Isotactic polypropylene/carbon nanotube composites prepared by latex technology: Electrical conductivity study

Several series of nanocomposites were prepared using a latex-based process, the main step of which consisted of mixing an aqueous suspension of exfoliated carbon nanotubes (CNTs) and a polymer latex. In the present work, a systematic study on the electrical properties of fully amorphous (polystyrene - PS) as well as semi-crystalline (isotactic polypropylene - iPP) nanocomposites containing either single-wall (SWCNTs) or multi-wall carbon nanotubes (MWCNTs) has been conducted. Percolation thresholds as low as 0.05 wt.% or 0.1 wt.% were observed for SWCNT/iPP and MWCNT/iPP nanocomposites, respectively. The formation of a conductive percolating network at such a low CNT concentration is favored by the high intrinsic conductivity and the low viscosity of the polymer matrix. The electrical percolation threshold of the iPP-based system was found to be lower than its rheological percolation threshold. Beyond the percolation threshold, MWCNT-based nanocomposites generally exhibited higher conductivity levels than those based on SWCNTs, most probably due to the higher intrinsic conductivity of the MWCNTs as compared to that of the SWCNTs. These excellent electrical properties, associated with the strong nucleating effect of the CNTs reported earlier [1] and [2], render this type of nanocomposites extremely attractive from a technological point of view.     

An experimental investigation on the conductive behavior of carbon nanotube-reinforced natural polymer nanocomposites

It is well known that carbon nanotubes (CNTs) have excellent electrical properties and can be used as the nanofiller in natural polymers to produce conductive CNT/polymer nanocomposites. In this study, the conductive behavior of CNT-reinforced natural polymer nanocomposites was investigated. The effect of CNT concentration on the conductivity of CNT/natural polymer nanocomposites was also investigated. The natural polymers used were plasticized starch (PS) and chitosan (CS). FTIR spectroscopy was used to examine the interactions between PS, CS, and CNTs. TEM analysis on both nanocomposites were made to study the dispersion states of CNTs in both polymers. The results showed that the surface resistivities of both CNT/PS and CNT/CS nanocomposites decreased steeply with increasing CNT concentration. Particularly, the CNT/CS nanocomposites showed a better conductivity than the CNT/PS composites at the same CNT concentration. The TEM result showed that CNT/CS nanocomposites had better dispersibility and formation of fully connected, three-dimensional network structures between the CNTs than the CNT/PS nanocomposites, which results in the superior conductive property of CNT/CS nanocomposites compared to the CNT/PS nanocomposites.     

A Review Featuring Fabrication,Properties and Applications of Carbon Nanotubes (CNTs) Reinforced Polymer and Epoxy Nanocomposites

Carbon nanotubes (CNTs) have long been recognized as the stiffest and strongest man-made material known to date.In addition,their high electrical conductivity has roused interest in the areas of electrical appliances and communication related applications.However,due to their miniature size,the excellent properties of these nanostructures can only be exploited if they are homogeneously embedded into light-weight matrices as those offered by a whole series of engineering polymers.In order to enhance their chemical affinity to engineering polymer matrices,chemical modification of the graphitic sidewalls and tips is necessary.The mechanical and electrical properties to date of a whole range of nanocomposites of various carbon nanotube contents are also reviewed in this attempt to facilitate progress in this emerging area.Recently,carbonaceous nano-fillers such as graphene and carbon nanotubes (CNTs) play a promising role due to their better structural and functional properties and broad range of applications in every field.Since CNTs usually form stabilized bundles due to van der Waals interactions,they are extremely difficult to disperse and align in a polymer matrix.The biggest issues in the preparation of CNTs reinforced composites reside in efficient dispersion of CNTs into a polymer matrix,the assessment of the dispersion,and the alignment and control of the CNTs in the matrix.An overview of various CNT functionalization methods is given.In particular,CNT functionalization using click chemistry and the preparation of CNT composites employing hyperbranched polymers are stressed as potential techniques to achieve good CNT dispersion.In addition,discussions on mechanical,thermal,electrical,electrochemical and applications ofpolymer/CNT composites are also included.     

Comparative study on the properties of poly(trimethylene terephthalate) ‐based nanocomposites containing multi‐walled carbon (MWCNT) and tungsten disulfide (INT‐WS2) nanotubes

Multi‐walled carbon (MWCNT) and tungsten disulfide (INT‐WS₂) nanotubes are materials with excellent mechanical properties, high electrical and thermal conductivity. These special properties make them excellent candidates for high strength and electrically conductive polymer nanocomposite applications. In this work, the possibility of the improvement of mechanical, thermal and electrical properties of poly(trimethylene terephthalate) (PTT) by the introduction of MWCNT and INT‐WS₂ nanotubes was investigated. The PTT nanocomposites with low loading of nanotubes were prepared by in situ polymerization method. Analysis of the nanocomposites' morphology carried out by SEM and TEM has confirmed that well‐dispersed nanotubes in the PTT matrix were obtained at low loading (<0.5 wt%). Thermal and thermo‐oxidative stability of nanocomposites was not affected by the presence of nanotubes in PTT matrix. Loading with INT‐WS₂ up to 0.5 wt% was insufficient to ensure electrical conductivity of PTT nanocomposite films. In the case of nanocomposites filled with MWCNT, it was found that nanotube incorporation leads to increase of electrical conductivity of PTT films by 10 orders of magnitude, approaching a value of 10^?3 S/cm at loading of 0.3 wt%. Tensile properties of amorphous and semicrystalline (annealed samples) nanocomposites were affected by the presence of nanotubes. Moreover, the increase in the brittleness of semicrystalline nanocomposites with the increase in MWCNT loading was observed, while the nanocomposites filled with INT‐WS₂ were less brittle than neat PTT. Copyright © 2016 John Wiley & Sons, Ltd.     

形状记忆聚偏氟乙烯/丙烯酸酯/碳纳米管纳米复合材料的导电及导热性能

利用聚偏氟乙烯（PVDF）微小结晶的物理交联点作用,制备了形状记忆性能优异的聚偏氟乙烯/丙烯酸酯聚合物（PVDF/ACM）共混材料,为提高其导电及导热性能,于其中引入了碳纳米管（CNT）,系统研究了PVDF/ACM/CNT三元体系纳米复合材料的导热及导电性能。 结果表明,碳纳米管在PVDF/ACM体系中分散均匀;在基本保持其形状记忆性能的前提下,碳纳米管的加入使材料导热性能及导电性能有较大程度的提高：质量分数为4%的CNT使材料25 ℃的电阻值降低至5000 Ω/square,导热系数提高至0.157 W/(m·K)。     

Carbon Nanotube Reinforced Supramolecular Hydrogels for Bioapplications

Nanocomposite hydrogels based on carbon nanotubes (CNTs) are known to possess remarkable stiffness, electrical, and thermal conductivity. However, they often make use of CNTs as fillers in covalently cross‐linked hydrogel networks or involve direct cross‐linking between CNTs and polymer chains, limiting processability properties. Herein, nanocomposite hydrogels are developed, in which CNTs are fillers in a physically cross‐linked hydrogel. Supramolecular nanocomposites are prepared at various CNT concentrations, ranging from 0.5 to 6 wt%. Incorporation of 3 wt% of CNTs leads to an increase of the material's toughness by over 80%, and it enhances electrical conductivity by 358%, compared to CNT‐free hydrogel. Meanwhile, the nanocomposite hydrogels maintain thixotropy and processability, typical of the parent hydrogel. The study also demonstrates that these materials display remarkable cytocompatibility and support cell growth and proliferation, while preserving their functional activities. These supramolecular nanocomposite hydrogels are therefore promising candidates for biomedical applications, in which both toughness and electrical conductivity are important parameters.     

Efficacy of clay content and microstructure of curing agents on the structure–property relationship of new‐generation polyurethane nanocomposites

The physicomechanical properties of new polyurethanes (PUs) derived from toluene diisocyanate, poly(propylene glycol), and cured by third‐generation hyperbranched polyester polyol (HB3), trimethylolpropane (TMP), or glycerol and their nanocomposites have been investigated. An apparent microphase‐segregated morphology of PU nanocomposites cured by HB3 has been observed by transmission electron microscopy and atomic force microscopy. Morphological studies reveal regions of mostly exfoliated and some intercalated morphology in the case of the nanocomposites, which have been further ascertained by X‐ray diffraction analysis. The HB3‐cured PU nanocomposite containing 8 wt% of modified montmorillonite (Cloisite 30B) clay shows approximately 140% increase in tensile strength along with improvement in thermal and dynamic mechanical properties in comparison with the control hyperbranched PU. It has also been found from Fourier transform infrared spectroscopy analysis that the extent of tethering reactions between the polymer chains carrying residual –NCO groups and the reactive hydroxyl (?OH) groups of HB3 is significant, and the nanofiller has been found to preferentially react with the –NCO group of the prepolymer. Furthermore, the properties of HB3‐cured PU have been compared with the glycerol and TMP‐cured PUs and their nanocomposites. The physicomechanical and thermal properties for nanocomposites of HB3‐cured PUs are superior to those of the conventionally cured PUs. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication of super-macroporous nanocomposites by deposition of carbon nanotubes onto polymer cryogels

Electrically conducting super-macroporous carbon nanotube/polymer cryogel nanocomposites were fabricated by a novel approach based on deposition of carbon nanotubes (CNTs) onto the inner surface of pre-formed cryogels assisted by cryogenic treatment. Stable aqueous dispersions of multi-walled and single-walled carbon nanotubes were firstly obtained by non-covalent modification of pristine nanotubes with either pyrene containing polydimethylacrylamide or poly(ethylene oxide)₂₆-b-poly(propylene oxide)₄₀-b-poly(ethylene oxide)₂₆ copolymers and, then, exploited for the preparation of nanocomposites. The mechanical and electrical properties of nanocomposite materials were measured and compared to similar materials prepared by established method. The novel approach provided super-macroporous nanocomposites with high electrical conductivity (>10^?2 S/m) at much lower nanotube content (0.12 wt.%).     

Carbon nanotube-polyaniline hybrid materials

A hybrid material of carbon nanotubes (CNTs)-polyaniline (PANI) was prepared by in situ emulsion polymerization. The structural characterization showed that some CNTs were linked up by PANI chains, which appears to be like a network including PANI fiber and nanotubes. This network results in the hybrid material having highly conductivity with new conductive passageway. The conductivity and thermal properties of hybrid materials depend on the content of CNTs. The CNTs do not affect the structure of PANI chains.     

Effects of processing conditions on rheological,thermal, and electrical properties of multiwall carbon nanotube/epoxy resin composites

We report on the effect of processing conditions on rheology, thermal and electrical properties of nanocomposites containing 0.02–0.3 wt % multiwall carbon nanotubes in an epoxy resin. The influence of the sonication, the surface functionalization during mixing, as well as the application of external magnetic field (EMF) throughout the curing process was examined. Rheological tests combined with optical microscopy visualization are proved as a very useful methodology to determine the optimal processing conditions for the preparation of the nanocomposites. The Raman spectra provide evidence for more pronounced effect on the functionalized with hardener compositions, particularly by curing upon application of EMF. Different chain morphology of CNTs is created depending of the preparation conditions, which induced different effects on the thermal and electrical properties of the nanocomposites. The thermal degradation peak is significantly shifted towards higher temperatures by increasing the nanotube content, this confirming that even the small amount of carbon nanotubes produces a strong barrier effect for the volatile products during the degradation. The ac conductivity measurements revealed lower values of the percolation threshold (pc) in the range of 0.03–0.05 wt %. CNTs for the nanocomposites produced by preliminary dispersing of nanotubes in the epoxy resin, compared to those prepared by preliminary functionalization of the nanotubes in the amine hardener. This is attributed to the higher viscosity and stronger interfacial interactions of the amine hardener/CNT dispersion which restricts the reorganization of the nanotubes. The application of the EMF does not influence the pc value but the dc conductivity values (σ_dc) of the nanocomposites increased at about one order of magnitude due to the development of the aforementioned chain structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Morphology,rheological and crystallization behavior in non-covalently functionalized carbon nanotube reinforced poly(butylene succinate) nanocomposites with low percolation threshold

Multi-walled carbon nanotubes (CNTs) were non-covalently functionalized by surface wrapping of poly(sodium 4-styrenesulfonate) (PSS) with the aid of ultrasound. The functionalized CNTs were incorporated into poly(butylene succinate) (PBS) through solution coagulation to fabricate CNTs filled PBS nanocomposites. The morphologies of the PBS/CNT nanocomposites were studied by scanning electron microscope (SEM) and transmission electron microscope (TEM), and the effect of loading of functionalized CNT on the rheological behavior, electrical conductivity and mechanical properties of the nanocomposites was investigated systemically. SEM observation indicates that functionalized CNTs dispersed in PBS matrix without obvious aggregation and showed good interfacial adhesion with the PBS phase. TEM observation reveals that a CNT network was formed when the loading of CNTs increased from 0.1 to 0.3 wt%. Rheological investigation indicates the formation of a CNT network with a percolation threshold of only 0.3 wt%. Significant improvement in electrical conductivity occurred at CNT loading of 0.3 wt%, with the value of electrical conductivity increasing by six orders of magnitude compared to neat PBS. Differential scanning calorimetry indicates that the melt crystallization temperature of PBS was improved by ∼14 °C with addition of only 0.05 wt% functionalized CNTs. Tensile tests indicate that both the yield strength and Young's modulus of PBS were apparently reinforced by incorporation of functionalized CNTs, while the elongation at break was reduced gradually.     

Effect of dispersion and selective localization of carbon nanotubes on rheology and electrical conductivity of polyamide 6 (PA6), Polypropylene (PP), and PA6/PP nanocomposites

Nanocomposites were prepared by adding 1–3 vol % multiwalled carbon nanotubes (MWCNTs) to polyamide 6 (PA6), polypropylene (PP), and their co‐continuous blends of 60/40 and 50/50 volume compositions. Because of the good interaction and interfacial adhesion to the PA6, nanotubes were disentangled and distributed evenly through nanocomposites containing PA6. In contrast, lack of active interactions between the matrix and the CNTs resulted in poor tube dispersion in PP. These observations were then verified by studying the rheology and electrical conductivity of their respective nanocomposites. Absence of percolated CNT clusters and possible wrapping of the tubes by PA6 resulted in low electrical conductivity of PA6/CNT nanocomposites. On the other hand, despite the weak dispersion of the tubes, electrical conductivities of PP/CNT nanocomposites were much higher than all other counterparts. This could be the result of good three‐dimensional distribution of the agglomerated bundles and secondary aggregation of tubes in PP. Adding CNTs to blends of PA6/PP (60/40 and 50/50) resulted in almost full localization of carbon nanotubes in PA6, leading to their higher effective concentration. At the same CNT loadings, the blend nanocomposites had three to seven orders of magnitude higher electrical conductivity than pure PA6. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 368–378     

Enhancing dielectric and mechanical behaviors of hybrid polymer nanocomposites based on polystyrene,polyaniline and carbon nanotubes coated with polyaniline

The dielectric and mechanical properties of hybrid polymer nanocomposites of polystyrene/polyaniline/carbon nanotubes coated with polyaniline(PCNTs) have been investigated using impedance analyzer and extensometer. The blends of PS/PANI formed the heterogeneous phase separated morphology in which PCNTs are dispersed uniformly. The incorporation of a small amount of PCNTs into the blend of PS/PANI has remarkably increased the dielectric properties. Similarly, the AC conductivity of PS/PANI is also increased five orders of magnitude from 1.6 × 10~(-10) to 2.0 × 10~(-5) S·cm~(-1) in the hybrid nanocomposites. Such behavior of hybrid nanocomposites is owing to the interfacial polarization occurring due to the presence of multicomponent domains with varying conductivity character of the phases from insulative PS to poor conductor PANI to highly conductive CNTs. Meanwhile, the tensile modulus and tensile strength are also enhanced significantly up to 55% and 160%, respectively, without much loss of ductility for three phase hybrid nanocomposites as compared to the neat PS. Thereby, the hybrid nanocomposites of PS/PANI/_P CNTs become stiffer, stronger and tougher as compared to the neat systems.     

Fundamental study of crystallization,orientation, and electrical conductivity of electrospun PET/carbon nanotube nanofibers

The morphology, structure, and properties of polyethylene terephthalate (PET)/Carbon Nanotubes (CNT) conductive nanoweb were studied in this article. Nanocomposite nanofibers were obtained through electrospinning of PET solutions in trifluoroacetic acid (TFA)/dichloromethane (DCM) containing different concentrations and types of CNTs. Electrical conductivity measurements on nanofiber mats showed an electrical percolation threshold around 2 wt % multi‐wall carbon nanotubes (MWCNT). The morphological analysis results showed smoother nanofibers with less bead structures development when using a rotating drum collector especially at high concentrations of CNTs. From crystallographic measurements, a higher degree of crystallinity was observed with increasing CNT concentrations above electrical percolation. Spectroscopy results showed that both PET and CNT orientation increased with the level of alignment of the nanofibers when the nanotube concentration was below the electrical percolation threshold; while the orientation factor was reduced for aligned nanofibers with higher content in CNT. Considerable enhancement in mechanical properties, especially tensile modulus, was found in aligned nanofibers; at least six times higher than the modulus of random nanofibers at concentrations below percolation. The effect of alignment on the mechanical properties was less important at higher concentrations of CNTs, above the percolation threshold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2052–2064, 2010     

Requirements of amount of carbon nanotubes for damage detection in large polymer composite structures

Due to their very high electrical conductivity, the addition of carbon nanotubes (CNTs) into polymers such as epoxies makes these materials conductive. This conductivity has been utilized to provide damage sensing in composite structures. Usually, the amount of CNTs needs to be more than the percolation threshold to assure electrical conductivity. The percolation threshold is usually determined using small samples. For large samples, the amount of CNTs needs to be higher to take into account some non-uniformity of the dispersion. More CNTs would provide better conductivity. One normally expects that more CNTs would also provide better damage detection. However, it was found that this is not the case. Certainly, the amount of CNTs needs to be more than a certain lower limit to assure conductivity throughout the large structures. Once this condition is met, adding more CNTs would reduce the sensitivity for damage detection. The sensitivity of damage detection can be measured by the change in electrical resistance (due to the occurrence of damage) between grid points that are attached on the surface of the composite structure. Higher sensitivity in damage detection would enable coarse grids (larger distance between grid points). Coarse grid points would mean lower number of grid points, less space, less wiring and less weight. This paper describes this phenomenon in detail. It provides models that simulate the conductivity configurations. It also introduces a new term call “Aggregately Conductive Materials” to distinguish the particular conductive characteristics of materials that are made conductive by the addition of nano-particles.     

Thermal degradation and kinetic analysis of biodegradable PBS/multiwalled carbon nanotube nanocomposites

In this study, carbon nanotubes (CNTs) were first modified using N,N′‐ dicyclohexylcarbodiimide (DCC) dehydrating agents. Subsequently, the poly(butylene succinate)/multiwalled carbon nanotube (PBS/MWNTs) nanocomposites were prepared through facile melt blending. Thermal degradation of these PBS/MWNT nanocomposites was investigated; the kinetic parameters of degradation were calculated using the Coats and Redfern, Ozawa, and Horowitz and Metzger methods, respectively. It was found that the degradation reaction mechanism of PBS and the CNT‐C18 containing nanocomposites at lower temperature was likely to produce an F1 model through reaction of random chain cleavage (cis‐elimination). However, the reaction mechanism at higher temperature was likely to be a D1 model because of the dominant diffusion control effect. Moreover, it was found that the activation energies of CNT‐C18‐containing PBS nanocomposites were first increased with the content of CNT‐C18, but then decreased after the content was larger than 0.5 wt % for all models at differing heating rates. This may be due to the formation of a conductive network of CNTs in the polymer matrix at higher content of CNTs, which lead to better heat and electrical conductivity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1231–1239, 2009     

Thermal,mechanical and electroactive shape memory properties of polyurethane (PU)/poly (lactic acid) (PLA)/CNT nanocomposites

Polymer blend nanocomposites based on thermoplastic polyurethane (PU) elastomer, polylactide (PLA) and surface modified carbon nanotubes were prepared via simple melt mixing process and investigated for its mechanical, dynamic mechanical and electroactive shape memory properties. Chemical and structural characterization of the polymer blend nanocomposites were investigated by Fourier Transform infrared (FT-IR) and wide angle X-ray diffraction (WAXD). Loading of the surface modified carbon nanotube in the PU/PLA polymer blends resulted in the significant improvement on the mechanical properties such as tensile strength, when compared to the pure and pristine CNT loaded polymer blends. Dynamic mechanical analysis showed that the glass transition temperature (T_g) of the PU/PLA blend slightly increases on loading of pristine CNT and this effect is more pronounced on loading surface modified CNTs. Thermal and electrical properties of the polymer blend composites increases significantly on loading pristine or surface modified CNTs. Finally, shape memory studies of the PU/PLA/modified CNT composites exhibit a remarkable recoverability of its shape at lower applied dc voltages, when compared to pure or pristine CNT loaded system.     

碳纳米管/高分子复合导电材料的研究进展

从碳纳米管的电性质出发,对以它为填料的导电性复合材料的制备方法和研究进展进行了综述,同时简单介绍了导电性复合材料电性质转变现象的理论分析模型,最后对碳纳米管/高分子复合导电材料的研究前景作了一定探讨。     

Preparation and characterization of polyurethane electrical insulating coatings derived from novel soybean oil‐based polyol

As a viable alternative to the petrochemical polyols in polyurethanes (PUs), a new soybean oil‐based polyol (PSBO) with high functionality of hydroxyl groups and built‐in (preformed) urethane bonds was introduced. At first, a facile and improved method was developed for the transformation of epoxidized soybean oil (ESBO) to carbonated soybean oil (CSBO). Then ring‐opening reaction of carbonated oil with ethanolamine (ETA) led to the polyol. After characterization by conventional spectroscopic and analytical methods, PSBO was used for the formulation of novel one‐pack PU electroinsulating wire enamels. Tunable mechanical, thermal, and electrical properties for the final PUs were achieved by replacing 10 wt% of PSBO with poly(propylene glycol) (PPG) at different number average molecular weights of 725, 1000, 2000, 4000. Investigation of the results showed that these soy‐based PUs offer excellent thermal and electrical insulating properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Microinjection molding of multiwalled carbon nanotubes (CNT)–filled polycarbonate nanocomposites and comparison with electrical and morphological properties of various other CNT‐filled thermoplastic micromoldings

A series of polycarbonate (PC)/multiwalled carbon nanotubes (CNT) nanocomposites were prepared by diluting a commercially available masterbatch using a neat PC resin in a lab‐scale batch mixer. The obtained nanocomposites were subjected to microinjection molding to fabricate microparts, which have a 3‐step decrease in thickness along the flow direction, under a defined set of processing conditions. The obtained microparts were mechanically divided into 3 different sections, namely, thick, middle, and thin sections, based on thickness. Morphology observations and electrical conductivity measurements were conducted to explore the evolution of microstructure within subsequent microparts. Additionally, a comparison of the electrical and morphological properties of stepped microparts of various thermoplastic polymers filled with CNT was studied. Results suggested that the selection of host polymers influences the dispersion of nanotubes within subsequent moldings, thereby affecting the electrical properties. The thermal stability of subsequent moldings deteriorated upon the addition of CNT, suggesting that the addition of CNT and the thermomechanical history experienced by the polymer melts in microinjection molding might cause a chain scission effect on PC. Raman spectroscopy analysis was used to study the orientation and properties of CNT in microparts.