Increasing Multi-walled Carbon Nanotubes Content Research Articles

Melt Mixed Composites of Poly(ethylene-co-methacrylic acid) Ionomers and Multiwall Carbon Nanotubes: Influence of Specific Interactions

Multiwall carbon nanotubes (MWNT) were melt-mixed with poly(ethylene-co-methacrylic acid) ionomers (Surlyn) using twin screw microcompounder. The specific interactions existing between the Na+ moieties in Surlyn and the π electron clouds of MWNT were supported by FTIR and Raman spectroscopic analysis. SAXS scattering patterns were found to be progressively broadened in presence of MWNT in Surlyn/MWNT composites. Morphological investigations revealed selective clustering of MWNT in the vicinity of the ionic domains in Surlyn. Further, the domain size of the ionic clusters was found to increase with increasing MWNT content disrupting the ionic pairs apart in the ionic domain. The melt rheological response of Surlyn was significantly affected in presence of MWNT and was profoundly dependent on the ionic clusters. The state of dispersion of MWNT was assessed by AC electrical conductivity measurements. The associated percolation threshold was observed between 1.5–2 wt% of MWNT.

Electrical and mechanical properties of multi‐walled carbon nanotubes reinforced PMMA and PS composites

AbstractThe use of multi‐walled carbon nanotubes (MWCNT) as reinforcing material for thermoplastic polymer matrices, polymethyl methacrylate (PMMA), and polystyrene (PS) has been studied. MWCNT were synthesized by chemical vapor deposition (CVD) technique using ferrocene‐toluene mixture. As‐prepared nanotubes were ultrasonically dispersed in toluene and subsequently dispersed in PMMA and PS. Thin polymer composite films were fabricated by solvent casting. The effect of nanotube content on the electrical and mechanical properties of the nanocomposites was investigated. An improvement in electrical conductivity from insulating to conducting with increasing MWCNT content was observed. The carbon nanotube network showed a classical percolating network behavior with a low percolation threshold. Electromagnetic interference (EMI) shielding effectiveness value of about 18 dB was obtained in the frequency range 8.0–12 GHz (X‐band), for a 10 vol% CNT loading. An improved composite fabrication process using casting followed by compression molding and use of functionalized MWCNT resulted in increased composites strength. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Mechanical, thermal, and fire behavior of bisphenol a polycarbonate/multiwall carbon nanotube nanocomposites

AbstractNanocomposites of bisphenol A polycarbonate with 2, 4, 6, and 15 wt% multiwall carbon nanotubes (MWNT) and their use in fire retardancy are investigated. Their thermal behavior and pyrolysis are characterized using thermogravimetry, differential scanning calorimeter, oscillatory shear rheology, and dynamic mechanical analysis. The flammability is addressed using LOI and UL 94; the fire behavior, with a cone calorimeter using different irradiation. With increasing MWNT content the storage modulus is increased (10–20%) and melt viscosity increases by several orders of magnitude, particularly for low shear rates. The melt flow, dripping, and deformation during fire are hindered, which influences UL 94 and cone calorimeter results. The peak heat release rate is reduced up to 40–50% due to an improved barrier for small amounts (2 wt%) of MWNT and for low irradiation, whereas the effect is reduced for increasing irradiation and nearly vanishes for increasing filling. Adjuvant but also deleterious mechanisms result in the complex dependency on the MWNT content. Significant flame retardancy effects are specific and limited to only some fire properties. This study allows the materials' potential for implementation in different fire scenarios and tests to be assessed and provides insight into active mechanisms. POLYM. ENG. SCI., 48:149–158, 2008. © 2007 Society of Plastics Engineers

Electrical Properties of Polyaniline and Multi-Walled Carbon Nanotube Hybrid Fibers

We have fabricated for the first time one-dimensional multiwalled carbon nanotube (MWNT) nanocomposite fibers with improved electrical properties using electrospinning. Polyaniline (PANi) and poly(ethylene oxide) (PEO) were used as a conducting and a nonconducting matrix, respectively, for hybrid nanofibers including MWNTs. The hybrid nanofibers fabricated by electrospinning had a length of several centimeters and a diameter ranging from approximately 100 nm to approximately 1 microm. Transmission electron microscopic analysis confirmed that the MWNTs were successfully oriented along the fiber axis without any severe aggregation during electrospinning. The hybrid nanofibers showed an enhanced electrical conductance with increasing MWNT content up to 0.5 wt%, and compared to PANi/PEO fibers, they also showed a stable linear ohmic behavior. These hybrid conducting nanofibers can be applied to chemical and biosensors that require a high sensitivity.

Dynamic Thermo-Mechanical Properties of Chemically Surface Modified MWCNTs Reinforced Polymeric Composites

The dynamic thermo-mechanical properties of two types of chemically surface modified (Carboxylated and Octadecylated) multi-walled carbon nanotubes (MWCNTs) and As produced MWCNTs reinforced epoxy matrix composites are investigated by Dynamic Mechanical Thermal Analyzer at 1.0 wt% concentration. Moreover, influence of MWCNTs concentration variations to the dynamic thermo-mechanical properties are evaluated at Carboxylated MWCNT reinforced polymeric composites (from 0.1 to 5.0 wt %). Higher interfacial bonding strength is achieved by introducing the chemical surface modification. Also MWCNTs reinforced polymer shows higher storage modulus (from 30°C to 70°C) than pure polymer. Moreover, the storage modulus of composites increases linearly by increasing MWCNTs concentration. However, glass transition temperature (Tg) of composites decreases linearly by increasing MWCNTs concentration.

Reinforcement of styrene–butadiene–styrene tri-block copolymer by multi-walled carbon nanotubes via melt mixing

Styrene–butadiene–styrene tri-block copolymer (SBS) was reinforced with multi-walled carbon nanotubes (MWCNTs) by the interaction through melt mixing. The tensile strength of SBS/MWCNT composites increased with increasing MWCNT content. The interactions between SBS and MWCNTs were characterized by solubility of MWCNTs in tetrahydrofuran, dynamic mechanical analysis, X-ray photoelectron microscope, ultraviolet spectra and transmission electron microscopy. The results showed that there were interactions between MWCNTs and SBS occurred during melt mixing, leading to an improvement of the mechanical properties of SBS/MWCNT composites, as well as the homogeneous dispersion of MWCNTs in SBS. The interactions between MWCNTs and SBS were supposed to consist of the π–π interaction between MWCNTs and the phenyl groups of SBS, as well as the chemical bonding of polybutadiene segments with MWCNTs.

Preparation and Characterization of Linear Low Density Polyethylene/Carbon Nanotube Nanocomposites

Linear low‐density polyethylene (LLDPE)/multiwalled carbon nanotube (MWNT) nanocomposites were prepared via melt blending. The morphology and degree of dispersion of nanotubes in the polyethylene matrix were investigated using scanning electron microscopy (SEM). Both individual and agglomerates of MWNTs were evident. The rheological behavior and mechanical and electrical properties of the nanocomposites were studied using a capillary rheometer, tensile tester, and Tera ohm‐meter, respectively. Both polyethylene and its nanocomposites showed non‐Newtonian behavior in almost the whole range of shear rate. Addition of carbon nanotubes increased shear stress and shear viscosity. It was also found that the materials experience a fluid‐solid transition below 1 wt% MWNT. Flow activation energy for the nanocomposites was calculated using an Arrhenius type equation. With increasing nanotube content, the activation energy of flow increases. A decrease of about 7 orders of magnitude was obtained in surface and volume resistivity upon addition of 5 wt% MWNT. In addition, a difference between electrical and rheological percolation thresholds was observed. The results confirm the expected nucleant effect of nanotubes on the crystallization process of polyethylene. A slight increase in Young's modulus was also observed with increasing MWNT content.

Preparation and properties of plasticized starch/multiwalled carbon nanotubes composites

AbstractIn this work we have studied the utilization of multiwalled carbon nanotubes (MWCNTs) as filler‐reinforcement to improve the performance of plasticized starch (PS). The PS/MWCNTs nanocomposites were successfully prepared by a simple method of solution casting and evaporation. The morphology, thermal behavior, and mechanical properties of the films were investigated by means of scanning electron microscopy, wide‐angle X‐ray diffraction, differential scanning calorimetry, and tensile testing. The results indicated that the MWCNTs dispersed homogeneously in the PS matrix and formed strong hydrogen bonding with PS molecules. Compared with the pure PS, the tensile strength and Young's modulus of the nanocomposites were enhanced significantly from 2.85 to 4.73 MPa and from 20.74 to 39.18 MPa with an increase in MWCNTs content from 0 to 3.0 wt %, respectively. The value of elongation at break of the nanocomposites was higher than that of PS and reached a maximum value as the MWCNTs content was at 1.0 wt %. Besides the improvement of mechanical properties, the incorporation of MWCNTs into the PS matrix also led to a decrease of water sensitivity of the PS‐based materials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Shape‐memory polyurethane/multiwalled carbon nanotube fibers

AbstractShape‐memory polyurethane/multiwalled carbon nanotube (SMP–MWNT) composites with various multiwalled carbon nanotube (MWNT) contents were synthesized, and the corresponding SMP–MWNT fibers were prepared by melt spinning. The influence of the MWNT content on the spinnability, fracture morphology, thermal and mechanical properties, and shape‐memory behavior of the shape‐memory polymer was studied. The spinning ability of SMP–MWNTs decreased significantly with increasing MWNT content. When the MWNT content reached 8.0 wt %, the fibers could not be produced because of the poor rheological properties of the composites. The melt‐blending, extrusion, and melt‐spinning processes for the shape‐memory fiber (SMF), particularly at low MWNT contents, caused the nanotubes to distribute homogeneously and preferentially align along the drawing direction of the SMF. The crystallization in the SMF was promoted at low MWNT contents because it acted as a nucleation agent. At high MWNT contents, however, the crystallization was hindered because the movement of the polyurethane chains was restricted. The homogeneously distributed and aligned MWNTs preserved the SMF with high tenacity and initial modulus. The recovery ratio and recovery force were also improved because the MWNTs helped to store the internal elastic energy during stretching and fixing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Electrical and rheological properties of polycarbonate/multiwalled carbon nanotube nanocomposites

Nanocomposites of polycarbonate (PC) and multiwalled carbon nanotube (MWCNT) were prepared using a precipitation method, and the surface resistivities and rheological properties of the nanocomposites were investigated. The nanocomposites showed a threshold decrease in their surface resistivities with increasing MWCNT content at a relatively low concentration of 0.91vol.%. The low concentration required for the threshold decrease in the surface resistivities was attributed to the pristine MWCNT, without modifications unfavorable for the electrically conductive fillers. Yield behavior was observed with the change in the steady shear viscosities with shear stresses. The viscosities of the nanocomposites were lower than that of the neat PC. It is postulated that the decreased viscosity had resulted from the increase in the mobilities of the PC molecules and free volumes in the PC/MWCNT nanocomposites, which were supported by the decreased glass transition temperatures of the nanocomposites compared to the neat PC.

In-Situ Synthesis of Soluble Poly(3-hexylthiophene)/Multiwalled Carbon Nanotube Composite: Morphology, Structure, and Conductivity

Soluble poly(3-hexylthiophene) (P3HT)−multiwalled carbon nanotube (MWNT) nanocomposites (PCNCs) are prepared by the in-situ oxidative polymerization of 3-hexylthiophene (3HT) in a dispersion of MWNT in CHCl3. The MWNT−P3HT nanocomposite produces blackish-brown solution in chloroform, making it an easily processable system. With increase in MWNT concentration the molecular weight of P3HT has increased, but at higher MWNT concentration (8% w/w) the molecular weight has decreased. The head−tail (H−T) regioregularity of the samples remains the same with that of pure P3HT. The TEM pictures of PCNC-1 and PCNC-8 [the number indicates percentage (w/w) of MWNT with respect to monomer in the composite] show uniform wrapping of MWNT with P3HT. The increase of outer diameter in wrapped MWNT decreases with increase in MWNT concentration, but the PCNC-2.5 exhibits phase segregation by the formation of separate spheroid-like species on the partially wrapped MWNT surface. The higher molecular weight P3HT produced in the PCNC-2.5 has been attributed to this difference in morphology. Type 1 P3HT crystal is formed in all the PCNCs, and melting temperature shows an increase with increasing MWNT concentration except for the PCNC-2.5 sample. The glass transition temperature (Tg) remains unchanged in the PCNCs, but the β-transition temperature (Tβ) varies differently in the different PCNCs. The storage modulus of PCNCs has increased abruptly (maximum increase 158%) in the PCNCs than that of pure P3HT. The UV−vis spectra of PCNCs show a red shift in the π−π* transition band while the emission spectra show a small blue shift with increase in MWNT concentration. Fluorescence quenching occurs in the PCNCs, and it increases with increase in MWNT concentration except for the PCNC2.5 sample. The conductivity values of both undoped and doped PCNCs have increased significantly with increase in MWNT concentration. FT-IR spectra and NMR spectra indicate the presence of both CH−π and π−π interaction between P3HT and MWNT. Thus, the increased conductivity and mechanical properties of P3HT in the easily processable MWNT−P3HT nanocomposite are interesting for its probable use in different optoelectronic appliances.

Effects of the addition of multi-walled carbon nanotubes on the positive temperature coefficient characteristics of carbon-black-filled high-density polyethylene nanocomposites

This study investigates the effects of the addition of multi-walled carbon nanotubes (MWNTs) on the positive temperature coefficient (PTC) characteristics of conventional carbon black (CB)/high-density polyethylene (HDPE) composites. MWNT/CB/HDPE hybrid nanocomposites were prepared by the combined solution and melt-mixing process. The obtained results indicated that the PTC intensity and repeatability of the hybrid nanocomposites were dramatically improved by adding a small amount of MWNT and that the optimal MWNT content corresponded to the CB content. The initial resistivity of the materials decreased with increasing MWNT content, but not always in the PTC intensity.

Adhesive strength of nano-size particles filled thermoplastic polyimides. Part-I: Multi-walled carbon nano-tubes (MWNT)–polyimide composite films

In this study, adhesive properties of thermoplastic polyimides (PI) filled with multi wall carbon nano-tubes (MWNT) are investigated. The PIs studied are ODPA/3, 4′-ODA/PA (amorphous) and BPDA/3, 4′-ODA/PA (semi-crystalline). The PIs are prepared via a two-step method involving poly(amide acid) (PAA) stage followed by thermal or chemical imidization to obtain polyimide in film or powder form. The MWNT are mixed in low wt% (0.1–1.5) during synthesis at PAA stage through mechanical agitation and sonication. PI-MWNT film composites were characterized using DMTA and tensile testing to determine viscoelastic behavior and mechanical properties. Adhesive strength and adhesive energy of bonded samples, prepared with PI-MWNT films and powder composites, were determined using single lap joints test and wedge test methods, respectively. The fractured bonded surfaces were examined by scanning electron microscope to determine failure patterns. The results showed that viscoelastic behavior of PI–MWNT composite films changes from liquid-like to solid-like by increasing MWNT content. Elastic modulus and strength at break of PI-MWNT composite films were found to increase with increase in MWNT wt%. However, elongation at break and breaking energy of PI–MWNT composite films and lap shear strength and adhesive energy of bonded samples were found to initially increase with increase in MWNT wt%, but then after a critical value decreases. The SEM analysis showed that bonded joints prepared with PI–MWNT composite films containing high wt% of MWNT failed in adhesive mode showing poor wetting of adherend surfaces.

Influence of multiwall carbon nanotube on physical properties of poly(ethylene 2,6‐naphthalate) nanocomposites

AbstractPolymer nanocomposites consisting of multiwall carbon nanotube (MWCNT) and poly(ethylene 2,6‐naphthalate) (PEN) were prepared by a melt blending process in a twin‐screw extruder. The storage modulus (G′) and loss modulus (G″) of the PEN/MWCNT nanocomposites increased with increasing frequency, and this increment being more significant at low frequency. The terminal zone slope of G′ for the PEN/MWCNT nanocomposites decreased with increasing MWCNT content, and the nonterminal behavior of those was related to the dominant nanotube–nanotube interactions at higher MWCNT content, leading to the formation of the interconnected or network‐like structures of MWCNT in the polymer nanocomposites. The decrease in the slope of the plot of log G′ versus log G″ for the PEN/MWCNT nanocomposites with increasing MWCNT content suggested the changes in the microstructures of the polymer nanocomposites by incorporating MWCNT. The incorporation of very small quantity of MWCNT significantly improved the mechanical properties of the PEN/MWCNT nanocomposites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1062–1071, 2006

Crystallization behavior of poly(ε‐caprolactone)/multiwalled carbon nanotube composites

AbstractDifferential scanning calorimetry (DSC), polarized optical microscopy, and X‐ray diffraction methods were used to investigate the isothermal crystallization behavior and crystalline structure of poly(ϵ‐caprolactone) (PCL)/multiwalled carbon nanotube (MWNT) composites. PCL/MWNT composites were prepared via the mixing of a PCL polymer solution with carboxylic groups containing multiwalled carbon nanotubes (c‐MWNTs). Both Raman and Fourier transform infrared spectra indicated that carboxylic acid groups formed at both ends and on the sidewalls of the MWNTs. A transmission electron microscopy micrograph showed that c‐MWNTs were well separated and uniformly distributed in the PCL matrix. DSC isothermal results revealed that introducing c‐MWNTs into the PCL structure caused strongly heterogeneous nucleation induced by a change in the crystal growth process. The activation energy of PCL drastically decreased with the presence of 0.25 wt % c‐MWNT in PCL/c‐MWNT composites and then increased with increasing MWNT content. The result indicated that the addition of c‐MWNT to PCL induced heterogeneous nucleation (lower total activation energy) at a lower c‐MWNT content and then reduced the transportation ability of polymer chains during crystallization processes at a higher MWNT content (higher total activation energy). A correlation between the crystallization kinetics, melting behavior, and crystalline structure of PCL/c‐MWNT composites was also discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 598–606, 2006

Preparation and Characterization of PS/Multi-Walled Carbon Nanotube Nanocomposites

Nanocomposites of polystyrene (PS) with multi-walled carbon nanotubes (MWNT) were produced by co-rotating twin-screw extruder. Characterization of these materials included scanning electron microscopy (SEM), transmission electron microscopy (TEM) and rheology in order to obtain the information on the dispersion of MWNT in the polymeric matrix. It is found that the MWNT dispersed uniformly through the PS matrix showing no significant agglomeration in the various compositions studied. In addition, we also investigated the thermal properties, glass transition temperature and thermal decomposition behavior as a function of the increasing MWNT content.

Melt processing and mechanical property characterization of multi-walled carbon nanotube/high density polyethylene (MWNT/HDPE) composite films

High density polyethylene (HDPE) was used as the matrix material for a carbon nanotube (CNT) polymer composites. This combination of composite constituents has not been previously reported in the literature. Multi-wall carbon nanotube (MWNT)/HDPE composite films were fabricated using the melt processing method. The composite films with 0, 1, 3 and 5% nanotube content by weight were analyzed under SEM and TEM to observe nanotube dispersion. The mechanical properties of the films were measured by small punch test. Results show increases in the stiffness, peak load and work to failure for the composite films with increasing MWNT content.