Influence of organo-clay on electrical and mechanical properties of PP/MWCNT/OC nanocomposites

The electrical, thermal and mechanical properties of nanocomposites, based on polypropylene (PP) filled by multi-walled carbon nanotubes (MWCNTs) and organo-clay (OC), were studied with the purpose of finding out the effect of OC on the microstructure of MWCNTs dispersion and PP/MWCNT/OC composites. It was found that addition of organo-clay nanoparticles improved nanotube dispersion and enhanced electrical properties of PP/MWCNT nanocomposites. Addition of organo-clay (MWCNT/OC ratio was 1/1) reduced the percolation threshold of PP/MWCNT nanocomposites from ?_c = 0.95 vol.% to ?_c = 0.68 vol.% of carbon nanotubes, while the level of conductivity became 2–4 orders of magnitude higher. The DSC and DMA analyses have shown that the influence of organo-clay on the thermal and mechanical properties of material was not significant in composites with both fillers as compared to PP/OC. Such an effect can be caused by stronger interaction of OC with carbon nanotubes than with polymer matrix.     

Electrical and rheological percolation of PMMA/MWCNT nanocomposites as a function of CNT geometry and functionality

Composites of poly(methyl methacrylate) (PMMA) with multi-walled carbon nanotubes (MWCNT) of varying aspect ratio and carboxylic acid functionality were prepared using melt mixing. The extent of dispersion and distribution of the MWCNTs in the PMMA matrix was investigated using a combination of high-resolution transmission electron microscopy (HRTEM), wide-angle X-ray diffraction (XRD) and Raman spectroscopy. The electrical resistivity and oscillatory shear rheological properties of the composites were measured as a function of MWCNT geometry, functionality, and concentration. The fundamental ballistic conductance of the pristine free-standing MWCNTs was investigated using a mechanically controlled break-junction method. The electrical conductivity of PMMA was enhanced by up to 11 orders of magnitude for MWCNT concentrations below 0.5 wt.%. MWCNTs having higher aspect ratio, above 500, or functionalized with carboxylic acid groups readily formed rheological percolated networks with thresholds, determined from a power law relationship, of 1.52 and 2.06 wt.%, respectively. The onset of pseudo-solid-like behaviour and network formation is observed as G′, η∗, and tan δ⁻¹ are independent of frequency as MWCNT loading increased. Sufficiently long and/or functionalized tubes are required to physically bridge or provide interfacial interactions with PMMA to alter polymer chain dynamics. Carboxylic acid functionalization disrupts the crystalline order of MWCNTs due to a loss of π-conjugation and electron de-localisation of sp² C-C bonds resulting in non-ballistic electron transport in these tubes, irrespective of how highly dispersed they are in the PMMA matrix.     

Properties of matrix-grafted multi-walled carbon nanotube/poly(methyl methacrylate) nanocomposites synthesized by in situ reversible addition-fragmentation chain transfer polymerization

Multi-walled carbon nanotubes (MWCNT)/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized by the in situ reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in the presence of MWCNTs, at which the bulk polymer was grafted onto the surface of nanotubes through the ??grafting through?? strategy. For this purpose, MWCNTs were formerly functionalized with polymerizable MMA groups. MMA and PMMA-grafted MWCNTs were characterized by Fourier-transform infrared spectroscopy, Raman, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Dissolution of nanotubes was examined in chloroform solvent and studied by UV?Cvis spectroscopy. Thermogravimetric and degradation behavior of prepared nanocomposites was investigated by TGA. MWCNTs had a noticeable boosting effect on the thermal stability of nanocomposites. TGA thermograms showed a two-step weight loss pattern for the degradation of MWCNT-PMMA/PMMA nanocomposites which is contrast with neat PMMA. Introduction of MWCNTs also improved the dynamic mechanical behavior and electrical conductivity of nanocomposites. TEM micrograph of nanocomposite revealed that the applied methods for functionalization of nanotubes and in situ synthesis of nanocomposites were comparatively successful in dispersing the MWCNTs in PMMA matrix.     

基于弱相互作用的石墨化CNT/PMMA复合材料的热电传输性能

从理论上计算了碳纳米管(CNT)与聚甲基丙烯酸甲酯(PMMA)的相互作用及浸润性, 并测试了CNT/PMMA复合材料的电学、热学和光学性能. 发现石墨化CNT/PMMA复合材料具有较好的导热和导电性能, 其渗流阈值在0.8%左右, 当CNT质量分数为3%时, 复合材料的导热系数提高193%. 这种电学及热学性能的提高一方面与石墨化CNTs的规整结构有关, 另一方面与石墨化CNT-PMMA体系的弱相互作用、CNT间的有效接触以及高效的CNT网络输运性能有密切关系. 研究结果表明, 通过调控CNT与聚合物基体的表面性质、相互作用及浸润性, 可以有效地构建优化的CNT输运网络, 获得性能优异的功能复合材料.     

Poly(methyl methacrylate)/multiwalled carbon nanotube microspheres fabricated via in‐situ dispersion polymerization

Poly(methyl methacrylate)/multiwalled carbon nanotube (PMMA/MWCNT) microspheres were successfully prepared by in situ dispersion polymerization in an alcohol phase in which the acid‐treated MWCNTs were dispersed before polymerization. The PMMA and PMMA/MWCNT microspheres were monodisperse. The diameters of the microspheres decreased from about 11.6–6.0 μm as the MWCNT content was increased from 0 to 0.03 wt %. The morphology of the PMMA/MWCNT microspheres was investigated by scanning electron microscopy, atomic force microscopy, and transmission electron microscopy, and the experimental results showed that the MWCNTs were present both in the interior and on the surface of the microspheres. The synthesized PMMA/MWCNT microspheres were also characterized by electrical resistance measurements to analyze their electrical conductivity. They showed electrorheological (ER) fluid characteristics when they were dispersed in silicone oil. Their ER properties were confirmed by using optical microscopy to examine a suspension of the PMMA/MWCNT microspheres dispersed in insulating silicone oil to which an electric field of 2.5 kV/cm was applied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 182–189, 2008     

Rheological and electrical properties of polypropylene/MWCNT composites prepared with MWCNT masterbatch chips

Melt compounded PP/MWCNT (polypropylene/multi-walled carbon nanotube) composites were prepared by diluting highly concentrated masterbatch chips. Maleic anhydride grafted polypropylene (PP-g-MAH) was used as a compatibilizer to promote dispersion and interaction of MWCNTs. Rheological properties were investigated with respect to the MWCNT and compatibilizer loadings, and related to morphological and electrical properties. As the MWCNT loading was increased, shear viscosity and yield stress were increased at low shear rate region because of increased interaction between MWCNT particles. When the MWCNT loading was low, MWCNT dispersion was improved by the PP-g-MAH compatibilizer because MWCNTs were wetted sufficiently due to the presence of the compatibilizer. However, rheological and electrical properties of highly concentrated MWCNT composites with the compatibilizer were not improved compared with PP/MWCNT composites without the compatibilizer because the compatibilizer did not provide sufficient wrapping of MWCNT particles. Electrical and morphological properties of PP/MWCNT composites were correlated with the rheological properties in steady and dynamic oscillatory shear flows.     

Noncovalent functionalization of multiwalled carbon nanotubes using graft copolymer with naphthalene and its application as a reinforcing filler for poly(styrene‐co‐acrylonitrile)

A new compatibilizer, poly(vinyl benzyloxy ethyl naphthalene)‐graft‐poly(methyl methacrylate), for poly(styrene‐co‐acrylonirile) (SAN)/multi‐walled carbon nanotubes (MWCNTs) composites was synthesized. It has been identified that naphthalene unit in backbone of compatibilizer interacts with MWCNTs via π? π interaction and that the PMMA graft of the compatibilizer is miscible with the SAN matrix. When a small amount of compatibilizer was added to SAN/MWCNT composites, MWCNTs were more homogeneously dispersed in SAN matrix than the case without compatibilizer, indicating that the compatibilizer improves the compatibility between SAN and MWCNTs. As a consequence, mechanical and electrical properties of the composites with compatibilizer were largely improved as compared with those of composites without compatibilizer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4184–4191, 2010     

玻璃纤维对碳纳米管填充聚合物/热塑性聚氨酯共混体系导电性能的影响

研究了表面带有环氧基团的玻璃纤维(GF)对聚丙烯(PP)/热塑性聚氨酯(TPU)/多壁碳纳米管(MWCNT)、 聚甲基丙烯酸甲酯(PMMA)/TPU/MWCNT和聚乳酸(PLA)/TPU/MWCNT体系导电性能的影响. 研究结果表明, 未添加GF时, 由于MWCNTs选择性地分布在TPU分散相中, PP/TPU/MWCNT, PMMA/TPU/MWCNT和PLA/TPU/MWCNT材料的导电性能很差; 加入20%的GF使3个体系的电阻率均大幅度下降, 最高下降约13个数量级, 表明填充GF是一种具有普适性的改善以TPU为分散相的共混体系导电性能的有效方法. GF使体系电阻率降低的机理主要是形成了TPU包覆GF结构, 该结构可以看作长径比较高的导电棒, 可以有效协助导电通路的构建; 同时GF还起到了体积占位的作用, 提高了体系中导电组分在基体中的有效浓度.     

Coagulation method for preparing single-walled carbon nanotube/poly(methyl methacrylate) composites and their modulus,electrical conductivity,and thermal stability

A coagulation method providing a better dispersion of single-walled carbon nanotubes (SWNTs) in a polymer matrix was used to produce SWNT/poly(methyl methacrylate) (PMMA) composites. Optical microscopy and scanning electron microscopy showed an improved dispersion of SWNTs in the PMMA matrix, a key factor in composite performance. Aligned and unaligned composites were made with purified SWNTs with different SWNT loadings (0.1–7 wt %). Comprehensive testing showed improved elastic modulus, electrical conductivity, and thermal stability with the addition of SWNTs. The electrical conductivity of a 2 wt % SWNT composite decreased significantly (>10⁵) when the SWNTs were aligned, and this result was examined in terms of percolation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3333–3338, 2003     

Significant enhancement of electrical and thermal conductivities of polyethylene carbon nanotube composites by the addition of a low amount of silver nanoparticles

Electrically and thermally conductive high‐density polyethylene composites filled with hybrid fillers, multiwall carbon nanotubes (MWCNTs) and silver nanoparticles (Ag‐NPs), have been prepared in the melt state. The investigation of their electrical and thermal conductivities while comparing with high‐density polyethylene/MWCNT binary composites shows that the addition of only 3 vol% of Ag‐NPs does not reduce the electrical percolation threshold (P_c) that remains as low as 0.40 vol% of MWCNTs but leads to an increase in the maximum dc electrical conductivity of PE/MWCNT composites by two orders of magnitudes. Moreover, the association of both Ag‐NPs and carbon nanotube particles improved our composite's thermal conductivity. Copyright © 2014 John Wiley & Sons, Ltd.     

十二烷基硫酸钠对多壁碳纳米管/聚对苯二甲酸乙二酯复合材料性能的影响

用十二烷基硫酸钠(SDS)作为一种改性剂处理多壁碳纳米管(MWCNT),SDS处理后的MWCNT命名为SCNT,并采用微型挤出机和微型注塑机分别制备了MWCNT/PET和SCNT/PET复合材料.从材料的微观结构,导电性能,结晶性能和机械性能等角度,研究了SDS对MWCNT/PET复合材料性能的影响.结果表明,SDS处...     

Highly enhanced electrical and mechanical properties of methyl methacrylate modified natural rubber filled with multiwalled carbon nanotubes

Developing conductive networks in a polymer matrix with a low percolation threshold and excellent mechanical properties is desired for soft electronics applications. In this work, natural rubber (NR) functionalized with poly(methyl methacrylate) (PMMA) was prepared for strong interfacial interactions with multiwalled carbon nanotubes (MWCNT), resulting in excellent performance of the natural rubber nanocomposites. The MWCNT and methyl methacrylate functional groups gave good filler dispersion, conductivity and tensile properties. The filler network in the matrix was studied with microscopy and from its non-linear viscoelasticity. The Maier-Göritze approach revealed that MWCNT network formation was favored in the NR functionalized with PMMA, with reduced electrical and mechanical percolation thresholds. The obvious improvement in physical performance of MWCNT/methyl methacrylate functionalized natural rubber nanocomposites was caused by interfacial interactions and reduced filler agglomeration in the NR matrix. The modification of NR with poly(methyl methacrylate) and MWCNT filler was demonstrated as an effective pathway to enhance the mechanical and electrical properties of natural rubber nanocomposites.     

Preparation of conductive PTFE nanocomposite containing multiwalled carbon nanotube via latex heterocoagulation approach

Conductive poly(tetrafluoroethylene) (PTFE) composites containing surface-modified multiwalled carbon nanotubes (MWCNTs) were prepared by a simple heterocoagulation process in water. Two different types of MWCNT were used and compared: carboxylated MWCNT and cetyltrimethyl ammonium bromide (CTAB)-stabilized MWCNT. Aqueous PTFE dispersion was mixed with the well-dispersed MWCNT dispersions and they were heterocoagulated with the aid of a flocculant, polyaluminum chloride at an elevated temperature. After particle growth and successive stabilization step, particulated PTFE/MWCNT composites were prepared in the size range of 10–100 μm. The MWCNT-containing PTFE composites have improved thermal stability and electrical conductivity. Importantly, the percolation threshold for the electrical conductivity was achieved at a low concentration of MWCNT using this heterocoagulation process.     

Complementary effects of multiwalled carbon nanotubes and conductive carbon black on polyamide 6

This article introduces a newly innovative idea for preparation of superconductive ternary polymeric composites of polyamide 6 (PA6), conductive carbon black (CCB), and multiwalled carbon nanotubes (MWCNTs) with different weight ratios by a melt‐mixing technique. The complementary effects of CCB and MWCNTs at different compositions on rheological, physical, morphological, thermal, and dynamic mechanical and electrical properties of the ternary composites have been examined systematically. We have used a novel formulation to produce high‐weight fraction ternary polymer composites that show extremely higher conductivity when compared with their corresponding binary polymer composites at the same carbon loading. For example, with an addition of 10 wt % MWCNTs into the CCB/PA6 composite preloaded with 10 wt % CCB, the electrical conductivity of these ternary composites was about 5 S/m, which was 10 times that of the CCB/PA6 binary composite (0.5 S/m) and 125 times that of the MWCNT/PA6 binary composite (0.04 S/m) at 20 wt % carbon loading. The incorporation of the MWCNTs effectively enhanced the thermal stability and crystallization of the PA6 matrix in the CCB/PA6 composites through heterogeneous nucleation. The MWCNTs appeared to significantly affect the mechanical and rheological properties of the PA6 in the CCB/PA6 composites, a way notably dependent on the MWCNT contents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1203–1212, 2010     

Design and synthesis of the polyaniline interface for polyamide 66/multi-walled carbon nanotube electrically conductive composites

A polyaniline interface had been designed and built between multi-walled carbon nanotubes (MWCNTs) and polyamide 66 (PA66) in order to help in the dispersion of MWCNTs in PA66 and improve the interfacial combination between them. Transmission electron microscopy characterizations indicated that functionalized MWCNTs (f-MWCNTs) could be well-distributed in PA66 matrix and the interfacial boundary between them was indiscernible. The mixing conditions, such as f-MWCNT content, temperature, and mixing speed, played important roles in determining the formation of the conductive network and the electrical conductivities of PA66/f-MWCNT composites synthesized. A continuous conductive network was formed at 10 wt% f-MWCNT content, and the corresponding PA66/f-MWCNT composite exhibited an electrical conductivity of 8 orders of magnitude higher than pure PA66. The conducting mechanism agreed well with a thermal fluctuation-induced tunneling model.     

The effect of crystallization behavior on high conductivity,enhanced mechanism and thermal stability of poly(ε-caprolactone)/multi-walled carbon nanotube composites

Poly(ε-caprolactone) (PCL) composites filled by multi-walled carbon nanotubes (MWCNTs) which was non-covalently modified by the combined surfactants of poly(sodium 4-styrenesulfonate) and cetyltrimethyl-ammonium bromide (PSS-CTAB) were fabricated via simple solution precipitation method. PCL/MWCNTs composites provided with the low procolation threshold (0.4?wt%) and high electrical conductivity due to good dispersion of MWCNTs. And the excellent mechanical properties and enhanced thermal stability were also obtained with the addition of modified MWCNTs. In addition, all PCL composites showed significantly enhanced crystallization with increasing the MWCNTs contents, which demonstrated that the MWCNT-induced crystallization of PCL could effectively regulate the properties of composites. In a word, introducing non-covalent functionalized MWCNTs in the polymer system was a promising way for developing excellent conductive composites.     

Thermal and electrical properties of poly(l-lactide)-graft-multiwalled carbon nanotube composites

The dispersion of the nanometer-sized carbon nanotubes in a polymer matrix leads to a marked improvement in the properties of the polymer. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(l-lactide) (PLLA), which has received a great deal of attention due to environmental concerns. In this study, PLLA was melt compounded with multiwalled carbon nanotubes (MWCNTs). A high degree of dispersion of the MWCNTs in the composites was obtained by grafting PLLA onto the MWCNTs (PLLA-g-MWCNTs). After oxidizing the MWCNTs by treating them with strong acids, they were reacted with l-lactide to produce the PLLA-g-MWCNTs. The morphology of the composite was observed with scanning electron microscopy. The mechanical properties of the PLLA/PLLA-g-MWCNT composite were higher than those of the PLLA/MWCNT composite. The thermal stability of the composites was studied using thermogravimetric analysis and their activation energy during thermal degradation was determined using the Kissinger and Flynn-Wall-Ozawa methods. The activation energy of PLLA/PLLA-g-MWCNT was higher than that of PLLA/MWCNT, which indicates that the composite made with the PLLA-g-MWCNTs was more thermally stable than the composite made with the MWCNTs.     

多壁碳纳米管对聚甲醛性能的影响

将多壁碳纳米管(MWCNTs)和聚甲醛(POM)在转矩流变仪中熔融混合得到POM/MWCNT复合材料.研究了复合材料的形态,导热性能,导电性能,流变性能和结晶性能.结果表明,MWCNTs在没有经过处理的情况下能够均匀地分散在POM基体中;当向POM中添加1.0 wt%含量MWCNTs时,复合材料的导热系数上升到0.5289 W/(K m),比纯POM的导热系数0.198 W/(K m)提高1.5倍,通过有效介质方法(EMA)验证了体系导热系数提高幅度不大的原因是MWCNTs与POM之间形成了很高的界面热阻;当MWCNTs的含量为1.0 wt%时,体系产生了导电逾渗效应,逾渗值在0.5 wt%~1.0 wt%之间;MWCNTs对POM有显著的成核作用,当向POM中添加0.5 wt%含量的MWCNTs时,POM的结晶温度提高6℃左右,但当MWCNTs的添加量进一步增加时,结晶温度几乎不再变化,成核效果呈现"饱和"状态.另外,材料的复数黏度,储能模量和损耗模量随MWCNTs含量的增加而增加.     

Electro-responsive transdermal drug delivery behavior of PVA/PAA/MWCNT nanofibers

The electro-responsive transdermal drug delivery system was prepared by electrospinning of poly(vinyl alcohol)/poly(acrylic acid)/multi-walled carbon nanotubes (MWCNTs) nanocomposites. The surface modification of MWCNTs was carried out by oxyfluorination to introduce the functional groups on the hydrophobic MWCNTs. The dispersion of MWCNTs and the compatibility with polymer matrices were improved by oxyfluorination. The MWCNT content and oxyfluorination condition played important roles in the swelling and drug release characteristics of nanofibers. The conductivity of nanofibers increased by increasing the content of MWCNTs and performing oxyfluorination with higher oxygen content. Uniform distribution of the oxyfluorinated MWCNTs in the nanofibers was crucial to the electro-responsive swelling and drug releasing behaviors of nanofibers.     

Preparation and Characterization of Poly(methyl methacrylate)-functionalized Carboxyl Multi-wall Carbon Nanotubes

"An in situ polymerization process was used to prepare poly (methyl methacrylate) (PMMA)-functionalized carboxyl multi-walled carbon nanotubes using carboxylate carbon nanotubes and methyl methacrylate as reactants and benzoyl peroxide as an initiator agent. The functionalized multi-walled carbon nanotubes were characterized using transmission electron microscope, scanning electron microscope, nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis and Raman. The results indicate that the PMMA chains are covalently linked with the surface of carboxylate carbon nanotubes. The surface morphology is controlled by the content of carboxylate carbon nanotubes in the reactants. The PMMA functionalized multi-walled carbon nanotubes are soluble in deuterated chloroform. The storage modulus and tanffi magnitude increase as the content of CCNTs increases up to 0.3%."