Epoxy/p‐phenylenediamine functionalized graphene oxide composites and evaluation of their fracture toughness and tensile properties

In an attempt to enhance the mechanical properties of epoxy/graphene‐based composites, the interface was engineered through the functionalization of graphene oxide (GO) sheets with p‐phenylenediamine; this resulted in p‐phenylenediamine functionalized graphene oxide (GO–pPDA). The morphology and chemical structure of the GO–pPDA sheets were studied by spectroscopic methods, thermal analysis, X‐ray diffraction, and transmission electron microscopy. The characterization results show the successful covalent functionalization of GO sheets through the formation of amide bonds. In addition, p‐phenylenediamine were polymerized on graphene sheets to form crystalline nanospheres; this resulted in a GO/poly(p‐phenylenediamine) hybrid. The mechanical properties of the epoxy/GO–pPDA composite were assessed. Although the Young's modulus showed improvement, more significant improvements were observed in the strength, fracture strain, and plane‐strain fracture toughness. These improvements were attributed to the unique microstructure and strong interface between GO–pPDA and the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43821.     

Thermal and mechanical properties of liquid silicone rubber composites filled with functionalized graphene oxide

To improve the thermal and mechanical properties of liquid silicone rubber (LSR) for application, the graphene oxide (GO) was proposed to reinforce the LSR. The GO was functionalized with triethoxyvinylsilane (TEVS) by dehydration reaction to improve the dispersion and compatibility in the matrix. The structure of the functionalized graphene oxide (TEVS‐GO) was evaluated by Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, X‐ray diffraction (XRD), and energy dispersive X‐ray spectroscopy (EDX). It was found that the TEVS was successfully grafted on the surface of GO. The TEVS‐GO/LSR composites were prepared via in situ polymerization. The structure of the composites was verified by FTIR, XRD, and scanning electron microscopy (SEM). The thermal properties of the composites were characterized by TGA and thermal conductivity. The results showed that the 10% weight loss temperature (T₁₀) increased 16.0°C with only 0.3 wt % addition of TEVS‐GO and the thermal conductivity possessed a two‐fold increase, compared to the pure LSR. Furthermore, the mechanical properties were studied and results revealed that the TEVS‐GO/LSR composites with 0.3 wt % TEVS‐GO displayed a 2.3‐fold increase in tensile strength, a 2.79‐fold enhancement in tear strength, and a 1.97‐fold reinforcement in shear strength compared with the neat LSR. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42582.     

Mechanical and thermal properties of biphenyldiol formaldehyde resin/gallic acid epoxy composites enhanced by graphene oxide

In this study, the gallic acid‐based epoxy resin (GA‐ER) and alkali‐catalysed biphenyl‐4,4′‐diol formaldehyde resin (BPFR) are synthesized. Glass fibre‐reinforced GA‐ER/BPFR composites are prepared. Graphene oxide (GO) is used to improve the mechanical and thermal properties of GA‐ER/BPFR composites. Dynamic mechanical properties and thermal, mechanical, and electrical properties of the composites with different GO content are characterized. The results demonstrate that GO can enhance the mechanical and thermal properties of the composites. The glass transition temperature, T_g, of the BPFR/GA‐ER/GO composites is 20.7°C higher than the pure resin system, and the 5% weight loss temperature, T_d5, is enhanced approximately 56.6°C. When the BPFR: GA‐ER mass ratio is at 4 : 6 and GO content is 1.0–1.2 wt %, the tensile and impact strengths of composites are 60.97 MPa and 32.08 kJ/m² higher than the pure resin composites, respectively. BPFR/GA‐ER composites have better mechanical properties, and can replace common BPA epoxy resins in the fabrication of composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42637.     

Effect of Dodecyal Amine Functionalized Graphene on the Mechanical and Thermal Properties of Epoxy‐Based Composites

Simultaneous surface functionalization and reduction of graphene oxide (GO) was achieved by using dodecyl amine (DA) as surface modifying agent. The DA modified reduced GO (DA‐G) was used for subsequent preparation of DA‐G/epoxy composites by solution mixing. Fourier transform infrared spectroscopy analysis, X‐ray diffraction (XRD) and electrical conductivity measurements were conducted to establish the concurrent functionalization and reduction of GO. The effect of DA‐G on the epoxy composites at 0 to 0.75 wt% loadings was studied by investigating its static and dynamical mechanical properties. XRD study was performed to verify the dispersion of DA‐G in the epoxy polymer. Field emission scanning electron microscopy was used to investigate the fracture surface morphology of the composites and Transmission electron microscopy was employed to further confirm the dispersion of DA‐G in the matrix. It was found that the tensile strength of the composite was increased by 38.8% with the addition of 0.5 wt% of DA‐G. The good adhesion/interaction between DA‐G and epoxy resulted in the increase of storage modulus; however, glass transition temperature (T_g) value of the composites shifted to lower temperature in comparison to the neat epoxy. Thermogravimetric analysis showed small decrease in onset degradation temperature for the composites as compared to neat epoxy except for the composites containing 0.75 wt% of DA‐G. POLYM. ENG. SCI., 56:1221–1228, 2016. © 2016 Society of Plastics Engineers     

Characterization and performance of dodecyl amine functionalized graphene oxide and dodecyl amine functionalized graphene/high‐density polyethylene nanocomposites: A comparative study

Dodecyl amine (DA) functionalized graphene oxide(DA‐GO) and dodecyl amine functionalized reduced graphene oxide (DA‐RGO) were produced by using amidation reaction and chemical reduction, then two kinds of well dispersed DA‐GO/high‐density polyethylene (HDPE) and DA‐RGO/HDPE nanocomposites were prepared by solution mixing method and hot‐pressing process. Thermogravimetric, X‐ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, X‐ray diffractions, and Raman spectroscopy analyses showed that DA was successfully grafted onto the graphene oxide surface by uncleophilic substitution and the amidation reaction, which increased the intragallery spacing of graphite oxide, resulting in the uniform dispersion of DA‐GO and DA‐RGO in the nonpolar xylene solvent. Morphological analysis of nanocomposites showed that both DA‐GO and DA‐RGO were homogeneously dispersed in HDPE matrix and formed strong interfacial interaction. Although the crystallinity, dynamic mechanical, gas barrier, and thermal stability properties of HDPE were significantly improved by addition of small amount of DA‐GO or DA‐RGO, the performance comparison of DA‐GO/HDPE and DA‐RGO/HDPE nanocomposites indicated that the reduction of DA‐GO was not necessary because the interfacial adhesion and aspect ratio of graphene sheets had hardly changed after reduction, which resulting in almost the same properties between DA‐GO/HDPE and DA‐RGO/HDPE nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39803.     

Interface engineering for the improvement of mechanical and thermal properties of covalent functionalized graphene/epoxy composites

Functionalized reduced graphene oxide (GO)/epoxy composites are fabricated through solution mixing. GO is functionalized using 3‐amino‐1,2,4‐triazole (TZ) in presence of potassium hydroxide (KOH). KOH is expected to serve dual role as catalyst for nucleophilic addition reaction between GO and TZ, and also as reducing agent. The grafting of TZ moiety on GO is confirmed by Fourier transform infrared spectroscopy, X‐ray diffraction, and thermogravimetric analysis. The prepared composites show remarkable improvement in mechanical and thermal stability. The fracture toughness of the composites (critical stress intensity factor, K_IC) achieved from single edge notched bending testing is improved by ～111% against pure epoxy at 0.1 wt % loading of TZ functionalized GO. Further, the tensile strength and Young's modulus are improved by ～30.5% and 35%, respectively. Thermal stability of the composites as investigated by thermogravimetric analysis showed 29 °C rise in onset degradation temperature for 0.1 wt % TZ functionalized GO incorporated composite. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46124.     

Influence of structure of amines on the properties of amines‐modified reduced graphene oxide/polyimide composites

Graphene oxide (GO), as an important precursor of graphene, was functionalized using alkyl‐amines with different structure and then reduced to prepare reduced amines grafted graphene oxide (RAGOs) by N₂H₄ · H₂O. The successful chemical amidation reaction between amine groups of alkyl‐amines and carboxyl groups of GO was confirmed by Fourier transform infrared (FTIR), X‐ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA). Then RAGOs/polyimide nanocomposites were prepared via in situ polymerization and thermal curing process with different loadings of RAGOs. The modification of amine chains lead to homogenous dispersion of RAGOs in the composites and it formed strong interfacial adhesion between RAGOs and the polymer matrix. The mechanical and electrical properties of polyimide (PI) were significantly improved by incorporation of a small amount of RAGOs, the influence of structure of amines grafted on RAGOs on the enhancement effects of composites was discussed. The research results indicated that the proper structure of amine could effectively enhance the properties of composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43820.     

Synthesis and properties of fluorinated graphene oxide bisphenol a epoxy nanocomposites

This study thoroughly studied the implements of fluorosilane modified graphene oxide (GO) on the mechanical, thermal, and water absorption properties of the epoxy composites built up by specific content of modified GO. Fluorosilane graphene oxide (GOSiF) was analyzed using Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, X‐ray photoelectron spectroscopy, and X‐ray diffractometer. The epoxy composites tensile and bending modulus were increased by 11.46% and 62.25% with 0.1 and 0.5 wt% GOSiF loading, respectively. The good interfacial interaction was observed between epoxy matrix and GOSiF nanosheets under scanning electron microscopy. The thermal stability increases with GOSiF loading. Epoxy composite with 0.3 wt% GOSiF shows 5 °C increases in the T_10%. The residual weight raised by 58.67% with 0.3 wt% GOSiF content. The water absorption study revealed small water uptake was obtained for all GOSiF composites. With 0.3 wt% loading of GOSiF, the maximum water content drops from 4.97% for neat epoxy to 1.98%. POLYM. ENG. SCI., 59:1250–1257 2019. © 2019 Society of Plastics Engineers     

Mechanical and thermal properties of hierarchical composites enhanced by pristine graphene and graphene oxide nanoinclusions

Epoxy resin nanocomposites incorporated with 0.5, 1, 2, and 4 wt % pristine graphene and modified graphene oxide (GO) nanoflakes were produced and used to fabricate carbon fiber‐reinforced and glass fiber‐reinforced composite panels via vacuum‐assisted resin transfer molding process. Mechanical and thermal properties of the composite panels—called hierarchical graphene composites—were determined according to ASTM standards. It was observed that the studied properties were improved consistently by increasing the amount of nanoinclusions. Particularly, in the presence of 4 wt % GO in the resin, tensile modulus, compressive strength, and flexural modulus of carbon fiber (glass fiber) composites were improved 15% (21%), 34% (84%), and 40% (68%), respectively. Likewise, with inclusion of 4 wt % pristine graphene in the resin, tensile modulus, compressive strength, and flexural modulus of carbon fiber (glass fiber) composites were improved 11% (7%), 30% (77%), and 34% (58%), respectively. Also, thermal conductivity of the carbon fiber (glass fiber) composites with 4% GO inclusion was improved 52% (89%). Similarly, thermal conductivity of the carbon fiber (glass fiber) composites with 4% pristine graphene inclusion was improved 45% (80%). The reported results indicate that both pristine graphene and modified GO nanoflakes are excellent options to enhance the mechanical and thermal properties of fiber‐reinforced polymeric composites and to make them viable replacement materials for metallic parts in different industries, such as wind energy, aerospace, marine, and automotive. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40826.     

Microwave‐Assisted Reversible Coordination‐Mediated Polymerization for Self‐Healing Hybrid Materials: RGO@PDA Simultaneous as Catalyst and Nanocomposites in One‐Pot

In this article, polydopamine (PDA) is efficiently adhered on the surface of graphene oxide (GO) by mussel‐inspired chemistry. The obtained reduced GO/PDA (RGO@PDA) nanocomposites are used for catalyzing reversible coordination‐mediated polymerization under microwave radiation. Well‐defined and iodine‐terminated polyacrylonitrile‐co‐poly(n‐butyl acrylate) (PAN‐co‐PnBA) is successfully fabricated by using RGO@PDA nanocomposites as catalysts. Importantly, green and novel strategy of PAN‐co‐PnBA‐type self‐healing nanocomposite materials is further fabricated with RGO@PDA as additive after polymerization as catalyst in one‐pot. As a reinforcement agent, RGO@PDA can also improve the mechanical and self‐healing properties of hybrid materials, which opens up a novel and green methodology for the preparation of self‐healing hybrid materials.     

Functionalized graphene‐reinforced rubber composite: Mechanical and tribological behavior study

A functionalized graphene, fluorinated graphene nanosheets (FGS), and SiO₂ nanoparticles as reinforcing fillers were employed to improve the mechanical properties of the solution styrene butadiene and butadiene rubber composites (SSBR‐BR). The results showed that the mechanical properties of SSBR‐BR composite filled with FGS were substantially improved than those of the unfilled and equivalent filler loaded graphene oxide (GO) and reduced graphene oxide (rGO) filled SSBR‐BR composites. It can be ascribed to the fact that the hydrophobic surface of FGS can be endowed the good dispersion in rubber matrix and stronger interfacial interaction between rubber and fillers. The tribological properties of these composites are also investigated. The results reveal that incorporation of GO, rGO, and FGS in SSBR‐BR composites can decrease antiwear properties because the existence of layered graphene promotes to tear and peel off. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44970.     

Perspectives of Epoxy/Graphene Oxide Composite: Significant Features and Technical Applications

In this article, advancement in epoxy/graphene oxide composites is presented. These materials are comprised of graphene oxide (GO) as filler (carbon-based material, thermodynamically stable, two-dimensional, planar and layered structure). Due to improved properties (mechanical response, low density, electrical resistance, and thermal stability), epoxy resins are used in several applications. Graphene oxide proposes unique properties to epoxy composites as high surface area, thermal and electrical conductivity as well as mechanical and barrier properties, relative to neat matrix. The corresponding significance of epoxy/GO-based materials, related challenges, and potential exploitation regarding technical applications (aerospace, gas sensor, electronic devices, etc.) have been overviewed.     

Effects of graphene functionalization on the long‐term behavior of epoxy/graphene composites evaluated by dynamic mechanical analysis

Graphene oxide (GO) and its reduced version (RGO) were prepared and functionalized with phenyl glycidol chlorophosphate (PGC) to obtain the corresponding GO‐PGC and RGO‐PGC materials. These graphene systems were used to prepare thermosetting composites with a tetrafunctional epoxy resin, 4,4′‐methylenebis(N,N‐diglycidylaniline) (TGMDA) cured with 4,4′‐diamino‐diphenyl‐sulfone (DDS). The systems were evaluated by dynamic mechanical analysis at constant strain and temperature sweeps to estimate the viscoelastic properties and relaxation phenomena at long time, which is important for modeling the mechanical long‐term behavior. The time temperature superposition (TTS) principle was employed for the construction of a master curve. The addition of the graphene‐type fillers shifted the time when the relaxation phenomena start to occur towards higher values, suggesting a better working temperature and durability of the corresponding nanocomposites when compared to the neat epoxy network. This phenomenon is more pronounced for the systems prepared with functionalized graphenes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44816.     

Preparation of polyimide/siloxane‐functionalized graphene oxide composite films with high mechanical properties and thermal stability via in situ polymerization

An effective approach to prepare polyimide/siloxane‐functionalized graphene oxide composite films is reported. The siloxane‐functionalized graphene oxide was obtained by treating graphene oxide (GO) with 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetra‐methyldisiloxane (DSX) to obtain DSX‐GO nanosheets, which provided a starting platform for in situ fabrication of the composites by grafting polyimide (PI) chains at the reactive sites of functional DSX‐GO nanosheets. DSX‐GO bonded with the PI matrix through amide linkage to form PI‐DSX‐GO films, in which DSX‐GO exhibited excellent dispersibility and compatibility. It is demonstrated that the obvious reinforcing effect of GO to PI in mechanical properties and thermal stability for PI‐DSX‐GO is obtained. The tensile strength of a composite film containing 1.0 wt% DSX‐GO was 2.8 times greater than that of neat PI films, and Young's modulus was 6.3 times than that of neat PI films. Furthermore, the decomposition temperature of the composite for 5% weight loss was approximately 30 °C higher than that of neat PI films. © 2015 Society of Chemical Industry     

Simultaneously Improved Thermal Conductivity and Dielectric Properties of NBR Composites by Constructing 3D Hybrid Filler Networks

This work aims to address the heat accumulation issue in electronic components during high-frequency operation through the preparation of novel thermally conductive composites. First, polydopamine (PDA) and in-situ growth of silver (Ag) nanoparticles are applied for the surface modification of graphene oxide (GO) and carbon nanotube (CNT) to prepare pGO@Ag and pCNT@Ag hybrid filler, respectively. Then, nitrile butadiene rubber (NBR) is chosen as the polymeric matrix and simultaneously incorporated with both pGO@Ag and pCNT@Ag to prepare polymeric composites with excellent thermal conductivity (TC) and dielectric constant (ɛ_r). Due to the construction of 3D heat conduction networks by utilizing 2D pGO@Ag and 1D pCNT@Ag, the fabricated NBR composites achieved the maximum TC of 1.0112 W/(mK), which is 636% higher than that of neat NBR (0.1373 W (mK)⁻¹). At the filler loading of 9 vol%, the TC of pGO@Ag/pCNT@Ag/NBR composite is 152% that of GO/CNT/NBR composite (0.6660 W (mK)⁻¹). Moreover, due to electron polarization effect of GO and CNT and micro-capacitor effect of Ag nanoparticles, a large ɛ_r of 147.12 is attained at 10 Hz for NBR composites. Overall, the development of dielectric polymer materials with high TC is beneficial for enhancing the service life and safety stability of the electronic components.     

Effect of flake size on thermal properties of graphene oxide/poly(methyl methacrylate) composites prepared via in situ polymerization

The effect of graphene oxide (GO) flake size on thermal properties of GO/poly(methyl methacrylate) (GO/PMMA) composites prepared via in situ polymerization was investigated. Two styles of GO sheets were synthesized from different sizes of graphite powders by modified Hummers' method and GO/PMMA composites with GO of different sizes were prepared via in situ polymerization. Transmission electron microscopy verified that GO sheets produced from large graphite powders was obviously larger than that from small graphite powders. The similar number of layers and disorder degree of two types of GO sheets were proved by X‐ray diffraction and Raman, respectively. X‐ray diffraction and scanning electron microscopy results of GO/composites proved the homogenous dispersion of both two types of GO sheets in polymer matrix. Dynamic mechanical analysis and thermogravimetric analysis results showed that large GO sheets exhibit better improvement than small GO sheets in thermal properties of the composites. Compared with neat PMMA, the glass transition temperature and decomposition temperature of the composites with large GO sheets (0.20 wt %) were increased by 15.9 and 25.9 °C, respectively. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46290.     

Preparation of functional reduced graphene oxide and its influence on the properties of polyimide composites

Homogeneous dispersion and strong filler–matrix interfacial interactions were vital factors for graphene for enhancing the properties of polymer composites. To improve the dispersion of graphene in the polymer matrix and enhance the interfacial interactions, graphene oxide (GO), as an important precursor of graphene, was functionalized with amine‐terminated poly(ethylene glycol) (PEG–NH₂) to prepare GO–poly(ethylene glycol) (PEG). Then, GO–PEG was further reduced to prepare modified reduced graphene oxide (rGO)–PEG with N₂H₄·H₂O. The success of the modification was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and Raman spectroscopy. Different loadings of rGO–PEG were introduced into polyimide (PI) to produce composites via in situ polymerization and a thermal reduction process. The modification of PEG–NH₂ on the surface of rGO inhibited its reaggregation and improved the filler–matrix interfacial interactions. The properties of the composites were enhanced by the incorporation of rGO–PEG. With the addition of 1.0 wt % rGO–PEG, the tensile strength of PI increased by 81.5%, and the electrical conductivity increased by eight orders of magnitude. This significant improvement was attributed to the homogeneous dispersion of rGO–PEG and its strong filler–matrix interfacial interactions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45119.     

Synthesis of modified graphene oxide and its improvement on flame retardancy of epoxy resin

In this work, the small molecule with double-phosphaphenanthrene structure was successfully grafted on the surface of graphene oxide (GO), which is called functionalized graphene oxide (FGO). The introduction of FGO improved the poor interfacial compatibility between graphene and epoxy matrix. And FGO could be used as the highly effective flame retardant. The thermogravimetric analysis results showed a significant improvement in the char yield of cured FGO/EP. When the content of FGO was 3 wt %, the limiting oxygen index value reached 30.4%. At the same time, the three-point bending and thermomechanical tests confirmed that the mechanical properties of the epoxy resin composites were improved. Based on the char analyses of SEM images and Raman spectroscopy, the flame retardant could promote the formation of a stable carbon layer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47710.     

Incorporation of hyperbranched polyamide‐functionalized graphene oxide into epoxy for improving interfacial and mechanical properties

The incorporation of hyperbranched polyamide‐functionalized graphene oxide (HPA‐GO) into epoxy was proposed to improve the interfacial and mechanical properties. Benefiting from improved dispersion and strengthened interfacial interaction, epoxy composites with HPA‐GO showed significant improvements in mechanical and thermomechanical properties at low GO loading. The interaction at the HPA‐GO/epoxy interface was investigated to confirm the occurrence of chemical bonding. Strong interfacial bonding improved the stress transfer and distribution of HPA‐GO/epoxy interface. Accordingly, the overall strength of epoxy composites was effectively improved on account of the uniform dispersion of HPA‐GO and interfacial chemical interaction between HPA‐GO and epoxy. Compared with neat epoxy resin, the inclusion of 0.10 wt% HPA‐GO led to 310.5 and 37.2% increase in impact strength and tensile strength, respectively. © 2019 Society of Chemical Industry     

Simultaneous in situ reduction,self-alignment and covalent bonding in graphene oxide/epoxy composites

Graphene oxide (GO)/waterborne epoxy (EP) composites are prepared using an easy, all aqueous, in situ polymerization method. GO is reduced in situ using hydrazine to achieve highly stable reduced graphene oxide (rGO)/EP dispersions, leading to the formation of composites with a self-aligned layered structure and highly anisotropic properties between the direction of alignment and that perpendicular to it. The strong covalent bonding between the epoxy and rGO and the highly aligned, ultralarge rGO sheets give rise to a remarkable percolation threshold of 0.12 vol.%, as well as much improved mechanical, electrical and thermal properties of the composites in the alignment direction. They outperform those containing GO sheets that are bonded to the epoxy matrix through a weaker π–π stacking mechanism.