Electrical and mechanical properties of electrically conductive adhesives from epoxy,micro-silver flakes,and nano-hexagonal boron nitride particles after humid and thermal aging

In this study, we incorporated micro-silver flakes and nano-hexagonal boron nitride (BN) particles into a matrix resin to prepare electrically conductive adhesives (ECAs). The humid and thermal aging results under a constant relative humidity level of 85% at 85 °C revealed that the aged ECAs containing 3 wt% of nano-hexagonal BN particles had high reliability. The contact resistance was low and the shear strength high. Nano-hexagonal BN particles have a good effect on the reliability of ECAs that can be used to improve the properties of ECAs.     

Enhanced mechanical properties of glass fibre epoxy composites by 2D exfoliated graphene oxide filler

Graphene oxide (GO) received a significant attention in the scientific community due to their excellent mechanical properties identifying themselves as an alternative and combinatory to various other metals and composites. Though GO possess excellent strength, it was observed from the literature that graphene oxide consisting of hydroxyl group elements ensue in poor bonding. Thus reduced functional group density (rFGD) graphene is preferred which has an advantage of good bonding, alongside very small quantity as a filler is required to achieve the enhancement equivalent to graphene oxide which forms the novelty of the current work. In current case, 3, 6 and 9 wt% of rFGD is dispersed into E-glass fibre reinforced composite by traditional hand layup technique. The obtained results revealed that, the tensile, flexural and impact strength have shown superior enhancement with 3 and 6 wt% of rGO than neat E-glass epoxy (0 wt% rGO), whereas an asymptotic decrement is noticed at 9 wt% when tested with ASTM standards except for impact strength. The microstructural studies also indicated the proper adhesion and alignment of fibres without any agglomerations corroborate the enhancement of properties. These overall finding supports the suitability of the developed laminates for potential use in structural applications in aerospace industry.     

Tailoring the properties of spark plasma sintered SiAlON containing graphene nanoplatelets by using different exfoliation and size reduction techniques: Anisotropic mechanical and thermal properties

SiAlON ceramics are intensively used in different areas but still there is a need to improve the mechanical and thermal properties as well as ease of machinability and reduce the weight. In this study, the effect of graphene nanoplatelets (GNPs) exfoliation and dispersion techniques on the microstructure and properties of SiAlON ceramics were investigated. For this purpose, 2, 4 and 8 wt% GNPs were dispersed by using traditional sonication and newly proposed microfluidization techniques. Then, composites were densified in spark plasma sintering (SPS) furnace. Scanning electron microscope (SEM), x-ray diffraction analyses (XRD) and property measurements were performed in through-plane and in-plane directions. The microfluidization technique found to be more effective than sonication for the exfoliation, size reduction and homogenization of GNPs. Addition of GNPs prepared by both techniques increased the fracture toughness and in-plane direction thermal conductivity whereas decreased the hardness and through-plane direction thermal conductivity of the SiAlON.     

Investigation of thermal behaviour and mechanical property of the functionalised graphene oxide/epoxy resin nanocomposites

ABSTRACT

Graphite oxide (GO) and functionalised graphite oxide (FGO) were successfully prepared with -NH₂-terminated GO in the paper, and their chemical structures were characterised with Fourier transform infrared (FTIR), Energy-Dispersive X-ray Spectroscopy (EDS), UV spectrum analysis and XRD, their microstructures were researched by a scanning electron microscope (SEM) and a transmission electron microscope (TEM), and their thermal properties were characterised by TG. The result showed the carbon residue of FGO was 82.1% and the residual char of GO was 48%, the composite materials were prepared with curing for epoxy resin. The thermal stability, mechanical properties, and morphology after impacting tests of composite materials were investigated using thermogravimetric analysis, tensile and charpy impact tests and SEM. The result showed when the 0.2% FGO was filled into the epoxy, the tensile strength was 55.4?MPa, the impact strength was 17.3?KJ/m², the flexural strength was 82?MPa, and the flexural modulus was 2760?MPa. The mechanical properties of composite materials were higher than those of pure epoxy and improved the strength and toughness of epoxy nanocomposites.     

Mechanical,electrical, and thermal properties of graphene nanosheet/aluminum nitride composites

Graphene nanosheet (GNS)/aluminum nitride (AlN) composites were prepared by hot-pressing and effects of GNSs on their microstructural, mechanical, thermal, and electrical properties were investigated. At 1.49 vol% GNSs content, the fracture toughness (5.09 MPa m^1/2) and flexural strength (441 MPa) of the composite were significantly increased by 30.17% and 17.28%, respectively, compared to monolithic AlN. The electrical conductivity of the composites was effectively enhanced with the addition of GNSs, and showed a typical percolation behavior with a low percolation threshold of 2.50±0.4 vol%. The thermal conductivity of the composites decreased with the addition of GNSs.     

Directional properties and microstructures of spark plasma sintered aluminum nitride containing graphene platelets

Graphene platelets (GPLs) containing aluminum nitride (AlN) composites were produced by using both pressureless sintering and spark plasma sintering (SPS). Poor densifications were obtained when composites were pressureless sintered whereas highly dense composites were successfully produced by using SPS. In addition, the applied uniaxial load in the SPS resulted in the orientation of GPLs in the microstructure of composites, indicating that composites would have anisotropic properties. All the mechanical, thermal and electrical properties in the in-plane direction were better than the through-plane direction. Fracture toughness of composites with the addition of 1 wt% GPLs were increased more than 30% compared to AlN matrix. Increased anisotropic effect with increasing amount of GPLs led to even larger differences on the thermal conductivities in through-plane and in-plane directions. AlN also became an electrically conducting material after ∼1 wt% GPLs addition in both through-plane and in-plane directions.     

Enhanced mechanical,thermal and adhesion properties of polysilsesquioxane spheres reinforced epoxy nanocomposite adhesives

ABSTRACT

Epoxy-based systems serve as excellent adhesives to join a wide range of substrates such as metal, ceramics, plastics, etc. The mechanical properties of such systems can be improved considerably by the addition of filler to the epoxy matrix. Herein, polymethylsilsesquioxane (PMS) and poly(methyl/vinyl)silsesquioxane (PMVS) nanosphere were synthesised by hydrolytic condensation of oraganosilane as a precursor in aqueous phase. The epoxy nanocomposite adhesives were prepared by adding different weight percentages (1–4 wt%) of the PS nanospheres. Tensile and compressive strength of the adhesive formulations were studied using the universal testing machine (UTM) and it was observed that the mechanical properties of the composites showed an increasing trend on increasing the filler loading. Adhesive strength of the epoxy composites on mild steel substrate was studied by conducting the lap shear test and EPV-4 exhibited a 31% increase in adhesive strength on the mild steel compared to the neat epoxy. Surface morphology of the epoxy composites were visualised from the SEM images and the composites also showed enhanced thermal conductivity. Higher mechanical and adhesive strength indicates the potential of the prepared nanocomposites to be used as an effective formulation in adhesive-based systems.     

Effect of carbon nanoparticle reinforcement on mechanical and thermal properties of silicon carbide ceramics

This research presents an analysis of the influence of graphene reinforcement on the thermal and mechanical properties of silicon carbide ceramics, at 2.5% (wt%) graphene content. The SiC composites, containing various carbon nanofillers (graphene oxide and graphene nanoparticles), were sintered by the classical two stage spark plasma sintering method. Two current modes were used, the continuous mode and the pulsed current mode. The results from photothermal radiometry and investigations of the mechanical properties showed that graphene additives significantly improve the thermal properties and toughness of material, sintered from a SiC powder. An 45% growth in the toughness was observed, which increased from 1.21 to 1.75?MPa/m^1/2. The thermal diffusivity value also increased from 0.60 to 0.71?cm²/s and giving an improvement in thermal properties of 18%. The friction coefficient reached 7% giving an increase in value from 0.62 to 0.66. Microscopic investigations supported the photothermal radiometry (PTR) results. Whilst, thermal imaging revealed homogeneity of the local thermal properties of the products fabricated from the starting SiC powder.     

Mechanical properties of polybutadiene reinforced with octadecylamine modified graphene oxide

Octadecylamine-modified graphene-oxide (OMGO) polybutadiene nanocomposites with different OMGO loadings were prepared by solution mixing. The dispersion of OMGO in chloroform is greatly improved compared to GO. Toughness and elongation of PBD–OMGO nanocomposites increase by 332% and 191% respectively compared with pure PBD. However, Young's modulus of PBD–OMGO nanocomposite decreases by 10% at 2-wt% loading. Graphene sheet crumpling accounts for the increased toughness, the absence of modulus reinforcement and the absence of a Payne effect for PBD–OMGO. The oxidation susceptibility of PBD is greatly reduced after the addition of OMGO, which is particularly desirable in the tire industry.     

Post-curing process and visco-elasto-plastic behavior of two structural adhesives

The aim of this paper is to reveal original visco-elasto-plastic phenomena for two commercial epoxy adhesives (D609 and E20HP) subjected to uniaxial tension and compression. First, a post-curing heat treatment is proposed by means of thermal analyses in order to ensure stable mechanical properties. Bulk adhesive specimens are prepared to analyze the mechanical response of both materials. Monotonic tensile and compressive tests are carried out at different strain rates. Both adhesives exhibit first a linear elastic behavior but once a yield stress is reached, a visco-elasto-plastic behavior appears. Creep tensile tests are also carried out and confirm that strain rate phenomena take place and that non-negligible negative volumetric inelastic strains appear. Cyclic tests are also performed and reveal ratcheting effects. The applicability of the results to thin bondlines is discussed. The experimental observations must be taken into account in any model which aims at predicting accurately the behavior of the adhesives considered in this paper.     

The chemical,kinetic and mechanical characterization of tannin-based adhesives with different crosslinking systems

Network formation, cure characteristics and bonding performance of tannin-based resins were investigated in order to establish structure–property relationships between the stage B and stage C. Tannin–aldehyde and base-catalyzed autocondensed tannin resins were synthesized and characterized for molecular weight distribution, cure kinetics and cure chemistry by means of GPC, DMA and ¹³C CP/MAS NMR spectroscopy and solvent stability tests. The resins performance as wood adhesives was further established from lap-shear tests and microscopic observation of the bondline. Resins prepared with highly reactive aldehydes, such as formaldehyde or glyoxal, exhibited a significant extent of hetero-condensation reactions, fast cure kinetics, a high storage modulus and good solvent stability of the stage C-resin. In contrast, resins prepared with bulky aldehydes of low reactivity, such as citral, were dominated by autocondensation reactions, and exhibited slower cure kinetics, a lower storage modulus and solvent-stability of the stage C-resin, alike those neat autocondensed tannin resins. However, all resin systems fulfilled the standard requirements for wood adhesive bonding for interior applications. Additionally, storage modulus increase during cure was found to be a good predictor of the stiffness of the wood-bonded assembly, useful to discriminate between the autocondensation and heterocondensation cure chemistries.     

Silane-functionalized graphene oxide/epoxy resin nanocomposites: Dielectric and thermal studies

Improved dispersion of graphene oxide (GO) in the epoxy resin, as nanofiller, requires surface modification. Hence, functionalization of GO with small silane (GONSi) and bulky silane moieties (GOSi) has been carried out. Structural confirmation analysis of the prepared GO and modified forms have been performed using different analytical techniques. Cationic photocuring polymerization of pure aliphatic epoxy resin (CE) and loaded samples with GO, GOSi, or GONSi in amounts 0.5 and 1 wt % has been followed by FTIR. Loading of CE showed a passive effect for the modified filler on the conversion of the CE during photocuring, whereas the thermal stability of loaded epoxy resin is enhanced. Dielectric properties investigations revealed that the insulation feature of CE is not seriously reduced by the addition of GO or its modified forms. The secondary relaxation β process originating from the fluctuations of the side functional hydroxyl group can be described by the semi-empirical Cole–Cole function. The dielectric loss values are decreasing in the order GONSi > GOSi > GO > CE. Furthermore, it was found that the activation energy of the dynamic process is related to the conversion and to the ratio of the modified filler. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48253.     

Electrostatic self-assembly preparation of reduced graphene oxide-encapsulated alumina nanoparticles with enhanced mechanical properties of alumina nanocomposites

In this study, we employed facile self-assembly methods to synthesize reduced graphene oxide-encapsulated alumina (Al₂O₃/rGO) nanoparticles. The Al₂O₃/rGO nanoparticles were subsequently incorporated into an Al₂O₃ matrix as filler to prepare nanocomposites. The microstructural analysis showed that relatively thin rGO sheets were homogeneously dispersed in the matrix and bonded with the Al₂O₃ grains forming a three-dimensional rGO network structure. The specific structure caused the rGO sheets to be anchored and bound to the matrix grains, resulting in a high contact area between the rGO sheets and the matrix, whilst the fracture mode alteration, grain refinement and improved interfacial strength of the nanocomposites were related to the unique structure. The results indicated that the nanocomposites with 2.5?vol.% rGO exhibited outstanding mechanical properties, increasing both the flexural strength by 105%, with a maximum value of 636?MPa, and the fracture toughness by 90% (5.9?MPa?m^1/2) when compared with monolithic Al₂O₃.     

Enhanced mechanical and thermal properties of polyurethane/functionalised graphene oxide composites by in situ polymerisation

ABSTRACT

Isocyanate-functionalised graphene (iGO) was prepared and incorporated into a thermoplastic polyurethane via an in situ polymerisation. Firstly, graphene oxide was successfully modified using a mixture of isocyanate- and diisocyanate-containing compounds, leading to the formation of good dispersions of resulting functional graphene oxide in organic solvents, such as N,N-dimethylacetamide and N,N-dimethylformamide. The addition of iGO into polyurethane matrix improved both mechanical and thermal properties in the polyurethane/iGO composites relative to neat polyurethane. An addition of only 0.03?wt-% of functionalised graphene into the polyurethane increased Young’s modulus by 1.4 times and tensile strength by two times. Meanwhile, the elongation at break was similar to that of the neat polymer. In addition, dynamic mechanical analysis also confirmed the improvement in storage modulus of the polymer composites especially at high-temperature range. We believe that the developed modification approach for graphene oxide and polyurethane/graphene composites presented herein could be useful in polymer/graphene composite development.     

Effect of SiC whiskers and graphene nanosheets on the mechanical properties of ZrB2-SiCw-Graphene ceramic composites

Ultrahigh temperature ZrB₂-SiC_w-Graphene ceramic composites are fabricated by hot pressing ZrB₂-SiC_w-Graphene oxide powders at 1950 °C and 30 MPa for 1 h. The microstructures of the composites are characterized by Scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The results show that multilayer graphene nanosheets are achieved by thermal reduction of graphene oxide during sintering process. Compared with monolithic ZrB₂ materials, flexural strength and fracture toughness are both improved due to the synergistic effect of SiC whisker and graphene nanosheets. The toughening mechanisms mainly are the combination of SiC whisker and graphene nanosheets crack bridging, pulling out.     

Facile synthesis and thermal properties of waterglass-based silica xerogel nanocomposites containing reduced graphene oxide

In this study, new rGO-silica xerogel nanocomposites (SX-rGO) and its glass fiber reinforced composites (GFR-SX-rGO) were prepared, and its microstructure and thermal properties were evaluated. The raw material was a mixed dispersion prepared by adding 0.01–2.5?wt% of reduced graphene oxide (rGO) to waterglass (6% SiO₂). A hydrogel was prepared via sol-gel reaction of this raw material, which was then immersed in hydrochloric acid, hydrophobized in a siloxane/2-propanol reaction system, and then dried at ambient pressure to obtain a hydrophobic carbon-silica xerogel composite. The obtained samples were characterized by N₂ physisorption (at 77?K), solid ²⁹Si Magic angle spinning nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, thermogravimetric analysis, hydrophobicity, and thermal conductivity. It was found that as the amount of rGO was increased, the specific surface area of the nanocomposite decreased by ~25% from 535 to 403?cm²/g, and the average pore size and pore volume were almost halved. The thermal decomposition temperature of the SX-rGO was increased markedly by the addition of rGO. Moreover, the GFR-SX-rGO-0.5 showed low density (0.208?g/cm³), high contact angle (146°) and low thermal conductivity (0.0199?W/mK).     

Exploring the methods of synthesis,functionalization, and characterization of graphene and graphene oxide for supercapacitor applications

Graphene and graphene oxide, are attracting more attention over the last decades in the area of supercapacitor research and researchers concentrate on extensive exploration, owing to their dominating electrical conductivity, combined with mechanical properties. This review is a panoramic approach, giving insights into various aspects related to graphene and graphene oxide such as their properties, production methods, functionalities, and their applications in supercapacitors. The study ought to be beneficial to novice as well as to the domain experts. Various properties of both materials are explored and both synthesis methods are elaborated. Extra emphasis is given to bring out the role of graphene and graphene oxide in promoting the performance of supercapacitors. Synthesis methods are tabulated based on the evaluation metrics like specific capacitance and capacitance retention. Finally, the application of graphene and graphene oxide in supercapacitors are highlighted. Before concluding, perspectives along with challenges for further development are proposed and are expected to facilitate researchers in shedding light on further studies in this explorative area.     

Investigation of mechanical and thermal properties of nanostructure-doped bulk nanocomposite adhesives

ABSTRACT

In recent years, findings in nanoscience and nanotechnology have deeply influenced many disciplines including the material and mechanical sciences. Polymers including nanostructures have attracted attention as their adoptions in general engineering composites have yielded efficient results. In this study, three different two-component (epoxy-hardener) adhesives were doped with graphene nanoplatelets, graphene oxide nanoplatelets, carbon nanotube, and fullerene C60 at three different rates (0.5%, 1%, and 2% by weight) and the mechanical and thermal properties of the nanocomposite adhesives were examined. The nanocomposite adhesives’ mechanical properties were analyzed via tensile tests and thermal properties were analyzed via Differential Scanning Calorimeter (DSC) thermograms and Fourier Transform Infrared Spectroscopy (FT-IR) spectra. Results showed that doping nanostructures improve the stress-strain capacity of the adhesives. Both mechanical and thermal properties of the nanocomposite adhesives seem to change depending on the amount of nanostructure. Additionally, DSC and FT-IR curves showed an agreement with these improvements in the adhesives’ mechanical properties.     

Mechanical properties of graphene oxide reinforced alumina matrix composites

Graphene oxide (GO) reinforced alumina matrix composites have been fabricated by using graphene oxide synthesized by a modified Hummer's method. Samples were prepared by powder metallurgy and consolidated by Spark Plasma Sintering (SPS). The influence of GO addition on the microstructure and mechanical properties of the composites was investigated. Results show a significant increase (almost 35%) of the fracture toughness for composites containing 0.5 wt% graphene oxide compared to sintered pure alumina. In order to find reasons for this improvement Scanning/Transmission Electron Microscopy (SEM/TEM) observations were carried out. They reveal a good interface between the reinforcement and the matrix as well as such mechanisms like branching, deflection and bridging of crack propagation.