Development of conducting polychloroprene rubber using imidazolium based ionic liquid modified multi-walled carbon nanotubes

A simplified and an eco-friendly approach to develop polychloroprene rubber composites with high electrical conductivity is reported. The usage of room temperature ionic liquid, 1-butyl 3-methyl imidazolium bis(trifluoromethylsulphonyl)imide and a low concentration (5 phr) of commercial grade multi-walled carbon nanotubes (MWCNTs) in polychloroprene rubber exhibited an electrical conductivity of 0.1 S/cm with a stretchability >500%. The physical (cation-pi/pi-pi) interaction between the ionic liquid and the MWCNTs is evidenced by Raman spectroscopy. Transmission electron microscopy images exhibit an improved dispersion of the BMI modified tubes in matrix at various magnification scales. The dependency of dynamic properties on the concentration of ionic liquid at constant loading of nanotubes supports the fact that ionic liquid assists in the formation of filler-filler networks. The tensile modulus of 3 phr loaded modified MWCNT/CR composite is increased by 50% with regard to that of the unmodified MWCNT/CR composite. Mooney-Rivlin plot displays the existence of rubber-filler interactions.     

Electromagnetic interference shielding behavior of poly(trimethylene terephthalate)/multi-walled carbon nanotube composites

Poly(trimethylene terephthalate) [PTT]/multiwalled carbon nanotube [MWCNT] composites having varying amounts of MWCNTs were fabricated with an aim to investigate the potential of such composites as an effective light weight electromagnetic interference (EMI) shielding material in the frequency range of 12.4-18 GHz (Ku-band). PTT/MWCNT composite with shielding effectiveness (SE) of 36-42 dB was obtained at 10% (w/w) MWCNT loading. Shielding mechanism was studied by resolving the total SE into absorption (SE_A) and reflection loss (SE_R). PTT/MWCNT composite showed absorption dominated shielding; thus it can be used as microwave, radar absorbing and stealth material. The effect of MWCNT loadings on electrical conductivity (σ) and dielectric properties of PTT and the correlation among conductivity, tan δ, absorption loss and reflection loss were also studied.     

Effects of grafted chain length on mechanical and electrical properties of nanocomposites containing polylactide-grafted carbon nanotubes

We herein report the effects of interfacial reinforcement on mechanical and electrical properties of nanocomposites based on polylactide (PLA) and multi-walled carbon nanotube (MWCNT). For this purpose, a series of MWCNTs grafted with PLA chains of various lengths (MWCNT-g-PLAs) were prepared by ring-opening polymerization of l-lactide with carboxylic acid-functionalized MWCNT (MWCNT-COOH). MWCNT-g-PLAs were then mixed with commercial PLA to obtain PLA/MWCNT-g-PLA nanocomposites with 1.0 wt.% MWCNT content. It was revealed that morphological, mechanical, and electrical properties of PLA/MWCNT-g-PLA nanocomposites were strongly dependent on the PLA chain length of MWCNT-g-PLAs. FE-SEM images exhibited that the nanocomposites containing MWCNT-g-PLA with longer PLA chain length exhibited better dispersion of MWCNTs in the PLA matrix. Initial moduli and tensile strengths of PLA/MWCNT-g-PLA composites increased with the increment of chain length of PLA grafted on MWCNTs, which attributes to the improved interfacial adhesion between the grafted PLA chains of MWCNT-g-PLA and the PLA matrix. As a result, the experimental initial modulus (2775 ± 193 MPa) of the nanocomposite including MWCNT-g-PLA with PLA chains of average molecular weight of 530 g/mol was quite close to the theoretical value (2911 MPa) predicted for the nanocomposite with perfect interfacial adhesion. Unexpectedly, electrical resistivities of PLA/MWCNT-g-PLA nanocomposites were found to increase from ∼10⁴ to ∼10¹² Ω/sq with increasing the PLA chain length of MWCNT-g-PLA, which is due to the fact that the PLA chains grafted on MWCNTs prevent the formation of the electrical conduction path of MWCNTs in the PLA matrix.     

Effect of aspect ratio on thermal conductivity of high density polyethylene/multi-walled carbon nanotubes nanocomposites

This study aims to investigate experimentally the effects of aspect ratio (length/diameter ratio) and concentration of multiwalled carbon nanotubes (MWCNTs) on thermal properties of high density polyethylene (HDPE) based composites. The aspect ratios of two types of MWCNT fillers are in the range of 200–400 and 500–3000. Composite samples were prepared by melt mixing up to weight fraction of 19% filler content, followed by a compression molding. Measurements of density, specific heat and thermal diffusivity (by modulated photothermal radiometry, PTR) were performed and effective thermal conductivities k_e of nanocomposites were calculated using these values. The results show that the composites containing MWCNTs with higher aspect ratio have higher thermal conductivities than the ones with lower aspect ratio. In terms of conductivity enhancement k_e/k_m − 1, the results indicate that MWCNTs with higher aspect ratio provide three to fourfold larger enhancement than the ones with lower aspect ratio, at low filler concentrations.     

Fabrication of alizarin red S/multi-walled carbon nanotube nanocomposites and their application in hydrogen peroxide detection

In this work, an easy and effective method to synthesize alizarin red S/multi-walled carbon nanotube (ARS/MWCNT) nanocomposites based on the π–π stacking non-covalent interactions between ARS and MWCNTs was introduced. The characters of ARS/MWCNT nanocomposites were investigated by Fourier transformation infrared spectroscopy, UV–Vis spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscope, and electrochemical techniques. ARS tightly coating on MWCNTs surface makes the nanocomposites good dispersibility in water and excellent electrochemical activity. Because of the combination of the excellent electroactivity of ARS and the unique properties of MWCNTs, ARS/MWCNT nanocomposites-modified glassy carbon electrode exhibits a good response to the reduction of hydrogen peroxide and takes on a promising prospect of the practical application in electrochemical sensors field.     

Percolation behaviour of polypropylene glycol filled with multiwalled carbon nanotubes and Laponite

The percolation behaviour of the hybrid composites of polypropylene glycol (PPG) filled with multiwalled carbon nanotubes (MWCNTs) and Laponite RD (Lap), or with MWCNTs and organo-modified Laponite (LapO) was studied by wide angle X-ray diffraction (XRD), microscopic image analysis, and electrical conductivity measurements. Cetyltrimethylammoniumbromide (CTAB) was used as an organo-modifier of Laponite. The Lap and LapO were found to have rather different affinity to PPG. XRD data have evidenced finite PPG integration inside Lap and complete exfoliation of LapO stacks in a PPG matrix. In PPG + MWCNT composites containing no Lap or LapO, increase of MWCNT concentration above the critical value C_p ∼ 0.4 wt% resulted in percolation. The value of the percolation threshold, C_p, was practically the same for hybrid PPG + MWCNT + Lap composites. However, it noticeably decreased (C_p ∼ 0.2 wt%) in PPG + MWCNT + LapO materials. The observed behaviour of the percolation threshold may be attributed to the effects exerted by LapO on the size of MWCNT aggregates, state of their dispersion and homogeneity of their spatial distribution.     

Enhanced electrochemical detection performance of multiwall carbon nanotubes functionalized by aspartame

Inexpensive, non-toxic, and biocompatible materials that can disperse multiwall carbon nanotubes (MWCNTs) in aqueous solutions through a non-covalent approach while retaining their unique electronic and photonic properties are highly preferred. In this article, we introduce the use of an amphiphilic dipeptide derivative, aspartame, as an effective dispersing agent in preparing highly stable suspensions under ultrasonication. The results demonstrate that aspartame was absorbed by the nanotube surface possibly because of non-covalent π–π stacking between the aromatic group of aspartame and the CNT backbone. In addition, the resulting MWCNT/aspartame composites remained stably dispersed over a wide range of pH values. The chronoamperometric measurements of MWCNT/aspartame composite-coated electrodes for hydrogen peroxide demonstrated better electrochemical detection performance, as characterized by significantly enhanced step current, higher sensitivity, and reduced potential compared with bare electrodes.     

Role of matrix modification on interlaminar shear strength of glass fibre/epoxy composites

Interlaminar shear properties of fibre reinforced polymer composites are important in many structural applications. Matrix modification is an effective way to improve the composite interlaminar shear properties. In this paper, diglycidyl ether of bisphenol-F/diethyl toluene diamine system is used as the starting epoxy matrix. Multi-walled carbon nanotubes (MWCNTs) and reactive aliphatic diluent named n-butyl glycidyl ether (BGE) are employed to modify the epoxy matrix. Unmodified and modified epoxy resins are used for fabricating glass fibre reinforced composites by a hot-press process. The interlaminar shear strength (ILSS) of the glass fibre reinforced composites is investigated and the results indicate that introduction of MWCNT and BGE obviously enhances the ILSS. In particular, the simultaneous addition of 0.5 wt.% MWCNTs and 10 phr BGE leads to the 25.4% increase in the ILSS for the glass fibre reinforced composite. The fracture surfaces of the fibre reinforced composites are examined by scanning electron microscopy and the micrographs are employed to explain the ILSS results.     

Influence of different carbon nanotubes on the electrical and mechanical properties of melt mixed poly(ether sulfone)-multi walled carbon nanotube composites

Commercial Udel® poly(ether sulfone) (PSU) was filled with three different commercially available multiwalled carbon nanotubes (MWCNTs) by small scale melt mixing. The MWCNTs were as grown NC 7000 and two of its derivatives prepared by ball milling treatment. One of them was unmodified (NC 3150); the other was amino modified (NC 3152). The main difference beside the reactivity was the reduced aspect ratio of NC 3150 and NC 3152 caused by ball milling process. All PSU/MWCNT composites with similar filler content were prepared under fixed processing conditions and comparative analysis of their electrical and mechanical properties were performed and were correlated with their microstructure, characterized by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A non-uniform MWCNT dispersion was observed in all composites. The MWCNTs were present in form of agglomerates in the size of 10–60 μm whereas the deagglomerated part was homogeneously distributed in the PSU matrix. The differences in the agglomeration states correlate with the variations of properties between different PSU/MWCNT composites. The lowest electrical percolation threshold of 0.25–0.5 wt.% was observed for the shortened non-functionalized MWCNT composites and the highest for amine-modified MWCNT composites (ca. 1.5 wt.%). The tensile behavior of the three composites was only slightly altered with CNT loading as compared to the pure PSU. However, the elongation at break showed a reduction with MWCNT loading and the reduction was least for composite with best MWCNT dispersion.     

Preparation,characterization and properties of polycaprolactone diol-functionalized multi-walled carbon nanotube/thermoplastic polyurethane composite

Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized to prepare thermoplastic polyurethane (PU) composites with enhanced properties. In order to achieve a high compatibility of functionalized MWCNTs with the PU matrix, polycaprolactone diol (PCL), as one of PU’s monomers, was selectively grafted on the surface of MWCNTs (MWCNT–PCL), while carboxylic acid groups functionalized MWCNTs (MWCNT–COOH) and raw MWCNTs served as control. Both MWCNT–COOH and MWCNT–PCL improved the dispersion of MWCNTs in the PU matrix and interfacial bonding between them at 1 wt% loading fraction. The MWCNT–PCL/PU composite showed the greatest extent of improvement, where the tensile strength and modulus were 51.2% and 33.5% higher than those of pure PU respectively, without sacrificing the elongation at break. The considerable improvement in both mechanical properties and thermal stability of MWCNT–PCL/PU composite should result from the homogeneous dispersion of MWCNT–PCL in the PU matrix and strong interfacial bonding between them.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

Effects of stretching on mechanical properties of aligned multi-walled carbon nanotube/epoxy composites

Composites based on epoxy resin and differently aligned multi-walled carbon nanotube (MWCNT) sheets have been developed using hot-melt prepreg processing. Aligned MWCNT sheets were produced from MWCNT arrays using the drawing and winding technique. Wavy MWCNTs in the sheets have limited reinforcement efficiency in the composites. Therefore, mechanical stretching of the MWCNT sheets and their prepregs was conducted for this study. Mechanical stretching of the MWCNT sheets and hot stretching of the MWCNT/epoxy prepregs markedly improved the mechanical properties of the composites. The improved mechanical properties of stretched composites derived from the increased MWCNT volume fraction and the reduced MWCNT waviness caused by stretching. With a 3% stretch ratio, the MWCNT/epoxy composites achieved their best mechanical properties in this study. Although hot stretching of the prepregs increased the tensile strength and modulus of the composites considerably, its efficiency was lower than that of stretching the MWCNT sheets.     

Synthesis and characterization of well-dispersed multi-walled carbon nanotube/low-bandgap poly(3,4-alkoxythiophene) nanocomposites

In this study, we prepared nanocomposites of multi-walled carbon nanotubes (MWCNTs) and low-energy-bandgap conjugated polymers incorporating 3,4-alkoxythiophene monomers. Poly(3,4-dihexyloxythiophene) (PDHOT) and poly(3,4-dimethoxythiophene-co-3,4-dihexyloxythiophene) [P(DMOT-co-DHOT)] have relatively low-energy-bandgaps (ca. 1.38 and 1.34 eV, respectively), determined from the onsets of absorbances in their UV–Vis spectra, because of the electron-donating effects of their alkoxy groups. MWCNTs have poor solubility in common organic solvents; after surface modification with alkyl side chains using the Tour reaction, however, the p-hexylaniline modified MWCNT derivative (MWCNT-HA) was readily dispersed in CHCl₃ and could be mixed with the low bandgap polymers. Scanning electron microscopy images revealed that MWCNT-HA was dispersed well in each polythiophene derivative; only a few MWCNT-HA bundles could be observed at a high MWCNT-HA content (≧20 wt.%). The electrical conductivities of the MWCNTs/PDHOT composites were dependent on their MWCNT content, reaching 16 S/cm at 30 wt.% MWCNT-HA. We suspect that the two hexyloxy chains of PDHOT enhanced its solubility and allowed it to wrap around the surfaces of the MWCNTs more readily.     

Optimization of the mechanical properties of calcium phosphate/multi-walled carbon nanotubes/bovine serum albumin composites using response surface methodology

Response surface methodology (RSM) coupled with the central composite design (CCD) was used to optimize the mechanical properties of calcium phosphate cement/multi-walled carbon nanotubes/bovine serum albumin (CPC/MWCNTs/BSA) composites. In this study, CPC composites were reinforced by multi-walled carbon nanotubes (MWCNTs) and bovine serum albumin (BSA) in order to induce high mechanical properties in the CPC/MWCNTs/BSA system. The effect of various process parameters on the compressive strength of CPC/MWCNTs/BSA composites was studied using design of experiments (DOE). The process parameters studied were: wt.% of MWCNTs (0.2–0.5 wt.%), wt.% of BSA (5–15 wt.%) and type of MWCNTs (e.g. as-pristine MWCNT (MWCNT-AP), hydroxyl group functionalized MWCNT (MWCNT-OH) and carboxyl group functionalized MWCNT (MWCNT-COOH)). Based on the CCD, a quadratic model was obtained to correlate the process parameters to the compressive strength of CPC/MWCNTs/BSA composites. From the analysis of variance (ANOVA), the most significant factor affected on the experimental design response was identified. The predicted compressive strength after process optimization was found to agree well with the experimental value. The results revealed that at 0.5 wt.% of MWCNT-OH and 15 wt.% of BSA, the highest compressive strength of 14 MPa was obtained.     

Rheological and mechanical properties of surface modified multi-walled carbon nanotube-filled PET composite

Poly(ethylene terephthalate) (PET)/multi-walled carbon nanotube (MWCNT) composites were prepared by in situ polymerization. To improve the dispersion of MWCNTs in PET matrix, the surface modified MWCNTs having acid groups (acid-MWCNT) and diamine groups (diamine-MWCNT) were used. The functional groups on the surface of modified MWCNTs were confirmed by infrared (IR) spectrometry. SEM analysis showed better dispersion of diamine-MWCNTs as compared to pristine-MWCNTs and acid-MWCNTs in the PET. The reaction between PET and diamine-MWCNTs was evidenced by the shifting of the G band to a higher frequency in Raman spectroscopy and an increase of the complex viscosity in rheological properties. The composites containing functionalized MWCNTs showed a large increase in the tensile strength and modulus. The PET/diamine-MWCNT composites showed maximum tensile strength and modulus increases by 350% and 290% at 0.5 and 2.0 wt%, respectively, as compared to pure PET.     

In situ process monitoring of hierarchical micro-/nano-composites using percolated carbon nanotube networks

We report a method to monitor the manufacturing process of hierarchical micro-/nano-composites that uses integrated and percolated multi-walled carbon nanotube (MWCNT) networks with the aim of reducing part-to-part variability. Composites were fabricated by VARTM. Fiber textiles were spray-coated with MWCNTs, electrodes were embedded prior to vacuum bagging. In situ process monitoring was achieved by measurement of the electrical resistance of electrode pairs. The effects of MWCNT density and length on the ability to monitor the manufacturing process were evaluated. Experiments showed that monitoring the changes in resistance between electrode pairs on the conductive MWCNT network allowed various events during the manufacturing process, including part infusion, onset of crosslinking, and gel point of the resin, which are necessary for accurate evaluation of part quality. Our simple yet effective method to monitor the manufacturing processes and predict the final-part quality of multiscale composites can be integrated into existing processes with minimal modifications.     

Thermal conductivity of polymer composites based on the length of multi-walled carbon nanotubes

The anisotropic development of thermal conductivity in polymer composites was evaluated by measuring the isotropic, in-plane and through-plane thermal conductivities of composites containing length-adjusted short and long multi-walled CNTs (MWCNTs). The thermal conductivities of the composites were relatively low irrespective of the MWCNT length due to their high contact resistance and high interfacial resistance to polymer resins, considering the high thermal conductivity of MWCNTs. The isotropic and in-plane thermal conductivities of long-MWCNT-based composites were higher than those of short-MWCNT-based ones and the trend can accurately be calculated using the modified Mori-Tanaka theory. The in-plane thermal conductivity of composites with 2 wt% long MWCNTs was increased to 1.27 W/m·K. The length of MWCNTs in polymer composites is an important physical factor in determining the anisotropic thermal conductivity and must be considered for theoretical simulations. The thermal conductivity of MWCNT polymer composites can be effectively controlled in the processing direction by adjusting the length of the MWCNT filler.     

Dye sensitized solar cell based on platinum decorated multiwall carbon nanotubes as catalytic layer on the counter electrode

In this study we have employed multiwall carbon nanotubes (MWCNT), decorated with platinum as catalytic layer for the reduction of tri-iodide ions in dye sensitized solar cell (DSSC). MWCNTs have been prepared by a simple one step pyrolysis method using ferrocene as the catalyst and xylene as the carbon source. Platinum decorated MWCNTs have been prepared by chemical reduction method. The as prepared MWCNTs and Pt/MWCNTs have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In combination with a dye adsorbed TiO₂ photoanode and an organic liquid electrolyte, Pt/MWCNT composite showed an enhanced short circuit current density of 16.12 mA/cm² leading to a cell efficiency of 6.50% which is comparable to that of Platinum.     

Characterization of rheological behaviors of polypropylene/carbon nanotubes composites and modeling their flow in a twin-screw mixer

This paper focuses on the numerical simulation of the polypropylene/multi-walled carbon nanotubes (PP/MWCNT) flow into a twin-screw mixer, during the mixing phase. The PP/MWCNT behavior obeys an innovating Carreau law enriched temperature built on the rheological properties carried out previously. The polypropylene was mixed with different MWCNTs contents (1, 2, 4 and 8 wt.% of MWCNT content) and the rheological tests were performed at shear rate ranges from 10⁻¹ to 2 × 10⁴ s⁻¹ at four temperatures (180, 200, 220 and 240 °C). Thus the effects of the temperature and the MWCNTs content on the rheological properties of the PP/MWCNT composites were investigated. The finite element (FEM) analysis of the PP/MWCNT flow allows to compute the velocity, the shear rate and the temperature during the mixing phase period. A good agreement between the experimental measured torque on the screw and the calculated one is shown. Therefore, one can consider that the physical flow is generally well described, awaiting a numerical simulation of the PP/MWCNT mixing phase.     

Synthesis of poly(3-hexylthiophene)-graft-poly(t-butyl acrylate-co-acrylic acid) and its role of compatibilizer for enhancement of mechanical and electrical properties of Nylon 66/multi-walled carbon nanotube composites

A compatibilizer, poly(3-hexylthiophene)-graft-poly(t-butyl acrylate-co-acrylic acid) was synthesized, where the acrylic aid was formed by hydrolysis of t-butyl acrylate unit. It has been identified that poly(3-hexylthiophene) backbone of the compatibilizer interacts with multi-walled carbon nanotubes (MWCNTs) via π–π interaction and the acrylic acid unit of the graft chain interacts with Nylon 66 (N66) matrix via hydrogen bonding. When a small amount of compatibilizer was added to N66/MWCNT composites, MWCNTs were more homogeneously dispersed in N66 matrix than the case without compatibilizer. As a consequence, mechanical and electrical properties of the composites with compatibilizer were largely improved as compared with those of composites without compatibilizer.