CNTs表面包覆PPy对PVC复合材料电导率的影响

为促进碳纳米管(CNTs)更为有效地应用于聚合物抗静电复合材料,采用原位聚合在CNTs表面生成聚吡咯(PPy)包覆层得到CNT-PPy,其组成通过傅立叶变换红外光谱分析和热重分析确认。CNT-PPy作为导电剂添加到聚氯乙烯(PVC)中制备PVC/CNT-PPy复合材料,对比分析PVC/CNT-PPy复合材料电导率的变化规律可得:PPy修饰CNTs可降低PVC/CNT-PPy复合材料中CNTs的逾渗阈值;当PPy包覆层在CNT-PPy中质量分数约为51.1%,CNT-PPy在复合材料中的质量分数为3%时,制得PVC复合材料的电导率可达到10–7 S/cm量级。由此可知,CNTs表面可控的PPy修饰量对PVC/CNTs复合材料抗静电性能起到显著的提升作用,为CNTs作为高性能导电剂应用提供更多的空间。     

PP/碳纳米管复合材料的结晶动力学研究

采用原子转移自由基(ATRP)活性聚合方法在多壁碳纳米管(MWNT)表面接枝丙烯酸丁酯聚合物(PBA),并以接枝聚合物MWNT-PBA对聚丙烯(PP)进行改性。红外光谱(FT-IR)及透射电子显微镜(TEM)测试结果表明,采用ATRP法成功地将PBA接枝到MWNT表面上。利用差示扫描量热仪(DSC)对PP/MWNT复合材料的非等温结晶动力学进行了研究。结果表明,PP/MWNT复合材料中由于MWNT的加入明显地提高了复合材料的结晶温度和结晶速率,并降低了结晶活化能。MWNT-PBA和MWNT-COOH(酸化MWNT)加入PP都有异相成核的作用,而MWNT-PBA比MWNT-COOH的作用更加明显。     

MWNT-g-PBA的制备及对PVC的改性

采用原子转移自由基聚合(ATRP)方法在多壁碳纳米管(MWNT)表面接枝聚丙烯酸丁酯(PBA),制备得到PBA接枝MWNT(MWNT-g-PBA),并以此对聚氯乙烯(PVC)行改性。红外光谱(FTIR)及射电子显微镜(TEM)分析结果表明,采用ATRP法成功地将PBA接枝到MWNT的表面。采用熔融共混法制备了PVC/MWNT-g-PBA复合材料,对其力学性能和耐热性能进行了研究。结果表明,MWNT-g-PBA可以显著提高复合材料的拉伸强度和冲击强度,同时复合材料的耐热性能并未受到较大影响。     

聚合物改性碳纳米管及其对PVC增韧的研究

通过原子转移自由基聚合法合成了PMMA-Br、PBA-Br和PMMA-b-PBA-Br3种聚合物,采用叠氮法分别用它们修饰单壁碳纳米管(SWNT)。通过红外光谱、拉曼光谱、热失重法和透射电子显微镜综合分析了其修饰效果;并用经聚合物修饰的SWNT制备了PVC/SWNT纳米复合材料。结果表明,在100gPVC中加入0.1g经聚合物修饰的SWNT后,纳米复合材料的力学性能明显提高,其中PVC/PMMA-b-PBA-SWNT纳米复合材料的冲击强度是纯PVC的4倍;PVC/PMMA-SWNT纳米复合材料的冲击强度是纯PVC的3.2倍,断裂伸长率提高了2.5倍,拉伸强度提高了16%,弯曲强度提高了18%;PVC/PBA-SWNT纳米复合材料的拉伸强度和断裂伸长率分别是纯PVC的1.13倍和2.26倍;通过扫描电子显微镜分析了聚合物的增韧机理。     

MWNT对长玻纤增强PP/膨胀阻燃剂体系性能的影响

用熔融共混法制备了长玻纤增强聚丙烯/膨胀阻燃剂/多壁碳纳米管(LGFPP/IFR/MWNT)复合材料。通过极限氧指数、垂直燃烧测试、热失重分析、力学性能测试等手段研究了MWNT对LGFPP/IFR的阻燃性能、热性能和力学性能的影响。结果表明,MWNT的加入提高了LGFPP/IFR阻燃体系的阻燃性能,在LGFPP/IFR阻燃体系中添加1%MWNT后,LGFPP/IFR/MWNT复合材料的氧指数提高到23.5%;MWNT可显著增加LGFPP/IFR的热稳定性,添加1%MWNT可使LGFPP/IFR热分解起始温度提高12.34℃;MWNT的加入还提高了LGFPP/IFR阻燃体系的力学性能,在LGFPP/IFR阻燃体系中添加1%MWNT后,LGFPP/IFR/MWNT复合材料的拉伸强度、弯曲强度和冲击韧性分别提高了5.7%、12.7%和1.0%。     

原位聚合法制备热塑性聚氨酯/多壁碳纳米管复合材料及其性能研究

采用原位聚合法制备了热塑性聚氨酯/多壁碳纳米管(TPU/MWNT)复合材料,利用热重分析(TGA)、体积电阻率测试、维卡软化点测试、力学性能测试,研究了多壁碳纳米管(MWNT)质量分数对复合材料热稳定性、导电性以及力学性能的影响。结果表明,经酸化处理的MWNT可以显著提高复合材料的热稳定性和力学性能,质量分数为0.8%的TPU/MWNT复合材料具有最优异的热稳定性和力学性能。同时,一定含量的MWNT能够搭建三维网络结构,使材料的导电性和耐热性也得到了显著提高。     

湿敏性碳纳米管在聚氯乙烯抗静电复合材料中的研究与应用

利用碳纳米管(CNTs)与十六烷基三甲基溴化铵(CTAB)的吸附作用,制得具有湿敏特性的CNTs,并通过红外光谱分析和热失重分析确定其组成;将其作为抗静电剂加入到聚氯乙烯(PVC)中,通过模拟潮湿环境研究其湿敏特性对PVC/CNTs复合材料体积电导率的影响规律。结果表明,CNTs的有机化改性可降低其在复合材料中的逾渗阈值;当CNTs添加量为4%(质量分数,下同)时,经过潮湿处理的PVC复合材料的电导率可升高4个数量级。     

PET中添加MWNT对其性能及结构的影响测定

将多壁碳纳米管(MWNT)在聚对苯二甲酸乙二醇酯(PET)聚合时加入,制备包含MWNT不同含量的MWNT/PET复合材料,并通过扫描电子显微镜(SEM)分析了复合材料的结构;借助差示扫描量热仪对MWNT/PET复合材料的结晶性能进行测试。     

HIPS/多壁碳纳米管复合材料炭层结构对阻燃性能的影响

通过熔融共混法制备了高抗冲聚苯乙烯(HIPS)/多壁碳纳米管/(MWNT)复合材料,采用热重分析仪和锥形量热仪评价了复合材料的阻燃性能,并用数码相机、扫描电子显微镜观察了燃烧残余物的结构。结果表明:与HIPS相比,w(MWNT)分别为3%,5%,10%的HIPS/MWNT复合材料的热释放速率峰值分别下降了21.66%,40.12%,56.21%,质量损失速率也明显降低,同时形成了对阻燃有关键作用并具有特殊结构的炭渣残余物。HIPS/MWNT复合材料燃烧后形成的炭渣具有蜂窝状的亚微观结构,以及纳米尺度的微观网络结构。     

PVC/高岭土复合材料的制备及其力学性能研究

针对PVC加工过程中韧性差、冲击强度低、热不稳定等问题,制备了PVC/N-十六烷基马来酰胺酸镧(Ⅲ)-高岭土复合材料。通过刚果红实验、傅里叶红外光谱(FTIR)、X-射线衍射(XRD)、热重分析(TGA)等表征了其结构与热性能;通过扫描电镜(SEM)观察复合材料表观形貌;研究了插层后的高岭土对PVC材料抗冲击强度的影响。结果表明,插层改性后的高岭土层间距增大;PVC复合材料圆形度得到了提高,外形变得更加规整;获得的复合材料断裂伸长率和冲击强度都有所增强,复合材料的热稳定性能也得到了提高。     

Dielectric spectroscopy on melt processed polycarbonate—multiwalled carbon nanotube composites

Complex permittivity and related AC conductivity measurements in the frequency range between 10⁻⁴ and 10⁷ Hz are presented for composites of polycarbonate (PC) filled with different amounts of multiwalled carbon nanotubes (MWNT) varying in the range between 0.5 and 5 wt%. The composites were obtained by diluting a PC based masterbatch containing 15 wt% MWNT by melt mixing using a Micro Compounder. From DC conductivity measurements it was found that for samples processed at a mixing screw speed of 150 rpm for 5 min, the percolation occurs at a threshold concentration (p_c) between 1.0 and 1.5 wt% MWNT. For concentrations of MWNT near the percolation threshold, the processing conditions (screw speed and mixing time) were varied. The differences in the dispersion of the MWNT in the PC matrix could be detected in the complex permittivity and AC conductivity spectra, and have been explained by changes in p_c. The AC conductivity and permittivity spectra are discussed in terms of charge carrier diffusion on percolation clusters and resistor-capacitor composites.     

Low percolation thresholds of electrical conductivity and rheology in poly(ethylene terephthalate) through the networks of multi-walled carbon nanotubes

Coagulation method was first used to prepare nanocomposites of multi-wall carbon nanotubes (MWNT) and poly(ethylene terephthalate) (PET). The morphology of nanocomposites is characterized using transmission electronic microscopy and scanning electronic microscopy. A coating on MWNT by PET chains is observed by comparison of micrographs of purified MWNT and MWNT encapsulated by PET chains in the nanocomposites, and this coating is considered as evidence of interfacial interaction between MWNT and PET chains. Both electrical conductivity and rheological properties have been well characterized. With increasing MWNT loading, the nanocomposites undergo transition from electrically insulative to conductive at room temperature, while the melts show transition from liquid-like to solid-like viscoelasticity. The percolation threshold of 0.6 wt% (based on viscosity) for rheological property and 0.9 wt% for electrical conductivity has been found. The low percolation threshold results from homogeneous dispersion of MWNT in PET matrix and high aspect ratio of MWNT. The less rheological percolation threshold than electrical percolation threshold is mainly attributed to the fact that a denser MWNT network is required for electrical conductivity, while a less dense MWNT network sufficiently impedes PET chain mobility related to the rheological percolation threshold.     

AC conductivity of carbon fiber–polymer matrix composites at the percolation threshold

This paper reports results on experimental investigation of the conductivity behavior of carbon fiber filled polymer composites at the percolation threshold. Two types of carbon fiber‐epoxy matrix composites have been studied and comparison of the measured data has been made. These two types of composites differ in the surface modification of carbon fibers (in one case the surface of carbon fibers is covered with polymer beads using the microencapsulation technology, in the other their surface stayed unmodified). Experimental data reveal that surface modification of carbon fibers influences greatly the DC conductivity (percolation threshold moves to higher concentrations) but does not influence the AC electrical properties. From the frequency dependence of conductivity upon fiber concentration it becomes clear that it is not possible to predict the high frequency conductivity (electromagnetic interference shielding properties) based on the DC conductivity. Percolation behavior of conductivity as a function of conductive filler concentration is typical only for DC or low frequency AC conductivity. The percolation threshold gradually vanishes for high frequencies of electromagnetic field. The temperature dependence of electrical properties has also been studied. Composites with concentration near the percolation threshold show the switch‐off effect (at the specific temperature the DC conductivity drops by several orders of magnitude). This switch‐off effect does not occur for high frequency AC conductivity.     

Electrical and mechanical properties of polyimide-carbon nanotubes composites fabricated by in situ polymerization

Polyimide (PI)-carbon nanotubes composites were fabricated by in situ polymerization using multi wall carbon nanotubes (MWNT) as fillers. It suggested that in situ polymerization is an ideal technique to make a perfect dispersion of carbon nanotubes into matrixes. Besides it, the pre-treatment of carbon nanotubes in solvent to make the networks untied enough and to let solvent percolated into the networks is very important for forming uniform entanglements between carbon nanotubes and polymer molecular chains. The results imply that the percolation threshold for the electric conductivity of the resultant PI-MWNT composites was ca. 0.15 vol%. The electrical conductivity has been increased by more than 11 orders of magnitude to 10⁻⁴ S/cm at the percolation threshold. The mechanical properties of the polyimide composite were not improved significantly by addition of carbon nanotubes.     

Electrical conductivity and microwave absorbing properties of nickel‐coated multiwalled carbon nanotubes/poly(phthalazinone ether sulfone ketone)s composites

Nickel‐coated multiwalled carbon nanotubes (Ni‐MWNT) were prepared by electroless deposition with ultrasonic vibrations. The morphologies and components were characterized by scanning electron microscope and energy dispersive spectroscopy. Two types of fillers, multiwalled carbon nanotubes (MWNT) and Ni‐MWNT, were blended with poly(phthalazinone ether sulfone ketone)s (PPESK) by the solution‐mixing method, respectively. The electrical conductivity and microwave absorbing properties of the composites were investigated. The results show that Ni‐MWNT/PPESK composites have relatively lower electrical resistivity values than MWNT/PPESK, and in both cases the decrease in electrical resistivity indicates a similar percolation transition behavior in the same MWNT content region. Moreover, as MWNT loading is 5 parts per hundred parts of resin (phr), Ni‐MWNT/PPESK composite has the wider frequency region (9.5–13.5 GHz) of the reflection loss (RL) less than ?10 dB and the lower minimum value of RL (?27.5 dB) compared with MWNT/PPESK. The better microwave absorption properties can be attributed to the improved dielectric and magnetic properties of the fillers. A good correlation between electrical conductivity and microwave absorption was found for MWNT/PPESK composites. In addition, tensile test and thermogravimetric analysis indicate that introducing Ni‐MWNT into PPESK is favorable for the improvement of the mechanical properties and high temperature stability of the composites. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Kinetics of dynamic percolation in polymer/carbon composites

Dynamic percolation differs from static percolation in polymer composites owing to its occurrence at a particular filler fraction under thermal activation. Mechanistic insights into dynamic percolation might lead to develop polymer composites with controlled electrical properties at lower filler fractions and improved temperature coefficient of resistance phase transitions. Although attempts have been made to kinetically describe the dynamic percolation in polymer composites, a generalized mechanism-based approach has not yet been reported. In this article, a systematic and generalized theoretical approach to kinetically model the dynamic percolation in polymer/carbon composites has been put forward. Based on the proposed approach, a kinetic expression to predict the quasi-thermodynamic equilibrium state in a polymer/carbon composite at constant temperature is derived. The soundness of the proposed approach is justified by its effective applications on poly(vinylidene fluoride)/multiwalled carbon nanotube (PVDF/MWNT), poly(vinylidene fluoride)/carboxyl-functionalized MWNT (PVDF/MWNT), high-density polyethylene/carbon black, and poly(methyl methacrylate)/carbon black composites. Certain mechanistic complexities of dynamic percolation are also pointed out and discussed. POLYM. ENG. SCI., 60: 423–433, 2019. © 2019 Society of Plastics Engineers     

Effects of carbon nanotubes aspect ratio on the qualitative and quantitative aspects of frequency response of electrical conductivity and dielectric permittivity in the carbon nanotube/polymer composites

To study the effect of carbon nanotube aspect ratio (AR) on the frequency response of the electrical properties, the alternating current (AC) electrical conductivity and dielectric permittivity of different AR multi-wall carbon nanotubes (MWCNTs)/thermoplastic elastomer (TPE) composites were studied in the AC frequency range of 100 Hz to 10  MHz. Qualitatively, the effect of frequency on the electrical properties of the composites was the same for all AR MWCNTs and shared many typical features of electrically percolative composites. Quantitatively, the frequency responses of electrical properties were found to be independent of nominal AR, concentration, percolation threshold, and the diameter of the MWCNT. Instead, frequency response of electrical properties was dependent on the MWCNT length and initial electrical conductivity of the composites. With the same initial conductivity of the MWNT composites, frequency-conductivity sensitivity varied inversely with the nominal length of the MWCNTs. Composites with MWCNTs of the same nominal length and similar electrical conductivity values, regardless of whether the MWCNT concentration was below or above the percolation threshold, exhibited quantitatively similar frequency-conductivity sensitivity. The frequency-dielectric sensitivity at the percolation threshold was a reflection of frequency-conductivity sensitivity and was also found to be dependent on the initial conductivity of the composites.     

Electrical and mechanical properties of pre-localized polypyrrole/poly(vinyl chloride) conductive composites

A novel process for preparation of conductive polypyrrole/poly(vinyl chloride) (PPy/PVC) composites by pre-localization of an intrinsically conducting PPy phase in a PVC matrix has been developed. This process involves encapsulating PVC particles with a thin layer of PPy, and subsequently compacting this PPy-encapsulated PVC powder by compression molding. The current-voltage characteristics and electrical conductivity of the pre-localized PPy/PVC composites were determined. The change of the current-voltage characteristics from linear to nonlinear behavior with increasing PPy content in the composites is discussed in the view of the intermolecular hopping and tunneling of electrons. The tensile properties, dynamic mechanical behavior, and microhardness of the pre-localized PPy/PVC composites were studied as a function of PPy content. A percolation threshold of 0.3 wt% is achieved in the pre-localized PPy/PVC composites. This value is much lower than those of the conventional conductive composite materials containing a random distribution of PPy fillers. The samples with a PPy content of 1.6 wt% or above have high conductivity and still preserve reasonable mechanical properties.     

High electrical conductivity of nylon 6 composites obtained with hybrid multiwalled carbon nanotube/carbon fiber fillers

The synergetic effect of multiwalled carbon nanotubes (MWNTs) and carbon fibers (CFs) in enhancing the electrical conductivity of nylon 6 (PA6) composites was investigated. To improve the compatibility between the fillers and the PA6 resin, we grafted γ‐aminopropyltriethoxy silane (KH‐550) onto the MWNTs and CFs after carboxyl groups were generated on their surface by chemical oxidation with nitric acid. Fourier transform infrared spectroscopy and thermogravimetric analysis proved that the KH‐550 molecules were successfully grafted onto the surface of the MWNTs and CFs. Scanning electron microscopy and optical microscopy showed that the obtained modified fillers reduced the aggregation of fillers and resulted in better dispersion and interfacial compatibility. We found that the electrical percolation threshold of the MWNT/PA6 and CF/PA6 composites occurred when the volume fraction of the fillers were 4 and 5%, respectively. The MWNT/CF hybrid‐filler system exhibited a remarkable synergetic effect on the electrically conductive networks. The MWNT/7% CF hybrid‐filler system appeared to show a second percolation when the MWNT volume fraction was above 4% and a volume resistivity reduction of two orders of magnitude compared with the MWNT/PA6 system. The mechanical properties of different types of PA6 composites with variation in the filler volume content were also studied. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40923.     

Electrical properties of poly(phenylene sulfide)/multiwalled carbon nanotube composites prepared by simple mixing and compression

Poly(phenylene sulfide) (PPS)/multiwalled carbon nanotubes (MWNTs) conductive composites were prepared through the simple mixing of PPS granules with MWNT powder and subsequent compression. The electrical properties as a function of MWNT loading clearly showed a low percolation threshold of about 0.22 vol % and a high critical exponent value of 3.55 for composites prepared by this method. A comparison study with composites prepared via melt mixing was also carried out, where a random dispersion of MWNTs was achieved. There existed a striplike morphology of MWNTs in the PPS matrix and MWNTs were selectively located in strips caused by compression. The effects of temperature and pressure on the conductivity of the PPS/MWNT composites as prepared via simple mixing and compression are discussed. In addition, the conductivity also showed a dependence on the flow direction of the compression, with higher conductivity in the direction parallel to the flow direction than in the direction perpendicular to the flow direction. So the relationship of the processing and morphological properties was investigated in detail. The possible conductive mechanisms of conventional melt blending and preparation via sample mixing and compression are also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008