Development of rigid toughened photocurable epoxy foams

This study present a fast and efficient method for preparing photocurable rigid epoxy foams. A system based on the anionic photopolymerization of diglycidyl ether of bisphenol A (DGEBA) combined with a thiol-ene photopolymerization, was used. A tertiary diamine curing agent functionalized with four allyl groups was used in conjunction with a multifunctional thiol. The presence of several basic species, like tertiary amines, thiolates, polythioethers and alkoxide groups induced the anionic ring opening polymerization of the epoxy groups. At the same time the double bonds of the curing agent reacted with the multifunctional thiol generating polythioethers. The flexibility of the polythioethers modified the properties of the epoxy polymers, improving their toughness. Benzenesulfonyl hydrazide as foaming agent and zinc oxide as activator were added to DGEBA to produce the epoxy foams. The photopolymerization kinetics showed that conversion of the epoxide groups reached 80% in 600 s. Thermal curing studies performed by DSC showed that the main curing exotherm were determined at 84–89 °C, which match the temperature at which the photocuring was carried out in the UV light chamber (85 °C). It was found that the viscosity of the formulations plays a key role in the pore size of the foamed polymer, the higher the viscosity the larger the pore sizes. It was also determined that the impact resistance of the produced foams increased with increasing concentration of the thiol-ene system, as a consequence of a greater amount of polythioethers present in the co-network.     

Mechanical properties of graphene nanoplatelet/epoxy composites

Because of their high‐specific stiffness, carbon‐filled epoxy composites can be used in structural components in fixed‐wing aircraft. Graphene nanoplatelets (GNPs) are short stacks of individual layers of graphite that are a newly developed, lower cost material that often increases the composite tensile modulus. In this work, researchers fabricated neat epoxy (EPON 862 with Curing Agent W) and 1–6 wt % GNP in epoxy composites. The cure cycle used for this aerospace epoxy resin was 2 h at 121°C followed by 2 h at 177°C. These materials were tested for tensile properties using typical macroscopic measurements. Nanoindentation was also used to determine modulus and creep compliance. These macroscopic results showed that the tensile modulus increased from 2.72 GPa for the neat epoxy to 3.36 GPa for 6 wt % (3.7 vol %) GNP in epoxy composite. The modulus results from nanoindentation followed this same trend. For loadings from 10 to 45 mN, the creep compliance for the neat epoxy and GNP/epoxy composites was similar. The GNP aspect ratio in the composite samples was confirmed to be similar to that of the as‐received material by using the percolation threshold measured from electrical resistivity measurements. Using this GNP aspect ratio, the two‐dimensional randomly oriented filler Halpin–Tsai model adjusted for platelet filler shape predicts the tensile modulus well for the GNP/epoxy composites. Per the authors' knowledge, mechanical properties and modeling for this GNP/epoxy system have never been reported in the open literature. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Carbon nanotubes and graphene into thermosetting composites: Synergy and combined effect

This work analyzes the morphology and behavior of hybrid composites reinforced with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). In order to avoid the weak interface of laminar nanofillers, GNPs were functionalized with amine groups. Different tendencies were observed as a function of the measured property. Storage modulus showed a synergic trend, being the stiffness of hybrid CNT/GNP/epoxy composites higher than the corresponding ones measured in neat epoxy composites reinforced with CNTs or GNPs. In contrast, the thermal and electrical conductivity increased with the nanofiller addition, the final value of the mentioned properties in the hybrid composites was strongly influenced by specific graphitic nanofiller. Neat GNP/epoxy composites showed the highest thermal conductivity, while neat CNT/epoxy composites presented the highest electrical conductivity. This behavior is explained by the observed morphology. All composites exhibited a suitable nanofiller dispersion. However, on hybrid GNP/CNT/epoxy composites, CNTs tend to be placed between nanoplatelets, forming bridges between nanoplatelets. This morphology implies a less effective electrical network, limiting the synergic effect in the properties, which requires percolation. In spite of this, the hybrid GNP/CNT/epoxy composites showed a better combination of properties than the neat composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46475.     

Barrier properties of thermal and electrical conductive hydrophobic multigraphitic/epoxy coatings

Epoxy composites doped with different content of graphene nanoplatelets (GNPs) and/or carbon nanotubes (CNTs) have been manufactured. Their chemical, thermal, electrical, and mechanical behaviors have been studied, evaluating also their performance as coatings of glass fiber composite substrates. It is confirmed that the graphitic nanofillers present different efficiency as nanofillers as a function of their geometry. CNTs are much higher efficient electrical nanofillers than graphene, but an important synergetic effect is determined in the electrical conductivity of hybrid GNP/CNT/epoxy composites. In contrast, the thermal conductivity scarcely depends on the geometry of graphitic nanofillers but on the graphitic nanofiller content. Adding up to 12 wt% GNP and 1 wt% CNT, the thermal conductivity of the epoxy resin can be increased more than 300%. GNP presents high efficiency to increase the barrier properties, reducing the water absorption up to 30%. The stiffness of nanocomposites proportionally increases with graphitic addition, up to 50%, regard to the modulus of the neat epoxy resin. The adherence of coatings over glass fiber composite substrates increases by nanofiller addition due to the nanomechanical anchoring. However, the water uptake induces a higher weakening on nanodoped composites due to the preferential water absorption by the interface.     

Physical properties and shape memory behavior of thermoplastic polyurethane/poly(ethylene-<Emphasis Type="Italic">alt</Emphasis>-maleic anhydride) blends and graphene nanoplatelet composite

A new thermoplastic polyurethane (TPU) was prepared from polylactide-b-poly(ethylene glycol)-b-polylactide (soft segment) and 2,4-toluene diisocyanate (hard segment). Then, TPU in various proportions (i.e., 50, 70, and 90 wt%) was blended with poly(ethylene-alt-maleic anhydride) (PEMA) to form samples coded as TPU/PEMA50, TPU/PEMA70, and TPU/PEMA90. The TPU and PEMA blend at ratio of 50:50 was reinforced by various graphene nanoplatelets (GNPs) contents. Three novel strategies were opted in this research, including design of novel thermoplastic polyurethane, blend of TPU with poly(ethylene-alt-maleic anhydride), and fabrication of graphene nanoplatelet-based nanocomposites. Hydrogen bonding between blend component and GNPs directed the formation of regular nanostructure. Consequently, unique self-assembled flower-shaped morphology was observed in blends as well as hybrid materials using the scanning electron microscopy technique. Physical interlinking between blend components and nanofiller was also responsible for rise in tensile modulus (39.3 MPa) and Young’s modulus (4.04 GPa) of the TPU/PEMA/GNP 5 hybrid compared with the neat blend. The crystallization property was studied by the X-ray diffraction analysis and differential scanning calorimetry. The melting temperature of about 70 °C was preferred for the shape recovery studies. The results from heat-induced shape recovery were compared with those of electroactive shape memory effects. Electrical conductivity was increased to 0.18 S cm^?1 using 5 wt% GNP nanofiller, which was dependent on the applied temperature, as well. The original shape of TPU/PEMA/GNP 5 sample was almost 95 % recovered using heat-induced shape memory effect, while 98 % recovery was observed in an electric field of 40 V. Electroactive shape memory results were found to be better than those induced by heat stimulation effect.     

Graphene nanoplate and multiwall carbon nanotube–embedded polycarbonate hybrid composites: High electromagnetic interference shielding with low percolation threshold

This study has reported the preparation of polycarbonate (PC)/graphene nanoplate (GNP)/multiwall carbon nanotube (MWCNT) hybrid composite by simple melt mixing method of PC with GNP and MWCNT at 330°C above the processing temperature of the PC (processing temperature is 280°C) followed by compression molding. Through optimizing the ratio of (GNP/MWCNT) in the composites, high electromagnetic interference shielding effectiveness (EMI SE) value (∼21.6 dB) was achieved at low (4 wt%) loading of (GNP/MWCNT) and electrical conductivity of ≈6.84 × 10⁻⁵ S.cm⁻¹ was achieved at 0.3 wt% (GNP/MWCNT) loading with low percolation threshold (≈0.072 wt%). The high temperature melt mixing of PC with nanofillers lowers the melt viscosity of the PC that has helped for better dispersion of the GNPs and MWCNTs in the PC matrix and plays a key factor for achieving high EMI shielding value and high electrical conductivity with low percolation threshold than ever reported in PC/MWCNT or PC/graphene composites. With this method, the formation of continuous conducting interconnected GNP‐CNT‐GNP or CNT‐GNP‐CNT network structure in the matrix polymer and strong π–π interaction between the electron rich phenyl rings and oxygen atom of PC chain, GNP, and MWCNT could be possible throughout the composites. POLYM. COMPOS., 37:2058–2069, 2016. © 2015 Society of Plastics Engineers     

Graphene nanoplatelets for electrically conductive 3YTZP composites densified by pressureless sintering

3 mol% yttria tetragonal zirconia polycrystalline (3YTZP) ceramic composites with 2.5, 5 and 10 vol% graphene nanoplatelets (GNP) were pressureless sintered in argon atmosphere between 1350 and 1450 °C. The effects of the GNP content and the sintering temperature on the densification, microstructure and electrical properties of the composites were investigated. An isotropic distribution of GNP surrounding ceramic regions was exhibited regardless the GNP content and sintering temperature used. Electrical conductivity values comparable to the ones of fully dense composites prepared by more complex techniques were obtained, even though full densification was not achieved. While the composite with 5 vol% GNP exhibited electrical anisotropy with a semiconductor-type behaviour, the composite with 10 vol% GNP showed an electrically isotropic metallic-type behaviour.     

Epoxy composites with carbon nanotubes and graphene nanoplatelets – Dispersion and synergy effects

Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) at different mix ratios were dispersed by ultrasonication into an epoxy matrix and the effects of CNT:GNP ratios on the mechanical and electrical properties of the hybrid composites were investigated. The combination of CNT and GNP in a ratio 8:2 was observed to synergistically increase flexural properties and to reduce the electrical percolation threshold for the epoxy composites, indicating easier formation of a conductive network due to the improved state of CNT dispersion in the presence of GNPs. The state of dispersion was evaluated at different length scales by using optical microscopy, UV–Vis spectroscopy, rheological measurements, scanning electron microscopy, transmission electron microscopy and sedimentation tests. The Fourier transform infrared spectra for CNT and GNP indicate that the GNPs contain oxygen moieties responsible for better interactions with the epoxy matrix.     

Progress in shape memory epoxy resins

This review analyses the progress in the field of shape memory epoxy resins (SMEPs). Partial crystallisation and vitrification are the basis of shape memory effect in SMEPs. Several synthetic approaches for SMEPs, their composites and foams have been reviewed. Strategically incorporated thermally reversible segments induce the shape memory effect in epoxy resins. By varying the nature and concentration of shape memory segments, wide range of shape memory properties and transition temperatures (shape memory temperatures) can be achieved. Triple shape memory, self-healability and electroactive capability are some of the additional features that can be created in SMEPs. Among the thermoset resins, shape memory epoxies are the most attractive systems because of the ease of processability, composite forming properties and dimensional stability. Shape memory epoxy polymers that can be processed into elastic memory composites are candidate materials in the processing of many smart engineering systems. In this background, a review consolidating the progress in SMEP has contemporary relevance. The present article takes a stock of the trend in SMEP with a view to assess the direction of future initiatives in this area. It is concluded that there is tremendous scope for research leading to technological evolution in the field of SMEP.     

Joule effect self-heating of epoxy composites reinforced with graphitic nanofillers

Self-heating of conductive nanofilled resins due to the Joule effect is interesting for numerous applications, including computing, self-reparation, self-post-curing treatment of resins, fabrication of adhesive joints, de-icing coatings and so on. In this work, we study the effect of the nature and amount of graphitic nanofiller on the self-heating of epoxy composites.The addition of graphitic nanofillers induced an increase in the thermal conductivity of the epoxy resins, directly proportional to the nanofiller content. Percolation was not observed because of the heat transport through phonons. In contrast, the electrical conductivity curves present a clear percolation threshold, due to the necessity of an electrical percolation network. The electrical threshold is much lower for composites reinforced with carbon nanotubes (CNTs, 0.1 wt.%) than for the resin filled with graphene nanoplatelets (GNPs, 5 %). This fact is due to their very different specific areas.The composites filled with CNTs reach higher temperatures than the ones reinforced with GNPs, applying low electrical voltage because of their higher electrical conductivity. In contrast, the self-heating is more homogeneous for the GNP/epoxy resins due to their higher thermal conductivity. It was also confirmed that the self-heating is repetitive in several cycles, reaching the same temperature when the same voltage is applied.     

Incorporation of graphene into polyester/carbon nanofibers composites for better multi-stimuli responsive shape memory performances

Graphene oxide was directly reduced into graphene in N-methyl-pyrrolidone with the assisted-dispersion of vapor grown carbon nanofibers (VGCF), resulting in a homogeneous dispersion of VGCF–graphene hybrid filler (VGCF–G). In the hybrid filler, VGCF served as effective stabilizers for graphene by adsorbing VGCF onto graphene through π–π interaction. Subsequently, the as-prepared VGCF–G was incorporated into a bio-based polyester (BE) to prepare BE/VGCF–G composites by solution blending. In the composites, graphene was complete exfoliated with the assisted-dispersion of VGCF. Simultaneously, graphene acted as “compatibilizer” to improve the dispersion of VGCF and enhance the interfacial adhesions. As a consequence, the binary combination of VGCF and graphene showed remarkable synergistic effects in improving the electrical conductivity and mechanical properties of the BE/VGCF–G composites. For example, at the filler content of 4.8 vol%, the electrical conductivity of BE/VGCF–G composite is about 4 orders of magnitude higher than BE/VGCF composite containing VGCF alone, and the ultimate stress and modulus of BE/VGCF–G composite is 58% and 45% higher than those for BE/VGCF composite. Furthermore, multi-stimuli responsive shape memory performances (electro-activated and infrared-triggered) of the composites were investigated. BE/VGCF–G composites showed a combination of higher shape memory recovery, stronger recovery stress and faster response, compared with BE/VGCF composites.     

Mechanical properties of graphene nanoplatelet/carbon fiber/epoxy hybrid composites: Multiscale modeling and experiments

Because of the relatively high specific mechanical properties of carbon fiber/epoxy composite materials, they are often used as structural components in aerospace applications. Graphene nanoplatelets (GNPs) can be added to the epoxy matrix to improve the overall mechanical properties of the composite. The resulting GNP/carbon fiber/epoxy hybrid composites have been studied using multiscale modeling to determine the influence of GNP volume fraction, epoxy crosslink density, and GNP dispersion on the mechanical performance. The hierarchical multiscale modeling approach developed herein includes Molecular Dynamics (MD) and micromechanical modeling, and it is validated with experimental testing of the same hybrid composite material system. The results indicate that the multiscale modeling approach is accurate and provides physical insight into the composite mechanical behavior. Also, the results quantify the substantial impact of GNP volume fraction and dispersion on the transverse mechanical properties of the hybrid composite while the effect on the axial properties is shown to be insignificant.     

Multi-functional polyurethane composites with self-healing and shape memory properties enhanced by graphene oxide

Development of shape memory polymer materials with integrated self-healing ability, shape memory property, and outstanding mechanical properties is a challenge. Herein, isophorone diisocyanate, polytetramethylene ether glycol, dimethylglyoxime, and glycerol have been used to preparation polyurethane by reacting at 80°C for 6 h. Then, graphene oxide (GO) was added and the reaction keep at 80°C for 4 h to obtain polyurethane/GO composite with self-healing and shape memory properties. Scanning electron microscopy shows that the GO sheets were dispersed uniformly in the polyurethane matrix. The thermal stability was characterized by thermogravimetric analyses. The tensile test shows that the Young's modulus of the composites increases from 38.57 ± 4.35 MPa for pure polyurethane to 95.36 ± 10.35 MPa for the polyurethane composite with a GO content of 0.5 wt%, and the tensile strength increases from 6.28 ± 0.67 to 15.65 ± 1.54 MPa. The oxime carbamate bond and hydrogen bond endow the composite good self-healing property. The healing efficiency can reach 98.84%. In addition, the composite has excellent shape memory property, with a shape recovery ratio of 88.6% and a shape fixation ratio of 55.2%. This work provides a promising way to fabricate stimulus-responsive composite with versatile functions.     

TPU/PCL/nanomagnetite ternary shape memory composites: studies on their thermal, dynamic-mechanical, rheological and electrical properties

Shape memory polymer composites based on a blend of thermoplastic polyurethane (TPU) segmented block copolymer and poly(ε-caprolactone) (PCL) with weight ratio of 70/30 and various nanomagnetite contents (0–5 wt%) were prepared by melt blending of TPU and PCL, together with a masterbatch of TPU/nanomagnetite. The samples were compounded for 10 min at 200 °C using an internal mixer. Synthesized nanomagnetite powder was introduced to the masterbatch via a solution mixing method using a high-intensity ultrasonic horn. Subsequently, thermal, mechanical, rheological and electrical properties of the TPU/PCL/nanomagnetite shape memory composites were investigated through various tests. The degree of crystallization of the PCL component in the composite structure was inspected by differential scanning calorimetry (DSC) and X-ray diffraction measurements. The results revealed that the percentage of crystallinity and the melting temperature of the PCL component changed in the presence of magnetite nanoparticles, which was related to the nanoparticles acting as nucleants. Observing a single glass transition temperature (T _g) in DSC thermograms of the samples was indicative of good compatibility of the TPU and PCL components in the composite structure. This was also confirmed by dynamic-mechanical analysis in which the loss modulus curves showed a single glass transition temperature. Moreover, the loss modulus peak at glass transition was lowered and broadened by addition of nanomagnetite, by which it was assumed that introducing nanoparticles into the system changed the mechanism of glass transition due to particle–matrix interactions. The dynamic rheological and electrical resistivity experiments verified the existence of a low percolation threshold at about 2 wt% nanomagnetite. The state of nanomagnetite dispersion in the masterbatch and the microstructure of the ternary composites were characterized by scanning electron microscopy. Finally, adding nanomagnetite led to weakening of shape recovery of the polymer blend, with shape recovery dropping to 70 % at 5 % of nanomagnetite.     

Effect of phase transitions on the electrical properties of polymer/carbon nanotube and polymer/graphene nanoplatelet composites with different conductive network structures

Multi‐walled carbon nanotube (MWCNT)‐ and graphene nanoplatelet (GNP)‐filled high‐density polyethylene (HDPE) composites with dispersed and segregated network structures were prepared by solution‐assisted mixing. Simultaneous DC conductivity and differential scanning calorimetry were used to measure electrical conductivity during composite thermal phase transitions. It was found that the conductive network is deformed during melting and rebuilt again during annealing due to the re‐agglomeration of nanofillers. The rebuilding of the structure is significantly affected by the original network structure and by the shape and loading of the nanofillers. Both deformation and reorganization of the network lead to drastic changes in the conductivity of the composites. The crystallization process also affects the conductive network to some extent and the subsequent volume shrinkage of the polymeric matrix after crystallization results in a further decrease in the resistivity of HDPE/GNP composites. Classical electrical percolation theory combined with a kinetic equation is used to describe the conductivity recovery of composites during annealing, and the results are found to be in good agreement with experimental data. © 2017 Society of Chemical Industry     

聚丙烯/石墨烯微片/碳化硅复合材料微观形态与导电导热性能研究

采用熔融共混法制备聚丙烯/石墨烯微片/碳化硅(PP/GNP/SiC)复合材料,研究了SiC用量对PP/GNP/SiC复合材料的微观形态、结晶度和导电导热性能的影响。SEM与XRD测试结果表明,SiC粒子有助于提高拉伸力场对GNP的剥离效果以及GNP在PP基体中的分散程度,随着SiC粒子用量的增加,GNP的片径尺寸和片层厚度均减小,并与SiC粒子相互搭接。导电导热分析结果表明,随着SiC粒子用量的增加,PP/GNP/SiC复合材料的电导率先升高后降低,热导率逐渐提高。SiC用量为5%时,复合材料的电导率最高;SiC用量为20%时,复合材料的热导率最高。     

Preparation of antistatic and biodegradable packaging of PLA/PHBV blend-based glassy carbon and graphene nanoplatelets composites

Glassy carbon (GC) and graphene nanoplatelets (GNP) were used as fillers for the preparation of antistatic and biodegradable composites based on poly (lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PLA/PHBV) blend. In this work, PLA/PHBV (80/20) blends with the addition of different GC contents (0.1, 0.3, and 0.5 wt%) were prepared by melt mixing using a twin-screw extruder, and specimens were injection molded. Furthermore, hybrid composites were prepared with the addition of 5 wt% of GNP and different GC contents (0.1, 0.3, and 0.5 wt%) using the same processing. The effect of the addition of GC and GNP on the mechanical, electrical, and electromagnetic properties and its effect on the biodegradability of the PLA/PHVB blend was evaluated. The simultaneous addition of GC (0.3 and 0.5 wt%) and GNP (5 wt%) significantly increases the elastic modulus and decreases the electrical resistivity, becoming suitable for electrostatic discharge protection packaging applications. The hybrid composite GC0.5/GNP5 reached a maximum value of total attenuation (4.5 dB), which corresponds to 60% EMI shielding. The degree of crystallinity affects biodegradability more than the type or presence of carbon material. After 110 days of anaerobic biodegradation, the hybrid composite exhibited 10% biodegradability due to the high degree of crystallinity that hinders the biodegradability process. The hybrid composites with the addition of GC and GNP are very promising for use in antistatic packaging.     

Effect of dopant and oxidant on the electrochemical properties of polyaniline/graphite nanoplate composites

Optimizing the synthesis parameters of polyaniline/graphite nanoplate (PANI/GNP) composite is essential to the final electrochemical performance. Herein, the electrochemical properties of PANI/GNP composites, prepared by in situ chemical polymerization using varying amounts of different oxidants, with or without the addition of 4‐dodecylbenzenesulfonic acid (DBSA) as dopant, were investigated. Cyclic voltammetric results suggested that a stoichiometric amount of the oxidant iron chloride (FeCl₃) was beneficial to the electrochemical properties of the composites. The use of ammonium persulfate (APS) instead of FeCl₃ as oxidant largely increased the actual PANI content, conductivity and specific capacitance of the PANI/GNP composites. The dopant DBSA increased the conductivity of the PANI/GNP composites but did not show a positive effect on the electrochemical behavior. The cyclic voltammograms of the PANI/GNP composites indicated that the pseudocapacitance of PANI contributes more than the electrical double‐layer capacitance of GNP to the capacitance of the composites, while the presence of GNP plays an essential role in the rate capability of the composites. In this study, PANI/GNP (1:1) composite synthesized with an APS to aniline molar ratio of 1 showed a balanced combination of high specific capacitance (180.5 F g^?1 at 20 mV s^?1) and good rate capability (78% retention at 100 mV s^?1). © 2018 Society of Chemical Industry     

The effect of an anhydride curing agent,an accelerant,and non‐ionic surfactants on the electrical resistivity of graphene/epoxy composites

This study investigated different contents of an anhydride curing agent, an accelerant, and non‐ionic surfactants on the electrical resistivity of cured graphene/epoxy composites. The anhydride curing agent was hexahydrophthalic anhydride (HHPA), the accelerant was 2‐ethyl‐4‐methyl‐1H‐imidazole‐1‐propanenitrile (EMIP), and the non‐ionic surfactants were Triton X surfactants with different numbers of polyethylene oxide (PEO) groups (m) that influence the electrical resistivity of cured graphene/epoxy composites. During the curing process, differential scanning calorimetry (DSC) was used to determine the effects of the extent of the crosslinking for different contents of the curing agent and how different enthalpy (ΔH) on the electrical resistivity of the cured graphene/epoxy composites was then generated. The cured graphene/epoxy composite—which consisted of a 1 : 0.85 weight ratio of epoxy resin and anhydride, a 0.5 wt % accelerant, and a 13 wt % graphene powder—had a low electrical resistivity of 11.68 Ω·cm and a thermal conductivity of 1.7 W/m·K. In addition, the cured composites contained a 1.0 wt % polyethylene glycol p‐isooctylphenyl ether (X‐100) surfactant, which effectively decreased their electrical resistivity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41975     

Temperature dependence of the conductivity behavior of graphite nanoplatelet‐filled epoxy resin composites

In this article, epoxy/graphite nanoplatelet (GNP) conductive composites with the low percolation threshold of ～ 0.5 vol % were prepared. The effect of microstructure, particularly the spatial distribution of fillers in the matrix on the resistivity and its dependence on temperature, also was investigated. It is suggested that the high aspect ratio and good distribution of GNPs in the matrix contribute to the low threshold of the composite. The thermal–electrical behavior of the composite is also significantly influenced by the GNP content and microstructure of the composite. When the GNP content is greater than percolation threshold, a noticeable positive temperature coefficient of resistivity disappears. It is explained by the unique conductive network formed by plane contact between GNPs, which is hardly affected by the expansion of matrix during heating. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009