Multifunctional polypropylene composites produced by incorporation of exfoliated graphite nanoplatelets

The potential of using exfoliated graphite nanoplatelets, xGnP^TM, as a reinforcement that can produce multifunctional polymer composites was explored. xGnP-polypropylene (PP) composites fabricated by melt mixing using a twin-screw extruder followed by injection molding were investigated for their thermal, viscoelastic and barrier properties as a function of xGnP concentration and aspect ratio. These properties of the xGnP-PP composites were compared to the properties of composites made with PAN-based carbon fibers, VGCF, carbon black and nanoclay. Results indicate that when oriented properly, the xGnP will not only stiffen the composite but also reduce the coefficient of thermal expansion in two directions rather than in one as in the case of aligned fiber composites. Furthermore, the large aspect ratio of xGnP, even at low loadings, increases the oxygen barrier of PP at least as effectively as the commonly used nanoclays and finally, addition of xGnP significantly enhances the thermal conductivity of the polymer matrix.     

Thermal conductivity of ceramic/metal composites from preforms produced by freeze casting

Porous alumina and zirconia preforms, processed by ice templating, have been used to manufacture ceramic/metal composites by aluminium alloy infiltration. The aim of the present work is to study the influence of the ceramic material nature and of the initial porous structure on the thermal conductivity anisotropy of the composite in order to assess potential applications in the field of thermal management. The materials are characterised in terms of pore volume fraction and pore size before and after metal infiltration. The freeze casted preforms exhibit anisotropic lamellar structures with ellipsoidal pores ranging from 35 µm to 40 µm and porosity fractions from 64 to 67%. After metal infiltration, composite parts present the same anisotropic morphology, which correspond to alternating ceramic and metal layers. Thermal conductivities have been determined, with an average of 80 W m⁻¹ K⁻¹ and 13 W m⁻¹ K⁻¹ parallel and perpendicular to the freezing direction respectively, for zirconia/metal composites. Theoretical values of thermal conductivity can be calculated using the Maxwell-Eucken relation, to handle the residual porosity, in combination with series and parallel resistance models to describe the overall anisotropic character. These give good agreement to experiment.     

Pentadecane functionalized graphite oxide sheets as a tool for the preparation of electrical conductive polyethylene/graphite oxide composites

Covalent functionalization of pentadecane-decorated thermally reduced graphite oxide (GO) sheets has been studied as a tool for the preparation of polyethylene/GO composites exhibiting rheological and electrical percolation thresholds. It was accomplished through pentadecane based radical addition onto unsaturated bonds located on the GO sheets' surface using dicumyl peroxide as hydrogen abstractor. This chemical functionalization influences the affinity of the formed pentadecane grafted GO sheets for various solvents. Then, the compounding of the composites pentadecane grafted GO/PE was performed at a processing temperature of 140 °C with 25, 20, 15, 10, 8 and 5 wt% loadings. Rheological and electrical percolation thresholds were found between 10 and 15 wt% for polyethylene/pentadecane functionalized graphene oxide composites while the composite graphite/PE at the same loading percentage did not reach any percolation threshold.     

Exfoliated graphene sheets decorated with metal/metal oxide nanoparticles: Simple preparation from cation exchanged graphite oxide

We produced carbon hybrid materials of graphene sheets decorated with metal or metal oxide nanoparticles of gold, silver, copper, cobalt, or nickel from cation exchanged graphite oxide. Measurements using powder X-ray diffraction, transmission electron microscopy, and X-ray absorption spectra revealed that the Au and Ag in the materials (Au–Gr and Ag–Gr) existed on graphene sheets as metal nanoparticles, whereas Cu and Co in the materials (Cu–Gr and Co–Gr) existed as a metal oxide. Most Ni particles in Ni–Gr were metal, but the surfaces of large particles were partly oxidized, producing a core–shell structure. The Ag–Gr sample showed a catalytic activity for the oxygen reduction reaction in 1.0 M KOH aq. under an oxygen atmosphere. Ag–Gr is superior as a cathode in alkaline fuel cells, which should not be disturbed by the methanol cross-over problem from the anode. We established an effective approach to prepare a series of graphene-nanoparticle composite materials using heat treatment.     

Physical properties of graphite/aluminium composites produced by gas pressure infiltration method

Graphite/aluminium composites have been produced by means of gas pressure infiltration method. Two porous graphite preforms with a porosity of 10 and 13 vol%, respectively, have been infiltrated using either a commercially 99.85 pure aluminium or an AlSi7Mg alloy. Thermal expansion coefficient, electrical conductivity and flexural strength have been determined as a function of graphite preforms and metal matrices. To investigate the susceptibility of this composite system to thermal damage, specimens were thermally cycled between 60 and 300 °C up to 1020 cycles. Infiltrated graphites exhibited a significantly higher electrical conductivity (0.34-0.51 m/Ω mm²) compared to porous graphite preforms depending on graphite type and metal matrix. Thermal cycling did not influence electrical conductivity. The coefficients of thermal expansion of the composites were at least three times lower than for monolithic aluminium. Thermal cycling has reduced these values even more, most likely due to stress relaxation processes. The infiltration of porous graphite preforms with AlSi7Mg alloy or Al99.85 has increased the flexural strength of the composites resulting in values up to 105 MPa. The decrease in mechanical strength due to thermal cycling was about 10%.     

Nitroxide-functionalized graphene oxide from graphite oxide

A facile method for preparing functionalized graphene oxide single layers with nitroxide groups is reported herein. Highly oxidized graphite oxide (GO = 83.1%) was obtained, slightly modifying an improved Hummer’s method. Oxoammonium salts (OS) were investigated to introduce nitroxide groups to GO, resulting in a one-step functionalization and exfoliation. The mechanisms of functionalization/exfoliation are proposed, where the oxidation of aromatic alcohols to ketone groups, and the formation of alkoxyamine species are suggested. Two kinds of functionalized graphene oxide layers (GOFT1 and GOFT2) were obtained by controlling the amount of OS added. GOFT1 and GOFT2 exhibited a high interlayer spacing (d₀₀₀₁ = 1.12 nm), which was determined by X-ray diffraction. The presence of new chemical bonds C–N (∼9.5%) and O–O (∼4.3%) from nitroxide attached onto graphene layers were observed by X-ray photoelectron spectroscopy. Single-layers of GOFT1 were observed by HRTEM, exhibiting amorphous and crystalline zones at a 50:50 ratio; in contrast, layers of GOFT2 exhibited a fully amorphous surface. Fingerprint of GOFT1 single layers was obtained by electron diffraction at several tilts. Finally, the potential use of these materials within Nylon 6 matrices was investigated, where an unusual simultaneous increase in tensile stress, tensile strain and Young’s modulus was observed.     

Preparation and characterization of graphite oxide/polypyrrole composites

Graphite oxide (GO)/polypyrrole (PPy) composites (GPs) and 1,5-naphthalene disulfonic acid (1,5-NDA) doped GPs (1,5-NGPs) have been successfully synthesized via in situ polymerization of pyrrole on GO. The conductivity of 1,5-NGPs is as high as 7 S/cm, seven orders of magnitude higher than that of pristine GO. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show PPy “dressed” on the surface of GO layers, while Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirm the interaction between GO and PPy. The results of thermogravimetric analysis (TGA) and heat treatment at 1000 °C show that the “dressed” PPy on the surface of GO layers in GPs and 1,5-NGPs has effectively prevented the deflagration of GO.     

Azines from one-pot reaction of thiosemicarbazones

Thermolysis and/or microwave irradiation of thiosemicarbazones gave the corresponding isothiocyanates, which on addition of either activated nitriles or aldehydes furnished various types of azines. The mechanism was discussed. The structures of products were proved by MS, IR, NMR, and elemental analyses.     

Mechanical properties of polydicyclopentadiene/graphite nanosheet composites prepared by reaction injection moulding

Abstract

Polydicyclopentadiene (PDCPD)/expanded graphite nanosheets treated with silane coupling agent (TEG) composites were prepared by simulating reaction injection moulding. Studies on the mechanical and tribological properties of the composites were carried out. The results showed that TEG of low content had an effect on reinforcing the PDCPD matrix. The incorporation of TEG in PDCPD greatly decreased wear rates and slightly increased friction coefficients under both dry sliding and oil lubricated conditions. The SEM images of the worn surface revealed their wear mechanisms. Unfilled PDCPD was characterised by spalling, with adhesive wear being the major wear form. Polydicyclopentadiene composites were characterised by plastic deformation, fatigue microcracking, spalling and ploughing effect in dry sliding. The wear forms for PDCPD composites under oil lubricated condition were also complicated, and several wear forms such as adhesive, abrasive and fatigue wears co-existed.     

Monolayer graphene from graphite oxide

Graphene, a new carbon material, is attracting presently an increasing research interest. It stems from the unique electrical and mechanical properties of graphene predicted by theory. Experimental studies of graphene are, however, severely curtailed by a lack of an appropriate technique for its preparation. Mechanical cleavage of graphite proved to be ineffective, since it yields only very small (a few microns in size) particles of monolayer graphene. The rapidly developing approach based on chemical exfoliation of graphite produces large-area coatings composed primarily of arbitrarily oriented multilayer graphene particles. We have developed a technique for preparation of monolayer graphene sheets involving liquid exfoliation of crystalline graphite, which includes synthesis of graphite oxide by deep oxidation as an intermediate stage. Electron diffraction traces, as well as the variation of diffracted intensities with local orientation of graphene sheets, AFM, and HRTEM images testify to a remarkably good monolayer structure of the graphite oxide particles obtained by our technique. These results open a way to setting up high-efficiency production of monolayer graphene sheets appropriate for electrical and optical measurements and fabrication of structures for use in the field of applications.     

Electronic transport in composites of graphite oxide with carbon nanotubes

We show that the presence of electrically insulating graphite oxide (GO) within a single wall carbon nanotube (SWCNT) network strongly enhances electrical conductivity, whereas reduced graphite oxide, even though electrically conductive, suppresses electrical conductivity within a composite network with SWCNTs. Measurements of Young’s modulus and of Raman spectra strongly support our interpretation of the “indirect” role of the oxide groups, present in GO within the SWCNT-GO composite, through electronic doping of metallic SWCNTs.     

Preparation of two-dimensional graphite oxide modified chlorinated polyethylene rubber composites

<正>Herein,a two-dimentional graphite oxide (GO) modified chlorinated polyethylene rubber(CM) was utilized to prepare GO/CM composite. The vulcanization system which is suitable for this composite was     

氧化铝-氧化石墨烯复合材料制备及性能研究

采用超声溶剂热法制备氧化石墨烯-氧化铝复合材料,用于催化降解亚甲基蓝。结果表明,氧化石墨烯-氧化铝复合材料可作为光催化剂或吸附剂来去除有机染料污染物,氧化石墨烯的引入使氧化铝催化剂催化活性提高;当初始亚甲基蓝质量浓度为10 mg/L时,光照射335 min后亚甲基蓝的降解可达90%;降解率随初始亚甲基蓝质量浓度的增加而减小;氧化石墨烯-氧化铝具有很高的可见光催化活性和稳定性。     

Fiber reinforced nylon-6 composites produced by the reaction injection pultrusion process

Reaction injection pultrusion (RIP) combines the injection pultrusion process with reaction injection molding (RIM) techniques to yield one of the more novel methods of thermoplastic matrix pultrusion. An experimental set-up was designed and built to pultrude nylon-6 RIM material and continuous E-glassfiber. Well-impregnated nylon-6 composites with 66.5, 68.8, 71.1, and 73.3 vol% fiber were produced. Internal temperature profile within the die was recorded during the process, and physical properties of resulting composites were measured. This paper presents results of the effect of fiber content, die temperature profile and pulling speed variations on internal temperature profile, monomer conversion, and physical properties. The study showed that increasing pulling speed lowered both peak temperature and monomer conversion. Higher die temperatures accelerated the reaction, resulting in a higher exotherm, a higher peak temperature, and a higher monomer conversion within the range investigated. Shear strength, flexual strength, flexual modulus, and transverse tensile strength were proportional to monomer conversion. Flexual modulus increased with higher fiber content within the range observed. Data allow the proper combination of die temperature profile and pulling speed to be selected to achieve a desired level of monomer conversion and physical properties. Results of this study provide basic information required for product design with nylon-6 composites as well as tool design, selection of processing conditions, and quality control for the process.     

B4C/metal boride composites derived from B4C/metal oxide mixtures

This study examines the reactions occurring from room temperature to 2180 °C during the heating under argon of mixtures of B₄C and metal oxides, as well as the properties of the ceramic composites prepared by these reactions. The cations of the oxides investigated, belonged to the transition metal and to the lanthanide groups. The mixtures underwent solid-state reactions in the range between 1100 and 1900 °C. These reactions resulted in composites in which the metal borides and B₄C are the majority phases. The boron carbide/metal boride(s) mixtures resulted from these reactions exhibited a sintering aptitude significantly higher than that of pure boron carbide. The improvement in the sintering aptitude was proportional to the oxide content present in the initial mixture, up to an upper limit. B₄C/boride(s)-type composites, exhibiting bulk densities ≥97% TD, could be prepared for certain compositions by pressureless heating at 2180 °C. The ceramic parts prepared under these conditions are characterized by strength and hardness values similar to those determined for pure boron carbide.     

Microwave-assisted one-pot synthesis of metal/metal oxide nanoparticles on graphene and their electrochemical applications

An effective synthesis strategy of hybrid metal (PtRu)/metal oxide (SnO₂) nanoparticles on graphene nanocomposites is developed using a microwave-assisted one-pot reaction process. The mixture of ethylene glycol (EG) and water is used as both solvent and reactant. In the reaction system for the synthesis of SnO₂/graphene nanocomposite, EG not only reduces graphene oxide (GO) to graphene, but also results in the formation of SnO₂ facilitated by the presence of a small amount of water. On the other hand, in the reaction system for preparation of PtRu/graphene nanocomposites, EG acts as solvent and reducing agent for reduction of PtRu nanoparticles from their precursors and reduction of graphene from graphene oxide. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) characterizations confirm the feasibility of the microwave-assisted reaction system to simultaneously reduce graphene oxide and to form SnO₂ or PtRu nanoparticles. The as-synthesized SnO₂/graphene hybrid composites show a much higher supercapacitance than the pure graphene, and the as-prepared PtRu/graphene show much better electrocatalytic activity for methanol oxidation compared to the commercial E-TEK PtRu/C electrocatalysts.     

Chemically modified graphene sheets produced by the solvothermal reduction of colloidal dispersions of graphite oxide

Chemically modified graphene sheets are obtained through solvothermal reduction of colloidal dispersions of graphite oxide in various solvents. Reduction occurs at relatively low temperatures (120-200 °C). Reaction temperature, the self-generated pressure in the sealed reaction vessel and the reducing power of the solvent influences the extent of reduction of graphite oxide sheets to modified graphene sheets.     

Evolution from graphite to graphene elastomer composites

Elastomer composites have established a unique position among technologically important materials because of their extensive and potential applications. Considerable interest has been devoted to graphite derived elastomer composites, known as new generation materials, due to their exceptional electrical, mechanical and permeability properties. The discovery of graphene opened a promising aspect towards the synthesis of elastomer nanocomposites. A thorough investigation of the properties of various graphitic fillers, such as natural graphite flakes, expanded graphite (EG), graphite nanoplatelets (GNP) and graphene is undertaken in this review. The dependence of these fillers on the rheological, electrical (sensing), mechanical, thermal, dielectric and barrier properties of elastomer composites is discussed, giving special emphasis to particle size and mode of interactions with the matrix. A systematic evolution from microcomposites to nanocomposites is shown to give definitive evidence of the importance of graphene nanocomposites. Most preparation methods of these composites are covered, including, solution blending, latex compounding, in situ polymerization, and melt intercalation. Graphene exhibits very good dispersion in most elastomers and substantially improves the mechanical and electrical properties of the matrix compared to all other graphite derivative composites. A review of the potential applications of these composites and current challenges is provided in order to guide future progress on the development of more promising materials.     

Active centres produced in graphite by powdering

Structural defects are evidently introduced into graphite by powdering in a ball-mill. They have a considerable reactivity to oxygen and can also provide sites at which impurities such as potassium and halogens may be incorporated into the structure to produce an accelerating or an inhibiting effect on combustion. Electron spin resonance examination has shown that the number of unpaired electrons formed during the powdering process is quite small. The observed effects might be accounted for if ball-milling introduces new dislocations into the solid or causes damage to those already present. The mechanical damage centres can be removed progressively by annealing.