In situ polymerization of polyimide‐based nanocomposites via covalent incorporation of functionalized graphene nanosheets for enhancing mechanical,thermal, and electrical properties

In this study, we report an effective method to fabricate high‐performance polyimide (PI)‐based nanocomposites using 3‐aminopropyltriethoxysilane functionalized graphene oxide (APTSi‐GO) as the reinforcing filler. APTSi‐GO nanosheets exhibit good dispersibility and compatibility with the polymer matrix because of the strong interfacial covalent interactions. PI‐based nanocomposites with different loadings of functionalized graphene nanosheets (FGNS) were prepared by in situ polymerization and thermal imidization. The mechanical performance, thermal stability, and electrical conductivity of the FGNS/PI nanocomposites are significantly improved compared with those of pure PI by adding only a small amount of FGNS. For example, a 79% improvement in the tensile strength and a 132% increase in the tensile modulus are achieved by adding 1.5 wt % FGNS. The electrical and thermal conductivities of 1.5 wt % FGNS/PI are 2.6 × 10^?3 S/m and 0.321 W/m·K, respectively, which are ～10¹⁰ and two times higher than those of pure PI. Furthermore, the incorporation of graphene significantly improves the glass‐transition temperature and thermal stability. The success of this approach provides a good rationale for developing multifunctional and high‐performance PI‐based composite materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42724.     

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.     

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     

Enhanced mechanical and electrical properties of polyimide film by graphene sheets via in situ polymerization

In this study, polyimide/graphene nanocomposite films which exhibited significant enhancements in mechanical properties and electrical conductivity were successfully fabricated. Graphene oxide (GO) synthesized by Hummer’s method was chemically modified with ethyl isocyanate to give ethyl isocyanate-treated graphene oxide (iGO), which is readily dispersed in N,N′-dimethylformamide (DMF). The iGO dispersion in DMF was then used as media for synthesis of polyimide/functionalized graphene composites (PI/FGS) by an in situ polymerization approach. It was shown that addition of only 0.38 wt% of FGS, Young’s modulus of the PI/FGS composite film was dramatically increased from 1.8 GPa to 2.3 GPa, which is approximately 30% of improvement compared to that of pure PI film, and the corresponding tensile strength was increased from 122 MPa to 131 MPa. In addition, the electrical conductivity of the PI/FGS with this graphene content was increased by more than eight orders of magnitude to 1.7 × 10⁻⁵ S m⁻¹.     

Synthesis of polythiophene/graphene oxide composites by interfacial polymerization and evaluation of their electrical and electrochemical properties

We report a new method for the synthesis of polythiophene (PTh)/graphene oxide (GO) nanocomposites by interfacial polymerization. Polymerization occurred at the interface of two immiscible solvents, i.e. n‐hexane containing thiophene and nitromethane containing GO and an initiator. Characterizations were done using Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and electrochemical and electrical conductivity measurements. Spectroscopic analyses showed successful incorporation of GO in the PTh matrix. Morphological analysis revealed good dispersion of GO sheets in the polymer matrix. The PTh/GO composites showed marked improvements in thermal stability and electrical conductivity (2.7 × 10^?4 S cm^?1) compared to pure PTh. The composites exhibited excellent electrochemical reversibility compared to pure PTh at a scan rate of 0.1 V s^?1. The composites were stable even up to 100 electrochemical cycles, indicating good cycle performance. The specific capacitance of the composites was calculated using cyclic voltammetry and was found to be 99 F g^?1. © 2014 Society of Chemical Industry     

Enhanced thermal conductivity and dimensional stability of flexible polyimide nanocomposite film by addition of functionalized graphene oxide

Polyimide (PI) nanocomposites with both enhanced thermal conductivity and dimensional stability were achieved by incorporating glycidyl methacrylate‐grafted graphene oxide (g‐GO) in the PI matrix. The PI/g‐GO nanocomposites exhibited linear enhancement in thermal conductivity when the amount of incorporated g‐GO was less than 10 wt%. With the addition of 10 wt% of g‐GO to PI (PI/g‐GO‐10), the thermal conductivity increased to 0.81 W m^?1 K^?1 compared to 0.13 W m^?1 K^?1 for pure PI. Moreover, the PI/g‐GO‐10 composite exhibited a low coefficient of thermal expansion (CTE) of 29 ppm °C^?1. The values of CTE and thermal conductivity continuously decreased and increased, respectively, as the g‐GO content increased to 20 wt%. Combined with excellent thermal stability and high mechanical strength, the highly thermally conducting PI/g‐GO‐10 nanocomposite is a potential substrate material for modern flexible printed circuits requiring efficient heat transfer capability.     

Mechanical,thermal conductive,and dielectric properties of fluoroelastomer/reduced graphene oxide composites in situ prepared by solvent thermal reduction

Fluoroelastomer (FKM)/reduced graphene oxide (rGO) composites are in situ prepared by solvent thermal reduction method in N,N‐dimethylformamide (DMF) solution. The reduction of graphene oxide (GO) is characterized by X‐Ray photoelectron (XPS), ultraviolet–visible (UV–vis), and Fourier transform infrared (FTIR) spectra. GO and rGO are both efficient fillers to improve the mechanical properties of FKM. The dispersibility of rGO is improved after solvent thermal reduction which is confirmed by scanning electron micrograph (SEM) and X‐ray diffraction (XRD). The homogenous suspension of FKM/rGO composites in DMF can stay stable for more than a month. The dielectric permittivity of FKM/rGO (5 phr) is 26.4 at the frequency of 10⁻¹ Hz, higher than the pure FKM (8.1). The thermal conductivity of rGO/FKM composites increases. POLYM. COMPOS., 35:1779–1785, 2014. © 2013 Society of Plastics Engineers     

Solvothermally reduced graphene oxide/polyimide composites: Structures and thermal and mechanical properties

Solvothermally reduced graphene oxide (SRGO)/polyimide (PI) composites were prepared by in situ polymerization. The structures and components were carefully investigated by X-ray diffraction. Thermal properties were measured by thermogravimetry and dynamic thermomechanical analysis. Mechanical properties were carefully evaluated by tensile testing and scanning electron microscopy. The SRGO/PI composites exhibit extremely high tensile strength and elastic modulus, which is 30% higher than that of pure PI film. Meanwhile, the thermal stability of SRGO/PI composites also displays an obvious enhancement. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47164.     

The effect of graphite oxide on the thermoelectric properties of polyaniline

Graphite oxide (GO)/ordered polyaniline (PANI) composites have been prepared through an in situ polymerization. TEM, XRD, FTIR and XPS analyses show that the PANI grew along the surface of exfoliated GO as a template to form a more ordered structure with high crystallinity during polymerization. Compared with pure PANI, both higher electrical conductivity and higher Seebeck coefficient of GO/PANI composites result from the increased carrier mobility, which is confirmed by Hall measurement. Strong interactions exist between graphene oxide and PANI, including electrostatic forces, hydrogen bonding and π–π stacking. There is no significant difference in thermal conductivity between GO/PANI composites and PANI. The maximum electrical conductivity and Seebeck coefficient of the composites reach 751 S m^?1 and 28.31 μV K^?1, respectively. The maximum thermoelectric figure of merit is up to 4.86 × 10^?4, 2 orders of magnitude higher than that of pure PANI.     

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.     

Latex co‐coagulation approach to fabrication of polyurethane/graphene nanocomposites with improved electrical conductivity,thermal conductivity,and barrier property

This study describes a simple and effective method of synthesis of a polyurethane/graphene nanocomposite. Cationic waterborne polyurethane (CWPU) was used as the polymer matrix, and graphene oxide (GO) as a starting nanofiller. The CWPU/GO nanocomposite was prepared by first mixing a CWPU emulsion with a GO colloidal dispersion. The positively charged CWPU latex particles were assembled on the surfaces of the negatively charged GO nanoplatelets through electrostatic interactions. Then, the CWPU/chemically reduced GO (RGO) was obtained by treating the CWPU/GO with hydrazine hydrate in DMF. The results of X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Raman analysis showed that the RGO nanoplatelets were well dispersed and exfoliated in the CWPU matrix. The electrical conductivity of the CWPU/RGO nanocomposite could reach 0.28 S m^?1, and the thermal conductivity was as high as 1.71 W m^?1 K^?1. The oxygen transmission rate (OTR) of the CWPU/RGO‐coated PET film was significantly decreased to 0.6 cm³ m^?2 day^?1, indicating a high oxygen barrier property. This remarkable improvement in the electrical and thermal conductivity and barrier property of the CWPU/RGO nanocomposite is attributed to the electrostatic interactions and the molecular‐level dispersion of RGO nanoplatelets in the CWPU matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43117.     

Electrostatic self-assembly of graphene–silver multilayer films and their transmittance and electronic conductivity

By alternating deposition of graphene oxide (GO) sheets and silver nitrate by means of an electrostatic self-assembly method, a GO–Ag⁺ film was prepared. After thermal annealing, a graphene–silver nanoparticle (GE–Ag) multilayer film, with high transparency and electrically conductivity, was obtained. The transmittance of a film with four assembly cycles was 86.3%, at a wavelength of 550 nm, better than that of a pure GE film (73.8%). While the surface resistance was 97 kΩ □^?1, much lower than that of a pure GE film (430 kΩ □^?1). The Ag nanoparticles play a crucial role in improving the properties of the GE–Ag film, acting as conductive paths and light-trapping nanoparticles, which not only reduces the reflection of the film, but also prevents the GE sheets from aggregation and provides conductive paths between sheets, improving the electrical conductivity.     

Highly electrically and thermally conductive silicon carbide-graphene composites with yttria and scandia additives

Dense silicon carbide/graphene nanoplatelets (GNPs) and silicon carbide/graphene oxide (GO) composites with 1 vol.% equimolar Y₂O₃–Sc₂O₃ sintering additives were sintered at 2000 °C in nitrogen atmosphere by rapid hot-pressing technique. The sintered composites were further annealed in gas pressure sintering (GPS) furnace at 1800 °C for 6 h in overpressure of nitrogen (3 MPa). The effects of types and amount of graphene, orientation of graphene sheets, as well as the influence of annealing on microstructure and functional properties of prepared composites were investigated. SiC-graphene composite materials exhibit anisotropic electrical as well as thermal conductivity due to the alignment of graphene platelets as a consequence of applied high uniaxial pressure (50 MPa) during sintering. The electrical conductivity of annealed sample with 10 wt.% of GNPs oriented parallel to the measuring direction increased significantly up to 118 S·cm⁻¹. Similarly, the thermal conductivity of composites was very sensitive to the orientation of GNPs. In direction perpendicular to the GNPs the thermal conductivity decreased with increasing amount of graphene from 180 W·m⁻¹ K⁻¹ to 70 W·m⁻¹ K⁻¹, mainly due to the scattering of phonons on the graphene – SiC interface. In parallel direction to GNPs the thermal conductivity varied from 130 W·m⁻¹ K⁻¹ up to 238 W·m⁻¹ K⁻¹ for composites with 1 wt.% of GO and 5 wt.% of GNPs after annealing. In this case both the microstructure and composition of SiC matrix and the good thermal conductivity of GNPs improved the thermal conductivity of composites.     

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.     

Investigation of thermomechanical properties and matrix–filler interaction on polyimide/graphene oxide composites

We report, the preparation of nanocomposites having polyimide (PI) as matrix and graphene oxide (GO) as filler, analyses of matrix–filler interactions, and enhancements in thermomechanical properties of PI/GO as compared with pristine PI. The matrix–filler interactions were analyzed by ¹H NMR, X‐ray photoelectron spectroscopy, and density functional theory calculations. The data suggested stronger matrix–filler interactions in PI/GO as compared with PI/G composites. The stronger matrix–filler interactions and homogeneous dispersion of fillers lead to a significant enhancement in mechanical properties in PI/GO nanocomposites. Thus, with just 1 wt% GO content, the modulus of PI/GO composite increased by ～106% as compared with pristine PI. Finally, thermal expansion coefficients of the nanocomposites are also investigated. A plausible hypothesis has been proposed in the text to explain the observed matrix–filler interactions and the subsequent property enhancements in nanocomposites. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Wire electrical discharge machinable SiC with GNPs and GO as the electrically conducting filler

SiC based composites filled with graphene nano-platelets (GNPs) or graphene oxide (GO) prepared by rapid hot-pressing exhibit sufficient electrical conductivity for their machinability by wire electro-discharge machining (WEDM). Composites microstructure anisotropy caused by graphene alignment as a consequence of rapid hot pressing was confirmed by measuring of electrical conductivity and thermal diffusivity. Electrical conductivity increased significantly with increased weight fraction of graphene in both measured directions. Highest value of 2031 S/m was obtained for composites with 15 wt. % of GNPs in parallel direction and only 1246 S/m in perpendicular direction to aligned GNPs. Thermal diffusivity is 63.3 mm²/s in parallel and only 23.3 mm²/s in perpendicular direction. The increase of the electrical conductivity has resulted in successful WEDM. The MRR was almost doubled when the filler concentration increased from 5 wt. % GNPs/GO to 15 wt. % GNPs. At the same time, the surface roughness decreased.     

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.     

Synthesis of click‐coupled graphene sheets with hyperbranched polyurethane: Effective exfoliation and enhancement of nanocomposite properties

Graphene oxide (GO) was functionalized with hyperbranched polyurethane (HBPU) via click coupling between azide‐functionalized HBPU and alkynyl‐decorated GO. HBPU‐functionalized GO composites of various compositions were prepared. The azide‐containing HBPU was characterized using Fourier‐transform infrared (FT‐IR) spectroscopy and ¹H‐nuclear magnetic resonance spectroscopy. The HBPU‐functionalized GO composites were characterized using transmission electron microscopy and FT‐IR spectroscopy. The functionalized GO showed excellent dispersion in the HBPU matrix, giving composites with enhanced mechanical and thermal properties. The material properties were effectively regulated by click‐coupled exfoliation of GO with HBPU, enabling the production of high‐performance materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44631.     

Ultra-high compression and wear resistant hybrid filled polyimide composite: Synergistic effect of Fe2O3 decorated RGO

Herein, the tribological performance, thermal and compression resistance behavior of polyimide (PI) reinforced by Fe₂O₃ decorated reduced graphene is systematically investigated. The remarkable synergistic effect of Fe₂O₃ decorated reduced graphene oxide (RGO) is demonstrated in its PI wear resistance, and PI/RGO/Fe₂O₃ composites show good thermal stability and much higher compression resistant ability than PI, PI/RGO, and PI/Fe₂O₃ composites when the filling contents are same. Additionally, the PI/RGO/Fe₂O₃ composites also exhibited ultra-wear-resistant properties under high load condition, and the lowest wear rate is 3.18 × 10⁻⁸ mm³N⁻¹ m⁻¹, which is an order of magnitude lower than that of pure PI. The investigation of its tribological mechanism also showed strong synergistic effect and interface force of Fe₂O₃ decorated RGO, which contribute to its high-performance friction-reducing behaviors. These findings give an inside view to Fe₂O₃ decorated RGO and its polyimide composites, and open an avenue for the graphene oxide (GO) based composite to act as compression wear-resisting solid fillers and lubricants when polymer composite with excellent compressive, thermal and tribological properties is required.     

Influence of graphene oxide on thermal,electrical, and morphological properties of new achiral polyimide

In this study, a new diamine N‐[2‐(1H‐indol‐3‐yl)ethyl]‐3,5‐diaminobenzamide (IEDAB) was synthesized using tryptamine as starting material and characterized by FT‐IR, ¹H‐NMR, ¹³C‐NMR, and mass spectroscopy. Then, it was polymerized with 3,3',4,4'‐benzophenone tetracarboxylic dianhydride (BTDA) via thermal imidization to produce polyimide (PI). A series PI/GO nanocomposite films were prepared by incorporating different ratios (1, 3, and 5 wt%) of synthesized GO by solution casting method. The synthesized PI was confirmed by Ubbelohde viscometer and FT‐IR spectroscopy. SEM and Raman spectroscopy showed that GO was well dispersed in the PI matrix. XRD patterns indicated the PI and PI/GO nanocomposite films were highly amorphous in nature. The synthesized PI and their nanocomposites show high thermal stability as their T_10% weight loss are in the range of 498 to 563°C with 30.6 to 40% of char yield and the glass transition temperatures (T_g s) are in the range of 188 to 262°C. The limited oxygen index (LOI) values increased from 31.4% to 56.0% with increases of 5% GO content in the PI/GO nanocomposite. They have high dielectric constant in the range of 2.6 to 5.1 at 1 MHz and also good mechanical properties with tensile strength of 81 to 116 MPa, elongation at break 5 to 9%. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers