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.     

PVDF-HDPE双相PTC材料的制备、结构与性能

分别以聚偏氟乙烯(PVDF)、高密度聚乙烯(HDPE)为基体,炭黑(CB)为导电填料,采用两步熔融混合法,制备了PVDF-HDPE-CB导电复合材料。通过差示扫描量热(DSC)、溶剂抽提、扫描电子显微镜(SEM)等方法表征了复合材料的结构,采用电阻测试仪等仪器测试了复合材料的性能。研究了PVDF与HDPE体积比与复合材料结构的关系,以及对复合材料导电性、正温度系数(PTC)特性、耐电压性能的影响。结果表明,复合材料具有双相PTC材料结构,在复合材料中,HDPE易形成连续相,少量添加即可显著提高以PVDF为基体的PTC材料的导电性和耐电压性能。     

具有纳米结构的聚偏氟乙烯/1-乙烯基-3-丁基咪唑氯盐离子液体复合材料的结晶行为

用示差扫描量热(DSC)、偏光显微镜(POM)及X射线衍射(XRD)分析考察了具有纳米结构的聚偏氟乙烯(PVDF)/1-乙烯基-3-丁基咪唑氯盐离子液体([VBIM][Cl])复合材料(PVDF/[VBIM][Cl])中经[VBIM][Cl]接枝的PVDF(PVDF-g-[VBIM][Cl])纳米微区对PVDF结晶行为的影响.研究结果表明,[VBIM][Cl]化学接枝在PVDF的分子链上,在PVDF/[VBIM][Cl]复合材料中,PVDF-g-[VBIM][Cl]嵌段形成大量纳米微区,分散在PVDF基体中.PVDF-g-[VBIM][Cl]纳米微区能够显著提高PVDF熔体结晶温度(Tc)并显著降低PVDF晶体的等温结晶时间.与纯PVDF相比,在纳米结构的PVDF/[VBIM][Cl]复合材料中,PVDF-g-[VBIM][Cl]纳米微区大大提高了PVDF晶体的成核速率,PVDF的球晶尺寸明显减小.由于[VBIM][Cl]完全"受限"于PVDF-g-[VBIM][Cl]纳米微区中,无法与PVDF分子链发生相互作用,因此纳米结构的PVDF/[VBIM][Cl]复合材料最终以非极性的α晶体为主.由于PVDF-g-[VBIM][Cl]纳米微区与PVDF基体具有热力学不相容性,因此其界面处的PVDF分子链处于部分有序的状态,有助于PVDF晶体的成核,加速了PVDF晶体的结晶速率.     

HDPE/HIPS/CB复合材料的制备及PTC性能

以高抗冲击聚苯乙烯(HIPS)和高密度聚乙烯(HDPE)为基体,炭黑(CB)为导电填料,采用熔融法制备聚合物基正电阻率温度系数效应(PTC)复合材料.通过扫描电子显微镜(SEM)研究了CB在复合材料两相基体中的选择分布,采用热敏电阻温度(RT)曲线测试仪研究复合材料PTC性能随CB含量的变化规律.结果表明,在HIPS/CB体系中加入HDPE后,复合材料的渗流阈值降低,PTC强度增强,耐电压强度有所提高.     

HDPE/EPDM/CB复合物的PTC效应

聚合物正温度系数 (PTC)材料 ,是由聚合物基体与炭黑、碳纤维、金属粉末等导电填料共混而成的一种功能导电复合材料 ,其特点是 :当温度升高时 ,在聚合物结晶熔点附近 ,材料的电阻率随温度升高急剧增加 ,可发生几个数量级的突跃 .聚合物 PTC材料可用作自限温加热器、过电流保护器、传感器等 ,有广阔的发展前景 .目前对聚合物 PTC材料的研究主要以聚乙烯 [1～ 5]、乙烯 -醋酸乙烯酯共聚物[6] 、偏氟乙烯 [7] 等单一组分聚合物作为基体材料 .本文研究了以高密度聚乙烯 (HDPE) /三元乙丙胶(EPDM)共混物为基体材料的炭黑 (CB)导电复合材…     

聚乳酸/凹凸棒土纳米复合材料的结构与性能

采用熔融复合方法制备了不同填料质量分数的聚乳酸/纳米凹凸棒土复合材料,纳米凹凸棒土的加入可以显著提高聚乳酸纳米复合材料的拉伸强度和断裂伸长率.扫描电镜结果表明,凹凸棒土粒子在复合材料中实现了均匀分散.DSC曲线在降温过程中出现明显结晶峰,说明纳米凹凸棒土对聚乳酸有一定的成核作用.当纳米凹凸棒填料含量>8%时,在聚合物基体中可形成完善的网络状结构.填料粒子作为体系中的物理缠结点使得复合材料熔体的应力松弛时间延长.红外谱图显示纳米凹凸棒土和聚乳酸分子间存在较强的相互作用.我们推测,纳米凹凸棒土的加入减少了PLA基体层的厚度,使其由三维应力转变为二维应变状态,导致最大切应力可以达到剪切屈服强度,产生剪切滑移形变带,使得呈现出韧性材料性质,有效提高了材料的断裂伸长率.     

聚丙烯/硫酸钡复合体系的界面相互作用与流变性质和结晶行为的关系

制备了一系列具有不同界面状态的聚丙烯 (PP) 硫酸钡 (BaSO4)复合体 .PP BaSO4的界面分别用硅烷、硬脂酸、马来酸酐接枝聚丙烯 (PP g MAH)改性 .研究表明 ,填充体系的熔体粘度和熔体弹性均高于基体 .以硅烷和PP g MAH进行界面改性后 ,PP BaSO4的界面相互作用加强 ,导致复合体系中的熔体粘度和熔体弹性进一步提高 ,同时BaSO4对PP的成核活性提高 .填料用硬脂酸处理后 ,硬脂酸能够在填料粒子表面上形成一个包覆层 ,使粒子与PP的亲和性改善 .同时该包覆层具有润滑作用 ,使得复合体系的熔体粘度和熔体弹性下降 ,并使得该体系中BaSO4的成核活性低于硅烷和处理的体系 .本文探讨了由复合体系的熔体粘度定量比较填充复合体系中聚合物 填料界面相互作用的方法 ,讨论了界面改性对复合体系流变性质和结晶行为影响的机理     

低熔体黏度聚醚醚酮的合成与性能

<正>高性能聚合物及其复合材料因优异的热性能和机械性能备受关注[1~4].高性能聚合物分子链的芳香性结构使其具有优异的性能,但分子链的刚性结构导致热塑性高性能聚合物具有很高的熔体黏度,限制了其应用.聚醚醚酮连续纤维增强复合材料因熔体黏度高而难以预浸[5~8].为了降低聚醚醚酮的熔体黏度,人们进行了大量的实验探索.     

超高分子量聚苯乙烯的流变性能

以毛细管流变仪和Hakke转矩流变仪对稀土催化合成的超高分子量聚苯乙烯 (UHMWPS)的流变与加工性能进行了研究 .结果表明 ,UHMWPS最显著的流变特征为超高的熔体粘度和低剪切速率下出现不稳定流动 .不稳定流动与超高分子量聚合物长的松弛时间有关 ,并提出了临界剪切速率与分子量和温度的定量关系式 .较低的分子量和较高的温度有利于提高临界剪切速率 ,改善挤出物外观质量和降低熔体粘度 .分子链极度缠结不仅导致超高的熔体粘度 ,也使UHMWPS链解缠加快 ,导致更高的剪切速率敏感性 .UHMWPS塑化时熔体粘度高 ,转矩大 ,加工性能劣于通用聚苯乙烯 (GPPS)     

超高分子量聚乙烯基导电复合材料的电性能和自发热性能的研究

超高分子量聚乙烯(UHMWPE)具有优异的综合性能,本文采用凝胶结晶溶液方法制备了分别以碳纤维(CF)和镀镍碳纤维(NiCF)为导电填料,UHMWPE为基体的3个系列导电聚合物复合材料—UHMWPE/CF、UHMWPE/NiCF和UHMWPE/EMMA/CF复合体系,并分别对它们进行了室温伽马射线辐射处理,重点研究了这些材料的电性能和自发热性能,利用DSC、SEM、WAXS、DMA和体积膨胀等仪器进行了一系列测试表征。结果表明,NiCF作为导电填料时体系的逾渗阈值最低,为3vol%。伽马射线辐射处理不仅能有效提高材料的PTC效应,而且在合适的辐射剂量时也能有效提高材料的自发热性能。对材料介电性能的研究揭示了材料的交流电阻率与温度、频率的依赖关系。     

Enhanced Reproducibility of Positive Temperature Coefficient Effect of CB/HDPE/PVDF Composites with the Addition of Ionic Liquid

Developing an effective method for improving the reproducibility of positive temperature coefficient(PTC) effect is of great significance for large-scale application of polymer based PTC composites, owing to its contribution to the security and reliability. Herein, we developed a carbon black(CB)/high density polyethylene(HDPE)/poly(vinylidene fluoride)(PVDF) composite with outstanding PTC reproducibility, by incorporating 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([OMIm][NTf_2]) into the composite. After multiple repeated temperature cycles, the PTC performance of as-prepared material keeps almost unchanged and the varition of resistance at room temperature is less than 7%. Our studies revealed that [OMIm][NTf2] contributes to the improvement of PTC reproducibility in two ways:(i)it acts as an efficient plasticizer for refining the co-continuous phase morphology of HDPE/PVDE blends;(ii) it inhibits the crystallization of PVDF through the dilution effect, leading to more overlaps of the volume shrinkage process of HDPE and PVDF melt which results in the decrease of interface gap between HDPE and PVDF. This study demonstrated that ionic liquids as the multifunctional agents have great potential for improving the reproducibility in the application of the binary polymer based PTC composites.     

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.     

iPP/HDPE/CB复合材料的制备及反常的温度-电阻效应

本文利用普通熔融挤出法制备了iPP/HDPE/CB复合材料, 分别采用注射成型及压制成型方法得到测试试样. 通过研究复合材料体积电阻率随温度的变化, 考察注塑试样和压制试样的PTC特性及复合材料形态结构与试样PTC特性之间的关系.     

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…     

YBa2Cu3O7-x/Thermoplastic polymer composite thermistors

Conducting YBa₂Cu₃O_7-x was incorporated in to polyethylene matrices to produce composite materials with low room temperature resistivity and sizable positive temperature coefficient (PTC) resistance effects. The intensity of the PTC effect for these composites was found to be as large as 10 orders of magnitude. The location of the PTC phenomenon is determined by the choice of polymer matrix. The mechanism for the PTC effect in crystalline polymer composites is related to the percolation behaviour of the composites and the thermal expansion of the polymer matrix.     

Carbon black‐filled polyolefins as positive temperature coefficient materials: The effect of in situ grafting during melt compounding

For the production of polymer‐based conducting composites serving as positive temperature coefficient (PTC) materials with lower room‐temperature resistivity and sufficiently high PTC intensity, carbon black has been pretreated with acrylic acid and some initiator and then melt‐mixed with low‐density polyethylene. Because of the in situ formation of covalent bonding at the filler/matrix interface, the distribution status and thermally induced displacement habit of the conductive fillers have changed accordingly. As a result, the electrical performance of the composites can be tailored as desired. The amount of acrylic acid and the treatment sequence of carbon black exert an important influence on the effectiveness of the modification. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 127–134, 2003     

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     

一类新型PTC复合材料的制备及性能

一类新型ＰＴＣ复合材料的制备及性能杜伟坊,杜海清（湖南大学材料科学及应用化学研究所,长沙,４１００８２）关键词正温度系数,聚乙烯,ＹＢａ_２Ｃｕ_３Ｏ_（７－ｘ）具有正温度系数（ＰＴＣ）的材料在其转化温度附近具有电阻率大幅度上升的特点,因而在温度检测与?..     

Roles of work of adhesion between carbon blacks and thermoplastic polymers on electrical properties of composites

The effect of the work of adhesion between carbon blacks and different thermoplastic polymers on the positive temperature coefficient (PTC) of composites was investigated. Thermoplastic polymers, such as EVA, LDPE, LLDPE, HDPE, and PP, were used with the addition of 30 wt% of carbon blacks. The work of adhesion based on the surface free energy of a composite was studied in the context of two-liquid contact angle measurements using deionized water and diiodomethane. It was observed that the resistivity on PTC behavior was greatly increased near the crystalline melting temperature, due to the thermal expansion of polymeric matrix. It was shown that the PTC intensity defined as the ratio of the maximum resistivity (rho(max)) to the resistivity at room temperature (rho(RT)) had the largest value on CB/HDPE composites. From the experimental results, the decrease in the work of adhesion induced by interactions between carbon black surfaces and polymer chains is an important factor in the fabrication of a PTC composite.