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This work studied few-layer graphene (FLG) dominant action mechanisms as a photo-stabilizer. High-density polyethylene (HDPE) containing 0-0.5 wt% FLG were exposed to UVA radiation in a QUV chamber, according to ASTM G154 for different exposure times, ranging from 0 to 672 h. The chemical, rheological, and mechanical properties were tracked using attenuated total reflection-Fourier transform infrared (ATR-FTIR), rheological measurements, and tensile tests. The experimental results showed that the addition of only 0.25 wt% FLG fully stabilized 1- to 3-mm thick HDPE for an exposure time of 672 h. Electron paramagnetic resonance (EPR) test was performed on the UV-exposed mixture of hydrogen peroxide ([H.sub.2][O.sub.2]) and the FLG aqueous suspensions (0, 0.2, 1, and 5 mg/mL), to study the FLG performance and mechanisms as a photo-stabilizer. The results showed that FLG effectively decreased the characteristic EPR signal intensity due to both UV absorption/reflection and free radical scavenging. Fifty-seven percent of the reduction was found to be due to UV absorption/ reflection and 43% due to free radical scavenging. It is demonstrated that UV absorption/reflection and free radical scavenging are the dominant ones among the three FLG photo-stabilizing mechanisms (UV absorption/reflection, free radical scavenging, and physical barrier to oxygen). Highlights * FLG showed potential as a photo-stabilizer for HDPE. * Addition of 0.25 wt% FLG fully stabilized HDPE for 672 h of UVA exposure. * FLG demonstrated UV absorption/reflection and free radical scavenging effects. KEYWORDS graphene, photo-oxidative degradation, photo-stabilizer, physical barrier, radical scavenger, UV absorption/reflection, 1 | INTRODUCTION Graphene, a two-dimensional carbon-based material, has attracted the attention of both academics and industrialists due to its exceptional chemical and physical properties. (1-3) In recent years, graphene [...]

The self-healing performance of epoxidized deproteinized natural rubber (EDPNR) and EDPNR/graphene oxide (GO) composites was investigated. Composites of EDPNR25 and EDPNR50 with GO contents of 0.5 and 1.0 phr were prepared by adding a GO dispersion into a EDPNR latex and the product was subsequently cast into films. Tensile strengths of the original samples and after self-healing were used to evaluate self-healing performance. The tensile strength of EDPNR25 after self-healing achieved about 65% of tensile strength of original EDPNR25. The recovery of tensile strength for the composite increased to 81% for EDPNR25/GO0.5 and 105% for EDPNR25/GO1.0 for self-healing at 25[degrees]C for 24 h. At 70[degrees]C, EDPNR25/GO0.5 and EDPNR25/GO1.0 composite achieved ~100% recovery after 24 h. On the other hand, the tensile strength recoveries of EDPNR50, EDPNR50/GO0.5, and EDPNR50/GO1.0 were relatively low (33%, 28%, and 24%, respectively) at 25[degrees]C. At 70[degrees]C, recoveries increased to 63%, 67%, and 52%, respectively. This result demonstrated that the interdiffusion of epoxidized natural rubber molecules plays a key role in the self-healing performance rather than hydrogen bonds between GO and functional groups on EDPNR molecules. KEYWORDS epoxidized deproteinized natural rubber, graphene oxide, hydrogen bonds, interdiffusion, self-healing, 1 | INTRODUCTION In recent years, humans have been facing environmental problems of discharging thermoset plastics and vulcanized natural rubber (VNR) products since these materials are difficult to be recycled [...]

The discovery of radiation-shielding materials remains a critical technology to enable long-term space travel and extraterrestrial colonization. Hydrocarbon polymers, such as high-density polyethylene (HDPE), are among the best radiation attenuators due to their rich H content and lightweight. Due to their simple chemical structure that lacks larger heteroatoms, HDPE is also resistant to numerous radiation-induced degradation pathways that often limit the applicability of more sophisticated polymers. One drawback of hydrocarbon polymers is their inferior mechanical properties, such as tensile strength and impact toughness, relative to metals and other high-performance polymer systems. In this report, we develop an alkylated reduced graphene oxide that is used as an additive to enhance the storage and tensile moduli of HDPE by 10-15% across the lunar temperature range. These additives outperform unmodified reduced graphene oxide by 30% due to better dispersion through the polymer matrix as observed by cross-sectional scanning electron microscopy., INTRODUCTION A major barrier to long-term space exploration is the development of technologies to protect astronauts and their equipment from harmful levels of radiation exposure [1, 2], which can lead [...]

Three-dimensional (3D) graphene aerogel (GA) with a spatial porous structure and network skeleton was facilely prepared via one-step self-assembly hydrothermal reduction. Such network structure is regarded as a critical advantage in resolving the dispersion of graphene in polymer matrix, thereby enhancing the damping property. Here, as-prepared GA was added to the carboxylated butadiene nitrile rubber/polyurethane blend (XNBR/PU) by melting/mechanical complex method. Their dynamic mechanical properties were investigated in detail, and the relationship between thermal aging and dynamic mechanical properties had also been studied. Finding that the storage modulus and loss modulus of XNBR/PU were continually improved with the increase in addition amount of high-performance GA, reaching 3,219 and 316 MPa with the content of 3 wt% GA, respectively. Loss factor (tano) of XNBR/PU with GA shows two sets of maximum values (0.22 and 0.61) at around -25 and 0.6[degrees]C, respectively. Results illustrate that GA can greatly improve the damping performance, damping temperature range, mechanical properties, and thermal aging resistance of XNBR/PU blend, mainly depending on the performance characteristics of GA and interface interaction between GA and XNBR/PU. Verifying that GA with 3D network structure holds a great prospect for damping materials., INTRODUCTION With the rapid development of modern industrial technology, the damage of vibration and noise has made severely negative influence on the reliability and safety of equipment [1, 2]. Vibrations [...]

The presented studies concern the effects of graphite flake (GF) on the properties of a specific and challenging type of composite, that is, phenolic-carbon fabric (PC) composites. This type of materials are commonly used in large scale, but the studies in this manuscript try to explain in detail the effects of graphite on the characteristics of composites. The results show that Young's modulus exhibits increasing trend however tensile strength and interlaminar shear strength show decrement on increasing the GF content in the PC-GF composites. Dynamic mechanical thermal analysis (DMTA) reveals that storage modulus (E') increases by ~42% and 139% upon addition of 10 and 40 wt% GF in the PC-GF composites, respectively. Loss modulus (E') of the composites shows a drastic improvement (~145%) upon addition of only 10 wt% GF. Moreover, various interfacial interaction parameters such as entanglement density (N), reinforcement efficiency factor (r), C factor (the effectiveness of fillers on the modulus of the composites), interphase adhesion factor (A), and 'b' factor (fiber volume correction factor) of the composites are also evaluated using the data obtained from DMTA and correlated with mechanical properties of the composites., INTRODUCTIONCarbon fiber reinforced composite materials are widely used because of their excellent physical, thermal and mechanical properties [1, 2]. Among polymers, phenolic resins are finding their increased applications due to [...]

The objective of this study was to prepare chitosan and starch composite films by the addition of 0-3 wt% graphene nanosheets. The film's tensile strength (TS), tensile modulus (TM), elongation at break (E), moisture uptake (Mu), and water vapor transmission rate (WVTR) were investigated. The surface morphology of the composite films was studied using scanning electron microscopy (SEM). Regardless of biopolymer type, both the TS and TM of the composite films first increased and then decreased with graphene loading. Composite film made with native (unmodified) starch showed lower TS and TM than those with chitosan. Composite films exhibit lower E values than pure chitosan and starch; this is attributed to the increase in the hardness of the films. SEM micrographs indicated that, the surface roughness and phase separation increased with increasing graphene content. This is due to the aggregation of graphene nanosheets, leading to the reduced compatibility of biopolymers. The addition of graphene considerably decreased WVTR and Mu of the composite films. These results indicated that graphene is a promising reinforcing agent for biopolymer composite films., INTRODUCTION Ecological concerns and the impending depletion of fossil fuels are driving the development of new biocomposites as green products [l]. Bio-composites are a new generation of composite materials that [...]

This study is an analytical investigation of processabil-ity of biopolymer-carbon based nanofiller composites primarily through rheological investigation of samples. The composites were fabricated via dry mixing and melt-blending of biodegradable polylactide (PLA) and nanographite platelets (NGP) in a Brabender twin screw extruder. A range of different nanofiller contents (1, 3, 5, 7, and 10 wt %) were studied for NGP containing composites. The morphology was studied with X-ray diffraction and transmission electron microscopy techniques and showed poor dispersion, with agglomerates, tactoids, and exfoliated layers present. Mechanical properties showed an optimum at 3 wt %, filler. Results showed that the composites exhibited higher elastic and viscous moduli than neat PLA. The rheological percolation threshold predicted by changes in slope (α) as well as liquid-solid transition theory of samples was found around 3 wt %. through the change from liquid-like behavior to pseudo-solid-like behavior at terminal region during dynamic oscillatory measurements. NGP nanofillers were found to enhance the viscoelastic and mechanical properties of PLA at low concentrations; however, an efficient dispersion of nanofillers within polymer by melt intercalation method of mixing was not achieved. POLYM. ENG. SCI., 54:175-188, 2014. © 2013 Society of Plastics Engineers, INTRODUCTION In the production of bioplastics, biodegradable natural polymers extracted from renewable resources such as pol-ylactide (PLA), polycaprolactone (PCL), cellulose, and starch are considered a more suitable alternative than petroleum-derived [...]

Graphite sheets are commonly used in introductory physics laboratories to model electric potential patterns for systems such as dipoles and parallel plates. Usually, silvered ink pens are used to draw patterns on the sheets and appropriate voltages are then applied. Quantitative experiments are often done at the intermediate level. Students are often puzzled by the failure of the patterns to confirm to the theoretical figure in the manual that came with the kit. I discuss measuring difficulties and some of the common theoretical methods for analyzing edge effects on the sheets. [DOI: 10.1119/1.3212462]

The strong correlation between the density and the physical and mechanical properties of graphite suggests that the method of nondestructive density evaluation could be developed into a characterization technique of great value for the overall improvement of the safety of graphite moderator reactors. In this study, the oxidation-induced density changes in nuclear graphite for very high temperature reactor were determined by a conventional destructive bulk density measurement method (BM) and by a new nondestructive method based on acoustic microscopy and image processing (AM). The results were compared in order to validate the applicability of the latter method. For a direct comparison of the results from both measurements, two specimens were prepared from a cylindrical graphite sample (1 in. diameter and 1 in. height, oxidized to 10% weight loss at 973 K in air for 5 h). The specimens were used for characterization by BM and AM methods, respectively. The results show that, even with a large standard deviation of the AM, the density changing trend from both methods appeared the same. The present observation may be attributed to the fact that AM images reflect characteristic density changes of the graphite sample through the acoustic impedance changes. This study demonstrates the possibility of using AM as a nondestructive technique for the evaluation of density changes in graphite when a database is prepared through a systematic series of experiments. [DOI: 10.1115/1.3098415]

Graphite and carbon short fiber (copper coated) reinforced (2 wt %) hypereutectic Al--17% Si alloy composites were prepared by liquid metallurgy route. Room temperature friction and wear properties of as-cast hypereutectic Al--Si alloy reinforced with copper coated graphite and short carbon fibers were investigated. Friction and wear tests were conducted using a pin-on-disk machine under dry sliding conditions. The loads (contact pressure) and sliding velocities have been varied from 10 N to 50 N (contact pressure of 0.12-9.60 MPa) and 0.3 m/s to 1.2 m/s, respectively. The results reveal that the coefficient of friction and the wear rate of the hybrid composite are lower than that of the matrix alloy. The coefficient of friction of the matrix alloy and its hybrid composite decreased with increased load of up to 30 N and increased beyond this load. The wear rates of both the matrix alloy and its hybrid composite increased with the increasing load. However, at all the loads and sliding velocities studied, the developed hybrid composite exhibited a lower coefficient of friction and wear rates when compared with the matrix alloy. Keywords: sliding wear, electroless copper coating, graphite, short carbon fiber

Graphite at the nanoscale is modeled as a material system consisting of a stack of parallel plates buffered by an elastic material While the plates represent individual graphene sheets, the buffer material models the Van der Waals interaction between the graphene sheets. As such, the loading on graphite at the nanoscale is characterized by the membrane force, the bending moment, and the shear force in the graphene sheets. Cylindrical nanoindentation of graphite is analyzed by applying a special boundary element method that employs Green's function for multilayers with platelike interfaces. Because Green's function satisfies the traction-free surface, the interfacial displacement continuity and the interfacial traction discontinuity conditions, only the indentation surface area where the boundary condition is altered, are numerically discretized. Numerical results of cylindrical nanoindentation are presented. It is shown that the bending moment and the shear force in the graphene sheets are concentrated around the edge of contact, consistent with the singularities existing in the second and the third derivatives of the surface displacement in the reduced case of a semi-infinite homogeneous solid under cylindrical contact. Kinks of single, double, and triple joints are related to the bending moment, the shear force, and the concentrated force, respectively. [DOI: 10.1115/1.2999412] Keywords: boundary elements, contact mechanics, graphene, graphite, kink banding, Kirchhoff plate, membrane, multilayers, nanoindentation, singularity

In order to adequately simulate the behavior of a Hall-Heroult electrolysis ceil a finite element model must take into account the properties of each material forming the cell structure and those contained in it. However, there is some lack of full knowledge of the mechanical behavior of these materials, e.g., the long term viscoelastic (creep/relaxation) behavior of the carbon cathode. In this present paper, a three-dimensional viscoelastic model is devised and proposed, being ready to be implemented in a finite element code. This 3D viscoelastic model was developed from the thermodynamics of irreversible processes, where the selection of the model's internal variables was based on a phenomenological approach. The model has been developed at a particular reference state; therefore, the model parameters are represented by constant constitutive tensors. The model's particular parameters were identified for three different types of cathode carbon, i.e., semigraphitic, graphitic, and graphitized. Keywords: graphite, cathodes, rheology, mechanical properties, viscoelasticity

Titanium/silicon codoped hydrogenated carbon film is deposited on the n-Si (100) substrates by reactive magnetron sputtering Ti80Si20 target in a mixture of argon and methane and the microstructure of the films is examined. The studies have shown that the mechanisms including transfer films, friction-induced graphitization, hydrogen-terminated carbon surface, trichemical reaction, are responsible for the superlow friction in the ambient air.

An Ar-[C.sub.2][H.sub.2] expanding thermal plasma chemical vapor deposition (ETP-CVD) is employed to deposit hydrogenated amorphous carbon (a-C:H). The changes in the Ar/[C.sub.2][H.sub.2] gas flow ratio tuned by the gas residence time in the ETP expansion helped to define the chemistry of the ETP-CVD.

The application of sputtered thin film platinum (Pt) as a catalytic metal for graphene growth on metal is demonstrated. The relatively lower carbon solubility in Pt and the good surface roughness of the thin film Pt is found to facilitate the formation of a uniform monolayer graphene on Pt over the entire region of the thin film Pt/Si[O.sub.2]/Si substrate.

The size-dependent Young's modulus and carbon-carbon binding energy in a homologous series of graphene nanoribbons (GNRs), [C.sub.4n][2.sub.+6n+2][H.sub.6n+4] (n=2-12), by using electron first principles computations. Linearity between the binding energy and Young's modulus is observed and a quantitative-structure-property relationship is derived that has correlated Young's modulus to the total energy and the number of carbon atoms within the ribbon.

Nonlocal elasticity theory is implemented to analyze the vibration response of single-layered graphene (SLGS) sheets. The results have shown that the fundamental frequencies of SLGS are strongly dependent on the small scale coefficients and a nonlinear frequency response is seen for the SLGS with larger nonlocal effects and 'Winkler-type modeled' surrounding medium.

The structure, mechanical properties and friction properties of hydrogenated graphitelike carbon film and typical hydrogen diamondlike carbon film are examined. The hydrogenated graphitelike carbon film has shown excellent friction behavior due to the extraordinary structure of hydrogenated graphitelike carbon film.

Studies were conducted to examine the detailed geometrical structures of zigzag and armchair type single-walled carbon nanotubes (SWCNTs) with infinite tubular length. The optimized structures of the SWCNTs were found to show two C-C bond lengths that decrease with an increase in the tubular diameter.

The molecular mechanics calculations for in-plane stiffness, shear modulus, and the bending rigidity of single-walled carbon nanotubes are reported. The calculation results are based on interaction of the strain energy for carbon nanotubes and graphite sheets subjected to various types of loading.

The density functional theory (DFT) is used for examining the adsorption of silver and gold atoms and [M.sub.2], [M.sub.6] and [M.sub.13] (M = Ag or Au) clusters on the (0001) graphite surface. The results have shown that the clusters have avoided hollow sites on the graphite surface and that the metal atoms have favored atop and bond sites.