Triple percolation behavior and positive temperature coefficient effect of conductive polymer composites with especial interface morphology

Selective localization of carbon black (CB) at the interface of polymer blends was achieved by the method that poly(styrene-co-maleic anhydride) (SMA) was first reacted with CB, and then blended with nylon6/polystyrene (PA6/PS). In the PA6/PS blends, CB was localized in PA6 phase and typical double percolation was exhibited. In the PA6/PS/(SMA–CB) blends, TEM results showed that CB particles were induced by SMA to localize at the interface, resulting in the especial interface morphology fabricated by SMA and CB. The especial interface morphology of PA6/PS/(SMA–CB) caused distinct triple percolation behavior and very low percolation threshold. The positive temperature coefficient (PTC) intensity of PA6/PS/(SMA–CB) composites was stronger than that of PA6/PS/CB and the negative temperature coefficient (NTC) effect was eliminated. The elimination of NTC effect was arisen from the especial interface morphology. A stronger PTC intensity was attributed to the low percolation threshold and the morphology.     

Economical conductive graphite-filled polymer composites via adjustable segregated structures: Construction,low percolation threshold,and positive temperature coefficient effect

The economical graphite-filled thermoplastic urethane/ultra-high molecular weight polyethylene (TPU/UHMWPE) composites with the segregated structure were constructed by the combination of mechanical crushing and melt blending method. The low percolation threshold of 1.89 wt% graphite in the adjustable segregated composites was obtained and high electrical conductivity was about 10⁻¹ S m⁻¹ at 10 wt% graphite loadings owing to the formation of three-dimensional conductive networks. Moreover, when the graphite loadings were over the percolation threshold, the remarkable positive temperature coefficient (PTC) effect of electrical resistivity for TPU/UHMWPE-Graphite composites were achieved, originating from the combined thermal motion of TPU and UHMWPE. Meanwhile, the outstanding repeatability of PTC effects was obtained after 5-time cycles. Therefore, economical conductive polymer composites were still the promising field in the practical application of PTC materials.     

Influence of morphology on positive temperature coefficient effect for conductive polymer composites with carbon black dispersed at interface

Selective localization of carbon black (CB) at the interface of polymer blends was achieved by the method that EBA‐g‐MAH was first reacted with CB, and then blended with poly(ethylene‐co‐butyl acrylate)/nylon6 (EBA/PA6). In CB‐filled EBA/PA6 blends, EBA and PA6 phases formed cocontinuous morphology and CB was localized in PA6 phase. The percolation threshold was 5 wt%. A single PTC (positive temperature coefficient) effect was observed in this composite. The appearance of PTC effect was originated from the thermal expansion of EBA phase. In the EBA‐g‐MAH filled EBA/PA6 blends, TEM results showed that CB particles were induced by EBA‐g‐MAH to localize at the interface, resulting that the percolation threshold was much lower than that of EBA/PA6/CB. Influence of morphology on PTC effect of EBA/PA6/EBA‐g‐MAH/CB composites was studied. In the composites with sea‐island morphology, the conductive network was fabricated by dispersed phase and CB at the interface. Thermal expansion of matrix interrupted the contact of dispersed phases and conductive network formed by CB particles at the interface, resulting in the double PTC effect. The composites with co‐continuous morphology exhibited single PTC effect due to the fact that conductive network was only fabricated by CB localized at the interface. POLYM. ENG. SCI., 53:2640–2649, 2013. © 2013 Society of Plastics Engineers     

Temperature dependence of electrical resistivity for carbon black filled ultra-high molecular weight polyethylene composites prepared by hot compaction

In this article, the temperature dependence of electrical resistivity is studied for carbon black (CB)/ultra-high molecular weight polyethylene (UHMWPE) composites. A new positive temperature coefficient (PTC) material with a very low percolation threshold is produced by the hot compaction method. The very low percolation threshold can be attributed to the segregation of CB in the interfacial regions of UHMWPE particles. The percolation threshold decreases with the increase of the molecular weight of UHMWPE, and with the decrease of the particle size of CB. For CB filled lower molecular weight UHMWPE (145M) composites, the PTC temperature, at which a sharp increase in the resistivity of the composite occurs, decreases with the increase of CB size. However, for a higher molecular weight UHMWPE (630M) filled with CB, the second PTC effect is observed and the negative temperature coefficient (NTC) effect is eliminated. A mechanism is proposed to explain these phenomena based on the optical microscopy and TEM observations. It can be concluded that the degree of the intermixing between CB and UHMWPE particles plays an important role in determining the electrical properties of the composites.     

Positive temperature coefficient to resistively characteristics of polystyrene/nickel powder/multiwall carbon nanotubes composites

Positive temperature coefficient to resistivity (PTCR) characteristics of polystyrene (PS)/Ni‐powder (40 wt%) composites in the presence of multiwall carbon nanotubes (MWCNTs) has been investigated with reference to PS/carbon black (CB) composites. The PS/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈110°C, above the glass transition temperature (T_g) of PS (T_g ≈95°C). Interestingly, the PTC trip temperature of PS/Ni‐powder (40 wt%)/MWCNT (0.75 phr) composites appeared at ≈90°C (below T_g of PS), indicating better dimensional stability of the composites at PTC trip temperature. The PTC trip temperature of the composites below the T_g of matrix polymer (PS) has been explained in terms of higher coefficient of thermal expansion (CTE) value of PS than Ni that led to a disruption in continuous network structure of Ni even below the T_g of PS. The dielectric study of PS/Ni‐powder (40 wt%)/MWCNT (0.75 phr) composites indicated possible use of the PTC composites as dielectric material. Dynamic mechanical analysis (DMA) and thermogravimetric analysis studies revealed higher storage modulus and improved thermal stability of PS/Ni‐powder (40 wt%)/MWCNT (0.75 phr) composites than the PS/CB (10 wt%) composites. POLYM. COMPOS., 33:1977–1986, 2012. © 2012 Society of Plastics Engineers     

PTC effect in carbon black‐filled ethylene–propylene–diene terpolymer systems

The positive temperature coefficient (PTC) effects of carbon black (CB)‐filled semicrystalline and amorphous ethylene–propylene–diene terpolymer (EPDM) composites were studied. The semicrystalline EPDM/CB composite exhibited a low PTC effect followed by a pronounced negative temperature coefficient (NTC) effect, while the amorphous EPDM/CB composite exhibited only an NTC effect. By the effect of γ‐ray irradiation, not only was the NTC effect of the composites eliminated, but also a high PTC effect appeared. The PTC intensity reached as high as six orders of magnitude even for an amorphous EPDM/CB composite and the PTC transition temperature decreased with the irradiation dose. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1571–1574, 2001     

Influence of morphology on PTC effect for poly (ethylene-co-butyl acrylate)/nylon6 blends with multiwall carbon nanotubes dispersed at interface and in matrix

Multiwall carbon nanotubes (MWCNTs) filled poly (ethylene-co-butyl acrylate)/nylon6 (EBA/PA6) blends were prepared by melt-mixing method. MWCNTs were localized in PA6 phase and the percolation threshold was 6 wt%. A weak PTC (positive temperature coefficient) effect was observed. The method that EBA-g-MAH was first reacted with MWCNTs, and then blended with EBA/PA6 was employed to prepare EBA/PA6/EBA-g-MAH/MWCNTs composites. TEM results showed that MWCNTs were localized both at the interface and in PA6 phase, resulting in the sharp decrease of the percolation threshold. Influence of morphology on the PTC effect of EBA/PA6/EBA-g-MAH/MWCNTs composites was studied. In composites with dispersed PA6 phase, the conductive pathways were fabricated by the contact of dispersed PA6 phase and MWCNTs in PA6 phase. The melt of polyethylene segment crystals in EBA and PA6 phase interrupted the contact of dispersed phases and conductive network formed by MWCNTs in PA6 phase, resulting in the double PTC effect. For composites with dispersed EBA phase, although the conductive pathways were similar with the composites with dispersed PA6 phase, the single PTC effect was observed. And the PTC effect was attributed to the melt of PA6 phase. The conductive pathways of composites with co-continuous morphology were fabricated by MWCNTs at the interface and in continuous PA6 phase. Two strong and a weak PTC effect were observed. PTC effects appeared at the melting temperature of PA6 crystals, polyethylene segment crystals and viscous flow temperature of butyl acrylate units in EBA.     

Effect of temperature on the electrical resistivity of YBa2Cu3O7−x/polyethylene composite materials

Heterogeneous materials composed of conducting YBa₂Cu₃O_7?x particles randomly dispersed inside an insulating low density polyethylene (LDPE) matrix were prepared. The resistivity of the composites was measured as a function of temperature between 293 and 400 K. A large positive temperature coefficient (PTC) of resistance was observed near 395 K. The mechanism of the PTC effect in the materials is related to the percolation behavior of the YBa₂Cu₃O_7?x/LDPE composites and the thermal expansion of the LDPE matrix. The intensity of the PTC effect for these composites was found to be as large as nine orders of magnitude. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers.     

Electrical behavior and positive temperature coefficient effect of graphene/polyvinylidene fluoride composites containing silver nanowires

Polyvinylidene fluoride (PVDF) composites filled with in situ thermally reduced graphene oxide (TRG) and silver nanowire (AgNW) were prepared using solution mixing followed by coagulation and thermal hot pressing. Binary TRG/PVDF nanocomposites exhibited small percolation threshold of 0.12 vol % and low electrical conductivity of approximately 10^-7 S/cm. Hybridization of TRGs with AgNWs led to a significant improvement in electrical conductivity due to their synergistic effect in conductivity. The bulk conductivity of hybrids was higher than a combined total conductivity of TRG/PVDF and AgNW/PVDF composites at the same filler loading. Furthermore, the resistivity of hybrid composites increased with increasing temperature, giving rise to a positive temperature coefficient (PTC) effect at the melting temperature of PVDF. The 0.04 vol % TRG/1 vol % AgNW/PVDF hybrid exhibited pronounced PTC behavior, rendering this composite an attractive material for making current limiting devices and temperature sensors.     

填充型多相聚合物导电复合材料的PTC效应

以聚丙烯和低密度聚乙烯共混物为基体,用碳黑为填充材料制备了复合导电材料,导电性能的测试表明多相复合体系的渗滤阈值低于两相复合体系的渗滤阈值。对复合材料PTC效应的分析以及对材料的热性能测试结果表明碳黑在共混体系中的分布。同时探讨了体系碳黑含量的变化对PTC效应的影响。     

CTBN对CB/EP基导电复合材料电性能的影响

以低结构CB(炭黑)为导电填料、EP(环氧树脂)为基体、CTBN(端羧基液体丁腈橡胶)为改性剂和2,4-EMI(2-乙基-4-甲基咪唑)为固化剂,采用超声分散法制备CB/EP基导电复合材料.研究结果表明:CB/EP基导电复合材料具有明显的导电渗流行为,其渗流阈值为w(CB)=7.1％;当w(CTBN)=12％时,含CT...     

Effect of incorporating ethylene‐ethylacrylate copolymer on the positive temperature coefficient characteristics of carbon black filled HDPE systems

In order to study the effect of introducing ethylene‐ethylacrylate copolymer (EEA) in carbon black‐HDPE composite systems, two HDPE‐EEA composites prepared by pre‐blending and masterbatch‐blending processes were compared with HDPE and EEA composites in terms of positive temperature coefficient (PTC) characteristics and percolation threshold. The percolation threshold of masterbatch‐blended composites occurred at the lowest carbon black concentration among four kinds of composites. The conduction path in the masterbatch‐blended composite is effectively formed as a result of the localization of carbon black distribution predominantly in the EEA phase, resulting in an increase of conductivity. I_peak values, the resistivity ratio of the peak to 25°C, of two blend composites were lower than those of HDPE composites. The I₈₅ values, the resistivity ratio of 85°C to 25°C, of masterbatch‐blended composites were higher than those of pre‐blended as well as HDPE composites. It is evident that since most carbon black is dispersed in the EEA phase of the masterbatch‐blended composites, the conduction networks are mainly broken by the crystal melting of EEA before the temperature reaches the crystal melting temperature of HDPE.     

Encapsulated graphenes through ultrasonically initiated in situ polymerization: A route to high dielectric permittivity,low loss materials with low percolation threshold

To improve dielectric performance of polystyrene (PS) without sacrificing its flexibility and processability, PS encapsulated graphene sheets (PSG) were synthesized by ultrasonically initiated in situ polymerization and was incorporated into PS matrix as fillers. The structure and properties of the obtained PSG were investigated by Fourier transform infrared, transmission electron microscopy, scanning electron microscope, and atom force microscopies. The results showed that the in situ formed PS layers attached on the surface of graphene and there were strong interfacial interactions between them. In virtue of this core‐shell architecture and intrinsic properties of PSG, PS/PSG nanocomposites exhibited improved dielectric performance and a typical percolation transition with very low percolation threshold of 0.2 wt %. Compared with pure PS, significantly increased dielectric permittivity and a low loss tangent were observed for the composites. These composites might be potential flexible dielectric materials for use in high‐frequency capacitors with low loss. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44628.     

超高相对分子质量聚乙烯/石墨烯微片复合材料的导电行为研究

采用溶液混合、超声波分散的方法制备了超高相对分子质量聚乙烯（PE UHMW）/石墨烯微片（GNPs）复合材料,研究了PE UHMW/GNPs复合材料的导电行为和阻温特性。结果表明,本方法可以使GNPs在PE UHMW基体中良好地分散;复合材料表现出典型的导电渗流行为,渗流阈值为2.8 %（质量分数,下同）;在高于渗流阈值的情况下,PE UHMW/GNPs复合材料的正温度系数效应（PTC）强度随GNPs含量的增加而减小,在渗流阈值附近复合材料的PTC强度最高;PE UHMW/GNPs复合材料的阻温特性重复性较好,多次热循环后PTC强度趋于稳定。     

高抗冲聚苯乙烯/炭黑导电复合材料 PTC效应的研究

采用SEM、XRP、DSC和体积膨胀等手段对非结晶形HIPS／CB（聚苯乙烯／炭黑）导电复合材料的导电行为进行分析。实验结果表明，HIPS／CB导电复合材料的渗流区域较窄，炭黑含量为30～40g时，电阻发生急剧降低，在渗流阀值附近导电复合材料的电阻率变化最大，跃迁强度为2.2个数量级；HIPS／CB导电复合材料的PTC起始转变温度在85℃左右，与HIPS的玻璃化转变温度接近，HIPS作为非晶材料其体积膨胀较弱，并不足以单独解释PTC效益。     

Improvement of polyimide/polysulfone composites filled with conductive carbon black as positive temperature coefficient materials

In this study, polyimide (PI)/polysulfone (PSF) blends filled with carbon black (CB) were developed for the use as positive temperature coefficient (PTC) materials in order to achieve the volume resistivity as lower than 10⁴ Ω.cm at room temperature. The weight ratios of PI/PSF were various from 100/0 to 10/90 with CB varied from 0 to 20 wt%. The use of conductive filler was reduced when PSF was blended with PI; the blends clearly possessed a percolation threshold decreased by 90%. The electrical conductivity of the CB-filled blends was higher than those of CB-filled pure PI. The transition temperature for PTC material was reported in the range of 180 to 210 °C. The preferential location of CB filler in PI domains could be observed using the optical microscope. In addition, the composites met the standards for the obtained mechanical and thermal properties, exhibiting the potential use as PTC materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48482.     

Influences of crystallization histories on PTC/NTC effects of PVDF/CB composites

Two switching phenomena of poly (vinylidene fluoride) (PVDF) containing carbon black (CB) with different crystallization histories are studied. Both the percolation threshold (Φpc) and the critical concentration of the positive temperature coefficient (PTC) materials (Φc) increase as the crystallization temperature declines. PTC and the negative temperature coefficient (NTC) effect become obvious when the cooling speed is reduced. The morphologies of PVDF crystals play an important role in modifying the shape of the resistivity-temperature (ρ-T) curves. The PTC and NTC intensities of these systems, whose CB contents lie between Φpc and Φc, increase with increasing crystallinity, which are realized by altering the crystallization histories of the matrices. © 1996 John Wiley & Sons, Inc.     

Effect of the carbon black structure on the stability and efficiency of the conductive network in polyethylene composites

Composites of high‐density polyethylene (HDPE) with different kinds of carbon black (CB) were prepared through melt blending. The influence of the CB structure on the stability and efficiency of the conductive network in HDPE/CB composites were mainly investigated. Scanning electron microscopy was used to observe the morphology of the CB primary aggregates. The relationship between the temperature‐resistivity behaviors of the composites and the crystallization behaviors of the matrix were also investigated. High‐structure CB built an effective conductive network at a low filler content compared to the low‐structure one because of its branched morphology. Therefore, the composite containing high‐structure CB revealed a lower percolation threshold. The composite containing low‐structure CB obtained a stronger positive temperature coefficient (PTC) intensity because the cluster network was fragile and easily damaged during matrix melting. The reproducibility of the results of PTC effect of the composite containing high‐structure CB was better than that of the composite containing a low‐structure one. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

PTC effect and structure of polymer composites based on polyethylene/polyoxymethylene blend filled with dispersed iron

The temperature dependence of resistivity, structure, and thermal expansion of composites based on polyethylene/polyoxymethylene (PE/POM) blends filled with dispersed iron (Fe) have been studied. The dependence of conductivity on filler content shows percolation behavior, with the values of the percolation thresholds equal to 21 vol% for PE-Fe, 24 vol% for POM-Fe, and 9 vol% for the filled blend PE/POM-Fe, with two-step character of the conductivity curve. The evolution of structure of the composite PE/POM-Fe demonstrates transition from polymer matrix POM-Fe, with inclusions of PE through cocontinuous phases of both POM-Fe and PE, to PE matrix, with inclusions of POM-Fe. Such a structure occurs due to localization of the filler only in one of the polymer phases, namely in POM. Measurements of the coefficient of thermal expansion α show the presence of two values of α: higher value (equal to α of PE) and lower value (equal to α of POM-Fe), the transition between them corresponding to the structure with cocontinuous phases. The PE/POM-Fe composites demonstrate double-positive temperature coefficient (PTC) effect, with the presence of two transitions and a plateau between them. In such a system, two contributions to the PTC effect coexist: the first contribution originates from the thermal expansion of the nonconductive PE phase with higher value of the coefficient α, which leads to the break of the continuity of the conductive POM-Fe phase; the second contribution originates from the break of the conductive structure of the filler inside the POM-Fe phase because of the morphological changes in the vicinity of the melting temperature of POM. The double PTC effect is explained in terms of these two processes (thermal expansion and melting). POLYM. ENG. SCI., 47:34–42, 2007. © 2006 Society of Plastics Engineers     

Effect of nanoclay on positive temperature coefficient to resistivity characteristics of high density polyethylene/silver‐coated glass bead composites

Positive temperature coefficient to resistivity characteristics of high density polyethylene (HDPE)/silver (Ag)‐coated glass bead (45 wt%) composites, without and with nanoclay, has been investigated with reference to HDPE/carbon black (CB) (10 wt%) composites. Plot of resistivity versus temperature of HDPE/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈128°C, close to the melting temperature (T_m) of HDPE. However, for HDPE/Ag coated glass bead (45 wt%) composites, the PTC trip temperature (≈88°C) appeared well below the T_m of HDPE. Addition of 1 phr clay in the composites resulted in an increase in PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites, whereas no significant effect of clay on PTC trip temperature was evident in HDPE/CB/clay composites. We proposed that the PTC trip temperature in HDPE/Ag‐coated glass bead composites was governed by the difference in coefficient of thermal expansion of HDPE and Ag‐coated glass beads. The room temperature resistivity and PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites were found to be very stable on thermal cycling. Dynamic mechanical analyzer results showed higher storage modulus of HDPE/Ag‐coated glass bead (45 wt%) composites compared with the HDPE/CB (10 wt%) composites. Thermal stability of HDPE/Ag‐coated glass bead (45 wt%) composites was also improved compared with that of HDPE/CB (10 wt%) composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers