STRUCTURAL MODEL OF THE COMBUSTION PROCESS OF POLYMER/CARBON NANOTUBE NANOCOMPOSITES

The interphase thickness in polymer carbon nanotube (CNT) nanocomposites (PCNT) is expressed by CNT characteristics and interfacial conductivity between CNT and polymer matrix. Also, the effective length and concentration of CNT are defined supposing interfacial conductivity to suggest the percolation threshold and the fraction of networked CNT. Furthermore, a simple model is developed to predict the conductivity of PCNT assuming tunneling effect, interphase region and interfacial conductivity. The influences of all parameters on the interphase thickness, percolation threshold, the fraction of networked CNT and the conductivity of PCNT are studied. In addition, some experimental results are provided to compare the predictions of developed model to the experimental measurements. The high levels of CNT radius, CNT length, CNT conductivity, interfacial conductivity and conductivity transferring can produce a thick interphase, but the waviness cannot change it. Moreover, the developed model can properly calculate the conductivity of studied samples. A desirable conductivity is obtained by thin and long CNT, medium CNT conductivity, poor waviness, high interfacial conductivity and good conductivity transferring, because they provide high effective CNT concentration and low percolation threshold in nanocomposites.

The material selection for shoe soles is important as it determines the long-term performance of sports shoes, especially the performances of athletes’ shoes with respect to comfort during walking, running and jumping. An effective approach is developed to establish a strong interface between the carbon nanotube and high-density polyethylene/ethylene propylene rubber matrix by introducing electron beam radiation to the nanocomposite as a crosslinking technique. This study focuses on the carbon nanotube variation in the polymer matrix of high-density polyethylene and ethylene propylene rubber. The mechanical properties of high-density polyethylene/ethylene propylene rubber–carbon nanotube nanocomposites with different carbon nanotube contents were investigated at 0.5, 1, 3 and 5 wt% of carbon nanotube content. The combinations of nanofillers and polymer matrix stimulate the performance of sports shoes soles since each of them exhibits superior properties. The aim of this article is to find the optimum carbon nanotube content over the mechanical properties of electron beam–irradiated high-density polyethylene/ethylene propylene rubber nanocomposite for shoe soles. These irradiated nanocomposites are melt blended before compression moulding of the specimens. The specimens were then irradiated under electron beams at 100 kGy. The irradiated nanocomposites were tested for their tensile, impact, hardness and wear properties. The morphology of the tensile failure fracture was analysed under a field emission scanning electron microscope. The addition of carbon nanotubes improved the mechanical properties of the samples for both unirradiated and irradiated nanocomposites; however, they dropped after 3 wt% of carbon nanotube content. The carbon nanotube content at 3 wt% was found to be the most effective in enhancing the mechanical properties, particularly wear in irradiated nanocomposite, due to the better crosslinking and carbon nanotube dispersion.

Additive manufacturing is an emerging method to produce customized parts with functional materials without big investments. As one of the common additive manufacturing methods, fused deposition modeling (FDM) uses thermoplastic-based feedstock. It has been recently adapted to fabricate composite materials too. Acrylonitrile butadiene styrene (ABS) is the most widely used material as FDM feedstock. However, it is an electrically insulating polymer. Carbon Nanotubes (CNTs) on the other hand are highly conductive. They are attractive fillers because of their high aspect ratio, and excellent mechanical and physical properties. Therefore, a nanocomposite of these two materials can give an electrically conductive material that is potentially compatible with FDM printing. This work focuses on the investigation of the relationships between the FDM process parameters and the electrical conductivity of the printed ABS/CNT nanocomposites. Nanocomposite filaments with CNT contents up to 10wt% were produced using a twin-screw extruder followed by 3D printing using FDM method. The starting material was pellets from a masterbatch containing 15 wt% CNT. Compression-molded samples of ABS/CNT were also prepared as the bulk baselines. The effects of CNT content and nozzle size on the through-layer and in-layer electrical conductivity of the printed nanocomposites were analyzed. Overall, a higher percolation threshold was observed in the printed samples, compared to that of the compression-molded counterparts. This resulted in the conductivity of the printed samples that is at least one order of magnitude lower. Moreover, at CNT contents up to 5 wt%, the in-layer conductivity of the printed samples was almost two orders of magnitudes higher than that in the through-layer direction. In ABS/3 wt% CNT samples, the through-layer conductivity continuously decreased as the nozzle diameter was decreased from 0.8 mm to 0.35 mm. These variations in the electrical conductivity were explained in terms of the CNT alignment, caused by the extrusion process during the print, quality of interlayer bonding during deposition, and the voids created due to the discrete nature of the printing process.

Polyelectrolyte–polyelectrolyte complexes/multiwall carbon nanotubes (PECs/MWCNTs) nanocomposites have not been prepared until now because PECs are generally insoluble and infusible. In this work, solution-processable PEC/MWCNT nanocomposites and their membranes were prepared by in situ incorporation of MWCNTs into bulk PECs. The ionic complexation between poly(diallyldimethylammonium chloride) (PDDA) and sodium carboxymethyl cellulose (CMCNa) in the presence of MWCNTs was followed by ζ potential and optical transmittance measurements. Structures of PEC/MWCNT nanocomposites were characterized by FT-IR, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). It is found that MWCNTs are encapsulated by a layer of PEC and dispersed in a PEC matrix mainly on a single nanotube level. Mechanical properties of the nanocomposite membrane loaded with 7 wt% MWCNTs are greatly improved, showing 2.6 times higher tensile strength and 1.8 times higher modulus as compared with that of the pristine PEC. PEC/MWCNT nanocomposite membranes also display very high performance in pervaporation dehydration of isopropanol. This high pervaporation performance is reproducible with cycling feed temperatures and stable with increasing operation time up to 20 days.

ABSTRACTPolymer and carbon nanotubes (CNTs) nanocomposites exhibit many properties that are not present in either the pure polymer or CNTs. The polymer crystallization kinetics and crystal forms are greatly changed by dispersion of CNTs nanotubes. In addition to various thermophysical properties, CNTs are metallic or semiconductive and highly anisotropic while the polymer hosts are typically excellent insulators and isotropic. In this work, measurements of the electrical conductivity, σ, of thin-film nanocomposites of isotactic polypropylene (iPP) and CNTs as a function of CNT concentration (0, 1, 2, and 5% by weight of CNT) and melt-shearing induced anisotropy in σ between parallel and perpendicular to the shearing axis is presented and compared them with analogous data for their thermal transport properties. The iPP host is itself one of the most widely used polymers, has liquid crystalline phases, and it is expected that iPP/CNT nanocomposites will be widely used in many polymer applications, some of which are for flexible electrodes, medical and electronics packaging and chemical sensors. The effect of melt-shearing is expected to induce anisotropy in the various properties of the iPP/CNT thin film that should be particularly apparent in the electrical conductivity of the polymer films, higher in the direction of the alignment and lower in the direction perpendicular to it. With increasing CNT content, the average conductivity 〈σ〉 increases slightly from 0 to 2% CNT then dramatically increases by eight orders of magnitude for 5%. The shear induced property of anisotropy, δσs = (σ‖ − σ┴) / 〈σ〉, overall increases with CNT content, revealing a large spike for the 1% sample, indicating the possibility of enhanced δσs due to optimized orienting procedures.

This paper expresses a simple equation for conductivity of polymer carbon nanotubes (CNT) nanocomposites (PCNT) based on Halpin-Tsai model supposing the volume fraction of networked CNT, CNT conductivity, CNT size and tunneling dimensions between adjacent CNT. The experimental results of several samples and the effects of all parameters on the conductivity examine the predictions of developed model. Long CNT, thick interphase, thin CNT, high percentage of networked CNT, short tunneling distance, poor waviness and large tunneling diameter advantageously improve the conductivity. The suitable agreements between experimental data and calculations as well as the sensible roles of all parameters in the conductivity justify the developed model. The developed model can provide the optimized levels of parameters introducing the most desirable conductivity.

The effective conductivity of polymer carbon nanotubes (CNT) nanocomposites

Effect of CNT concentration and agitation on surface heat flux during quenching in CNT nanofluids

The morphology, nucleation, and crystallization of polyethylene/carbon nanotubes nanocomposites were studied. The nanocomposites were prepared by in-situ polymerization of ethylene on carbon nanotubes (CNT) whose surface had been previously treated with a metallocene catalytic system. The effects of composition (5−22% CNT) and structure of the nanotube (single, double, or multiwall, i.e., SWNT, DWNT, and MWNT) were evaluated, and an excellent nucleating effect on polyethylene matrix was found regardless of the CNT type in comparison to neat high-density polyethylene (HDPE) prepared under identical conditions. The CNT were found to be more efficient in nucleating the HDPE than its own crystal fragments, a result obtained by self-nucleation studies. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) results showed that under both isothermal and dynamic crystallization conditions the crystals produced within the nanocomposite HDPE matrix were more stable than those produced in neat HDPE or in physical blends prepared by melt mixing of HDPE and untreated CNT. The remarkable stability of the crystals was reflected in melting points up to 5 °C higher than neat HDPE and concomitant thicker lamellae. The changes induced on HDPE by CNT are due to the way the nanocomposites were prepared; since the macromolecular chains grow from the surface of the nanotube where the metallocene catalyst has been deposited, this produces a remarkable nucleating effect and bottle brush morphology around the CNT. Isothermal crystallization kinetics results showed that the in-situ nanocomposites crystallize much faster at equivalent supercoolings than neat HDPE because of the nucleating effect of CNT. Wide-angle X-ray scattering studies demonstrated that the crystalline structure of the HDPE matrix within the in-situ-polymerized HDPE/CNT nanocomposites was identical to that of neat HDPE and did not change during isothermal crystallization, keeping its orthorhombic unit cell.

The silicon/carbon nanotube (core/shell) nanocomposite electrode model is one of the most promising solutions to the problem of electrode pulverization in lithium-ion batteries. The purpose of this study is to analyze the mechanical behaviors of silicon/carbon nanotube nanocomposites via molecular dynamics computations. Fracture behaviors of the silicon/carbon nanotube nanocomposites subjected to tension were compared with those of pure silicon nanowires. Effective Young’s modulus values of the silicon/carbon nanotube nanocomposites were obtained from the stress and strain responses and compared with the asymptotic solution of continuum mechanics. The size effect on the failure behaviors of the silicon/carbon nanotube nanocomposites with a fixed longitudinal aspect ratio was further explored, where the carbon nanotube shell was found to influence the brittle-to-ductile transition behavior of silicon nanowires. We show that the mechanical reliability of brittle silicon nanowires can be significantly improved by encapsulating them with carbon nanotubes because the carbon nanotube shell demonstrates high load-bearing capacity under tension.

Advanced polystyrene‐b‐polybutadiene‐b‐polystyrene (SBS) based nanocomposites containing bare carbon nanotubes (CNTs) and CNTs bearing hydroxyl functional groups (CNTs‐OH) have been formulated and fully characterized. In particular, the reinforcement effect of CNTs and CNTs‐OH on SBS was deeply investigated through mechanical and dynamical thermo‐mechanical analysis and the rheological response of SBS‐based nanocomposites was investigated and discussed. The mechanical properties of SBS/CNTs and even more of SBS/CNTs‐OH nanocomposites are substantially superior to those of neat SBS, due to the uniformly dispersed nanofillers throughout the polymeric matrix. The presence of ‐OH groups onto CNTs promotes the stress transfer from polymer to CNTs, strengthening the overall performance of the nanocomposite. Moreover, the durability of SBS‐based nanocomposites was monitored through mechanical, dynamic mechanical, and rheological analysis. SBS‐based nanocomposites showed a significant improved photo‐stability with respect to the neat matrix, due to the presence of CNTs that are able to stabilize efficiently SBS because of their acceptor‐like electron properties. The presence of ‐OH groups onto CNTs enhance the protection ability of CNTs due to the larger amount of surface defects, that improves their radical scavenging activity. Furthermore, CNTs‐OH can act as chain‐breaking electron donor, becoming responsible for radical termination during SBS degradation. POLYM. COMPOS., 38:E381–E391, 2017. © 2015 Society of Plastics Engineers

In this paper, carboxylic multi-walled carbon nanotubes (MWCNTs-COOH) were modified by a series of hyperbranched polyesters (HBP) with different molecular structures (different branching degree) through surface grafting, and then the epoxy resin (EP)/carbon nanotube composites were prepared to explore the influences of structure regulation of HBP modified carbon nanotubes on the toughening performance of the composites. The results of Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) of various HBP grafted carbon nanotubes confirmed that the HBP were successfully grafted onto MWCNTs-COOH via an esterification reaction between the carboxyl groups of MWCNTs-COOH and the hydroxyl groups of HBP, meanwhile, the higher the branching degree of the HBP, the higher its grafting ratio onto carbon nanotubes. Furthermore, the outcome of dynamic thermal mechanical analysis (DMA) indicated that the addition of MWCNTs-COOH increased the storage modulus and glass transition temperature (Tg) of the pure EP, and surface grafting of various HBP onto MWCNTs-COOH decreased the Tg and peak height of mechanical loss of composites. And as the branching degree of HBP increased, the interfacial bonding between MWCNTs and the EP matrix became stronger. The results of mechanical performance and morphology analysis also revealed that the addition of HBP grafted MWCNTs-COOH significantly improved its dispersion and interfacial bonding in the EP matrix, resulting in better performance in the enhancement of toughness of the composites. In addition, it was found that the higher the branching degree of HBP, the better the toughening performance of the composites.

This article presents the role of interfacial conductivity between the polymer matrix and nanoparticles in the electrical conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNT) by simple equations. In this methodology, CNT size, CNT conductivity, CNT waviness and interfacial conductivity express the effective length and effective concentration of CNT in PCNT. Additionally, the percolation threshold and the percentages of CNT in the conductive networks are defined by the above mentioned terms. Finally, a simple model is developed to suggest the electrical conductivity of PCNT by CNT dimensions, CNT conductivity, CNT waviness, interphase thickness, interfacial conductivity and tunneling distance. The developed model is applied to show the roles of all parameters in the conductivity. Also, the experimental levels of percolation threshold and conductivity for several samples are compared to the predictions to validate the developed equations. The interfacial conductivity directly controls the electrical conductivity of nanocomposites. In addition, thick interphase, low waviness and short tunneling distance increase the conductivity. Moreover, the predictions show good agreement with the experimental measurements, providing evidence in support of the developed equations.

Prediction of complex modulus in phase-separated poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes nanocomposites

With different mass ratios, titanium dioxide/carbon nanotube (0.1–10 wt% CNT content) nanocomposites were prepared with the aid of ultrasonication method. The structures of the various TiO2/CNT nanocomposites were characterized by electron microscopy (scanning electron microscopy, transmission electron microscopy). Their photocatalytic activity was tested by the degradation of phenol in aqueous solution under near‐UV irradiation. In parallel experiments, both (SW and MW) CNT samples were treated in a reflux system with nitric acid to functionalize the nanotubes, subsequently preparing the nanocomposites in the same method. At higher CNT concentration (5, 10 wt%) the nanocomposites exhibited lower photocatalytic activity compared to the samples with lower CNT concentration, probably because the higher CNT concentration reduces the light intensity on the surfaces of TiO2 particles. Our aim was to find the best synthesis method and the optimal composition of the TiO2/CNT nanocomposites for the degradation of phenol under UV irradiation. The highest degradation rate was achieved with Aldrich anatase/functionalized single wall carbon nanotube nanocomposite (AA + f‐SW1 wt%). The photocatalytic activity of this sample was significantly higher compared to the bare Aldrich anatase and Aeroxide P25 titanium dioxide reference samples which were the best photocatalysts among the investigated bare titanias.