Different filler effect of carbon nanotube and graphene nanoplatelet in the poly(arylene ether nitrile) matrix

The different filler effects of identical nitrile‐functionalized carbon nanotubes (CNTs) and graphene nanoplatelets (GNs) in a poly(arylene ether nitrile) (PEEN) matrix were investigated. PEEN/CNT and PEEN/GN composites were prepared by a facile solution‐casting method and systematically investigated for their differences in morphological, thermal and rheological properties. In the PEEN matrix GNs contact one another in a plane‐to‐plane manner, while CNTs are separated. Compared with PEEN/CNT composites, PEEN/GN composites below 2 wt% filler content exhibited higher thermal stability. Rheological properties of the resulting composites indicated that PEEN/GN composites were more sensitive to strain and exhibited higher η*, G′ and G″ than PEEN/CNT composites. The rheological percolation for CNTs is over 2 wt%, higher than that for GNs (around 1 wt%). All these differences originate from the different dimensions and structures of CNTs and GNs: GNs with a flake‐like structure and larger surface area can have stronger physical and interfacial interactions with the polymer matrix. This work gives a comparative view of the different filler effects that functionalized CNTs and GNs can have in the polymer host. With identical processing technology, GNs can show a stronger filler effect than CNTs. © 2012 Society of Chemical Industry     

Controlling morphology,electrical, and mechanical properties of polymer blends by heterogeneous distribution of carbon nanotubes

Electrical and mechanical properties of some new composites made of copolyamide/polypropylene/carbon nanotubes (CPA/PP/CNTs) in different ratios, in correlation with their morphology, were investigated. The polymer blends based on polypropylene and low melting point copolyamide filled with CNTs were prepared by two methods. In the first procedure, CNTs were orderly distributed into the heterogeneous polymer matrix where filler occupied only one polymer component creating a highly branched conductive phase that provides a low value of the percolation threshold. In second case, CNTs were randomly distributed in the heterogeneous polymer matrix created by the blend CPA/PP yielding in a higher value of percolation threshold. Four factors influence on the distribution of filler, namely: thermodynamics, kinetics, chemical factor, and processing. Both electrical and mechanical properties are defined by spatial distribution of the conductive nanofiller in the polymer blend. POLYM. COMPOS., 37:2467–2477, 2016. © 2015 Society of Plastics Engineers     

Effect of Carbon‐Based Particles on the Mechanical Behavior of Isotactic Poly(propylene)s

Different carbon‐based fillers such as carbon nanotubes (CNTs), graphite, and thermally reduced graphene oxide (TrGO) are melt mixed with an isotactic poly(propylene) (iPP) and the mechanical properties of the resulting composites in the solid and melt state are analyzed. The Young's modulus of composites is increased around 25% relative to the neat iPP at concentrations above 10 wt% of CNTs or graphite whereas composites with TrGO are increased around 40% at similar concentrations. These results are compared with theoretical models showing that the filler agglomeration and surface area are key parameters. The rheological results of the composites under oscillatory shear conditions at the melt state show that the viscous raw polymer melt experiences a solid‐like transition at a threshold concentration that strongly depends on the filler used. This transition appears at 10 wt% for CNTs, 8 wt% for TrGO, and 40 wt% for graphite. The viscosity of iPP/TrGO composites is further increased by adding CNTs particles, although the Young's modulus does not increase.

     

Melt spinning of conducting polymeric composites containing carbonaceous fillers

Fibers produced by melt spinning of conductive polymer composites are attractive for several applications; the main drawback is however reduced processability at high filler concentrations. Carbon nanotubes (CNTs) are considered suitable fillers for conductive polymer composites, replacing conductive grades of carbon black (CB). In this study, the fiber‐forming properties of conductive polymer composites based on a conductive grade of CB and two masterbatches with CNT in a polyethylene matrix were investigated. The CB was also used in a polypropylene matrix for comparison. The rheological properties of the filler‐containing melts in shear and their extensional behavior were evaluated. A piston‐driven device was used to extrude the molten materials through a capillary; different capillary geometries were tested. Fibers were produced at various draw ratios, and their conductivity was determined. To assess the ultimate extensibility, a modified Rheotens method was used. The results showed that a conductive CB grade can have a lower percolation threshold and higher conductivity than a material with CNT. Conductivity decreased with increasing melt draw ratio for both types of fillers. The spinnability of the materials decreased with increasing concentration of filler material and correlations were found between spinnability and melt elasticity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

AC conductivity of carbon fiber–polymer matrix composites at the percolation threshold

This paper reports results on experimental investigation of the conductivity behavior of carbon fiber filled polymer composites at the percolation threshold. Two types of carbon fiber‐epoxy matrix composites have been studied and comparison of the measured data has been made. These two types of composites differ in the surface modification of carbon fibers (in one case the surface of carbon fibers is covered with polymer beads using the microencapsulation technology, in the other their surface stayed unmodified). Experimental data reveal that surface modification of carbon fibers influences greatly the DC conductivity (percolation threshold moves to higher concentrations) but does not influence the AC electrical properties. From the frequency dependence of conductivity upon fiber concentration it becomes clear that it is not possible to predict the high frequency conductivity (electromagnetic interference shielding properties) based on the DC conductivity. Percolation behavior of conductivity as a function of conductive filler concentration is typical only for DC or low frequency AC conductivity. The percolation threshold gradually vanishes for high frequencies of electromagnetic field. The temperature dependence of electrical properties has also been studied. Composites with concentration near the percolation threshold show the switch‐off effect (at the specific temperature the DC conductivity drops by several orders of magnitude). This switch‐off effect does not occur for high frequency AC conductivity.     

VGCF填充PVDF/PMMA复合材料导电性能的研究

以气相生长碳纤维（VGCF）为导电填料，聚偏氟乙烯（PVDF）、聚甲基丙烯酸甲酯（PMMA）为基体制备复合型导电高分子材料。考察了填料用量、基体种类、配比以及PVDF结晶行为对复合材料导电性能的影响。结果表明，VGCF填充PMMA、PVDF、PVDF／PMMA（50／50）体系的渗滤阔值分别为5、4、3phr的填料用量。VGCF的加入会导致PVDF／PMMA体系发生微观相分离，而且VGCF会选择性富集在PVDF的非晶相中，所以PVDF／PMMA／VGCF体系的导电性呈现双重渗滤现象，该体系的体积电阻率不仅取决于富集相中VGCF的含量，而且还与PVDF相的连续性及其结晶行为密切相关。     

Poly(3-hexylthiophene) wrapped carbon nanotube/poly(dimethylsiloxane) composites for use in finger-sensing piezoresistive pressure sensors

We fabricated a piezoresistive composite using multi-walled carbon nanotubes (MWCNTs) as a conductive filler and polydimethylsiloxane (PDMS) as a polymer matrix, which operated in the extremely small pressure range required for finger-sensing. To achieve a homogeneous dispersion of MWCNTs in PDMS, the MWCNTs were modified by a polymer wrapping method using poly(3-hexylthiophene) (P3HT). The percolation threshold of the composites was significantly lowered by the presence of P3HT. The electrical conductivity and piezoresistive sensitivity of the composite were found to strongly depend on the P3HT concentration. The well-dispersed P3HT-MWCNT/PDMS composite showed good piezoresistive characteristics in the 0–0.12 MPa pressure range.     

Dynamic percolation phenomenon of poly(methyl methacrylate)/surface fluorinated carbon black composite

The electrical resistivity of polymer filled with conductive filler, such as carbon black (CB) particles, is greatly decreased by incorporating the conductive filler. This is called the percolation phenomenon and the critical CB concentration is called the percolation threshold concentration (Φ*). For CB particle–filled insulating polymer composite at lower than Φ*, the conductive CB network is constructed in the polymer matrix when the composite is maintained at a temperature higher than the glass‐transition temperature or the melting temperature of the polymer matrix. This phenomenon is called dynamic percolation and the time to reach the substantial decrease in resistivity is called percolation time (t_p). To investigate the relationship between the dynamic percolation process and the surface state of CB particles, we used three kinds of carbon black particles such as original carbon black (CB0) and fluorinated carbon black (FCB010 and FCB025)–filled poly(methyl methacrylate) (PMMA). It was observed that the dynamic percolation curves for CB0‐filled PMMA and FCB‐filled PMMA composites shifted to a shorter percolation time with increases in both the annealing temperature and the filler concentration. However, the dynamic percolation curves of FCB‐filled PMMA showed a gradually decreasing trend compared to that of CB0‐filled PMMA composites. The activation energy calculated from an Arrhenius plot of the t_p against the inverse of the annealing temperature was decreased by surface fluorine treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1151–1155, 2003     

The role of non-covalent interactions and matrix viscosity on the dispersion and properties of LLDPE/MWCNT nanocomposites

Linear low density polyethylene (LLDPE)/multi-walled carbon nanotube (MWCNT) composites were prepared by melt compounding, following two different compatibilization strategies that involved non-covalent interactions between the matrix and the filler. The first approach involved grafting pyridine aromatic moieties on the maleated polyolefin backbone, which are able to interact by π–π stacking with the surface of the nanotubes. The second method implemented non-covalent/non-specific surface functionalization of the MWCNTs with a hyperbranched polyethylene (HBPE). The enhanced interfacial interactions established in the composites containing LLDPE functionalized with pyridine grafts improved the dispersion of the nanotubes within the polymer matrix. Dispersion was also favoured by higher matrix viscosity. Composites containing finely dispersed MWCNTs exhibited an increase in the rheological and electrical percolation thresholds, and a significant improvement in mechanical properties. On the contrary the composites based on the low viscosity matrix contained large amounts of aggregates, which promoted lower percolation thresholds. Manipulation of matrix viscosity and compatibilization resulted in composites with good mechanical properties, and low percolation thresholds.     

Nonmonotonic piezoresistive effect in elastomeric composite films

We compared the change of electrical resistance with elongation (piezoresistive effect) in thin films made of conductive multiwalled carbon nanotubes embedded in eight different elastomers. Two distinct forms of piezoresistive effect were observed: (i) in the “monotonic” (M) case, the film resistance always increased with the applied strain; (ii) the “nonmonotonic” (NM) case showed an initial increase in the resistance, while with further elongation the resistance began to decrease. By varying the amount of nitrile and/or styrene groups in the polymer matrix one can alter the piezoresistive effect qualitatively: composites with ～25 wt % or more of nitrile or styrene functional side groups exhibited M piezoresistance, while others, with no, or methyl side groups only, showed NM piezoresistance. Influence of the second filler (either conductive carbon black or nonconductive nanoclay) in the ternary composites on the piezoresistive effect was explored. The possibility to modify the piezoresistive behavior of the conductive elastomer composites, for example, via chemical modification of the polymeric matrix, opens up a new venue for practical applications such as diverse types of sensors and, in NM case, complex dynamical systems (bistable elements, electromechanical oscillators, etc.) in the MEMS field. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43518.     

Low percolation threshold in single-walled carbon nanotube/high density polyethylene composites prepared by melt processing technique

A new method was developed to disperse carbon nanotubes (CNTs) in a matrix polymer and then to prepare composites by melt processing technique. Due to high surface energy and strong adsorptive states of nano-materials, single-walled carbon nanotubes (SWNTs) were adsorbed onto the surface of polymer powders by spraying SWNT aqueous suspected solution onto fine high density polyethylene (HDPE) powders. The dried SWNTs/powders were blended in a twin-screw mixture, and the resulting composites exhibited a uniformly dispersion of SWNTs in the matrix polymer. The electrical conductivity and the rheological behavior of these composites were investigated. At low frequencies, complex viscosities become almost independent of the frequency as nanotubes loading being more than 1.5 wt%, suggesting an onset of solid-like behavior and hence a rheological percolation threshold at the loading level. However, the electrical percolation threshold is ∼4 wt% of nanotube loading. This difference in the percolation thresholds is understood in terms of the smaller nanotube-nanotube distance required for electrical conductivity as compared to that required to impede polymer mobility. The measurements of mechanical properties indicate that this processing method can obviously improve the tensile strength and the modulus of the composites.     

Electrical and mechanical behavior of carbon black–filled poly(vinyl acetate) latex–based composites

The electrical and mechanical behaviors of carbon black‐filled. Poly(vinyl acetate) latex‐based polymer composites were examined. These composites were found to exhibit percolation thresholds in electrical conductivity near 2 vol% carbon black due to their segregated microstructures. Storage modulus and ultimate tensile strength (UTS) both exhibited discontinuities at 10 vol% carbon black, corresponding to a critical pigment volume concentration. Drying composites at 60°C rather than room temperature produced a higher percolation threshold and better mechanical properties at carbon black loadings above 10 vol% carbon black. A figure of merit was proposed to assess the balance of electrical conductivity, storage modulus and UTS. The figure of merit exhibited a peak value at 10 vol% for composites dried at room temperature and was shifted to higher carbon black concentrations when composites were dried at 60°C.     

Rheological and conductive percolation laws for syndiotactic polystyrene composites filled with carbon nanocapsules and carbon nanotubes

Semicrystalline syndiotactic polystyrene (sPS) composites with carbon nanocapsule (CNC) and carbon nanotube (CNT) fillers were prepared and good filler dispersion confirmed by electron microscopy. Their rheological and electrical properties were investigated to reveal the effect of filler aspect ratio. Amorphous atactic polystyrene (aPS) was used to prepare composites with a CNT filler to elucidate the effect of matrix tacticity. Percolation scaling laws are applied and the threshold concentration and exponent are determined. Above a threshold, the magnitudes of storage modulus (G′) and conductivity are related to the level of percolation network as well as the intrinsic properties of the matrix and filler. Master curves are obtained provided that an appropriate percolation function is selected. Different scaling laws are validated for the G′ and conductivity results.Composites with CNTs show a much lower threshold than those with CNCs. A lower threshold is derived from the G′ results compared to that obtained from the conductivity data regardless of the filler aspect ratio and matrix tacticity. Owing to the pronounced nucleating effects of CNT, crystalline sPS composites exhibit a four times larger conductivity threshold compared to their amorphous aPS counterparts, although their rheological thresholds are similar.     

A review of conductive polymer composites filled with low melting point metal alloys

Metal alloys with low melting temperatures may be blended into polymers to improve their electrical conductivity. We review the preparation, morphology, and electrical conductivity of polymer composites based on low melting point metal alloys, with or without additional filler particles. Since such alloys can be liquid under melt processing conditions, the composite morphology is determined by phenomena such as coalescence of liquid metal drops, orientation of the liquid metal phase, or selective wetting of a second filler by the liquid metal. None of these phenomena appear in conductive composites based on more common conductive fillers such as carbon black, carbon nanotubes, or metal particles. The published literature suggests that composites based on low melting metal alloys, with or without additional non‐melting filler particles, can have much higher percolation thresholds and much higher electrical conductivity (～1,000 S/m) than those based on fillers such as carbon black or carbon nanotubes. Changes in other properties such as rheological or mechanical properties are also discussed. POLYM. ENG. SCI., 58:1010–1019, 2018. © 2017 Society of Plastics Engineers     

Effect of Solvent on Segregated Network Morphology in Elastomer Composites for Tunable Piezoresistivity

Flexible, light‐weight, and wearable electronics have significant potential for the development of Internet of Things. Flexible sensors with tunable piezoresistive properties are in high demand for various practical applications. Herein, different morphology thermoplastic polyurethane (TPU)/ carbon nanostructure (CNS) composites with segregated network are obtained by swelling the TPU powders using various solvents. The better solvent for TPU, dimethylformamide (DMF), renders the composites with 0.7 wt% CNS stronger polymer‐filler interactions, resulting in significantly improved piezoresistive sensitivity at strain larger than 150%. Also the gauge factors (G_Fs) for these composites are 9.7 in the range 0–60% strain and 19.3 for 60–100% strain. In contrast, the composites with ethanol (EtOH) and tetrahydrofuran (THF) which swell less the TPU show delayed increase in piezoresistivity and G_Fs of 2.2 and 3.5 for strain up to 100%, respectively, suggesting potential applications for stretchable conductors.     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Comparative study on electrical properties of orientated carbon nanotubes/epoxy composites

The percolation threshold of carbon nanotubes (CNTs)/epoxy resin composites was simulated in the Bruggeman' Effective‐Medium Theory based on experiment. Both distinct percolation effect and low percolation threshold in the aligned CNTs/epoxy composites were predicted. With the CNTs loading larger than the percolation threshold, the critical exponent of CNTs/epoxy composites rises rapidly with the increase of aspect ratio of CNTs. It is shown that the electrical conductivity of composites presents distinct aeolotropism, the percolation threshold is sensitive relative to the tiny change of the orientation factor, the aspect ratio, and the structure of CNTs in the composites matrix. The simulated results are consistent with the experimental results basically, and the discrepancy between simulated results and experimental results has been interpreted reasonably. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrical and mechanical properties of melamine‐formaldehyde–based laminates with shungite filler

Processing issues and the electrical and mechanical properties of a novel combination of a natural carbonaceous filler, Karelian shungite, and a water soluble thermosetting polymer, melamine‐formaldehyde, were investigated. Two types of shungite with different carbon contents were investigated and compared to a commercial carbon black. The larger particle size and chemically more active surface of the shungites compared to carbon black leads to easy handling with little dusting and allows water to be used as dispersant. Laminates of melamine‐formaldehyde reinforced with random cellulose fibers and filler were prepared by film stacking. The layered structure results in anisotropic resistivities for the shungites with fairly low in‐plane percolation thresholds and a dissipative resistivity above the percolation transition. In comparison, carbon black had a lower percolation threshold and a low isotropic resistivity above the percolation transition. The mechanical properties of the composites were slightly deteriorated by all three fillers, indicating poor interfacial adhesion. The results of Fourier transform infrared (FTIR) measurements are interpreted as indicating hydrogen bonding and thus relatively weak adhesion between filler and polymer. Aqueous mixtures of melamine‐formaldehyde and shungite filler had lower viscosities than corresponding melamine‐formaldehyde and carbon black filler mixtures. POLYM. COMPOS., 26:552–562, 2005. © 2005 Society of Plastics Engineers     

聚合物纳米复合材料韧性和破坏行为

在总结高分子材料增韧机理、高分子纳米复合材料冲击破坏行为的基础上，探讨了高分子纳米复合材料的增韧机理。纳米无机粒子起应力集中的作用导致界面脱黏、空化与基体屈服是其增韧高分子材料的主要原因，而碳纳米管则起桥联裂纹、偏转裂纹方向、传递界面应力使聚合物基体屈服而增韧高分子材料。对聚合物／层状填料纳米复合材料而言，分散在聚合物基体中的插层或剥离的无机纳米片层对复合材料银纹的形成有抑制作用，其二维几何结构不利于片层周围基体的屈服与界面脱黏、空化，因而不能增韧高分子材料，反而还导致了聚合物／层状填料纳米复合材料抗冲击强度的降低。高分子材料的纳米复合目前很难达到橡胶增韧的效果，若同时采用纳米复合技术与官能化弹性体增韧技术，可望设计、制备出一系列高强度、高韧性的高分子纳米复合材料。     

Effects of the dispersion state and aspect ratio of carbon nanotubes on their electrical percolation threshold in a polymer

The electrical percolation threshold of carbon nanotubes (CNTs) is correlated with their dispersion state and aspect ratio through modeling. An analytical percolation model based on excluded volume theory and developed for systems containing two types of fillers is used. CNTs are modeled as two types of fillers: single CNT and m‐CNT bundle, and a variable P representing the dispersion state of CNTs is introduced. An equation showing the effects of the dispersion state and aspect ratio on the electrical percolation threshold of CNTs is established and verified with some of the published experimental data. It is useful for predicting the conductive behavior of polymer/CNT composites and for the design of their processing conditions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013