Investigation of mechanical properties of graphene decorated with graphene quantum dot-reinforced epoxy nanocomposite

In this investigation, the mechanical properties such as compression, impact, and flexural properties of graphene decorated with graphene quantum dots (GDGQD) epoxy composites with concentration of GDGQD ranging from 0.25 to 1 wt % were studied. Ideal mechanical properties are obtained by systematically varying the filler weight in the epoxy matrix. The morphological studies of GDGQD have been characterized using transmission electron microscope, X-ray diffraction, and Fourier transform infrared technique. The compression, impact, and flexural strengths were enhanced effectively by the GDGQD loading. With the addition of 0.75 wt % of GDGQD, the compressive strength, compressive modulus, flexural strength, and flexural modulus of the composites were improved by 22, 29, 31, and 63%, respectively. Also an improvement in impact strength of 102% for 0.75 wt % GDGQD epoxy sample was also obtained. Examination of fractured test specimens was performed with scanning electron microscope. The enhancement in the mechanical properties is due to the better stress transfer that is attributed by enhanced interfacial bonding between GDGQDs and the epoxy. Using the GDGQD aspect ratio in the two-dimensional randomly oriented filler modified Halpin–Tsai model, the theoretical flexural modulus for the GDGQD/epoxy composites has been established. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48680.     

Toughening of trifunctional epoxy system. V. Structure–property relationships of neat resin

This work presents an investigation into the structure–property relationships of a cured highly crosslinked epoxy/amine resin system. The mechanical, physical, and thermal properties of the cured and postcured networks were measured and compared to the chemical structures. Crosslink density was shown to be dependent upon secondary amine conversion and it determined the glass transition temperatures, water uptake, density, toughness, and compressive strength. Other properties such as compressive modulus and yield stress were determined by more short‐range molecular motions. Curing at a temperature of 150°C was shown to be the minimum temperature required to “completely” cure the network and achieve optimum mechanical, physical, and thermal properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 237–248, 2000     

Synthesis,fabrication, mechanical,electrical, and moisture absorption study of epoxy polyurethane–jute and epoxy polyurethane–jute–rice/wheat husk composites

Bisphenol‐C‐epoxy‐toluene diisocyanate polyurethane (PEBCT) has been synthesized and used for the fabrication of jute, jute–rice husk (JRH), and jute–wheat husk (JWH) composites. The composites have been fabricated by hand lay‐up technique under a hydraulic pressure of 30.4 MPa at 135°C for 2.5 h. PEBCT‐J, PEBCT‐JRH, and PEBCT‐JWH possess respectively, tensile strength of 37.4, 9.5, and 14.7 MPa, and flexural strength of 39.6, 12.9, and 21.3 MPa, electric strength of 1.3, 1.8, and 1.9 kV/mm and volume resistivity of 1.40 × 10¹³, 1.84 × 10¹³, and 1.91 × 10¹³ ohm cm. Tensile strength and flexural strength have decreased, while electric strength and volume resistivity are improved upon hybridization. PEBCT‐JWH has better interfacial bond strength and stiffness as compared to PEBCT‐JRH. Moisture uptake behavior of PEBCT‐J in water, 10% HCl and 10% NaCl at room temperature is quite different. Equilibrium moisture content of PEBCT‐J in 10% NaCl (5.5%) is almost half of those in water (11.3%) and 10% HCl (13.6%) environments. Equilibrium time for saline environment is also comparatively low. Equilibrium moisture uptake in boiling water has increased 1.84 times, while equilibrium time has decreased 15.3 times. The composites may be useful for low load bearing in construction industries and for marine applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Viscoelastic and mechanical characterization of graphene decorated with graphene quantum dots reinforced epoxy composites

The article explores viscoelastic and mechanical property analysis of graphene decorated with graphene quantum dots (GDGQD) reinforced epoxy composite. Tensile, nanoindentation, and nano-dynamic mechanical analysis (DMA) tests were conducted on the composite with 0 to 1 wt% filler variation (an interval of 0.25 wt% maintained). The hardness and elastic modulus for two different loading conditions under a frequency range of 10 to 250 Hz were performed. The viscoelastic properties described through loss tangent and storage modulus graphically and the various factors such as modulus and depth of penetration were influenced by force frequency and mobility of the molecular chain. The results revealed the role of GDGQDs as filler material for enhancing the nanomechanical and tensile properties of the epoxy matrix. The differences in the properties can be ascribed to the filler interfacial bonding with the polymer matrix at the molecular level. The macro-level properties like tensile properties following the same trend as that of the micro-level properties like nano-indentation and nano-DMA results. Further, with the GDGQD aspect ratio, and assuming three-dimensionally filled randomly orientation of filler, the Halpin-Tsai model was satisfied with the experimental tensile modulus values.     

Preparation and properties of TiO2‐filled poly(acrylonitrile‐butadiene‐styrene)/epoxy hybrid composites

Poly (acrylonitrile‐butadiene‐styrene) (ABS) was used to modify diglycidyl ether of bisphenol‐A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO₂ reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS‐cured epoxy/ABS/TiO₂ hybrid composites systems have two T_gs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO₂ particles. The addition of TiO₂ induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO₂ filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO₂ components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO₂ are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and properties of MWCNTs/poly(acrylonitrile‐ styrene‐butadiene)/epoxy hybrid composites

Poly(acrylonitrile‐styrene‐butadiene) (ABS) was used to modify diglycidyl ether of bisphenol‐A (DGEBA) type epoxy resin, and the modified epoxy resin was used as the matrix for making multiwaled carbon tubes (MWCNTs) reinforced composites and were cured with diamino diphenyl sulfone (DDS) for better mechanical and thermal properties. The samples were characterized by using infrared spectroscopy, pressure volume temperature analyzer (PVT), thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), thermo mechanical analyzer (TMA), universal testing machine (UTM), and scanning electron microscopy (SEM). Infrared spectroscopy was employed to follow the curing progress in epoxy blend and hybrid composites by determining the decrease of the band intensity due to the epoxide groups. Thermal and dimensional stability was not much affected by the addition of MWCNTs. The hybrid composite induces a significant increase in both impact strength (45%) and fracture toughness (56%) of the epoxy matrix. Field emission scanning electron micrographs (FESEM) of fractured surfaces were examined to understand the toughening mechanism. FESEM micrographs reveal a synergetic effect of both ABS and MWCNTs on the toughness of brittle epoxy matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Temperature effects on rigid nano‐silica and soft nano‐rubber toughening in epoxy under impact loading

The rigid nano‐silica and soft nano‐rubber toughening effects on neat epoxy under impact loading in a range of ?50 to 80 °C were investigated. Nanosilica particles (20 nm) toughened neat epoxy at all temperatures with a maximum toughening efficiency at ?50 °C and lower efficiency at elevated temperatures. In contrast, except at ?50 °C, nano‐rubber particles (100 nm) showed the deterioration effect on the impact fracture toughness of epoxy resin. Scanning electron microscopy examinations revealed that the crack pinning and local epoxy deformation induced by rigid particles in term of nano‐silica/epoxy and nano‐rubber/epoxy interfacial debonding (at ?50 °C) led to positive toughening efficiency on neat epoxy. However, at 20 and 80 °C, the rubber cavitations/void plastic growth was significantly suppressed under the impact loading, which led to the negative toughening efficiency on epoxy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45319.     

Mechanical,thermal, and hydrophobic properties of silica aerogel–epoxy composites

Epoxy composites were prepared with different contents of hydrophobic silica aerogel particles to investigate their mechanical, thermal, and hydrophobic properties. The composites, particularly the one containing 1 wt % silica aerogel, showed remarkable toughness and yielding behaviors compared to neat epoxy, with its brittle behavior. As the content of silica aerogel increased, the thermal properties of the composites (e.g., thermal conductivity and thermal stability) improved. This was due to the very low thermal conductivity and high thermal stability of the silica aerogel particles. Moreover, the use of the hydrophobic silica aerogel led to the development of composites with hydrophobic properties. To examine the hydrophobicity more deeply, a series of water‐uptake tests were performed, and the results show that the composite with 3 wt % silica aerogel absorbed 50% less water than the neat epoxy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45706.     

Mechanical properties–morphology relationships in nano‐/microstructured epoxy matrices modified with PEO–PPO–PEO block copolymers

Epoxy‐based blends containing poly(ethylene oxide)‐co‐poly(propylene oxide)‐co‐poly(ethylene oxide) (PEO–PPO–PEO) block copolymers with different PEO/PPO molar ratios have been investigated in order to analyze the effect of the generated morphologies and interactions between components on the mechanical properties of the blends. Mechanical, morphological and dynamic mechanical analyses indicate that the observed increase of flexural modulus can be related to the decrease of free volume. In modified systems that remain miscible, an increase of flexural modulus, strength and fracture toughness can be observed. Also, macrophase‐ and microphase‐separated systems show an increase of fracture toughness but not of flexural modulus and strength at low contents of block copolymers. Copyright © 2007 Society of Chemical Industry     

Development of high Tg epoxy resin and mechanical properties of its fiber‐reinforced composites

A new epoxy resin with high glass transition temperature (T_g) (～ 180°C) and a viscosity low enough for infiltration into dry reinforcements at 40°C was developed for the vacuum‐assisted resin transfer molding process. To study the curing behavior and viscosity, several blends were formulated using multifunctional resin, aromatic hardener, and reactive diluents. Effects of these components on the viscosity and T_g were investigated by thermomechanical analysis, dynamic scanning calorimetry, and rheometer. Experimental results showed that a liquid aromatic hardener and multifunctional epoxy resin should be used to decrease the viscosity to <1 Pa·s at 40°C. Moreover, the addition of a proper reactive diluent decreased the viscosity and simultaneously minimized the deterioration of T_g. Mechanical properties of the composite produced with the optimized blend were evaluated at both room‐temperature and high‐temperature conditions. According to the results, the composite showed comparable mechanical properties with that of the current commercial resin. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Morphology and thermal/mechanical properties of alkyl‐imidazolium‐treated rectorite/epoxy nanocomposites

A novel organic rectorite (OREC) was prepared by treating the natural sodium‐rectorite (Na‐REC) with ionic liquid 1‐hexadecyl‐3‐methylimidazolium bromide ([C₁₆mim]Br). X‐ray diffraction (XRD) analysis showed that the interlayer spacing of the OREC was expanded from 2.23nm to 3.14nm. Furthermore, two types of OREC/epoxy nanocomposites were prepared by using epoxy resin (EP) as matrix, 2‐ethyl‐4‐methylimidazole (2‐E‐4‐MI) and tung oil anhydride (TOA) as curing agents, respectively. XRD and transmission electron microscope (TEM) analysis showed that the intercalated nanocomposite was obtained with addition of the curing agent 2‐E‐4‐MI, and the exfoliated nanocomposite was obtained with addition of the curing agent TOA when the OREC content was less than 2 wt %. For the exfoliated nanocomposite, the mechanical and thermal property tests indicated that it had the highest improvement when OREC content was 2 wt% in EP. Compared to pure EP, 60.3% improvement in tensile strength, 26.7% improvement in bending strength, 34% improvement in bending modulus, 14°C improvement in thermal decomposition temperature (T_d) and 5.7°C improvement in glass transition temperature (T_g) were achieved. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Microstructural and mechanical characteristics of graphene oxide-fly ash cenosphere hybrid reinforced epoxy resin composites

An experimental investigation into the influence of incorporation of graphene oxide (GO) and fly ash cenospheres (FACs) on the mechanical properties of epoxy resin (EP) composites. Two fillers were studied: GO-FAC hybrid and single GO. The GO-FAC hybrid was synthesized using a solution blending method, and characterized by FTIR, XRD, and scanning electron microscope (SEM). The modified EP composite specimens were prepared by adding different contents of GO and GO-FAC hybrid. The investigation showed that the FACs were successfully carried on the GO layer. The experimental data indicated that the addition of GO-FAC hybrid effectively improved the tensile property and the wear resistance of the EP composites, superior to the addition of single GO samples. The best tensile properties and lowest wear rate of EP composites were obtained when the hybrid content was 0.5 wt %. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47173.     

Synthesis and characterization of bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane/epoxy/glass fiber composites

Bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane was prepared by treating CNBr with bis(4‐hydroxy‐3,5‐dimethylphenyl)anisylmethane and blended with commercial epoxy resin in different ratios and cured at 120°C for 2 h, 180°C for 1 h, and postcured at 220°C for 1 h using diamino diphenyl methane as curing agent. Castings of neat resin and blends were prepared and characterized. The composite laminates were also fabricated with glass fiber using the same composition. The tensile strength of the composites increased with increase in cyanate content (3, 6, and 9%) from 322 to 355 MPa. The fracture toughness values also increased from 0.7671 kJ/m², for neat epoxy resin, to 0.8615 kJ/m², for 9% cyanate ester‐modified epoxy system. The 10% weight loss temperature of pure epoxy (358°C) was increased to 390°C by the incorporation of cyanate ester resin. The incorporation of cyanate ester up to 9% in the epoxy resin increases the T_g from 143 to 147°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation,morphology, and properties of silane‐modified MWCNT/epoxy composites

Both epoxy resin and acid‐modified multiwall carbon nanotube (MWCNT) were treated with 3‐isocyanatopropyltriethoxysilane (IPTES). Scanning electron microscopy (SEM) and transmission electronic microscope (TEM) images of the MWCNT/epoxy composites have been investigated. Tensile strength of cured silane‐modified MWCNT (1.0 wt %)/epoxy composites increased 41% comparing to the neat epoxy. Young's modulus of cured silane‐modified MWCNT (0.8 wt %)/epoxy composites increased 52%. Flexural strength of cured silane‐modified MWCNT (1.0 wt %)/epoxy composites increased 145% comparing to neat epoxy. Flexural modulus of cured silane‐modified MWCNT (0.8 wt %)/epoxy composites increased 31%. Surface and volume electrical resistance of MWCNT/epoxy composites were decreased with IPTES‐MWCNT content by 2 orders and 6 orders of magnitude, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphology and mechanical properties of unidirectional sisal– epoxy composites

Plant fibers are of increasing interest for use in composite materials. They are renewable resources and waste management is easier than with glass fibers. In the present study, longitudinal stiffness and strength as well as morphology of unidirectional sisal–epoxy composites manufactured by resin transfer molding (RTM) were studied. Horseshoe‐shaped sisal fiber bundles (technical fibers) were nonuniformly distributed in the matrix. In contrast to many wood composites, lumen was not filled by polymer matrix. Technical sisal fibers showed higher effective modulus when included in the composite material than in the technical fiber test (40 GPa as compared with 24 GPa). In contrast, the effective technical fiber strength in the composites was estimated to be around 400 MPa in comparison with a measured technical fiber tensile strength of 550 MPa. Reasons for these phenomena are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2358–2365, 2002     

Mechanical properties of graphene nanoplatelet/epoxy composites

Because of their high‐specific stiffness, carbon‐filled epoxy composites can be used in structural components in fixed‐wing aircraft. Graphene nanoplatelets (GNPs) are short stacks of individual layers of graphite that are a newly developed, lower cost material that often increases the composite tensile modulus. In this work, researchers fabricated neat epoxy (EPON 862 with Curing Agent W) and 1–6 wt % GNP in epoxy composites. The cure cycle used for this aerospace epoxy resin was 2 h at 121°C followed by 2 h at 177°C. These materials were tested for tensile properties using typical macroscopic measurements. Nanoindentation was also used to determine modulus and creep compliance. These macroscopic results showed that the tensile modulus increased from 2.72 GPa for the neat epoxy to 3.36 GPa for 6 wt % (3.7 vol %) GNP in epoxy composite. The modulus results from nanoindentation followed this same trend. For loadings from 10 to 45 mN, the creep compliance for the neat epoxy and GNP/epoxy composites was similar. The GNP aspect ratio in the composite samples was confirmed to be similar to that of the as‐received material by using the percolation threshold measured from electrical resistivity measurements. Using this GNP aspect ratio, the two‐dimensional randomly oriented filler Halpin–Tsai model adjusted for platelet filler shape predicts the tensile modulus well for the GNP/epoxy composites. Per the authors' knowledge, mechanical properties and modeling for this GNP/epoxy system have never been reported in the open literature. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Poly(methyl methacrylate)–epoxy vitrimer composites

In this study, we synthesized poly(methyl methacrylate) (PMMA) epoxy vitrimer composites by doping methyl methacrylate (MMA) and benzoyl peroxide into a curing system of epoxy resin and citric acid. The vitrimer composites were characterized with dynamic mechanical thermal analysis, scanning electron microscopy, and stress‐relaxation and lap‐shear testing. The test results show that with increasing amount of MMA, the existence of PMMA in the epoxy vitrimer matrix in the form of intermiscible, slightly soluble, and phase separation became more evident. When the doping amount of PMMA reached 10–25 wt %, the bonding strength of the PMMA–epoxy vitrimer composites was about two times that of the epoxy vitrimer (from 2.3 to 4.3 MPa). This showed that the self‐healing strength of the vitrimer composites was better than that of the pure vitrimer. When the PMMA in the epoxy matrix was in a slightly soluble form, the linear PMMA improved the mechanical properties of the epoxy vitrimer by physical winding. At the same time, the doping of PMMA promoted the transesterification rate of the epoxy vitrimer and enhanced the bonding strength of the composites without lowering the epoxy vitrimer glass‐transition temperature. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46307.     

Dynamic mechanical properties of polystyrene–aluminum nitride composite

A composite of aluminum nitride (AlN) particles dispersed around polystyrene matrix particles was synthesized in this study. The purpose of using this microstructure is to improve the thermal properties of a polymer at a low filler content with a minimal increase in the dielectric constant of the polymer composite to meet the material requirements for electronic packaging. The dynamic mechanical properties of this type of polystyrene–AlN composite were investigated here. The experimental results indicate that the dynamic mechanical property of the polystyrene–AlN composite is a function of the polystyrene particle size, AlN filler concentration, and temperature under this dispersion state. The addition of an AlN concentration into polystyrene increases both the storage modulus and the α‐transition temperature. The smaller polystyrene particle size gives a higher storage modulus and damping peak. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1348–1353, 2000     

Flame retardant and mechanical properties of epoxy composites containing APP−PSt core−shell microspheres

Ammonium polyphosphate (APP)–polystyrene (PSt) core–shell microspheres (CSPs) were synthesized via in situ radical polymerization. The core–shell structure was confirmed by transmission electron microscope (TEM). The results of optical contact angle measurements demonstrated a significant improvement in hydrophobicity of the modified APP. The obtained APP–PSt CSPs were added into epoxy (EP) system with various loadings. Effects of CSP on flame retardancy, thermal properties, heat release rate (HRR), smoke production, and mechanical properties of EP/CSP composites were investigated by limiting oxygen index (LOI), UL‐94 tests, thermogravimetric analysis (TGA), cone calorimeter, and tensile test. LOI and UL‐94 indicated that CSP remarkably improved the flame retardancy of EP composites. TGA showed that the initial decomposition temperature and the maximum‐rate decomposition temperature decreased, whereas residue yields at high temperature increased with the incorporation of microspheres. Cone calorimetry gave evidence that HRR, peak release rate, average HRR, and smoke production rate of EP/CSP composites decreased significantly. The morphology of char residues suggested that CSP could effectively promote EP to form high‐quality char layer with compact outer surface and swollen inner structure. Tensile strength of EP was enhanced with the addition of CSP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40218.