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.     

Poly(L-lactide) (PLLA)/multiwalled carbon nanotube (MWCNT) composite: characterization and biocompatibility evaluation

Much effort has been directed at the fabrication of carbon nanotubes (CNTs)/polymer composites and the characterization of their physical properties. Among them, composites comprising CNTs and the biocompatible polymers are of special interest due to their potential for specific biomedical applications. we report the preparation of the MWCNT/poly(L-lactide) composite and the corresponding spectroscopic (Raman) and the microscopic (SEM, TEM) characterization. The electronic transport, thermal properties, and biocompatibility of this composite have also been investigated. The Raman spectroscopic analysis suggests the interaction between PLLA and MWCNT occurs mainly through the hydrophobic C-CH3 functional groups. The DC conductivity of the composite increases as the MWCNT loading is increased. Such behavior can be described by a percolation mechanism in which a percolation threshold at about 14 wt % MWCNT loading is observed with the maximum end conductivity of 0.1 S x cm(-1). The DSC study of the PLLA/MWCNT composite reveals that the MWCNTs in the composite have the effect of inducing crystallization and plasticizing the polymer matrix. The results from the cell culture test suggest that the presence of MWCNT in the composite inhibits the growth of the fibroblast cells.     

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     

Strengthening of liquid crystalline polymer by functionalized carbon nanotubes through interfacial interaction and homogeneous dispersion

Multiwalled carbon nanotubes (MWCNTs) were functionalized with two types of chemical moieties (i.e. carboxylic, ? COOH and hydroxyl benzoic acid groups, ‐HBA) on their sidewalls in order to improve their interaction with a liquid crystalline polymer (LCP) and dispersion in LCP. We have investigated the rheological, mechanical, dynamic mechanical, and thermal properties in detail with variation of HBA‐functionalized MWCNTs in the LCP matrix. Effect of the dispersion state of the functionalized MWCNTs in the LCP matrix on the rheological behavior was also studied. The composites containing HBA‐functionalized MWCNTs showed higher complex viscosity, storage, and loss modulus than the composites with the same loading of raw MWCNTs and MWCNT‐COOH. It was suggested that the HBA‐functionalized MWCNTs exhibited a better dispersion in the polymer matrix and formed stronger CNT‐polymer interaction in the composites than the raw MWCNTs and MWCNT‐COOH, which was also confirmed by FESEM and FTIR studies. As a result, the overall mechanical performance of the HBA‐MWCNT‐LCP composites could be improved significantly. For example, the addition of 4 wt% HBA‐MWCNT to LCP resulted in the considerable improvements in the tensile strength and modulus of LCP (by 66 and 90%, respectively). Copyright © 2010 John Wiley & Sons, Ltd.     

Surface modification of MWCNTs with glucose and their utilization for the production of environmentally friendly nanocomposites using biodegradable poly(amide‐imide) based on N‐trimellitylimido‐S‐valine matrix

In the present investigation, the preparation, characterization, and surface morphology of poly(amide‐imide) (PAI)/multi‐walled carbon nanotubes (MWCNTs) bionanocomposites (BNCs) were the main goals of the study. At first, an optically active PAI based on S‐valine as a biodegradable segment was synthesized. Then, carboxyl‐modified MWCNTs were functionalized with glucose (f‐MWCNT) as a biological active molecule in a green method to achieve a fine dispersion of f‐MWCNT bundles in the PAI matrix. The existence of S‐valine in the PAI matrix and functionalized MWCNT with glucose resulted in a series of potentially biodegradable nanocomposites. The obtained BNCs were characterized by various techniques. Field emission scanning and transmission electron microscopy micrographs of the composites showed a fine dispersion of f‐MWCNTs in the polymer matrix because of hydrogen bonding and π–π stacking interaction between f‐MWCNTs and polymer functional groups and aromatic moieties. Adding f‐MWCNTs into polymer matrix significantly improved the thermal stability of BNCs because of the increased interfacial interaction between the PAI matrix and f‐MWCNTs and also good dispersion of f‐MWCNT in the polymer matrix. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesize procedures, mechanical and thermal properties of thiazole bearing poly(amid-imide) composite thin films containing multiwalled carbon nanotubes

This research is aimed at characterizing the thermal, mechanical, and morphological properties of carbon nanotubes (CNTs) reinforced poly(amide-imide) (PAI) composites having thiazol and amino acid groups which were prepared by sonication-assisted solution compounding. To increase the compatibility between the PAI matrix and CNTs, carboxyl-functionalized multiwall CNTs (MWCNTs-COOH) were used in this study. The MWCNTs were dispersed homogeneously in the PAI matrix while the structure of the polymer and the MWCNTs structure are stable in the preparation process as revealed by transmission electron microscopy. MWCNT/PAI composite films have been prepared by casting a solution of precursor polymer containing MWCNTs into a thin film, and its tensile properties were examined. The thermal stability, Young’s modulus, and tensile strength of PAI were greatly improved by the incorporation of MWCNTs and their good dispersion. Composites were also characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis.     

Influence of MWCNT morphology on dispersion and thermal properties of polyethylene nanocomposites

In this study a series of multi-walled carbon nanotube (MWCNT)/Polyethylene (PE) composites with different kinds and several concentrations of carbon nanotubes (CNTs) were investigated. The morphology and degree of dispersion of the fillers in the polymer matrix at different length scales was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Both individual and agglomerated MWCNTs were evident but a good dispersion was observed for some of them. TGA measurements were performed on nanocomposites in order to understand if CNTs affect the stabilization mechanism during thermal and oxidative degradation. The analysis demonstrates that MWCNTs presence slightly delays thermal volatilisation (15-20 °C) without modification of thermal degradation mechanism. In contrast, thermal oxidative degradation in air is delayed up to about 100 °C dependently from MWCNTs concentration, in the range used here (0.1-2.0 wt%), and degree of dispersion. The stabilization is due to the formation of a thin protective layer of entangled MWCNTs kept together by carbon char generated on the surface of the nanocomposites as shown by SEM images taken on degradation residues.     

In situ polymerization of methyl methacrylate/multi-walled carbon nanotube composites using cationic stearyl methacrylate copolymers as dispersants

Novel water-soluble amphiphilic copolymers (poly[(stearyl methacrylate)-stat-([2-(methacryloyloxy)ethyl] trimethyl ammonium iodide)]) for dispersing multi-walled carbon nanotubes (MWCNTs) were used to carry out in situ methyl methacrylate (MMA) polymerization. The morphology of the poly(methyl methacrylate)/MWCNT composites and the dispersion of the MWCNTs were analyzed by transmission electron microscopy. The dispersion of multi-walled carbon nanotubes in the composites was excellent for cationic SMA (stearyl methacrylate) copolymers, even at high MWCNT loading (6.0 wt.%). The mechanical properties and electrical and thermal conductivities of the composites were also analyzed. Mechanical properties were improved by MWCNTs; the strain at break values remained stable up to 6.0 wt.% MWCNT loading. Both electrical and thermal conductivities were improved by the addition of MWCNTs.     

Preparation of HMWCNT/PLLA nanocomposite scaffolds for application in nerve tissue engineering and evaluation of their physical,mechanical and cellular activity properties

This study was aimed to prepare biodegradable and porous nanocomposite scaffolds with microtubular orientation structure as a model for nerve tissue engineering by thermally induced phase separation (TIPS) method using dioxane as the solvent, crystalline poly (L‐lactic acid) (PLLA) and multi‐walled carbon nanotubes (MWCNTs). In order to overcome dispersion of MWCNTs in the PLLA matrix, heparinization of MWCNTs was performed. Solvent crystallization, oriented structure, the mean pore diameter and porosity percentage of the scaffolds were controlled by fundamental system parameters including temperature‐gradient of the system, polymer solution concentration and carbon nanotube content. Scanning Electron Microscopy (SEM), ImageJ, software and dynamic mechanical thermal analysis (DMTA) were used to investigate the structural and mechanical properties. TEM observation was carried out for characterization of nanotube dispersion in PLLA. It was found that the scaffolds containing heparinized multi‐walled carbon nanotubes (HMWCNTs) exhibited higher storage modulus, better carbon nanotube (CNT) dispersion and tubular orientation structure than those with non heparinized MWCNTs. In‐vitro studies were also conducted by using murine P₁₉ cell line as a suitable model system to analyze neuronal differentiation over a 2‐week period. Immunofluorescence and DAPI staining were used to confirm the cells' attachment and differentiation on the PLLA/HMWCNT nanocomposite scaffolds. Based on the results, we can conclude that the PLLA/HMWCNT scaffolds enhanced the nerve cell differentiation and proliferation, and therefore, acted as a positive cue to support neurite outgrowth. Copyright © 2015 John Wiley & Sons, Ltd.     

碳纳米管改性聚苯硫醚熔纺纤维的结构与性能研究

将多壁碳纳米管(MWCNTs)和聚苯硫醚(PPS)经过熔融挤出后制备成复合材料切片,并采用熔融纺丝法制得碳纳米管改性聚苯硫醚复合纤维.采用扫描电镜(SEM)、拉曼光谱、示差扫描量热分析(DSC)、动态机械分析(DMA)以及力学性能测试等表征手段研究了复合纤维中碳管的分散状态,与基体的界面作用,复合纤维的结晶性能以及力学性能,从而探讨了聚苯硫醚/碳纳米管复合纤维体系的微观结构与宏观性能之间的关系.研究表明,聚苯硫醚分子结构与碳纳米管之间具有的π-π共轭作用使碳管较为均匀的分散在基体中,界面结合较为紧密.同时熔融纺丝过程中的拉伸作用使碳管进一步解缠并使碳管沿纤维拉伸方向取向.另一方面,拉曼光谱显示拉伸作用有效地增强了界面作用,有利于外界应力的传递.碳管的良好分散以及强的界面作用使复合纤维力学性能得到大幅度的提高,当碳管含量达到5 wt%时,复合纤维的模量有了明显的提高,拉伸强度较纯PPS纤维提高了近220%.     

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.     

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.     

Contribution of oriented structure and rigid nanofillers to mechanical enhancement of die-drawn PP/MWCNT composites

Oriented structure, mainly controlled by processing conditions, is another efficient method of reinforcing polymer materials in addition to compounding with rigid inorganic fillers such as carbon nanotubes (CNTs). The mechanical properties of oriented polypropylene (PP)/multiwalled CNT (MWCNT) composites, which are vital to their application fields, are investigated extensively in this paper, with an aim to distinguish the contribution of MWCNTs contents from that of the oriented structure to the final performance of the composite. The results indicate that MWCNTs mainly increase the modulus of the composites by approximately 140%. The oriented structure formed during the die-drawing process contributes more to the enhancement of tensile strength, increasing up to 550%. The modulus and tensile strength can be further improved by increasing the drawing speed. Moreover, the tensile stress field in the die-drawing process can vastly improve the dispersion of the MWCNTs in the matrix, thus providing a new idea for improving the dispersion of nanofillers in the polymer matrix.     

Dissolution of MWCNTs by using polyoxadiazoles,and highly effective reinforcement of their composite films

Nonmodified multiwalled carbon nanotubes (MWCNTs)/sulfonated polyoxadiazole (sPOD) nanocomposites are successfully prepared by a facile solution route. The pristine MWCNTs are dispersed in a sPOD solution, and the mixtures are fabricated into thin films by solution casting. The homogeneous dispersion of nanotubes in the composites is confirmed by transmission electron microscopy. The mechanical properties, thermal stability, and electrical conductivity are investigated. Tensile strength, elongation at break, and tensile energy to break are shown to increase by more than 28, 45, and 73%, respectively, by incorporating up to 1.0 wt % pristine MWCNTs. The experimental values for sPOD/MWCNTs composite stiffness are compared with Halpin‐Tsai and modified Halpin‐Tsai predictions. The storage modulus is found to increase up to 10% at low CNT loading. The composite films, which have an outstanding thermal stability, show an increase of up to 57 °C in the initial degradation temperature. The addition of 1.0 wt % MWCNTs increases the electrical conductivity of the sPOD matrix by two orders of magnitude. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Effects of electrically inert fillers on the properties of poly(<Emphasis Type="Italic">m</Emphasis>-xylene adipamide)/multiwalled carbon nanotube composites

The effects of three types of electrically-inert fillers, calcium carbonate (CaCO₃), talc and glass fiber (GF), on electrical resistivity, crystallization behavior and dynamic mechanical properties of poly(m-xylene adipamide) (MXD6)/multiwalled carbon nanotube (MWCNT) composites are investigated. The electrical resistivity of MXD6/MWCNT composites is significantly reduced with the addition of inert fillers due to the volume-exclusion effect that leads to increased effective concentration of MWCNTs in MXD6 matrix and also due to improved MWCNT dispersion. The crystallization temperature of MXD6 increases with the addition of MWCNTs, indicating that MWCNTs can act as nucleating agent and induce crystallization of MXD6. The incorporation of inert fillers has no further effect on crystallization behavior of MXD6, but significantly improves the storage modulus of MXD6/MWCNT composite, demonstrating that CaCO₃, talc and GF filled MXD6/MWCNT composites are very promising materials with not only improved electrical property but also excellent mechanical properties.     

The effect of mixing methods on the dispersion of carbon nanotubes during the solvent-free processing of multiwalled carbon nanotube/epoxy composites

Several solvent-free processing methods to disperse multiwalled carbon nanotubes (MWCNTs) in bisphenol F-based epoxy resin were investigated, including the use of a microfluidizer (MF), planetary shear mixer (PSM), ultrasonication (US) and combinations. The processed mixture was cured with diethyl toluene diamine. Three complimentary techniques were used to characterize the dispersion of the MWCNTs in cured composite samples: optical microscopy, micro Raman spectroscopy, and scanning electron microscopy (SEM). For sample MF + PSM, optical micrographs and Raman images showed reduced agglomeration and a homogeneous distribution of MWCNTs in the epoxy matrix. SEM analysis of fractured specimen after tensile testing revealed breakage of nanotubes along the fracture surface of the composite. A comparison of the MWCNT dispersion in the epoxy samples processed using different methods showed that a combination of MF and PSM processing yields a more homogeneous sample than the PSM or US + PSM processed samples. Mechanical testing of the composites showed about 15% improvement in the tensile strength of samples processed by the MF + PSM method over other methods. Thermogravimetric analysis (TGA) results showed a small decrease in the onset degradation temperature for poorly dispersed samples produced by PSM compared with the well-mixed samples (MF + PSM). These results strongly suggest that the MF + PSM processing method yield better-dispersed and stronger MWCNT/epoxy composites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Surfactant dispersed multi-walled carbon nanotube/polyetherimide nanocomposite membrane

Carbon nanotube based nanocomposite membranes have been fabricated through solution casting by embedding multi-walled carbon nanotubes (MWCNTs) within polyetherimide (PEI) polymer host matrix. In order to achieve fine dispersion of nanotubes and facilitate strong interfacial adhesion with the polymer matrix, the nanotubes were first treated with surfactants of different charges, namely anionic sodium dodecyl chloride, cationic cetyl trimethyl ammonium chloride and non-ionic Triton X100, prior to the dispersion in the PEI dope solution. Dispersion of MWCNTs in N-methyl-2-pyrrolidone solvent showed that the agglomeration and entanglement of the nanotubes were greatly reduced upon the addition of Triton X100. Scanning electron microscopy and atomic force microscopy examination has evidenced the compatibility of Triton X100 dispersed MWCNTs with the polymer matrix in which a promising dispersion and adhesion has been observed at the MWCNT-PEI interface. The increase in both thermal stability and mechanical strength of the resulting Triton X100 dispersed MWCNT/PEI nanocomposite indicated the improved interaction between MWCNTs and PEI. This study demonstrated the role of Triton X100 in facilitating the synergetic effects of MWCNTs and PEI where the resulting composite membrane is anticipated to have potential application in membrane based gas separation.     

Ultrasonic assisted polyol synthesis of highly dispersed Pt/MWCNT electrocatalyst for methanol oxidation

A novel chemical method based on ultrasonic assisted polyol synthesis for the fabrication of highly dispersed Pt nanoparticles on multi-walled carbon nanotubes (MWCNTs) was developed. The simple and green method took only about 10 min at ambient temperature. The structure and chemical nature of the resulting Pt/MWCNT composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectrometry (EDS). The results showed that the prepared Pt nanoparticles were uniformly dispersed on the MWCNT surface. The mean size of Pt nanoparticles was about 2.8 nm. Electrochemical properties of Pt/MWCNT electrode for methanol oxidation were examined by cyclic voltammetry (CV) and excellent electrocatalytic activities could be observed. The possible formation mechanism of Pt/MWCNTs was also discussed.     

Nanotubes as polymer composite reinforcing additive materials – A comparative study

Nitrogen-doped bamboo-shaped carbon nanotubes (N-BCNTs) and their non-doped conventional counterparts, multiwalled carbon nanotubes (MWCNTs) were compared as polymer reinforcing additives in polyvinyl chloride (PVC) matrix. The nanotubes were synthetized by catalytic chemical vapor deposition (CCVD) method. The purity of both nanotubes was measured by thermogravimetric analysis (TGA) and found to be >91%. Further analysis on the morphology and size of the carbon nanotubes (CNTs) were performed by transmission electron microscopy (TEM). The PVC powder was impregnated with CNTs in ethanol by using tip ultrasonicator. The dispersion media was evaporated, and the CNT/PVC powder was used to produce polymer fibers. The orientation of carbon nanotubes in the PVC matrix was characterized by scanning electron microscopy (SEM), and the presence of nanotubes were confirmed in case of all PVC samples. It can be observed on the SEM images that the nanotubes are fully covered with PVC. The tensile strength of the nanotube containing samples was tested and the N-BCNT/PVC composite was found to be better in this sense, thanks to the extraordinary structure of the nanotube. In case of the N-BCNT/PVC composite the measured young modulus was 39.7% higher, while the elongation at brake decreased by 33.6% compare to the MWCNT/PVC composite. These significant differences in the mechanical properties of the composites can be explained with the stronger interaction between N-BCNTs and PVC.