Free Carbon Nanotube Research Articles

Robust orientation-3D conductive network enabled high-performance flexible sensor for traffic monitoring: Role of surface functionalization on self-assembled microspheres arrays

Flexible strain sensors prepared by self-sensing nanocomposites using polydimethylsiloxane (PDMS) as the matrix material and carbon nanotubes (CNTs) as the conductive filler have received widespread attention due to their structural flexibility, outstanding weatherability and biocompatibility. Nevertheless, the high sensitivity, stable signal output, and durability are still limited by the uniform dispersion of the CNTs inside. In this paper, a novel preparation method different from direct dispersion was explored, in which CNTs were assembled on the surface of polystyrene (PS) microspheres to assist in CNT dispersion during the self-deployment of microspheres arrays. The free CNTs acted as a bridge to connect the conductive microspheres in the orientation-3D conductive network, which were essential for forming abundant conductive pathways. As numerous conductive fillers were added to the system to enhance conductivity, the self-alignment effect of the microsphere arrays was significantly inhibited, and it failed to assist well in the dispersion. Therefore, the covalent bonding strategy was employed to improve the dispersion and construct strong interfacial interaction, providing impressive electrical conductivity, structural stability, and outstanding durability and thermal stability. The PDMS/PS-C/CNT-N composites prepared with aminated CNT (CNT-N) and carboxylated PS microspheres (PS-C) showed better performance in sensitivity, achieving a gauge factor of over 70, a wide sensing range of 0–124%, and fast response of 330 ms and fast recovery of 190 ms. The developed sensory film was used as an intelligent sensor to monitor traffic flow information. It has been proved that not only the vehicle configuration can be accurately identified, but also the speed can be precisely back-calculated. It opens up new territory to develop high-performance flexible strain sensors for accurate, long-term, and stable acquisition of traffic flow information.

Self-healing, self-adhesive, stretchable and flexible conductive hydrogels for high-performance strain sensors.

Conductive hydrogels have been widely studied for their potential application as wearable sensors due to their flexibility and biocompatibility. However, the simultaneous incorporation of excellent stretchability, toughness, conductivity, self-healing, and adhesion via a simple method remains a great challenge. Herein, a multifunctional hydrogel with self-adhesion, self-healing, conductivity, and mechanical properties was fabricated by ionic cross-linking of chitosan (CS), the acrylic acid (AA) polymer, and tea polyphenols (TPs) in the presence of graphitized carbon nanotubes (CNTs) in this work. The resultant hydrogel has unique self-healing properties (94.11% for strain self-healing and 90.60% for stress self-healing) and mechanical properties. The fracture stress was 0.075 MPa when the strain was 1184%, and the toughness reached 0.48 MJ m-3. The synergistic effect of free ions and CNTs endows the hydrogel with an excellent electrical conductivity (6.67 S m-1). Moreover, the hydrogel can adhere to various organic and inorganic materials. It exhibits repeatable self-adhesion to human skin and can be peeled off completely without any residual, irritation or allergic reactions. Additionally, the hydrogel also has good strain sensitivity and exhibits stable output signals in motion monitoring of the human body as a biosensor. Therefore, this work provides a new prospect for the design of multifunctional hydrogels for their potential applications in wearable biosensors.

Structural modelling and quantitative analysis of mechanical gradient in CNT/Al composites

Carbon nanotube-reinforced aluminium normally considered to be composed of Carbon nanotube (CNT) free grain interior (GI) and CNT containing grain boundary affected zone (GBAZ). Research works showed that the property of GI varies with the distance from the boundary. To better understand the influence of this mechanical heterogeneity, we introduced a transition zone (TZ) to emphasise the mechanical heterogeneity of the GI. A dislocation-based plastic strain constitutive model was used to analyse the mechanical response, and the simulation results fit well with the experimental result. Moreover, the TZ thickness with a large simulation influence was found, and its strengthening mechanism, the influence of TZ thickness on the macroscopic mechanical response, geometrically necessary dislocation distribution were discussed in this study.

Utilization of charge-transfer complexation to generate carbon-based nanomaterial for the adsorption of pollutants from contaminated water: Reaction between urea and vacant orbital acceptors

In this study, the charge-transfer complexation between urea as a donor and vacant orbital acceptors (i.e., FeCl3 and NiCl2) was used to generate a NiFe2O4 composite. The resultant composite was used to increase the adsorption capacity of free fullerene carbon nanotubes (CNT) for two organic dyes as example models [toluidine blue (TB) and eosin B (EB)] by combining this CNT with the resultant composite. Fullerenes are a type of carbon nanomaterials which particularly well suited for environmental remediation applications due to their large surface area combined with unique physicochemical properties that render them easily biodegradable and nontoxic. They have great potential for the recovery and removal of dyestuff from water. Crushing the NiFe2O4 composite with fullerene CNTs at a 1:10 M ratio (composite to CNT) in the presence of a few drops of methanol yielded a solid, black, homogenous NiFe2O4-CNT adsorbent material. This environmentally friendly approach enhanced the adsorption efficiency of free fullerene CNT for TB dye by 33% and for EB dye by 25%.

Aligned Collagen-CNT Nanofibrils and the Modulation Effect on Ovarian Cancer Cells.

Fibrillar collagen is a one-dimensional biopolymer and is the most abundant structural protein in the extracellular matrix (ECM) of connective tissues. Due to the unique properties of carbon nanotubes (CNTs), considerable attention has been given to the application of CNTs in developing biocomposite materials for tissue engineering and drug delivery. When introduced to tissues, CNTs inevitably interact and integrate with collagen and impose a discernible effect on cells in the vicinity. The positive effect of the collagen-CNT (COL-CNT) matrix in tissue regeneration and the cytotoxicity of free CNTs have been investigated extensively. In this study, we aimed to examine the effect of COL-CNT on mediating the interaction between the matrix and SKOV3 ovarian cancer cells. We generated unidirectionally aligned collagen and COL-CNT nanofibrils, mimicking the structure and dimension of collagen fibrils in native tissues. AFM analysis revealed that the one-dimensional structure, high stiffness, and low adhesion of COL-CNT greatly facilitated the polarization of SKOV3 cells by regulating the β−1 integrin-mediated cell–matrix interaction, cytoskeleton rearrangement, and cell migration. Protein and gene level analyses implied that both collagen and COL-CNT matrices induced the epithelial–mesenchymal transition (EMT), and the COL-CNT matrix prompted a higher level of cell transformation. However, the induced cells expressed CD44 at a reduced level and MMP2 at an increased level, and they were responsive to the chemotherapy drug gemcitabine. The results suggested that the COL-CNT matrix induced the transdifferentiation of the epithelial cancer cells to mature, less aggressive, and less potent cells, which are inapt for tumor metastasis and chemoresistance. Thus, the presence of CNT in a collagen matrix is unlikely to cause an adverse effect on cancer patients if a controlled dose of CNT is used for drug delivery or tissue regeneration.

Changes in Surface Free Energy and Surface Conductivity of Carbon Nanotube/Polyimide Nanocomposite Films Induced by UV Irradiation.

Changes in surface energy and electrical conductivity of polyimide (PI)-based nanocomposite films filled with carbon nanotubes (CNTs) induced by UV exposure are gaining considerable interest in microelectronic, aeronautical, and aerospace applications. However, the underlying mechanism of PI photochemistry and oxidation reactions induced by UV irradiation upon the surface in the presence of CNTs is still not clear. Here, we probed the interplay between CNTs and PIs under UV exposure in the surface properties of CNT/PI nanocomposite films. Changes in contact angles and surface electrical conductivity at the surface of CNT/PI nanocomposite films after UV exposure were measured. The unpaired electron intensity of free radicals generated by UV exposure was monitored by electron paramagnetic resonance. Our study indicates that the covalent interactions between CNTs and radicals generated by UV irradiation on the PI surfaces tailor the surface energy and surface conductivity through anchoring radicals on CNTs. Surprisingly, adding CNTs into PI films exposed to UV leads to antagonistic contributions of dispersion and polar components to the surface energy. The surface electrical conductivity of the CNT/PI nanocomposite films has been improved due to an enhanced hopping behavior with dense π-conjugated CNT sites. To explain the observed changes in surface energy and surface conductivity of CNT/PI nanocomposite films induced by UV exposure, a qualitative model was put forward describing the covalent interactions between UV-induced PI free radicals and CNTs, which govern the chemical nature of surface components. This study is helpful for characterizing and optimizing nanocomposite surface properties by tuning the covalent interactions between components at the nanoscale.

Detection and quantification of free carbon nanotubes in abraded polymer nanocomposites using UV–vis spectroscopy

Here we report a simple and rapid method to quantify free carbon nanotubes (CNTs) in the debris of abraded nanocomposites using ultraviolet-visible (UV–vis) spectroscopy. The method uses a surfactant to disperse free CNTs and separates out these via centrifugation from the CNTs that are aggregated, completely embedded in the polymer fragments, or protruding from the polymer fragments. The UV–vis spectroscopy is then used to measure the absorbance of the dispersed CNTs which is correlated to the total free CNT content in the debris via a calibration curve. We find that the method detects free CNTs in the debris of sanded CNT-epoxy composites. We also determine that when CNT-based anticorrosive paint is removed via sandblasting after its useful lifetime, no free CNTs are present above the detection limit of 1.3 × 10−4 wt%. Finally, we also show that when various CNT-polylactic acid (PLA) coatings on three-dimensional (3D) printer PLA filaments are abraded, no free CNTs are found in the debris above the detection limit. In contrast to other methods of free CNT analysis, our method quickly provides reliable quantitative information about free CNT content which is useful for both industries and risk assessors in evaluating exposure potential of CNT-based products.

Review of techniques and studies characterizing the release of carbon nanotubes from nanocomposites: Implications for exposure and human health risk assessment.

Composites made with engineered nanomaterials (nanocomposites) have a wide range of applications, from use in basic consumer goods to critical national defense technologies. Carbon nanotubes (CNTs) are a popular addition in nanocomposites because of their enhanced mechanical, thermal, and electrical properties. Concerns have been raised, though, regarding potential exposure and health risks from nanocomposites containing CNTs because of comparisons to other high aspect ratio fibers. Assessing the factors affecting CNT release from composites is therefore paramount for understanding potential exposure scenarios that may occur during product handling and manipulation. Standardized methods for detecting and quantifying released CNTs, however, have not yet been developed. We therefore evaluated experimental approaches deployed by various researchers, with an emphasis on characterizing free versus composite bound CNTs. From our analysis of published studies characterizing CNT releases from nanocomposites, we found that the qualitative and quantitative methods used across studies varied greatly, thus limiting the ability for objective comparison and evaluation of various release factors. Nonetheless, qualitative results indicated that factors such as composite type, CNT functionalization, and energy input during manipulation (i.e., grinding) may affect CNT release. Based on our findings, we offer several recommendations for future product testing and assessment of potential exposure and health risks associated with CNT nanocomposites.

Piezoresistive Response of Integrated CNT Yarns under Compression and Tension: The Effect of Lateral Constraint

Carbon nanotube (CNT) yarns are fiber-like materials that exhibit excellent mechanical, electrical and thermal properties. More importantly, they exhibit a piezoresistive response that can be tapped for sensing purposes. The objective of this study is to determine experimentally the piezoresistive response of CNT yarns that are embedded in a polymeric medium while subjected to either tension or compression, and compare it with that of the free or unconstrained CNT yarns. The rationale is the need to know the piezoresistive response of the CNT yarn while in a medium, which provides a lateral constraint to the CNT yarn, thus mimicking the response of integrated CNT yarn sensors. The experimental program includes the fabrication of samples and their electromechanical characterization. The CNT yarns are integrated in polymeric beams and subjected to four-point bending, allowing the determination of their response under tension and compression. The electromechanical data from a combined Inductance–Capacitance–Resistance (LCR) device and a mechanical testing system were used to determine the piezoresistive response of the CNT yarns. At a strain rate of 0.006 min−1, the gauge factor obtained under tension for a maximum strain of 0.1% is ~29.3 which is higher than ~21.2 obtained under compression. The CNT yarn sensor exhibited strain rate dependence with a gauge factor of approximately 23.0 at 0.006 min−1, in comparison to 19.0 and 1.3, which were obtained at 0.0005 min−1 and 0.003 min−1, respectively. There is a difference of up to two orders of magnitude in the sensitivity of the constrained CNT yarn under bending with respect to that of the free CNT yarn under uniaxial tension. However, the difference becomes smaller when the constrained CNT yarn was tested under uniaxial tension. This data and information will be used for future modeling efforts and to study the phenomena that occur when CNT yarns are integrated in polymeric and composite materials and structures.

Release of particles by abrasion of CNT composites using a belt sander

There have been many reports on the effect of exposure to nanomaterials such as titanium dioxide, silver, and carbon nanotube (CNT) on human health. Several experiments have examined the abrasion of CNT composites, in which CNT nanoparticles are embedded within a resin or rubber matrix, yielding varying results. Separate study of free CNTs and CNT nanoparticles in relation to health is important due to the different physicochemical characteristics of the two types of material. This study investigated the abrasion of CNT composites using a belt sander inside an enclosed chamber, with variation in the applied load and belt sander speed. At lower speeds, the population of particles with diameters of ~100 nm was observed to increase (cf. mode values of ~10 nm), and we found a relationship between the amount of the raising dust and the abrasion conditions. From these results, we propose a robust and widely applicable method to create particles of nanomaterial-containing composite materials of various types in order to conduct accelerated exposure assessment studies.

(Invited) Carbon Nanotubes from Synthesis, Assembly to Electrochemical Sensors

The unique physical properties of individual Carbon Nanotubes (CNTs) surpass the properties of many advanced materials available today. Due to their large surface area, chemical stability, and electrical conductivity, they are the most promising candidates for a large number of electroanalytical applications. A material for these applications requires high purity CNT assemblies like fibers and films, that have good electrical conductivity, in some case additional insulation coatings. This talk will report the synthesis of catalyst free CNTs, their assembly into ribbons at 15.9 m/s speed, fiber processing and polymer coating into a micro-cable format. CNT micro-cable was used for detection of toxic metals contaminants in H2O, that are considered as the most significant potential threats to human health by ATSDR and EPA. Polystyrene coated CNT fiber was used as the working electrode; bare CNT thread was used as the auxiliary electrode; and a pseudo-reference electrode was fabricated by electroplating CNT fiber with Ag that is subsequently anodized in chloride solution to form a layer of AgCl. The Ag/AgCl coated CNT fiber electrode provides stable potential comparable to the conventional liquid-junction type Ag/AgCl reference electrode, while bare CNT fiber auxiliary electrode provided a stable current comparable to a Pt wire auxiliary electrode. This all-carbon CNT fiber three electrode cell is evaluated for simultaneous detection of trace levels of heavy metal ions by anodic stripping voltammetry (ASV). Hg2+, Cu2+ and Pb2+ in H2O were detected successfully, and the detection limits are 1.05 nM, 0.53 nM and 0.57 nM for Hg2+, Cu2+ and Pb2+, respectively. These electrodes significantly reduce the dimensions of the conventional three electrode electrochemical cell and have the potential to become low cost and disposable sensor.

Conductive plastics: comparing alternative nanotechnologies by performance and life cycle release probability

Nanocomposites can be considered safe during their life cycle as long as the nanofillers remain embedded in the matrix. Therefore, a possible release of nanofillers has to be assessed before commercialization. This report addresses possible life cycle release scenarios for carbon nanotubes (CNT), graphene, and carbon black (CB) from a thermoplastic polyurethane (TPU) matrix. The content of each nanofiller was adjusted to achieve the same conductivity level. The nanofillers reduced the rate of nanoscale releases during mechanical processing with decreasing release in the order neat TPU, TPU-CNT, TPU-graphene, and TPU-CB. Released fragments were dominated by the polymer matrix with embedded or surface-protruding nanofillers. During electron microscopy analysis, free CB was observed, however, there was no free CNT or graphene. Quantitatively, the presence of free nanofillers remained below the detection limit of <0.01% of generated dust. Further, both the production process and type of mechanical processing showed a significant impact with higher release rates for injection-molded compared to extruded and sanded compared to drilled materials. Due to its optimal performance for further development, extruded TPU-CNT was investigated in a combined, stepwise worst case scenario (mechanical processing after weathering). After weathering by simulated sunlight and rain, CNT were visible at the surface of the nanocomposite; after additional sanding, fragments showed protruding CNT, but free CNT were not detected. In summary, this preliminary exposure assessment showed no indication that recommended occupational exposure limits for carbonaceous nanomaterials can be exceeded during the life cycle of the specific TPU nanocomposites and conditions investigated in this study.

Characterization of Potential Exposures to Nanoparticles and Fibers during Manufacturing and Recycling of Carbon Nanotube Reinforced Polypropylene Composites

Carbon nanotube (CNT) polymer composites are widely used as raw materials in multiple industries because of their excellent properties. This expansion, however, is accompanied by realistic concerns over potential release of CNTs and associated nanoparticles during the manufacturing, recycling, use, and disposal of CNT composite products. Such data continue to be limited, especially with regards to post-processing of CNT-enabled products, recycling and handling of nanowaste, and end-of-life disposal. This study investigated for the first time airborne nanoparticle and fibers exposures during injection molding and recycling of CNT polypropylene composites (CNT-PP) relative to that of PP. Exposure characterization focused on source emissions during loading, melting, molding, grinding, and recycling of scrap material over 20 cycles and included real-time characterization of total particle number concentration and size distribution, nanoparticle and fiber morphology, and fiber concentrations near the operator. Total airborne nanoparticle concentration emitted during loading, melting, molding, and grinding of CNT-PP had geometric mean ranging from 1.2 × 10(3) to 4.3 × 10(5) particles cm(-3), with the highest exposures being up to 2.9 and 300.7 times above the background for injection molding and grinding, respectively. Most of these emissions were similar to PP synthesis. Melting and molding of CNT-PP and PP produced exclusively nanoparticles. Grinding of CNT-PP but not PP generated larger particles with encapsulated CNTs, particles with CNT extrusions, and respirable fiber (up to 0.2 fibers cm(-3)). No free CNTs were found in any of the processes. The number of recycling runs had no significant impact on exposures. Further research into the chemical composition of the emitted nanoparticles is warranted. In the meanwhile, exposure controls should be instituted during processing and recycling of CNT-PP.

Effect of Carbon Nanotubes Upon Emissions From Cutting and Sanding Carbon Fiber-Epoxy Composites.

Carbon nanotubes (CNTs) are being incorporated into structural composites to enhance material strength. During fabrication or repair activities, machining nanocomposites may release CNTs into the workplace air. An experimental study was conducted to evaluate the emissions generated by cutting and sanding on three types of epoxy-composite panels: Panel A containing graphite fibers, Panel B containing graphite fibers and carbon-based mat, and Panel C containing graphite fibers, carbon-based mat, and multi-walled CNTs. Aerosol sampling was conducted with direct-reading instruments, and filter samples were collected for measuring elemental carbon (EC) and fiber concentrations. Our study results showed that cutting Panel C with a band saw did not generate detectable emissions of fibers inspected by transmission electron microscopy but did increase the particle mass, number, and EC emission concentrations by 20% to 80% compared to Panels A and B. Sanding operation performed on two Panel C resulted in fiber emission rates of 1.9×108 and 2.8×106 fibers per second (f/s), while no free aerosol fibers were detected from sanding Panels A and B containing no CNTs. These free CNT fibers may be a health concern. However, the analysis of particle and EC concentrations from these same samples cannot clearly indicate the presence of CNTs, because extraneous aerosol generation from machining the composite epoxy material increased the mass concentrations of the EC.

Carbon nanotubes buckypapers for potential transdermal drug delivery.

Drug loaded buckypapers based on different types of carbon nanotubes (CNTs) were prepared and characterized in order to evaluate their potentialities for the design of novel transdermal drug delivery systems. Lab-synthesized CNTs as well as commercial samples were employed. Clonidine hydrochloride was used as model drug, and the influence of composition of the drug loaded buckypapers and processing variables on in vitro release profiles was investigated. To examine the influence of the drug nature the evaluation was further extended to buckypapers prepared with flurbiprofen and one type of CNTs, their selection being based on the results obtained with the former drug. Scanning electronic microscopy images indicated that the model drugs were finely dispersed on the CNTs. Differential scanning calorimetry, and X-ray diffraction pointed to an amorphous state of both drugs in the buckypapers. A higher degree of CNT-drug superficial interactions resulted in a slower release of the drug. These interactions were in turn affected by the type of CNTs employed (single wall or multiwall CNTs), their functionalization with hydroxyl or carboxyl groups, the chemical structure of the drug, and the CNT:drug mass ratio. Furthermore, the application of a second layer of drug free CNTs on the loaded buckypaper, led to decelerate the drug release and to reduce the burst effect.

Enhanced electrochemical sensitivity of enzyme precipitate coating (EPC)-based glucose oxidase biosensors with increased free CNT loadings

Enzymatic electrodes were fabricated by using three different immobilizations of glucose oxidase (GOx): covalent enzyme attachment (CA), enzyme coating (EC), and enzyme precipitate coating (EPC), here referred to as CA-E, EC-E, and EPC-E, respectively. When additional carbon nanotubes (CNTs) were introduced from 0 to 75wt% for the EPC-E design, its initial biosensor sensitivity was improved from 2.40×10−3 to 16.26×10−3 A∙M−1∙cm−2, while its electron charge transfer rate constant was increased from 0.33 to 1.47s−1. When a fixed ratio of CNTs was added for three different electrode systems, EPC-E showed the best glucose sensitivity and long-term thermal stability. For example, when 75wt% of additional CNTs was added, the initial sensitivity of EPC-E was 16.26×10−3 A∙M−1∙cm−2, while those of EC-E and CA-E were only 6.42×10−3 and 1.18×10−3 A∙M−1∙cm−2, respectively. Furthermore, EPC-E retained 63% of its initial sensitivity after thermal treatment at 40°C over 41days, while EC-E and CA-E showed only 12% and 1% of initial sensitivities, respectively. Consequently, the EPC approach with additional CNTs achieved both high sensitivity and long-term stability, which are required for continuous and accurate glucose monitoring.

Development of a conceptual framework for evaluation of nanomaterials release from nanocomposites: Environmental and toxicological implications

Despite the fact that nanomaterials are considered potentially hazardous in a freely dispersed form, they are often considered safe when encapsulated into a polymer matrix. However, systematic research to confirm the abovementioned paradigm is lacking. Our data indicates that there are possible mechanisms of nanomaterial release from nanocomposites due to exposure to environmental conditions, especially UV radiation. The degradation of the polymer matrix and potential release of nanomaterials depend on the nature of the nanofillers and the polymer matrix, as well as on the nature of environmental exposure, such as the combination of UV, moisture, mechanical stress and other factors. To the best of our knowledge there is no systematic study that addresses all these effects. We present here an initial study of the stability of nanocomposites exposed to environmental conditions, where carbon nanotube (CNT) containing polymer composites were evaluated with various spectroscopic and microscopic techniques. This work discusses various degradation mechanisms of CNT polymer nanocomposites, including such factors as UV, moisture and mechanical damage. An in vivo ingestion study with Drosophila showed reduced survivorship at each dose tested with free amine-functionalized CNTs, while there was no toxicity when these CNTs were embedded in epoxy. In addition to developing new paradigms in terms of safety of nanocomposites, the outcomes of this research can lead to recommendations on safer design strategies for the next generation of CNT-containing products.

Fabrication of Patterned Carbon Nanotube Field Emission Surfaces on SiC Substrates

ABSTRACTThis work focuses on the patterning of SiC substrates prior to carbon nanotube (CNT) formation using the surface decomposition growth method for the purpose of improving the field emission capabilities of the resultant CNT film. The thermal decomposition of silicon carbide (SiC) substrates is an established approach to create highly dense arrays of vertically aligned CNTs. The attractiveness of this growth approach is that the CNTs form without the aid of a catalyst metal, yielding potentially defect free CNTs ideal for various applications. Due to the high temperature anneals (1400-1700oC) and moderate vacuum conditions (10−2 – 10−5 Torr) necessary for the thermal decomposition process to initiate on the SiC substrate, patterning CNT outcroppings ideal for enhancing the surface’s field emission properties is more difficult when compared to metal catalyst based chemical vapor deposition growth processes on silicon substrates. The intent of the SiC patterning is to reduce field screening effects between neighboring emission sites during field emission while maintaining a high emission site density. Specifically, the SiC substrate is etched to form μm scale pillars on the SiC surface. Experimental findings show that SiC substrates patterned with μm scale pillars can be decomposed to form CNT topped field emission sites, yielding a field emission substrate that outperforms a non-patterned SiC/CNT film. A turn-on electric field of 4.0 V/μm was measured.

Evaluation of airborne particle emissions from commercial products containing carbon nanotubes

The emission of the airborne particles from epoxy resin test sticks with different CNT loadings and two commercial products were characterized while sanding with three grit sizes and three disc sander speeds. The total number concentrations, respirable mass concentrations, and particle size number/mass distributions of the emitted particles were measured using a condensation particle counter, an optical particle counter, and a scanning mobility particle sizer. The emitted particles were sampled on a polycarbonate filter and analyzed using electron microscopy. The highest number concentrations (arithmetic mean = 4670 particles/cm(3)) were produced with coarse sandpaper, 2% (by weight) CNT test sticks and medium disc sander speed, whereas the lowest number concentrations (arithmetic mean = 92 particles/cm(3)) were produced with medium sandpaper, 2% CNT test sticks and slow disc sander speed. Respirable mass concentrations were highest (arithmetic mean = 1.01 mg/m(3)) for fine sandpaper, 2% CNT test sticks and medium disc sander speed and lowest (arithmetic mean = 0.20 mg/m(3)) for medium sandpaper, 0% CNT test sticks and medium disc sander speed. For CNT-epoxy samples, airborne particles were primarily micrometer-sized epoxy cores with CNT protrusions. No free CNTs were observed in airborne samples, except for tests conducted with 4% CNT epoxy. The number concentration, mass concentration, and size distribution of airborne particles generated when products containing CNTs are sanded depends on the conditions of sanding and the characteristics of the material being sanded.

Development and costs calculation of lithium–sulfur cells with high sulfur load and binder free electrodes

A binder free thick film sulfur cathode based on a carbon structure with carbon nano tubes (CNT) is introduced. The sulfur mass can be varied between 3 and 20 mg cm−2 electrode leading to sulfur loads that are several times as high as in slurry electrodes. The electrode structure and thickness is examined by SEM, the surface area measured by BET and the in-plane conductivity is determined by a modified 4-point measurement. The achieved capacities for these extremely high sulfur loads are around 900 mAh g−1 sulfur at a current of 0.64 mA cm−2 electrode.Additionally the price of future Li–S cells (18650), both conventional sulfur slurry cathode and here introduced binder free CNT sulfur cathode were calculated and compared with a lithium-ion system (NCA-graphite).