties of the nanocomposites were studied by TGA in nitrogen and air, DSC and with a microscale combustion calorimeter. The TGA results showed that the addition of MWCNTs resulted in a substantial increase in the thermal stability and char yields of the nanocomposites compared with neat PA. The heat release rate and total heat release were significantly reduced in the presence of MWCNTs. © 2013 Society of Chemical Industry     

Electrical and dielectric properties of multiwall carbon nanotube/polyaniline composites

In this paper, electrical and dielectric properties of multiwall carbon nanotubes (MWCNTs)/insulating polyaniline (PANI) composites were studied. A mixture of MWCNTs and insulating polyaniline was dispersed in an ethanol solution by ultrasonic process, subsequently dried, and was hot-pressed at 200 °C under 30 MPa. Electrical and dielectric properties of the composites were measured. The experimental results show that the dc conductivities of the composites exhibit a typical percolation behavior with a low percolation threshold of 5.85 wt.% MWCNTs content. The dielectric constant of the composites increases remarkably with the increasing MWCNTs concentration, when the MWCNTs concentration was close to percolation threshold. This may be attributed to the critical behavior of the dielectric constant near the percolation threshold as well as to the polarization effects between the clusters inside the composites.     

碳纳米管预处理方法对天然橡胶/纯化碳纳米管复合材料力学性能的影响

纯化后的碳纳米管(CNT)分别经过球磨、表面活性剂十二烷基苯磺酸钠或分散-黏合体系预处理,再与100份(质量)天然橡胶(NR)混炼,可制备NR/纯化CNT复合材料。结果表明,纯化CNT直接与NR混炼,前者在NR中的分散效果不好,二者的界面结合欠佳。纯化CNT经球磨后,团聚程度增加,对复合材料力学性能影响不大。经表面活性剂十二烷基苯磺酸钠处理后的纯化CNT,内聚能下降,用差示扫描量热法(DSC)测定复合材料的DSC曲线表明,复合材料的结晶熔融峰面积增大,力学性能降低。用分散-黏合体系处理纯化CNT,可同时提高纯化CNT在橡胶中的分散效果及界面黏合性,试样结晶熔融峰变得不明显,因此该复合材料的邵尔A型硬度提高,拉伸强度、300％定伸应力和撕裂强度等优于其他试样。     

Morphological and nanomechanical characterization of anisotropic interfacial characteristic regions in CF/PA6 composites at different cooling rates

Macroscopic tensile tests on neat PA6 and CF/PA6 prepregs showed that the cooling rate significantly affects the mechanical properties of CF/PA6 composites because of their different crystallization behaviors both at the fiber surface and in the matrix. Polarizing optical microscopy, static nanoindentation (SNI), and dynamic mechanical imaging (DMI) tests were used to characterize the anisotropic morphologies and nanomechanical performances of the interfacial characteristic regions in CF/PA6 composites at five different cooling rates. As a result, the seven interfacial characteristic regions inside the CF/PA6 composites were clearly distinguished. The interphase thickness of the CF/PA6 composites decreased with a decrease in the cooling rate. On the contrary, the interphase modulus and transcrystallinity thickness and modulus showed significant increases with a decrease in the cooling rate. The DMI and SNI test results were in agreement with each other and with the macromechanical test results. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44106.