低熔点有机晶体对HIPS/CB复合材料导电性能的影响及分析

探讨低熔点有机晶体对高抗冲聚苯乙烯（HIPS）／炭黑（CB）复合材料室温电阻率及温度-电阻率曲线的影响，并采用SEM、XRP、DSC等测试手段对含有低熔点有机晶体的HIPS／CB复合材料的结构进行分析。实验结果表明，加入有机晶体后，HIPS／CB复合材料的室温电阻率明显降低，同时随晶体含量的变化呈不同强度的正温度系数PTC（Positive Temperature Coefficient）效应，且强度明显要高于未填充有机晶体的HIPS／CB材料，含有有机晶体的复合材料FFC转变温度在晶体熔点附近，可设想通过添加不同熔点的有机晶体达到控制复合材料FFC转变温度的目的。     

OMMT对PE–HD/CB导电复合材料电性能的影响

以炭黑(CB)为导电填料,高密度聚乙烯(PE–HD)为基体,有机蒙脱土(OMMT)为有机粒子,通过熔融共混法分别制备了PE–HD/CB与PE–HD/CB/OMMT导电复合材料,并研究了OMMT的加入对导电复合材料中CB分布的均一性及材料电性能的影响。研究发现,适当OMMT的加入可以改善CB在导电复合材料中的分布状态,在保持电性能的基础上降低导电复合材料的渗流阈值;当OMMT质量分数为3%时,PE–HD/CB/OMMT导电复合材料的渗流阈值为3.7%,与未添加OMMT的PE–HD/CB导电复合材料渗流阈值4.0%相比有所降低。在此基础上,选取PE–HD/CB导电复合材料(CB质量分数为5%)并测定其PTC强度为0.26;后加入质量分数为3%的OMMT,测得PE–HD/CB/OMMT导电复合材料(CB质量分数为5%)的PTC强度为0.79,后者有所提高。     

尼龙12/炭黑高转变温度PTC材料的研究

研究了以尼龙12(PA12)为基体树脂,炭黑(CB)为导电填料的高转变温度正温度系数(PTC)材料.采用熔融共混方法制备了尼龙12/炭黑聚合物PTC复合材料,考查了炭黑含量,热循环等因素对材料PTC性能的影响.并采用示差扫描量热分析(DSC)、热机械曲线分析(TMA)研究了材料PTC效应与材料结构的关系.实验结果表明尼龙12/炭黑复合材料具有高转变温度的PTC特性,将复合材料进行多次热循环实验,此复合材料仍具有较强的PTC效应.     

正温度系数自限温加热电缆放大效应研究

研究LDPE／CB（低密度聚乙烯／炭黑）导电复合材料经50L密炼机塑化造粒，再以Φ45挤出机制备自限温加热电缆的放大效应，考察了工艺放大对导电复合材料体积电阻率及其重复稳定性的影响。结果表明，1L密炼配方放大后可适当降低炭黑含量，得到均匀分散的LDPE／CB正温度系数（PTC）导电复合材料；而挤出放大工艺参数，如加工温度及螺杆速度提高，长径比小时，电缆的电阻率下降，与小试实验结果一致，且所得加热电缆轴向电阻均匀性及发热稳定性良好，可用于批量生产。     

溶液法制备的CB/HDPE/UHMWPE复合材料的导电性能

以导电炭黑(CB)为填料,高密度聚乙烯(HDPE)和超高摩尔质量聚乙烯(UHMWPE)为基体,通过超声溶液分散法制备了CB/HDPE/UHMWPE复合材料,并研究了CB含量对复合材料体积电阻率和阻-温特性的影响。研究发现,当HDPE∶UHMWPE质量比为7∶3,CB含量在5%左右时,CB/HDPE/UHMWPE复合材料能够形成完善的导电网络,材料具有较好的电性能;材料的体积电阻率随着温度的升高变大,在熔点附近时剧增,且材料的正温度效应(PTC)强度在CB含量大于渗流阈值的范围内,随着CB含量的增加而逐渐减小。通过多次对复合材料进行热循环测试发现CB/HDPE/UHMWPE复合材料具有良好的热稳定性。     

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。     

CB/MWCNTs/PP导电复合材料的制备与性能表征

通过熔融共混、注塑成型将多壁碳纳米管(MWCNTs)母粒、炭黑(CB)母粒与聚丙烯(PP)混合制备CB/MWCNTs/PP导电复合材料。复合材料中导电填料MWCNTs体积分数为1%,通过改变炭黑体积分数,探究CB含量的变化对复合材料导电性能、力学性能和流变性能的影响。导电测试结果表明,当CB体积分数介于3%~5%时,复合材料达到电流逾渗;超声共振结果表明,复合材料的弹性模量会随着CB含量的增大而增大,而泊松比对CB含量的变化并不敏感;DMA结果表明,复合材料玻璃化转变温度(T_g)会随着CB含量的增加而降低,而储能模量和损耗模量在低温区会随着CB的增大而上升;MCR分析结果表明,当CB体积分数介于1%~3%时,复合材料达到流变逾渗,复合黏度对低频率扫描不敏感,随着CB体积分数的增大而增加。随着频率上升,不同含量材料的复合黏度越来越逼近,并且呈现剪切变稀现象。     

聚偏氟乙烯在智能PTC自控温加热电缆研究中的应用

研究了以聚偏氟乙烯（PVDF）为基体,以油炉法炭黑（炉法CB）为导电载流子制备的PTC（positivetemperaturecoefficient）导电材料的逾渗行为、PTC阻温特性。并讨论了采用PVDF／CB导电复合材料制备的智能PTC自控温加热电缆的电致发热行为、功率行为、伏安情性及通断电稳定性,得到了自控温度130－140℃级防冻保温用新型电加热电缆。     

炭黑/环氧树脂复合材料导电行为的研究

分别采用不同的混合分散方法制备炭黑/环氧树脂(CB/EP)复合材料(CB牌号为F101、XE2,EP牌号为E-54、E-51和E-44),研究了制备工艺、CB用量和CB结构等对复合材料导电性能的影响。结果表明:不同方法制得的复合材料体积电阻率的大小依次为机械混炼法离心混合法超声分散法;CB/EP复合材料的导电性能随CB用量增加而显著提高,并且F101/E-54、XE2/E-54复合材料体系均表现出明显的导电渗流行为;CB结构对复合材料的导电性能影响较大,F101/E-54、XE2/E-54复合材料体系的导电渗流阈值分别为3.85%、0.47%。     

偶联处理对HDPE/炭黑复合材料PTC性能的影响

以HDPE／工业炭黑(CB)复合材料为研究对象，考察了炭黑及偶联剂种类、用量对高分子PTC(正温度系数)导电材料性能的影响，并探讨了偶联接技机理，从理论上对改性效果进行了分析。结果表明，对炭黑(尤其是槽法炭黑)进行表面处理可显著提高复合材料的电导率，减小NTC(负温度系数)效应；钛酸配偶联剂具有最佳改性效果，可明显改善炭黑粒子分散状态，增强材料的PTC效应，其最佳用量为1％。     

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     

Resistivity–volume expansion characteristics of carbon black‐loaded polyethylene

The resistivity and volume expansion of carbon black (CB)/high‐density polyethylene (HDPE) composite with different CB volume fractions at different temperatures were measured simultaneously. A model based on Meyer's theory is proposed to explain the positive temperature coefficient resistance (PTCR) effect. The relationship between resistivity and volume expansion was determined. It was found that the phase change is the main cause of the PTC effect in the crystalline polymer PTC materials. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 53–58, 2000     

Properties and thermo-switch behaviour of LDPE mixed with carbon black,zinc metal and paraffin wax

This paper reports on the presence of wax and radiation-induced crosslinking on the morphology, thermal and mechanical properties, as well as electrical conductivity and thermo-switch properties of LDPE containing different amounts of carbon black (CB) or carbon black plus zinc metal as filler. Although the filler was generally well dispersed in the polymer or polymer/wax blend, there were clear indications of the formation of conductive pathways. Different combinations of polymer, wax, CB and zinc filler and radiation induced crosslinking gave rise to different extents of crystallinity and/or chain immobilization, which had an influence on the mechanical and thermo-mechanical properties, and on the electrical conductivity and thermo-switch behaviour. Most importantly, the presence of wax, and CB and CB/Zn fillers, gave rise to increased electrical conductivity. The thermal expansion in the composites did not seem to play a significant role in obtaining larger values of the positive temperature coefficient of resistivity (PTC). We found that the presence of a small amount of paraffin wax significantly increased the PTC coefficients of the LDPE based conductive composites, and that γ-radiation induced crosslinking provided the thermo-mechanical stability of the amorphous regions in LDPE needed to obtain a high PTC intensity, which would provide a cheap material with good thermo-switch functionality, which is something not observed before.     

Resistivity–temperature characteristics of filler-dispersed polymer composites

Composites containing carbon nano tube (CNT) or carbon black (CB) conductive particle filler have the special characteristics of positive-temperature-coefficient (PTC) effects of resistivity. We quantitatively studied the relationship between poly(vinylidene fluoride) (PVDF) polymer's thermal volume expansion and the PTC effects of PVDF/CNT and PVDF/CB. The equation to revise filler content at each temperature due to the considerable thermal volume expansion rate of PVDF polymer indicates that filler content decreased with rising temperature. The graphs of filler content at room temperature plotted against apparent filler content with PTC effect were linear and their slopes were constant. From these graphs, we can determine the filler content necessary to occurring PTC effects. For example, the CNT content was 89% at room temperature, and the CB content was 93%. To our knowledge, this study is the first to report such phenomena.     

PVDF/CB composites prepared by novel solvent casting method for low voltage PTC temperature regulation applications

A novel solvent casting preparation technique utilizing three variants of poly(vinylidene fluoride) (PVDF) to achieve a thermal cut off and a self regulation effect at a low applied voltage is reported in this study. The positive temperature coefficient (PTC) composites were prepared by dissolving PVDF in 1‐methyl‐2‐pyrrolidone (NMP) solvent, blending with Vulcan® XC72 carbon black (CB) filler, crosslinking with vinyl trimethoxysilane (VTMOS) and quenching in water. All composites displayed a highly macrovoidal structure that promoted a PTC effect when subjected to a thermal expansion effect via an electrical current. Subsequently the current was cut off and self regulation behavior was exhibited. Kynar® 761A PVDF resulted in the strongest PTC effect, and displayed temperature regulation at around 100°C which may be attributed to the highly semi crystalline nature and the larger molecular weight of this polymer in comparison with the other PVDF composites studied. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrical behavior and structure of polypropylene/ultrahigh molecular weight polyethylene/carbon black immiscible blends

This study investigates the electrical behavior, which is the positive temperature coefficient/negative temperature coefficient (PTC/NTC), and structure of polypropylene (PP)/ultrahigh molecular weight polyethylene (UHMWPE)/carbon black (CB) and PP/γ irradiated UHMWPE (XL‐UHMWPE)/CB blends. As‐received UHMWPE or XL‐UHMWPE particles are chosen as the dispersed phase because of their unusual structural and rheological properties (extremely high viscosity), which practically prevent CB particles penetration. Because of their stronger affinity to PE, CB particles initially form conductive networks in the UHMWPE phase, followed by distribution in the PP matrix, thus interconnecting the CB‐covered UHMWPE particles. This unusual CB distribution results in a reduced electrical percolation threshold and also a double‐PTC effect. The blends are also investigated as filaments for the effect of shear rate and processing temperature on their electrical properties using a capillary rheometer. Because of the different morphologies of the as‐received and XL‐UHMWPE particles in the filaments, the UHMWPE containing blends exhibit unpredictable resistivities with increasing shear rates, while their XL‐UHMWPE containing counterparts depict more stable trends. The different electrical properties of the produced filaments are also related to differences in the rheological behavior of PP/UHMWPE/CB and PP/XL‐UHMWPE/CB blends. Although the flow mechanism of the former blend is attributed to polymer viscous flow, the latter is attributed to particle slippage effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 104–115, 2001     

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