Preparation of positive‐temperature coefficient heaters using platinum‐catalyzed silicone rubber

Various output heaters were extruded with acetylene black–filled platinum‐catalyzed silicone rubber. The resistivity–temperature behavior of extruded heaters exhibited a positive‐temperature coefficient (PTC) effect without any negative‐temperature coefficient (NTC) effect. Resistivity and thermal reproducibility of the extruded heaters were investigated during heating and cooling cycles at an applied voltage of 220 V. These heaters initially showed poor reproducibility of resistivity during the repeated cycles and this effect increased significantly as the acetylene black content decreased. PTC effect and electrical reproducibility were improved significantly during the thermal ageing process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1611–1617, 2004     

Thermal conductivity of silicone rubber filled with ZnO

Thermal conductivities of silicone rubber filled with ZnO in a wide volume range were measured in order to study the effect of formed conductive particle chains on thermal conductivities. With the increasing of content of ZnO particles in silicone rubber, the amount of formed conductive chains increases and the conductive chains tend linearly to increase the thermal conductivity of the composite. The experimental results obtained were also analyzed using the Nielsen and Agari models to explain the effect of ZnO filler on the formation of thermal conductive networks. Thermal conductivities of a polymer filled with high volume content of particles evidently increased with the adding of small size fillers. The scanning electron microscopy (SEM) showed that percolation threshold has been reached at 31.4 vol% ZnO filler loading, and the hybrid fillers are more densely packed than single fillers in the silicone rubber matrix. There occurs a positive temperature coefficient (PTC) phenomenon in thermal resistance in composites of silicone rubber filled with ZnO. POLYM. COMPOS., 28:125–130, 2007. © 2007 Society of Plastics Engineers     

热历史对LLDPE／EVA／CB导电材料PTC性能的影响

研究了淬火（液氮冷却）,空气自然冷却,空冷后退火,水冷,缓慢冷却等不同热历史条件下LLDPE／EVA／CB导电复合材料的PTC（正温度系数）特性,并借助DMA,DSC,SEM,TEM等手段揭示了LLDPE／EVA／CB导电复合材料PT特性与结晶形态等结构间的关系。结果表明,LLDPE／EVA／CB导电复合材料的PTC行为受结晶度和结晶形态影响很大,结晶度愈高,室温电阻愈小,PTC强度愈高;结晶形态愈复杂,从室温至PTC转变温度的低温PTC效应愈强,熔体缓慢冷却及退火工艺,可提高复合物结晶度,降低取向作用,使电阻率下降。     

Electrical conductivity of carbon black and carbon fibre filled silicone rubber composites

Electrically conductive silicone rubber composites have been prepared through incorporation of conductive acetylene black and short carbon fibre (SCF). The percolation limit for the attainment of high conductivity is found to be relatively less for silicone rubber based composites compared to EPDM or NBR based composites reported earlier. Percolation limit is found to be lower for SCF-filled systems (7.5 phr) compared to black-filled ones (14 phr). Both black- and SCF-filled systems exhibit an increase in resistivity with the increase in temperature (PCT effect). This PCT effect may be explained in terms of differences in the thermal expansion between the rubber matrix and the conductive filler. However, resistivity-versus-temperature plots are not identical during the heating-cooling cycle, leading to some hysteresis and electrical set. The current-voltage relationship is linear (Ohmic in nature) at room temperature but becomes non-linear (non-Ohmic) at elevated temperatures. The resistivity of these composites is measured under different conditions such as on applying pressure and being subjected to different mechanical stress and strain over the specimens. An effort has been made to correlate the effect of different parameters on electrical resistivity with the change in the conductive network structure under different conditions.     

Resistivity and thermal reproducibility of carbon black and metallic powder filled silicone rubber heaters

Flexible heaters were prepared by extruding platinum‐catalyzed silicone rubber composites with conductive carbon black (CB) and metallic fillers. The conductor resistivity of the extruded heaters decreased in order of conductive titanium dioxide (TiO₂) > aluminum powder ≈ zinc powder > copper powder. Thermoelectric switching phenomena were investigated for the silicone rubber/CB/metallic powder systems. The positive temperature coefficient effect was dependent mainly on the CB content rather than on the content of the metallic powders. Resistivity and thermal reproducibility of the extruded heaters were also investigated by periodically applying AC voltage of 110 V. The heaters containing copper and TiO₂ powders exhibited excellent electrical reproducibility. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1122–1128, 2005     

镀银玻璃微珠/硅橡胶导电复合材料导电性能的影响因素

研究镀银玻璃微珠的用量、粒径、表面改性工艺以及导电硅橡胶硫化程度等对镀银玻璃微珠/硅橡胶复合材料导电性能的影响.结果表明,镀银玻璃微珠的粒径越大,复合材料的导电性能越好;湿法预处理和原位改性-分散工艺制得复合材料的导电性能和导电稳定性优于直接干混工艺;导电硅橡胶硫化程度的提高有利于提高材料的导电性能;Payne效应的大小与导电硅橡胶的体积电阻率有很强的相关性.     

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.     

Temperature and time dependence of electrical resistivity in an anisotropically conductive polymer composite with in situ conductive microfibrils

An anisotropically conductive polymer composite (ACPC) based on conductive carbon black (CB) and binary polymer blend of polyethylene (PE) and polyethylene terephthalate (PET) was successfully fabricated under shear and elongational flow fields. The PET phase formed in situ the aligned conductive microfibrils whose surfaces were coated by CB particles. This ACPC material exhibited a strong electrical anisotropy within a broad temperature range. When the ACPC samples were subjected to isothermal treatment (IT), they showed anomalous variations of the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects. The PTC intensity was attenuated gradually with the increase of the IT time, and the NTC intensity was nearly eliminated after IT of 8 or 16 h. Beyond 16 h, the resistivity in the NTC region rose anomalously with the temperature after the elimination of NTC effect, which was the result of much transformation from the potential pathways to the intrinsic pathways due to the disordering of oriented conductive microfibrils. When the amount of potential pathways was very small, the effect of the intrinsic pathway separation surmounts that of the potential pathways, leading to the anomalous resistivity increase in the NTC region. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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...     

Temperature-Resistivity Behaviour of CNTs/UHMWPE Composites with a Two-Dimensional Conductive Network

Temperature-resistivity behaviour of carbon nanotubes (CNTs)/ultrahigh molecular weight polyethylene (UHMWPE) conductive composite with a 2-dimensional conductive network is investigated. The composite, in which CNTs were only dispersed in the interface of matrix particles, experiences a positive temperature coefficient of resistivity (PTCR) around the melting point followed by a negative temperature coefficient of resistivity (NTCR), and the resistivity begins to rise abruptly at the maximum crystallization temperature during cooling. The composite has a low PTC and NTC effec, which is determined by its 2-dimensional conductive network and the properties of the matrix.     

The Resistivity Response of an Anisotropically Conductive Polymer Composite with in-situ Conductive Microfibrils During Cooling

The resistivity response of anisotropically conductive polymer composite (ACPC) with carbon black (CB) particles selectively localizing at the surfaces of aligned polyethylene terephthalate (PET) microfibrils was investigated during cooling from 180°C in the parallel and perpendicular directions. The ACPC exhibited a cooling positive temperature coefficient (PTC) around the crystallization temperature of polyethylene (PE) matrix. With the increase of CB loading, the cooling PTC effect decreased gradually. When the ACPC experienced isothermal annealing, the aligned microfibrils disordered to form more conductive pathways. The increase of annealing time caused the gradual attenuation of the cooling PTC effect in both directions.     

梯形聚甲基倍半硅氧烷对脱醇型RTV-1硅橡胶性能的影响

以甲基三氯硅烷为主要原料,乙二胺为梯形控制剂,合成了梯形聚甲基倍半硅氧烷(PMSQ);以八甲基环四硅氧烷(D4)为原料,采用碱催化平衡聚合法,制备了α,ω-二羟基聚二甲基硅氧烷(107硅橡胶);采用107硅橡胶、交联剂、PMSQ等制备了脱醇型单组分室温硫化(RTV-1)导热硅橡胶。探讨了PMSQ用量对RTV-1硅橡胶导热、绝缘、物理性能、阻燃和热稳定性的影响。结果表明,温度高于90℃时,随PMSQ用量的增加,硅橡胶的热导率增大;当其用量为2.5 g(以50 g 107硅橡胶为基准)时,硅橡胶在30～150℃具有较好的导热性能。随PMSQ用量的增加,硅橡胶的拉伸强度、断裂伸长率均逐渐下降;硅橡胶的体积电阻率随PMSQ的增加先增后减,添加量为1.5 g时,体积电阻率增大了1.68倍。PMSQ能提高RTV-1硅橡胶的阻燃性能,并且能提高硅橡胶的热稳定性,减轻了RTV-1硅橡胶高温下迅速分解的状况,延缓了热失重的速度,PMSQ的较佳用量为2.5 g,此时,硅橡胶的热导率为0.425 W/m·K,拉伸强度为3.5 MPa,拉断伸长率为188%,体积电阻率为4.0×1015Ω·cm。     

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.     

真空热循环与质子辐照顺次作用对甲基硅橡胶性能的影响

利用空间环境地面模拟设备对甲基硅橡胶依次进行了真空热循环和质子辐照实验,讨论了真空热循环和质子辐照的顺次作用对甲基硅橡胶表面形态、拉伸强度、热膨胀系数、质量损失率和体积电阻率的影响,用傅里叶变换红外光谱仪研究了甲基硅橡胶微观结构的变化。结果表明,在真空热循环和质子辐照的顺次作用下,甲基硅橡胶表面出现老化裂纹,其拉伸强度和体积电阻率下降,热膨胀系数和质量损失率增加,但均不具有相加性,并且甲基硅橡胶发生了降解反应。     

制备工艺对PTC复合材料阻温特性的影响

研究了密炼工艺对聚乙烯／炭黑复合材料室温电阻率及ＰＴＣ强度的影响,针对一定配方找到了最佳密炼工艺条件。电子束辐照交联能有效消除ＮＴＣ现象和提高材料的电性能循环稳定性,有助于制备低电阻率、高ＰＴＣ强度并具有较好电性能循环稳定及热敏开关特性和电路保护元件。     

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     

石墨及其表面改性对硅橡胶导热性能的影响

用双辊混炼机将导热填料分散到聚甲基乙烯基硅氧烷中,再配以增强剂、硫化剂等,经模压硫化制得导热硅橡胶。研究了导热填料种类、石墨的表面改性和用量以及石墨与炭黑的复配对硅橡胶导热性和力学性能的影响。结果表明,在用量相同的情况下,导热填料的导热系数越高,其填充硅橡胶的导热性越好,且硅橡胶的导热系数随导热填料用量的增加而增大。石墨的表面改性改善了石墨与硅橡胶的界面相容性,使硅橡胶的力学性能和导热性都得到提高。不同粒径及颗粒形态的炭黑与石墨复合可改善硅橡胶的导热性和力学性能,导热硅橡胶的拉伸强度和扯断伸长率随复合填料中炭黑用量的增加而提高,当石墨与炭黑质量比为25/5时,硅橡胶的导热系数最高,综合性能较好。     

Performance stabilization of conductive polymer composites

Conductive polymer composites used as candidates for positive temperature coefficient (PTC) materials are faced with performance decay characterized by gradually increased room‐temperature resistivity and decreased PTC intensity. Considering that deterioration of the properties is mainly related to the capability of conductive networks established by conductive fillers to recover from the effect of repeated expansion/contraction in a timely manner, the present work introduces chemical bonding into the filler/matrix interphase. The experimental results indicate that in the composites consisting of conductive carbon black (CB), low‐density polyethylene (LDPE), and ethylene–vinyl acetate copolymer, CB particles can be covalently connected with LDPE through melt grafting of acrylic acid. As a result, the composites are provided with reduced room‐temperature resistivity and significantly increased PTC intensity. Compared with the composites filled with untreated CB, the present composites possess reproducible PTC behavior and demonstrate stable electrothermal output in association with negligible contact resistance at the composites/metallic electrodes contacts. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2438–2445, 2003     

Positive temperature coefficient effect and interaction based on low‐density polyethylene/graphite powder composites

In this article, the positive temperature coefficient (PTC) and interaction based on low‐density polyethylene (LDPE) filled with the loading of graphite (G) powder have been investigated. The dependence of the room temperature resistivity on filler content showed the significant decrease. The PTC behavior enhanced with increasing graphite content but this was not always the case. The maximum PTC effect was observed in LDPE/G composites (G, 45 wt %) with the relatively low room temperature resistivity. The thermal behavior was measured by differential scanning calorimetry (DSC). The structure characteristic for LDPE/G composites was examined by X‐ray diffraction (XRD), field‐emission scanning electron microscopy (SEM), and stress–strain test. The fact was revealed that the slight interaction between LDPE matrix and graphite may lead to change the thermal‐electric properties of the PTC materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Carbon-black-filled polyolefine as a positive temperature coefficient material: Effect of composition,processing, and filler treatment

Polymer-based positive temperature coefficient (PTC) composites are of special interest because they have great potential in temperature-sensitive devices. To obtain a reproducible PTC composite with acceptable PTC intensity, effect of conductive filler content, processing conditions and filler treatment with nitric acid, and titanate coupling agents on room temperature resistivity and PTC intensity of carbon-black-filled low-density polyethylene composites have been described and discussed herein. The results showed that filler arrangement is a key factor influencing the ultimate material performance, which can be tailored in various ways. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 559–566, 1998