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     

Highly reversible and repeatable PTCR characteristics of PMMA/Ag‐coated glass bead composites based on CTE mismatch phenomena

Positive temperature coefficient of resistivity (PTCR) behavior of poly(methyl methacrylate) PMMA/silver (Ag)‐coated glass bead composites has been investigated with reference to the conventional PMMA/carbon black (CB) composites. The PMMA/CB composites showed a sudden rise in resistivity (PTC trip) at 115°C, close to the glass transition temperature (T _g, 113°C) of the PMMA. However, the PTC trip temperature (92°C) of PMMA/Ag‐coated glass bead composites was appeared well below the T _g of PMMA. The room temperature resistivity and PTC trip temperature of the composites were also very much stable upon thermal cycling. Addition of 1 phr of nanoclay increased the PTC trip temperature of PMMA/CB composites to 120°C, close to the T _g (118°C) of PMMA/clay nanocomposites, while PMMA/clay/Ag‐coated glass bead nanocomposites showed the PTC trip at 98°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between PMMA and glass beads played a key role that led to a disruption in continuous network structure of Ag‐coated glass beads even at a temperature well below the T _g of PMMA. The decrease in dielectric permittivity of PMMA/Ag‐coated glass bead composites on increasing frequency indicated possible use of the PTC composites as dielectric material. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

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     

PTCR characteristics of poly(styrene‐co‐acrylonitrile) copolymer/stainless steel powder composites

Positive temperature coefficient of resistivity (PTCR) characteristics of poly(styrene‐co‐acrylonitrile) copolymer (SAN)/stainless steel (SS) powder (80 wt %) composites prepared by melt‐mixing method has been investigated with reference to SAN/carbon black (CB) composites. The SAN/CB (10 wt %) composites showed a sudden rise in resistivity (PTC trip) at 125°C, above the glass transition temperature (T_g) of SAN (T_g ≈ 107°C). However, the PTC trip temperature of SAN/SS (80 wt %) composites appeared at 94°C, well below the T_g of SAN. Addition of 1 phr of nanoclay increased the PTC trip temperature of SAN/CB (10 wt %) composites to 130°C, while SAN/SS (80 wt %)/clay (1 phr) nanocomposites showed the PTC trip at 101°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between SAN and SS played a key role that led to a disruption in continuous network structure of SS even at a temperature below the T_g of SAN. The dielectric properties study of SAN/SS (80 wt %) composites indicated possible use of the PTC composites as dielectric material. DMA results showed higher storage modulus of SAN/SS composites than the SAN/CB composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

High‐density polyethylene/carbon black conductive composites. II. Effect of electron beam irradiation on relationship between resistivity–temperature behavior and volume expansion

A study on the contribution of thermal volume expansion to electrical properties is carried out for high‐density polyethylene (HDPE)/carbon black (CB) composites irradiated by an electron beam. The results show that the volume expansion obviously generates the positive temperature coefficient (PTC) characteristic of resistivity for unirradiated HDPE/CB composites, but the contribution of volume expansion is decreased for crosslinked HDPE in the composites by electron beam irradiation. A higher degree of crosslinking produced by irradiation in the molten state limits the movability of HDPE chains and CB particles so effectively that it decreases the PTC intensity, which is compared with that irradiated at room temperature. It is suggested that the differences in the resistivity–temperature behavior are not explained satisfactorily on only the basis of the thermal volume expansion, and the decreased movability of HDPE chains and CB particles are believed to be the most fatal factors in lowering the PTC effect. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3117–3122, 2002; DOI 10.1002/app.10050     

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.     

Effects of thermal aging on morphology,resistivity, and thermal properties of extruded high‐density polyethylene/carbon black heating elements

Various output heating elements were extruded with carbon black (CB)‐filled high‐density polyethylene (HDPE) composites. After thermal aging near melting point of HDPE, the effects of thermal aging on the morphology, resistivity, and thermal properties of the extruded and electron beam (EB)‐irradiated heating elements were examined using scanning electron microscopy (SEM) megohmmeter and differential scanning calorimetry, respectively. The heating element was insulated with a polytetrafluoroethylene tape wrap. The SEM image of HDPE is covered with microvoids that leave a dimple‐like structure on the surface. As the percolation threshold is achieved, CB aggregates are usually located in oval cavities larger than the particles themselves. During the resistivity–temperature cycling test, significant change in resistivity was observed for extruded and EB‐irradiated heaters. In case of thermal‐aged samples at 140°C for 120 h, both heaters showed good stability without pronounced changes in resistivity after resistivity–temperature cycling test. After thermal aged at 140°C for 120 h, the Heater02‐EB composite recovered the oval cavity structure, whereas for Heater02, the amorphous region became narrower and formed a more electroconductive pathway. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Carbon black–filled immiscible blends of poly(vinylidene fluoride) and high density polyethylene: The relationship between morphology and positive and negative temperature coefficient effects

Conductive polymer composites were prepared by melt-mixing of an immiscible blend of poly(vinylidene fluoride) (PVDF), high density polyethylene (HDPE), and carbon black (CB). Three major factors—the carbon black content, the carbon black type, and the composite morphology—were shown to have remarkable effects on the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effect of the composites. The relationship between the morphology and the PTC and NTC effects of the composites was investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The OM micrographs indicated that CB was selectively located in the HDPE phase and the SEM micrographs showed that there were some gaps between the two phases. The PTC effect of the composites is caused by the thermal expansion as a result of the melting of the HDPE crystallites. The morphology of the composites greatly affects the PTC and NTC behaviors of the composites. When the CB-filled HDPE formed a continuous phase and the PVDF formed a dispersed phase, the PTC and NTC behaviors of the composites were similar to those of CB-filled neat HDPE composite without crosslinking. When the composite exhibited an interlocking structure, a normal PTC effect could also be observed, but the NTC effect was delayed to higher temperatures. A mechanism was proposed to explain this new physical phenomenon, and the mechanism was verified by another CB-filled polymer blend comprising an alternating copolymer of tetrafluoroethylene-ethylene and HDPE.     

PTCR characteristics of polycarbonate/nickel‐coated graphite‐based conducting polymeric composites in presence of poly(caprolactone)

The effect of poly(caprolactone) (PCL) on the positive temperature coefficient of resistivity characteristics of polycarbonate (PC)/nickel (Ni)‐coated graphite (40 wt%) composites was investigated. The PTC trip temperature of PC/Ni‐coated graphite composites appeared at 155°C. On addition of PCL to PC/Ni‐coated graphite composites, the PTC trip temperature reduced to 125°C, well below the T_g of the PC (∼147°C), as well as the PC/PCL (∼136°C) blend. It is noteworthy that the observed PTC effect for PC/PCL (8 wt%)/Ni‐coated graphite (40 wt%) composites is highly reproducible during many heating cycles. The coefficient of thermal expansion (CTE) of PC was increased in presence of PCL. Thus, the mismatch in CTE of the PC and Ni‐coated graphite at a temperature well below the T_g of PC was enough to disrupt the continuous network structure that increased the resistivity of the composites. Storage modulus of PC/PCL/Ni‐coated graphite composites was higher than PC/Ni‐coated graphite composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Influence of radiation structures on positive‐temperature‐coefficient and negative‐temperature‐coefficient effects of irradiated low‐density polyethylene/carbon black composites

The electrical‐resistivity/temperature behaviors of low‐density polyethylene (LDPE)/carbon black (CB) composites irradiated with ⁶⁰Co γ rays were studied. The experimental results showed that the irradiated composites could be separated into insoluble crosslinking networks with CB (gel) and soluble components (sol) by solvent‐extraction techniques. When the sol of an irradiated LDPE/CB composite was extracted, the electrical conductivity of the system increased. The positive‐temperature‐coefficient (PTC) and negative‐temperature‐coefficient (NTC) intensities of the gels of the irradiated composites became extremely small and independent of the radiation dose. The sols and gels of the irradiated LDPE/CB composites, which had different thermal behaviors, played important roles in the appearances of the PTC and NTC effects. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 700–704, 2005     

Positive temperature coefficient effect and mechanism of compatible LLDPE/HDPE composites doping conductive graphite powders

Linear low density polyethylene (LLDPE)/high density polyethylene (HDPE) blends doped conductive graphite powders were constructed by the traditional melt‐blending method to acquire the conductive compatible polymer composites, and corresponding positive temperature coefficient (PTC) effect of electrical resistivity was investigated. The results indicated that the room‐temperature resistivity gradually decreased and PTC effects were remarkably enhanced by regulating the graphite contents or LLDPE/HDPE ratios. Especially, with increasing graphite contents, the polymer‐fixed composites showed the notable double PTC effects, originating from the volume expansion of the co‐crystallization or their fraction. Whereas, with increasing the LLDPE/HDPE ratio, the PTC effects of the graphite‐fixed composites occurred at the lower temperature, even far below the melting points of the co‐crystallization. Therefore, the regulation of co‐crystallization morphology of compatible polymer matrices was a new idea in the improvement of PTC materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46453.     

Effects of thermal ageing treatment and antioxidants on the positive temperature coefficient characteristics of carbon black/polyethylene conductive composites

Polyethylene (PE)‐filled with carbon black (CB) is a prototypical composite that displays resistance switching. These materials can exhibit either a positive temperature coefficient (PTC) or negative temperature coefficient (NTC). The CB‐filled semicrystalline polymer composites ideally need antioxidants, which stabilize the composites against thermooxidative degradation, because they should be resistant to the severe conditions of high temperature. The characterization of PTC materials is affected by the crystallinity of the polymer, and the crystallinity of the polymer is changed with thermal ageing treatment. Thermal ageing of PTC samples was conducted in an oven in the range 50–140°C, in air. The composites, containing 0.5–3% (by weight) Irganox 1076 (Ciba‐Geigy), were irradiated under nitrogen at room temperature with different doses of gamma rays from a ⁶⁰Co source. The resulting composites were analyzed by differential scanning calorimetry, gel fractionation, X‐ray diffraction, and dynamic mechanical analysis. The conductivity of the composites depended on the amounts of antioxidants and the duration of the thermal ageing treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2316–2322, 2003     

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     

Resistivity‐temperature behavior and morphology of low density polyethylene/graphite powder/graphene composites

In this work, the positive‐temperature‐coefficient (PTC) effect of resistivity of low density polyethylene/graphite powder (45%) composites (LDPE/GP) in the presence of graphene before and after crosslinked was comparatively investigated by differential scanning calorimetry (DSC), X‐ray diffraction (XRD), scanning electron microscopy, Raman spectrum, and resistivity‐temperature test. The composites showed the repeatability of the PTC effect with heating cycles and a certain improvement in the room temperature resistivity. After crosslinked, the composites presented a higher PTC trip temperature at about 140°C than pure LDPE (T_m = 112°C), and stronger PTC intensity than room temperature resistivity (over 5 orders of magnitude). The results from DSC, XRD, and Raman spectrum indicated that the addition of graphene resulted in the gradual enhancement in the crystallization of LDPE matrix, which was the origin of the improvement of the PTC behavior of the composites. As a result, we could conclude that the additional conducting filler could improve the PTC effect of the conducting composite system. POLYM. COMPOS., 35:1453–1459, 2014. © 2013 Society of Plastics Engineers     

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.     

Electrical properties and morphology of carbon black‐filled HDPE/EVA composites

The sensitive effect of weight ratio of the high‐density polyethylene (HDPE)/ethylene‐vinylacetate copolymer (EVA) on the electrical properties of HDPE/EVA/carbon black (CB) composites was investigated. With the EVA content increasing from 0 wt % to 100 wt %, an obvious change of positive temperature coefficient (PTC) curve was observed, and a U‐shaped insulator‐conductor‐insulator transition in HDPE/EVA/CB composites with a CB concentration nearby the percolation threshold was found. The selective location of CB particles in HDPE/EVA blend was analyzed by means of theoretical method and scanning electron micrograph (SEM) in order to explain the U‐shaped insulator‐conductor‐insulator transition, a phenomenon different from double percolation in this composite. The first significant change of the resistivity, an insulator‐conductor transition, occurred when the conductive networks diffused into the whole matrix due to the forming of the conductive networks and the continuous EVA phase. The second time significant change of the resistivity, a conductor‐insulator transition, appeared when the amorphous phase is too large for CB particles to form the conductive networks throughout the whole matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nylon 6 induced morphological developments and electrical conductivity improvements of polypropylene/carbon black composites

In this study, a polar conductive filler [carbon black (CB)], a nonpolar polymer [polypropylene (PP)], and a polar polymer [nylon 6 (PA6)] were chosen to fabricate electrically conductive polymer composites by melt blending and compression molding. The morphological developments of these composites were studied. Scanning electron microscopy results showed that in a CB‐filled PP/PA6 (CPA) composite, CB particles were selectively dispersed in PA6 phases and could make the dispersed particles exist as microfiber particles, which could greatly improve the electrical conductivity. The PA6 and CB contents both could affect the morphologies of these composites. The results of electrical resistivity measurements of these composites proved the formation of conductive networks. The resistivity–temperature behaviors of these composites were also studied. For CB‐filled PP (CP) composites, there were apparent positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects and an unrepeatable resistivity–temperature characteristic. However, for CPA composites, there were no PTC or NTC effects from room temperature to 180°C, and the resistivity–temperature behavior showed a repeatable characteristic; this proved that CB particles were selectively dispersed in the PA6 phase from another point of view. All experimental results indicated that the addition of PA6 to a CP composite could lead to an expected morphological structure and improve the electrical conductivity of the CP composite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel polymer composite with double positive‐temperature‐coefficient transitions: effect of filler–matrix interface on the resistivity–temperature behavior

BACKGROUND: Sn–Pb alloy‐filled high‐density polyethylene (HDPE) composites exhibit double positive‐temperature‐coefficient (PTC) behavior, with the first transition at the melting point of HDPE and the second at that of Sn–Pb alloy. The objective of this study is to improve the reversibility and reproducibility of double‐PTC transitions of these composite materials by enhancing the filler–matrix interface. RESULTS: Fourier transform infrared spectroscopy, surface wettability and dynamic mechanical and rheological measurements confirm that surface‐treating Sn–Pb with titanate concentration ≤1 wt% enhances the interface adhesion between Sn–Pb alloy and HDPE matrix. Surface‐treating Sn–Pb with titanate concentration ≤1 wt% increases the PTC transition temperature, reduces the PTC intensity and improves the reversibility and reproducibility of the double‐PTC behavior of Sn–Pb/HDPE composites. CONCLUSION: It is demonstrated that adjusting the filler–matrix interface is an effective means to modify the double‐PTC behavior of Sn–Pb alloy‐filled HDPE composites. Copyright © 2007 Society of Chemical Industry     

HDPE/CB复合体系PTC行为的工艺研究

采用高结构导电炭黑(CB)Vxc—72与半晶聚合物高密度聚乙烯(HDPE)进行熔融共混，制备复合型导电高分子材料。研究了该复合体系中偶联处理、混炼时间、辐射及退火处理等工艺因素对其PTC(电阻—温度效应)性能的影响。结果表明，当辐照剂量为140—160kGy、炭黑非均匀分散且进行退火处理时复合体系具有最佳的PTC性能，但混炼时间过长、偶联处理均会使复合体系PTC强度降低。     

Factors influencing the resistivity–temperature behavior of carbon black filled isotactic polypropylene/high density polyethylene composites

The relationship between morphology and resistivity–temperature behavior of carbon black (CB) filled isotactic polypropylene/high density polyethylene (iPP/HDPE) composites was investigated. The positive temperature coefficient intensity for all composites studied in this paper was lower than one and the negative temperature coefficient (NTC) effect was obvious. The factors influencing resistivity–temperature behavior include the CB contents, types of the polymer matrices and their composition, which determine the phase morphology and thus the conductive network. The types of iPP and HDPE influenced the NTC effect, while the morphology of the composites mainly influenced the initial volume resistivity of the composites.