超高分子量聚乙烯对有机PTC复合材料的稳定作用研究

利用传统的熔融－混合方法制备碳黑填充的聚丙烯（PP）／超高分子量聚乙烯（UHMWPE）复合物。当PP／UHMWPE混合比大于3／7,碳黑填充PP／UHMWPE复合物的PTC和NTC效应类似于碳黑填充的纯净PP聚合物。然而当质量比等于或小于3／7时,复合物所表现的PTC效应非常相似于碳黑填充的纯净的UHMWPE聚合物。在复合物中应用粘度非常高的聚合物作为一种组分可以有效消除NTC效应。     

UHMWPE对有机PTC复合材料的稳定作用

利用传统的熔融－混合方法制备碳黑填充的聚丙烯（PP）／超高分子质量聚乙烯（UHMWPE）复合材料,当P／UHMWPE质量比大于3／7时,碳黑填充PP／UHMWPE复合物的正温度系数（PTC）和负温度系数（NTC）效应类似于碳黑填充的纯PP聚合物,但当质量比等于或小于3／7时,复合物所表现的PTC效应非常相似于碳黑填充充的纯UHMWPE聚合物,在复合物中采用粘度非常高的聚合物作为一种组分可以有效消除NTC效应。     

线性低密度聚乙烯—炭黑复合物的正温度效应

本文研究了炭黑填充线性低密度聚乙烯复合物的导电性与炭黑含量的关系，PTC强度与CB含量的关系，探讨了未交联与交联复合的PTC效应的热重复性和NTC效应。     

石墨纤维填充PVDF/UPE复合物的电阻-温度效应研究

本文制备了石墨纤维填充聚偏氟乙烯和超高分子量聚乙烯(GF/PVDF/UPE)复合体系。实验结果表明,少量UPE的加入能够很好的消除NTC效应;PVDF/UPE的质量比对体系的室温电阻率和PTC效应均产生了显著的影响：随着UPE比例的增加,体积电阻呈现先减小后增大的变化趋势;少量UPE时,在160℃处出现单PTC效应,而后随着含量增加的复合物分别在140℃附近和160℃附近出现两次PTC效应。     

用热压法制备炭黑填充UHMWPE的电阻率-温度关系

本文研究了炭黑（CB）/超高分子聚乙烯（UHMWPE）复合材料的温度和电阻率的关系。用热压法生成了逾渗阈很低的新型正温度系数（PTC）材料。其低逾渗阂归因于CB偏析在UHMWPE颗粒的界面区内。逾渗阈随UHMWPE分子量增大而减小，随CB粒度降低而减小。CB填充低分子量UHMWPE（145M）材料的PTC温度是指材料电阻率急剧增大时的温度，该温度随CB粒径增大而降低。不过，对于CB填充高分子量UHMWPE（630M）材料，观察到第二PTC效应，消除了负温度系数（NTC）效应。本文根据光学显微技术和TEM观察结果，提出了一种机理来解释这些现象。得出以下结论：CB和UHMWPE粒子间互相混合的程度在决定材料电性能方面起着重要作用。     

国外有关塑料助剂研究的期刊文摘

钛酸酯偶联剂对PP／CaCO3流变性能的影响，用甲基丙烯酸为偶联剂的TiO2-PMMA纳米复合物的合成,马来酸丙烯酯偶联剂对聚丙烯大麻纤维复合物的影响，偶联剂对PP／MAH—g-PP／CaCO3三元复合物性能的作用,超高相对分子质量聚乙烯（UHMWPE）在玻璃粒子填充复合物用作界面增韧剂.     

低密度聚乙烯/炭黑/季戊四醇复合材料PTC特性的研究

采用流变仪制备了低密度聚乙烯/炭黑(LDPE/CB)复合材料和LDPE/CB/PE(季戊四醇)复合材料,研究了PE对LDPE/CB体系正温度系数(PTC)效应及负温度系数(NTC)效应的影响;并对复合材料进行了热循环测试,研究季戊四醇对PTC材料重演性的影响。结果表明,PE对LDPE/CB体系的PTC强度没有影响,对NTC效应有一定的抑制作用,对重演性有一定的改善作用。     

复合型导电高分子材料温敏行为研究进展

复合型导电高分子材料(CPCs)的温敏响应行为主要包括正温度系数效应(PTC)和负温度系数效应(NTC)等。本文综述了PTC型CPCs的研究进展,包括PTC行为的发生机理,PTC强度及PTC行为可重复性的调控方法;概括了PTC后NTC行为的消除方法。分析了NTC型CPCs的工作机制,并对CPCs温敏行为的研究热点和难点进行了展望。     

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。     

GF/PVDF导电复合材料的PTC行为

以石墨纤维(GF)、乙炔炭黑(CB)为导电填料,聚偏氟乙烯(PVDF)为基体,通过熔融共混方法分别制备GF/PVDF、CB/PVDF导电复合材料。讨论了导电填料形状、含量对复合材料正温度系数效应(PTC)的影响。并通过实验现象分析认为具有长径比结构的GF是导电复合材料负温度系数效应(NTC)减弱的原因,结合差示扫描量热分析(DSC)证明PTC效应与聚合物结晶熔融有直接关系。     

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.     

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     

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     

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     

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.     

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     

Thermo‐electric behavior (PTC) of carbon black–containing PVDF/UHMWPE and PVDF/XL‐UHMWPE blends

This paper describes the structure and electrical performance of PTC/NTC (positive temperature coefficient/negative temperature coefficient) effects and their reproducibility upon healing/cooling cycles. The following three‐component blends were studied: PVDF/UHMWPE/CB, PVDF/XL‐UHMWPE/CB and γ‐irradiated compression molded plaques of these blends. Carbon black (CB) particles are attracted to the UHMWPE (ultra high molecular weight polyethylene) and XL (cross‐linked)UHMWPE particles, which constitute the dispersed phase in the PVDF (polyvinylidene fluoride) matrix, but practically cannot or only very slightly penetrate them because of their extremely high viscosity. A double‐PTC effect was exhibited by all unirradiated samples. Irradiation of compression molded PVDF/UHMWPE/CB plaques does not add to their already outstanding reproducibility, and it results In a wide single‐PTC effect. Irradiation of compression molded PVDF/XL‐UHMV/PE/CB plaque, slabilizes their structure upon heating/cooling cycles and thus makes them reproducible PTC/NTC materials, still exhibiting a double‐PTC effect. The carbon black concentrations studied in this report are extremely low (< 2 phr CB) in comparison to other literature reports.     

不同炭黑填充的PVC/EPDM复合NTC材料电性能的研究

首先研究了特导炭黑(HG-1P)和乙炔炭黑(ACET)填充聚氯乙烯(PVC)单组分复合材料的逾渗行为和阻温特性:特导炭黑导电性较好,较少的填充量就能达到较低的室温电阻率,在升温过程中表现出稳定的NTC效应;乙炔炭黑导电性能偏差,达到相同的导电性需要更多填充量,在升温过程中先是出现弱的PTC效应,继而出现NTC效应。然后,引入三元乙丙橡胶(EPDM)、乙丙橡胶(EPR)作为第二组分,EVA作为第三组分,发现多组分复合材料电阻降低,阻温曲线表现出一些新的特征。     

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。