导电介质填充聚合物分散工艺的模拟及研究

模拟了导电介质填充聚合物体系的二维点阵逾渗过程 ,研究了分散工艺对导电性复合材料逾渗形成过程的影响 ,以及HDPE/CB复合体系导电粒子的分布状态对其逾渗网络及导电特性的影响。根据在低填充体积分数时逾渗的发生是粒子不均匀分散这一原理 ,阐述了PTC材料设计制作的注意事项。     

填充型导电高分子基气敏纳米复合材料研究进展

简单介绍了填充型导电高分子基气敏纳米复合材料相对传统气敏材料的优势,综述了近些年来对该复合材料的研究进展,重点从导电逾渗理论和导电逾渗值方面进行综述,并以炭黑填充体系、碳纳米管填充体系以及其它填充体系对该复合材料的研究现状进行了阐述。最后对填充型导电高分子基气敏纳米复合材料的发展趋势进行了展望,指出降低导电逾渗值、构建完善的导电网络、提出更加完善和实用性广的逾渗模型,以及提高复合材料气敏响应灵敏度和恢复能力将是今后的研究重点。     

聚合物基PTC复合材料导电机理探讨

以导电炭黑填充聚乙烯复合体系为研究对象,阐述了炭黑粒子在体系中的分布状态及导电逾渗链形成过程,并在此基础上探讨了复合体系的导电机理。     

聚丙烯/炭黑复合材料的导电逾渗行为和PTC特性

以聚丙烯(PP)为基体、炭(黑CB)为填料制备复合材料,研究了不同CB种类的PP/CB复合材料的导电逾渗行为和电阻正温度系数效(应PTC)特性,同时利用扫描电镜对复合材料的微观形态进行了分析。结果表明:CB的结构性越高,比表面积越大,则其填充的复合材料逾渗阈值越低,PP/VulcanXC-72体系的逾渗阈值约为2.5%,而PP/40B2体系约为3.5%;CB的比表面积越小,结构性越低,则相同质量分数时其填充的复合体系的PTC强度越大P,P/40B2体系的PTC强度大于PP/VulcanXC-72体系。     

聚合物基复合材料导热模型及热导率方程的研究

根据导热填料在聚合物基体中的分布，提出了导热聚合物基复合材料两相体系的“海岛-网络”模型；并结合逾渗理论及其在导电复合材料中的应用，建立了导热复合材料的逾渗热导率方程。实验证明，该模型及热导率方程符合实际而且适用于高含量填充型导热聚合物基复合材料热导率的预测。     

炭黑填充型导电树脂的应用研究进展

综述了炭黑填充型导电树脂的特性,介绍了影响炭黑填充型导电树脂导电性的重要因素,包括加工工艺,基体与填料的关系等,讨论了研究现状及其技术进展,对其导电理论作了简要的介绍.     

填充型导电复合材料载荷作用下导电逾渗研究

以聚丙烯(PP)为基体材料,以多壁碳纳米管(MWCNT)、导电炭黑(CB)为填料,通过熔融共混、注塑成型的方法制备了填充型导电复合材料。测定在单轴压缩载荷作用下,不同填料体系的导电复合材料逾渗曲线的变化规律。通过扫描电子显微镜观察了导电填料的分布以及导电网络的形成状况。结果表明:对于PP/CB和PP/CB/MWCNT导电复合材料,在较小的应变情况下,单轴压缩使逾渗曲线向低阻方向移动,而随着应变逐渐增大,逾渗曲线又向高阻方向移动,其中PP/CB体系更为明显。这是由于纤维状的MWCNT能部分抑制由于压缩而导致材料内部导电通路的破坏,使材料内部导电网络遭到破坏的程度降低,同时,CB通过与拥有大长径比的MWCNT的协同作用提高了复合材料的导电性。     

钛化合物填充的聚合物导电复合材料的PTC特性及微观结构

以高密度聚乙烯 (PE HD)及热固性环氧树脂为基体 ,钛的硼化物、碳化物、氮化物或碳氮化物为导电粒子 ,研究了PE HD/钛化合物、环氧树脂 /钛化合物导电复合体系的逾渗行为、PTC/NTC现象及微观结构行为。结果表明 ,PE HD/钛化合物及环氧树脂 /钛化合物导电复合体系均具有强PTC开关特性 ,其逾渗阀值为 3 5 %～ 65 % (体积分数 ) ;电阻温度系数高达 (5 5 .7%～ 64 .3 % )·℃ -1。钛化合物导电颗粒以粒度不等的非均匀分布分散在聚合物基体中 ,其中在PE HD基体中颗粒之间在室温下紧密接触导通 ;而在环氧树脂基体中颗粒之间易产生团聚。     

一种阻燃抗静电聚丙烯的流变性能

采用毛细管流变仪和旋转流变仪分别研究了溴系阻燃剂、炭黑填充对聚丙烯熔体高剪切挤出畸变和动态黏弹特性的影响。发现低含量下随填充量的提高,发生挤出畸变的临界剪切速率提高,扩大了加工窗口。动态流变试验表明树脂中添加更多炭黑后剪切变稀时的复数黏度、储能模量和损耗模量都增大,但损耗因子下降。进一步用缠结模型和Cross模型定量分析表明,填料吸附高分子链段而减少其壁面吸附,减轻挤出畸变,进而提高临界剪切速率;粒子分布网络提高了平台模量和缠结密度,缩短了松弛时间,恢复更快而减小挤出胀大比。复合材料中添加3.5%（质量）炭黑后形成逾渗网络,表现为高零切黏度和长松弛时间,发生“类液-类固”转变;同时材料表面电阻下降明显,此时黏弹逾渗点与导电逾渗点基本一致。     

一种阻燃抗静电聚丙烯的流变性能

采用毛细管流变仪和旋转流变仪分别研究了溴系阻燃剂、炭黑填充对聚丙烯熔体高剪切挤出畸变和动态黏弹特性的影响。发现低含量下随填充量的提高,发生挤出畸变的临界剪切速率提高,扩大了加工窗口。动态流变试验表明树脂中添加更多炭黑后剪切变稀时的复数黏度、储能模量和损耗模量都增大,但损耗因子下降。进一步用缠结模型和Cross模型定量分析表明,填料吸附高分子链段而减少其壁面吸附,减轻挤出畸变,进而提高临界剪切速率;粒子分布网络提高了平台模量和缠结密度,缩短了松弛时间,恢复更快而减小挤出胀大比。复合材料中添加3.5%(质量)炭黑后形成逾渗网络,表现为高零切黏度和长松弛时间,发生"类液-类固"转变;同时材料表面电阻下降明显,此时黏弹逾渗点与导电逾渗点基本一致。     

Temperature and time dependence of conductive network formation: Dynamic percolation and percolation time

Temperature and time dependence of conductive network formation in vapor-grown carbon fiber (VGCF) filled high-density polyethylene (HDPE)/poly(methyl methacrylate) (PMMA), VGCF and ketjenblack (KB) filled HDPE/isotactic polypropylene (iPP) blends have been investigated. It is found that the filled conductive polymer composites are thermodynamically non-equilibrium systems, in which the conductive network formation is temperature and time dependent, a concept named as dynamic percolation is proposed. When the composites are annealed at a temperature above the melt point of polymer matrix, the dynamic process of conductive network formation can be monitored in a real time way. Such an in situ characterization method provides more interesting information about the dispersion of conductive particles in the polymer matrix. Furthermore, a thermodynamic percolation model is modified to predict the percolation time for VGCF and KB filled HDPE/iPP multi-phase systems during the annealing treatment, and it expresses experimental results well.     

Dynamic percolation phenomenon of poly(methyl methacrylate)/surface fluorinated carbon black composite

The electrical resistivity of polymer filled with conductive filler, such as carbon black (CB) particles, is greatly decreased by incorporating the conductive filler. This is called the percolation phenomenon and the critical CB concentration is called the percolation threshold concentration (Φ*). For CB particle–filled insulating polymer composite at lower than Φ*, the conductive CB network is constructed in the polymer matrix when the composite is maintained at a temperature higher than the glass‐transition temperature or the melting temperature of the polymer matrix. This phenomenon is called dynamic percolation and the time to reach the substantial decrease in resistivity is called percolation time (t_p). To investigate the relationship between the dynamic percolation process and the surface state of CB particles, we used three kinds of carbon black particles such as original carbon black (CB0) and fluorinated carbon black (FCB010 and FCB025)–filled poly(methyl methacrylate) (PMMA). It was observed that the dynamic percolation curves for CB0‐filled PMMA and FCB‐filled PMMA composites shifted to a shorter percolation time with increases in both the annealing temperature and the filler concentration. However, the dynamic percolation curves of FCB‐filled PMMA showed a gradually decreasing trend compared to that of CB0‐filled PMMA composites. The activation energy calculated from an Arrhenius plot of the t_p against the inverse of the annealing temperature was decreased by surface fluorine treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1151–1155, 2003     

Conductive polymer blends filled with carbon black: Positive temperature coefficient behavior

Electrical conductivity and positive temperature coefficient (PTC) behavior of carbon black (CB) filled incompatible polyblends of ethylene-vinyl acetate copolymer/low density polyethylene (EVA/LDPE) were investigated. In comparison with single polymer systems, more possibilities for tailoring composite performance were brought about with the employment of polymer blends as matrix resins in conductive composites. Based on the concepts of double percolation and two-step percolation, PTC-type composites with balanced performance, improved processability, and reproducibility can be made. Thermodynamical and kinetic factors including interfacial energy, melt viscosity, blending ratio, melt mixing time, sequence of blending as well as CB concentration were shown to be closely related to the ultimate properties obtained.     

Agglomeration and electrical percolation behavior of carbon black dispersed in epoxy resin

In conductive polymer compounds, the filler volume fraction at which a network of touching particles is formed is not a constant but depends on the manufacturing process. By applying three main features—particle-particle interaction, dynamics of agglomeration, and structure of agglomerates—which are well known in colloid science to filled polymers, the electrical percolation behavior can be understood. Thus, it is possible to explain the hitherto found low percolation thresholds of less than 0.5 vol% in carbon-black-filled resins and, hence, further reduce the threshold to 0.06 vol%. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1741–1746, 1997     

Processing and shape effects on silver paste electrically conductive adhesives (ECAs)

Various amounts of silver flakes and dendrites were used as conductive fillers in an electrically conductive adhesive (ECA) resin with DPM, BCA and xylene as diluent to help uniform distribution of filler particles in the matrix. Due to the fact that the higher the temperature, the higher the shrinkage rate of the polymer resin and, consequently, the larger the connecting area in-between fillers, a better curing condition for processing silver filled ECA was found to be a relatively higher curing temperature. The mechanism of conductivity achievement in conductive adhesives was analyzed by comparing processing conditions, resistivity and microstructures. In addition, the influence of adding nano-sized silver particles on the resistivity of the conductive adhesives was also investigated and the addition of nano-sized silver particles resulted in a lower percolation threshold for ECAs.     

Fabrication and electrical properties of CNT/PP conductive composites with low percolation threshold by solid state alloying

The carbon nanotube/polypropylene conductive composites with a percolation threshold as low as 0.25 wt% were fabricated by solid state alloying. This solid state alloying method uses the super‐high speed mechanical shearing (at 10,000 rpm) to process the entangled catalytically grown carbon nanotubes (CNTs) and the polymer matrix in solid state. The electrical properties of the nanocomposites and the structure and distribution of CNTs were investigated. The results indicated that via the shear‐intensive process, CNTs were truncated and dispersed effectively, and their length could be controlled properly to fully exert the advantage of high aspect ratios (length‐to‐diameter ratios). At the same time, a linear structure conductive network which may considerably lower the percolation threshold was also formed by this method. Moreover, the CNTs could be further dispersed under the action of thermo energy provided by increasing the processing temperature. The super‐high speed solid state alloying method is a favorable approach for the production of low percolation threshold conductive composites of CNTs filled high viscosity resins. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

炭黑填充复合型导电聚合物的研究进展

在聚合物基体中添加导电炭黑以降低聚合物的电阻率,是目前最为常用的制备导电聚合物的方法。综述了炭黑填充复合型导电聚合物的研究进展。对影响复合材料导电性能及渗滤阈值的因素进行了讨论。重点介绍了使用共混聚合物作基体,并利用炭黑在共混基体中的非均相分布来降低炭黑用量的研究。     

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