Thermoelectric behavior (PTC) of carbon black‐containing TPX/UHMWPE and TPX/XL‐UHMWPE blends

This article describes the structure and electrical performance of positive‐temperature‐coefficient/negative‐temperature‐coefficient (PTC/NTC) effects of the following three‐component blends: poly(4‐methyl pentene‐1)/ultra‐high molecular weight polyethylene/carbon black (TPX/UHMWPE/CB), poly(4‐methyl pentene‐1)/crosslinked‐ultra‐high molecular weight polyethylene/carbon black (TPX/XL‐UHMWPE/CB), and γ‐irradiated, compression‐molded plaques of these blends. CB particles are preferentially attracted to the UHMWPE and XL‐UHMWPE particles, which constitute the dispersed phase within the TPX matrix, but practically cannot or can only very slightly penetrate them because of their extremely high viscosity. Thus, CB particles initially form conductive networks on the UHMWPE phase; this is followed by distribution in the TPX matrix, electrically connecting the CB‐covered UHMWPE particles. This unusual CB distribution results in a reduced percolation threshold of all blends. A double‐PTC effect is exhibited by the XL‐UHMWPE‐containing samples. Irradiation of compression‐molded plaques improves their thermoelectric behavior by amplifying the PTC effect and reducing the NTC effect. A schematic model of the double‐PTC effect is suggested, describing the morphological changes of 70TPX/30XL‐UHMWPE/CB blends at different stages of heating with respect to their thermoelectric behavior. Irradiation of TPX/UHMWPE/CB plaques converts these systems into high‐intensity PTC materials free of the NTC effect. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1415–1428, 2001     

Study on synthesis of poly(N‐isopropylacrylamide) grafted carbon black and temperature‐dependence conductivity of grafted carbon black/epoxy composites

Carbon black nanoparticle grafted with poly(N‐isopropylacrylamide) (CB‐g‐PNIPAAm) was synthesized by surface‐initiated atom transfer radical polymerization (SI‐ATRP). The temperature‐responsive behavior of CB‐g‐PNIPAAm was proved by temperature‐variable ¹H NMR. A temperature‐dependent conductive composite was prepared by blending CB‐g‐PNIPAAm with epoxy resin. The relationship between temperature and resistivity of the composite was studied: the composite exhibited a negative temperature coefficient (NTC) phenomenon. Possible mechanism for the NTC phenomenon was suggested. The results showed that resultant composites can be used in intelligent temperature‐switching. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1529–1535, 2008     

Effects of thermal volume expansion on positive temperature coefficient effect for carbon black filled polymer composites

Polymeric positive temperature coefficient (PTC) materials have been prepared by incorporating carbon black (CB) into two different polymer matrices, crystalline high density polyethylene (HDPE) and amorphous polystyrene (PS). The effects of thermal volume expansion on the electrical properties of conductive polymer composites were studied. The volume fraction of conductive particles behaves like a switch from insulator to conductor in the polymeric PTC composite. Our mathematical model and experimental model have proved that the abrupt resistivity increase at PTC transition range and at the percolation curve close to the critical volume fraction for both polymeric PTC composites have the same conductive mechanism. The thermal expansion is one of the key factors responsible for the PTC effect and can be seen by comparing the PTC transition curves from model predictions and experiment. Furthermore, the model predicts PTC curves of CB/PS composite more successfully than it does for the CB/HDPE composite, and the reasons for this are also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3078–3083, 2007     

Resistivity-Temperature Behavior of CB-Filled HDPE Foaming Composites

High-density polyethylene/carbon black foaming conductive composites were prepared from acetylene black（ACEY） and super conductive carbon black（HG-1P） as conductive filler, low-density polyethylene（LDPE） as the second component, ethylene-vinyl acetate（EVA） and ethylene propylene rubber（EPR） as the third component, azobisformamide（AC） as foamer, and dicumyl peroxide（DCP） as cross-linker. The structure and resistivity-temperature behavior of high-density polyethylene（HDPE）/CB foaming conductive composites were investigated. Influences of carbon black, LDPE, EVA, EPR, AC, and DCP on the foaming performance and resistivity-temperature behavior of HDPE/CB foaming conductive composites were also studied. The results reveal that HDPE/CB foaming conductive composite exhibits better switching characteristic; ACET-filled HDPE foaming conductive composite displays better positive temperature coefficient（PYC） effect; whereas super conductive carbon black（HG-1P）-filled HDPE foaming conductive composite shows better negative temperature coefficient（NTC） effect.     

具有高灵敏性且稳定可重复的正温度系数效应的PVDF/CF导电复合材料

以碳纤维(CF)为填料,聚偏氟乙烯(PVDF)为基体,通过熔融共混法制备PVDF/CF导电复合材料.所得复合材料具有显著的正温度系数(PTC)效应,温度上升到聚合物熔点附近时,电阻率对温度变化敏感.在转折温度区间(155.5~171.0oC,(35)(28)15.5oC)内,其体积电阻率的增加速率约为1.3×105?cm K-1.在不同CF含量下,复合材料表现出不同的PTC行为.随着CF含量的增加,其峰值电阻略有下降.高导电粒子含量下,无负温度系数(NTC)效应.在冷却循环过程,导电网络的重构性良好.复合材料即使经过多次热循环,依然表现出良好的PTC特性重现性.     

PTC/NTC Behavior of PVDF Composites Filled with GF and CF

Conductive polyvinylidene fluoride（PVDF）matrix composites filled with graphited fiber（GF）or carbon fiber（CF）were prepared by the melt-mixing method.The breakage and length distribution of the fibers in the polymer matrix were studied by scanning electron microscope（SEM）and optical microscope（OM）observations,respectively. The differences in the positive temperature coefficient（PTC）effects of the composites were mainly attributed to inter-fiber contact ability.The elimination of the negative temperature coefficient（NTC）effect for CF/PVDF composite was because of an increase in the viscosity of the polymer matrix.With the same filler content,CF could be more effective,to eliminate the NTC effect when compared with GF.Addition of 2%CF（mass fraction）in the PVDF composite with 7%GF（mass fraction）could effectively eliminate the NTC phenomenon of the composite.     

Electrical and dielectric properties in carbon fiber‐filled LMWPE/UHMWPE composites with different blend ratios

Carbon fiber (CF) filled low‐molecular‐weight polyethylene (LMWPE) and ultra‐high molecular weight polyethylene (UHMWPE) composites were prepared by the gelation from solution and the kneading in the melting state. The content of carbon fibers was fixed to be 23.5 vol %. The resistivity, positive temperature coefficient (PTC), and dielectric behaviors of the composites became more pronounced with increasing content of LMWPE with much higher thermal expansion than that of UHMWPE. The PTC effect became most significant, when the blend ratio of LMWPE to UHMWPE was 9/1. Beyond 9/1, the PTC effect was less pronounced. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) revealed that the UHMWPE and LMWPE chains within the composite crystallized independently by gelation from solution and were virtually unaffected by the presence of carbon fibers. Consequently, it was confirmed that carbon fibers selectively were localized in the mixed region of LMWPE and UHMWPE for the composite (3/1 and 6/1) and mainly in the region of LMWPE for the 9/1, 12/1, and 15/1 composites. This indicated that the content of carbon fibers within LMWPE region was the highest for the 9/1 composite and the 9/1 composite provides the most significant PTC effect. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 359–369, 2008     

Volume‐exclusion effects in polyethylene blends filled with carbon black,graphite, or carbon fiber

Conductive polymer composites possessing a low percolation‐threshold concentration as a result of double percolation of a conductive filler and its host phase in an immiscible polymer blend afford a desirable alternative to conventional composites. In this work, blends of high‐density polyethylene (HDPE) and ultrahigh molecular weight polyethylene (UHMWPE) were used to produce ternary composites containing either carbon black (CB), graphite (G), or carbon fiber (CF). Blend composition had a synergistic effect on electrical conductivity, with pronounced conductivity maxima observed at about 70–80 wt % UHMWPE in the CB and G composites. A much broader maximum occurred at about 25 wt % UHMWPE in composites prepared with CF. Optical and electron microscopies were used to ascertain the extent to which the polymers, and hence filler particles, are segregated. Differential scanning calorimetry of the composites confirmed that the constituent polymers are indistinguishable in terms of their thermal signatures and virtually unaffected by the presence of any of the fillers examined here. Dynamic mechanical analysis revealed that CF imparts the greatest stiffness and thermal stability to the composites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1013–1023, 2002     

聚乙烯/碳纤维复合材料的PTC效应

近几年 ,由导电粒子 (如碳黑、碳纤维、金属和金属氧化物等 ) [1～ 3] 填充结晶或半结晶型聚合物的导电复合材料备受人们关注 ,并逐渐得到了开发与利用 .其中有一类功能材料 ,随温度的升高 ,相继呈现正温度系数 (PTC)和负温度系数 (NTC)效应[4～ 8] .这类材料广泛应用于发热体制造、抗静电、过电流保护和电磁屏蔽等领域 .长期以来 ,以碳黑填充聚合物的 PTC效应报道得较多 .近年来 ,以碳纤维为填料或部分填料的高聚物复合材料的 PTC效应 [9～ 11]开始引起了人们的兴趣和关注 .本文着重讨论了碳纤维的加入对聚合物结晶形态的影响以及γ射…     

聚乙烯/聚并苯复合材料室温电阻率变化规律研究

以新型导电材料聚并苯替代碳黑作为导电填料制备聚乙烯/聚并苯复合物.确定了复合物渗流转变区,并解释渗流转变现象的产生机理.从聚并苯含量和热处理过程,对聚乙烯/聚并苯复合物室温电阻率变化规律进行讨论.结果表明,聚并苯质量分数在20%～40%之间是聚乙烯/聚并苯复合物渗流转变区;热处理有利于聚乙烯晶区完善排列,也有利于导电链形成;以聚并苯作为导电填料所制备的复合物具有较高的PTC强度;辐射交联可以提高聚乙烯/聚并苯复合物PTC强度,抑制NTC效应.     

Relationship between the positive temperature coefficient of resistivity and dynamic rheological behavior for carbon black‐filled high‐density polyethylene

Studies on the relationship between resistivity and dynamic rheological properties of carbon black‐filled high‐density polyethylene (CB/HDPE) composites were carried out. Change of resistivity ρ is associated with the dynamic modulus before the positive temperature coefficient/negative temperature coefficient (PTC/NTC) transition temperature. When the temperature approaches the melting point of HDPE, ρ increases rapidly with a decreasing modulus, corresponding to PTC transition. The resistivity‐dynamic viscoelasticity relationship in the PTC region can be divided into two parts in which the changes of ρ with storage modulus G′ and loss modulus G″ can be described by the scaling laws given by the critical storage modulus and loss modulus G′_c and G″_c; adjustable parameters ρ′_1c, ρ′_2c, ρ″_1c and ρ″_2c; and nonlinear exponents n and m, respectively. The accordance between the experimental data and the scaling functions of the dimensionless quantities (G′/G′_c ? 1) and (G″/G″_c ? 1) in the PTC transition region suggests that the ρ jump may be the result of a modulus‐induced percolation. G′_c and G″_c increase, but the four scaling resistivitis, ρ′_1c, ρ′_2c, ρ″_1c, and ρ″_2c, decrease with increasing CB concentration, implying that the microstructure change of the composites is the determinant factor for the PTC behavior and the resistivity‐dynamic modulus relationship. However, ρ′_2c and ρ″_2c exhibit no scaling dependence. It is suggested that a threshold concentration exists for the modulus of the composites on the basis of examining the plot of both G′_c and G″_c against CB concentration. The scaling laws G′ ～ Φ^x and G″ ～ Φ^y hold for the concentration dependence of the critical modulus when Φ > Φ_c and the estimated values of x and y are 1.10 ± 0.10 and 0.89 ± 0.29, respectively. The resistivity‐dynamic modulus can shift to form a master curve. The horizontal factors a_G′ and a_G″ and the vertical factors a′ and a″ are relevant to the concentration dependence of the dynamic modulus or PTC behavior. It is believed that the former would be involved in changing the mechanical microstructure formed by the complicated interaction of CB particle and polymer segments, and the latter would be involved in the overall changes of conducting a network during the PTC transition region. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 983–992, 2003     

Properties of a carbon filled cyclic olefin copolymer

This article investigates electrical conductivity and rheological aspects of cyclic olefin copolymer (COC) composites containing both carbon fiber (CF) and carbon black (CB) at various concentrations. The different formulations of carbon filled COC were compression molded in such a manner that the formed circular sheets exhibited preferred in‐plane filler orientation. Through‐plane and in‐plane conductivity were measured by 2‐probe and 4‐probe methods, respectively, while an ARES rheometer in dynamic mode was employed to measure the storage modulus and complex viscosity. It was found that formulations with CF:CB ratios around 3 and where the CB content was close or below its critical percolation concentration resulted in higher electrical conductivity while maintaining the viscosity of the composite at a level acceptable for polymer processing machinery. For those composites containing both fillers, collaborative associations between the CB and CF fillers were found in the established percolating network structure, producing measured conductivities which exceeded the estimated values by the additive rule by up to sixfold. An empirical expression to handle hybrid filler systems is proposed in this work based on the standard percolation model. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1808–1820, 2007     

PE/CB复合材料的辐照效应

研究了两种炭黑(CB)对PE的影响及PTC功能材料挤出后的特性，发现挤出后粒子和聚合物取向对材料电性能都有较大影响。经γ射线辐照后HDPE／CB功能复合材料稳定性大为提高，初步探讨了辐射对PTC功能材料稳定性的影响。结合辐射交联等方法提高材料的稳定性。用扫描电镜(SEM)观测了一系列PE／CB的形态、CB的分布、链段的分子运动，并结合Fisher的toy model对PE／CB机制做了较系统的解释。     

Temperature-resistivity characteristics of a segregated conductive CB/PP/UHMWPE composite

A carbon black (CB)/polypropylene (PP)/ultrahigh-molecular-weight polyethylene (UHMWPE) composite with a segregated structure was fabricated by using binary polymer granules as matrices. In preparation, an ethanol-assisted dispersion method was employed to disperse CB particles on the surface of the two polymer granules. The segregated conductive network was then constructed by hot compaction based on the volume exclusion effect of the polymer matrices. The conductive composite shows an ultralow percolation threshold of 0.34 vol.%. In temperature-resistivity test, a double positive temperature coefficient (PTC) effect was observed. In addition, the negative temperature coefficient (NTC) effect was eliminated significantly. These interesting temperature-resistivity behaviors were ascribed to the introduction of the binary polymer matrices and the mobility limitation of CB particles located at the PP/UHMWPE interface. These characteristics were probed by in situ morphology observation in heating process. The present paper provides a novel route for preparing conductive composites with an ultralow percolation threshold, a wider PTC region, and a zero NTC effect.     

Electrical properties of conductive polymer composites prepared by an innovational method

<正>An innovational method that poly(styrene-co-maleic anhydride)(SMA),a compatibilizer of immiscible nylon6/polystyrene(PA6/PS) blends,was first reacted with carbon black(CB) and then blended with PA6/PS,has been employed to prepare the PA6/PS/(SMA-CB) composites of which CB localized at the interface.In PA6/PS/CB blends,CB was found to preferentially localize in the PA6 phase.However,in the PA6/PS/(SMA-CB) blends,it was found that CB particles can be induced by SMA to localize at the interface.The electrical porperties of PA6/PS/(SMA-CB) composites were investigated.The results showed that the composites exhibited distinct triple percolation behavior,i.e.the percolation is governed by the percolation of CB in SMA phase,the continuity of SMA-CB at the interface and the continuity of PA6/PS interface.The percolation threshold of PA6/PS/(SMA-CB) was only 0.15 wt%,which is much lower than that of PA6/PS/CB.Moreover,the PTC(positive temperature coefficient) 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 electrical properties of PA6/PS/(SMA-CB) were explained in terms of its special interface morphology:SMA and CB localize at interphase to form the conductive pathways.     

The stabilization effect of radiation crosslinking on positive temperature coefficient performances of carbon black-polymer composites

In this paper, we report the results of systematic study of effect of radiation crosslinking on PTC/NTC phenomena of carbon black(CB) filled vinyl polymers. We conclude that the effect of radiation crosslinking greatly improves the PTC intensity and electrical reproductivity in thermal cycling.     

Effect of carbon-black treatment by radiation emulsion polymerization on temperature dependence of resistivity of carbon-black-filled polymer blends

High dispersibility and stability of carbon black particles in low-density-polyethylene (LDPE) matrix were obtained by radiation emulsion polymerization on carbon particles surface, and electrical resistivities of its simple were examined. First carbon particles treatment on radiation emulsion polymerization on surface were synthesized by the reaction with a polymer-emulsion systems containing reactive group in the molecular unit, carbon particles and emulsifier. Then, the carbon particles treatment on radiation emulsion polymerization on surface was dispersed into LDPE, and its composites were prepared for electrical measurements. The effect of radiation crosslinking of the composite on the Positive temperature coefficient (PTC) and negative temperature coefficient (NTC) phenomenon was investigated. The experimental results showed that PTC and NTC effects of the composites were obviously influenced by the irradiation dose. Various microstructure-exploring means were used to study the conductive composite, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM).     

Influence of γ-ray Irradiation on the PTC Effect of EPDM/Carbon Black Composite

Introduction The positive temperature coefficient(PTC) effect is characterized by an increase of resistivity with an elevated temperature.The PTC effect of carbon black(CB) filled polymers is useful for self-regulation heaters,over-current protectors,sensors,etc.Much work has been done on the PTC effect of the carbon black filled crystalline polymer composite[1-4],whereas carbon black filled amorphous polymers have not drawn researchers much attention because the PTC effect in these composites is small or cannot be detected[5-7].In this work,the influence of γ-ray irradiation on the PTC effect of CB filled amorphous ethylene-propylene-diene terpolymer(EPDM) composites was studied.     

纤维状填料/HDPE复合体系的导电渗流与流变渗流行为的关系

研究了纤维状导电材料不锈钢纤维(SSF)填充高密度聚乙烯(HDPE)导电复合体系的导电渗流与流变渗流行为之间的关系,并与颗粒状导电颗粒炭黑(CB)/HDPE导电复合体系进行了比较.发现当SSF含量极低(0.3vol%)时,SSF/HDPE体系即发生导电渗流现象,且导电渗流转变区域极窄;而仅当SSF含量达到4.8vol%时,该复合体系才表现出流变渗流现象,这一结果与CB/HDPE体系及纳米级导电纤维填充体系截然不同.此外,通过正温度系数效应的研究发现SSF形成的导电通路稳定性高于CB/HDPE体系.我们认为,SSF/HDPE体系呈现的这些特点均与SSF较大的直径及长径比且其导电通路及流变渗流网络的形成机理不同有关.     

Effects of the reduction of PAni-coated oxidized multiwall carbon nanotubes on the positive temperature coefficient behaviors of their carbon black/high density polyethylene composites

Polyaniline (PAni)-coated reduced multiwall carbon nanotubes (PRMWNTs) and carbon black (CB)-filled high-density polyethylene (HDPE) composites (PRMWNTs/CB/HDPE) were prepared through a melt mixing method. Oxidized MWNTs (OMWNTs) were prepared by treating pristine multiwall carbon nanotubes (MWNTs) with an acid mixture (HNO₃:H₂SO₄), and PAni-coated OMWNTs (POMWNTs) were synthesized via in-situ polymerization of aniline monomer in the presence of OMWNTs. POMWNTs were further reduced using hydrazine monohydrate to obtain the PRMWNTs. Fourier transform infrared (FT-IR) spectra and thermogravimetric analysis (TGA) confirmed the formation of PRMWNTs. PRMWNTs showed significantly improved thermal stability and electrical conductivity comparing to POMWNTs. The positive temperature coefficient (PTC) behavior of PRMWNTs/CB/HDPE composites revealed enhanced PTC intensity and electrical conductivity at room temperature compared to POMWNTs/CB/HDPE composites. The PRMWNTs-10/CB/HDPE composite showed high peak resistivity (301.99 MΩ-cm) and low room temperature resistivity compared to the POMWNTs/CB/HDPE composite, and thus showed the highest PTC intensity value of 6.693 as well as very excellent cyclic stability.