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.     

Influence of graphene-based compounds on the mechanical toughness and thermal stability of polypropylene

A study of the improvement of the mechanical and thermal properties of nanocomposites prepared with polypropylene (PP) and different graphene samples [graphene oxide (GO), reduced GO (RGO), and commercial graphene (G)] is presented. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy characterization were applied to the graphene samples. The nanocomposites were characterized by thermogravimetric analysis, XRD, differential scanning calorimetry, transmission electron microscopy (TEM), tensile, and impact resistance tests. PP/RGO nanocomposites showed significant improvement in mechanical and thermal properties. Sample PP/RGO-0.75 resulted in an increment in Young's modulus (51%), tensile strength (24%), and elongation at break (15%). This is attributed to a good dispersion state, a higher crystallinity percentage, and a good interfacial adhesion between PP and RGO. Sample PP/RGO-0.50 exhibited an increase of 197 °C in the temperature at which a loss in weight of 5% occurred, compared to that for pure PP. The height of stacked layers calculated by XRD measurements was similar to the value observed by TEM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48258.     

Chemically modified graphene oxide/polybenzimidazobenzophenanthroline nanocomposites with improved electrical conductivity

Graphene/polybenzimidazobenzophenanthroline nanocomposites were prepared through the liquid-phase exfoliation of graphene oxide (GO) and reduced graphene oxide (rGO) in methanesulfonic acid with subsequent solution mixing. Various chemical and combined chemical-thermal methods were examined to be effective for producing rGO with highly graphitic structure and excellent electrical conductivity. Raman and X-ray photoelectron spectroscopy showed higher degree of reduction of the GO with the combined chemical-thermal method compared to other chemical reduction processes. Structural characterization of the nanocomposites by X-ray diffraction, scanning electron microscopy and transmission electron microscopy showed good exfoliation and dispersion of both GO and rGO fillers in the polymer matrix. The thermogravimetric analysis found that the nanocomposites with rGO have higher onset and maximum weight loss temperatures than those with GO. Compared with the pure polymer, the electrical conductivity of the nanocomposites containing 10 wt% GO and GO reduced by the combined chemical-thermal treatment showed a remarkable increase by four and seven orders of magnitude, respectively. Long-term in-situ thermal reduction was performed to further improve the conductivities of the nanocomposites.     

Preparation of well‐dispersed reduced graphene oxide and its mechanical reinforcement in polyvinyl alcohol fibre

The current work reports the preparation and characterization of polyvinyl alcohol (PVA) composite fibres reinforced with graphene reduced from graphene oxide (GO) by using oligomeric proanthocyanidin (OPC) as a reductant. After reduction, most of the oxygen‐containing groups were removed from the GO and reduced graphene oxide (rGO) was prepared. As a result of combined OPC as a dispersant, rGO could be well dispersed in a dimethyl sulfoxide/H₂O mixed solvent and in PVA matrix, and the PVA/rGO dispersion was wet spun followed by hot drawing to prepare continuous PVA/rGO composite fibres. The PVA/rGO composite fibres exhibited a significant enhancement of mechanical properties at low rGO loadings; in particular the tensile strength and Young's modulus of the 2.0 wt% rGO and PVA composite fibre increased to 244% and 294% respectively relative to neat PVA fibre. Moreover, the storage modulus (?10 °C) and T_g increased to 300% and 7.2 °C, respectively. © 2016 Society of Chemical Industry     

Impact of various oxidation degrees of graphene oxide on the performance of styrene–butadiene rubber nanocomposites

In this work, graphene oxide (GO) with various oxidation degrees were synthesized by adjusting the dosage of oxidation agent based on a modified Hummers' method, and were then used for the fabrication of the styrene–butadiene rubber (SBR)/GO nanocomposites through latex coagulation method, followed by a high‐temperature cure process. The vulcanization characteristics, thermal stability, mechanical properties, thermal conductivity as well as solvent resistance of SBR/GO nanocomposites were investigated. The results indicated that various surface structures of GO due to oxidation degrees may lead to different dispersion states of GO in the rubber matrix, and thus greatly influenced the cure rate, mechanical properties as well as thermal conductivity of SBR/GO nanocomposites. The optimal (moderate) oxidation degree of GO was achieved at the oxidation agent (KMnO₄)/graphite weight ratio 9/5, for which case the tensile strength, tear strength, and thermal conductivity of SBR/GO nanocomposites increased by 271.3%, 112.3%, and 28.6%, respectively, compared with those of neat SBR. In addition, the mentioned nanocomposites also showed the best solvent resistance in toluene. POLYM. ENG. SCI., 58:1409–1418, 2018. © 2017 Society of Plastics Engineers     

Simultaneous reduction and surface functionalization of graphene oxide and the application for rubber composites

The simultaneous reduction and functionalization of graphene oxide (GO) was realized through a chemical grafting reaction with a functionalization agent N,N-bis(3-aminopropyl)methylamine (APMEL). The reduced and functionalized reduced GO (rGO-APMEL) sheets can be well dispersed in water without any added surfactant and the formed stable rGO aqueous dispersion can be kept for a long time, which can be used for the preparation of rubber–graphene (GE) composites by latex mixing. The electrostatic interaction between rGO–APMEL (positively charged) and natural rubber latex particles (negatively charged) leads to the formation of NR/rGO–APMEL composites with strong interaction. Compared with blank NR, the tensile strength and modulus for NR/rGO–APMEL increase with the rGO–APMEL loading. Especially, when the filler content is 5 phr, the tensile strength of NR/rGO–APMEL-5 increases by 32.7%, as a control the tensile strength of NR/GO-5 and NR/rGO-5 decrease by 20.1 and 15.6%, respectively. The entanglement-bound rubber tube model was used to analyze the reinforcing effect of GE on NR/rGO–APMEL nanocomposites at a molecular level. This study may provide us a novel approach to prepare well dispersed and exfoliated rGO–polymer nanocomposites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47375.     

Fabrication of ZrO2/rGO nanocomposites by flash sintering under AC electric fields

Ceramic matrix nanocomposites containing graphene possess superior mechanical properties. However, these nanocomposites are very difficult to be prepared using the conventional methods due to severe grain growth and simultaneous degradation of the graphene at high sintering temperatures and long dwell time. Herein, the dense ZrO₂/rGO (reduced graphene oxide) nanocomposites are successfully fabricated by flash sintering of the green compacts consisting of ZrO₂ nanoparticles and graphene oxide (GO) at 893–951℃ in merely 5 seconds under the alternating current (AC) electric fields of 130–150 V cm⁻¹. The GO can be in situ thermal reduced during the flash sintering. The as-prepared ZrO₂/rGO nanocomposites exhibit excellent mechanical properties. This study presents a green and simple approach to fabricate the dense ceramic matrix nanocomposites reinforced with graphene at low temperatures in a short time.     

Thin polymer films based on poly(vinyl alcohol) containing graphene oxide and reduced graphene oxide with functional properties

In this article, the effect of the addition of graphene oxide (GO) and reduced graphene oxide (rGO) on the mechanical properties, thermal stability, and electrical conductivity of polyvinyl alcohol (PVA) has been investigated. Different weight percentages of nanofillers ranging from 0.5 to 5 wt% have been combined with PVA. The ultrasonic technique has been applied to disperse nanofillers in the PVA solution. The nanocomposite films have been prepared via solution casting technique and the dispersion of nanofillers into the PVA has been studied through optical microscopy. The microstructure, crystallization behavior, and interfacial interaction were characterized through X-ray diffraction and Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis have been applied to study the thermal properties of the prepared nanocomposites. The DSC results revealed that the crystallization temperature and melting temperature were enhanced in the presence of GO nanofiller. Besides, the tensile strength at break was improved along with the addition of GO; however, elongation at break for PVA/GO and PVA/rGO was diminished. Moreover, all specimens showed insulating behavior and the only sample was electrically conducting, which contain a high amount of rGO (5 wt%).     

Influence of functionalized reduced graphene oxide and compatibilizer on mechanical,thermal and morphological properties of polypropylene/polybutene-1 (PP/PB-1) blends

Polypropylene/Polybutene-1 (PP/PB-1) blends and nanocomposites containing pristine partially reduced graphene oxide (rGO) and chemically functionalized rGO (FrGO) with silane, and silane grafted with 1,12-dodecanediamine and 1,12-dodecanediol were studied. The effects of the chemical treatments on structure and thermal stability of rGO were first thoroughly investigated. Attenuated total reflectance Fourier infrared (ATR-FTIR) spectroscopy analyses of FrGO evidenced the existence of functional groups on rGO after each chemical treatment, while X-ray diffraction (XRD) results confirmed the effectiveness of the interlayer grafting process through shifting of the basal spacings as witnessed by increased d₀₀₂ values. Furthermore, thermogravimetric analysis (TGA) revealed that the functionalization of rGO resulted in improved thermal stability of rGO demonstrated by its increased thermal degradation temperature. The PP/PB-1 blends and their rGO and FrGO based nanocomposites were prepared by melt blending masterbatch process in the presence of an acrylic acid modified polypropylene compatibilizer (PP-g-AA). Mechanical testing showed that Young’s modulus and tensile strength of the PP/PB-1 blends significantly improved after co-addition of FrGO and PP-g-AA to form the nanocomposites, but it also endowed a drastic decrease in their elongation at break and especially in their impact strength. XRD analyses attested the successful formation of intercalated nanocomposites, and scanning electron microscopy (SEM) examinations disclosed a two-phase morphology consisting of PB-1 dispersed droplets in the PP matrix. SEM also indicated that the incorporation of PP-g-AA into the blends and the nanocomposites contributed to enhanced adhesion and dispersion of PB-1 phase and FrGO nanoparticles within the polymer matrix.     

Effect of the sheet size on the thermal stability of silicone rubber–reduced graphene oxide nanocomposites

The structures of differently sized reduced graphene oxides (rGOs), the dispersion state, and the compatibility of rGO with silicone rubber (SR) are important impact factors on the properties of SR–rGO nanocomposites. To analyze the influence of the size of rGO on the properties of SR-based nanocomposites, three differently sized rGO sheets were introduced into SR to fabricate a series of SR-based nanocomposites. The SR–middle-sized reduced graphene oxide (MrGO) nanocomposites showed the best mechanical and thermal properties. Compared with the blank sample, the SR–MrGO nanocomposites presented remarkable two-fold and three-fold increases in the tensile modulus and strength values. The initial degradation temperature increased nearly 40 °C. In this study, we investigated the size effect of graphene on the thermal stability by examining the thermal degradation mechanism of the different SR–rGO nanocomposites in detail. Ultimately, this research may suggest a facile approach for improving the thermal stability of SR. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47034.     

In situ polymerisation and characteristic properties of the waterborne graphene oxide/poly(siloxane-urethane)s nanocomposites

In this study, waterborne graphene oxide/poly(siloxane-urethane)s (GO/SWPUs) nanocomposites were in situ synthesised. Therein, siloxane units facilitated the crosslinking of polyurethanes, and GO imparted the nanocomposites with special functions. With increasing GO content, the average particle size, viscosity, and ionic conductivity of the GO/SWPU dispersion increased, but the absolute value of the zeta potential decreased; this was due to ionic interactions between the COO^?NH⁺(C₂H₅)₃ ions of the SWPU and COO^?H⁺ ions of the GO. The surface roughness of the GO/SWPU film was larger as GO content was higher, which was due to a strong interaction between the GO and SWPU phases. Increasing the GO content improved the thermal resistance, dynamic glass transition temperature, and tensile strength of the GO/SWPU film, but adding more than 0.1 wt% GO yielded unfavourable results. Thus, adding GO improved the thermal and mechanical properties of the GO/SWPU nanocomposites, but this improvement was observed only up to a certain GO concentration, possibly because of the agglutination of GO in SWPU. In addition, the surface and volumetric electrical resistivities of the GO/SWPU nanocomposites decreased when the GO content were increased.     

Effect of copper sulfate pentahydrate on the structure and properties of poly(vinyl alcohol)/graphene oxide composite films

Poly(vinyl alcohol) (PVA)/graphene oxide (GO)/copper sulfate pentahydrate (CuSO₄·5H₂O) composite films were prepared by the solution casting method, and the effect of CuSO₄·5H₂O on the structure and properties of the PVA/GO composites was investigated. Fourier transform infrared (FTIR) analysis proved the crosslinking interaction between CuSO₄·5H₂O and the ? OH group of PVA. The crystallinity of the composite films increased first and then decreased. For the composite films, the tensile strength, Young's modulus, and yield stress values improved with increasing CuSO₄·5H₂O, whereas the elongation at break decreased compared with that of the neat PVA/GO composite film. The thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) patterns of the PVA/GO/CuSO₄·5H₂O composite films showed that the thermal stability decreased; this was consistent with the TGA–FTIR analysis. A remarkable improvement in the oxygen‐barrier properties was achieved. The oxygen permeability coefficient was reduced by 60% compared to that of the neat PVA/GO composite film. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44135.     

Graphene induced carbonization of polyimide films to prepared flexible carbon films with improving-thermal conductivity

Carbon films prepared by polyimide (PI) films treated under 1500°C exhibit favorable thermal conductivity. However, the bonds of carbon films will fracture and recombine which will cause shrinking and forming defects. The flexibility of the carbon films will be greatly reduced, and then affect the application of the carbon films in the field of thermal conduction. When the films prepared by the graphene oxide/polyimide (GO/PI) composite films and the reduced graphene oxide/polyimide (rGO/PI) composite films, respectively, rGO and GO can fill the defects, then increasing the flexibility of the carbon films and inducing the carbonation process. Because of the high thermal conductivity and the six-membered ring structure of rGO and GO, the carbonization temperature will decrease and save costs. When the composite films treated under 1500°C, the thermal conductivity increases with the content of rGO and GO. There are connections between PI and graphene. As the amount of rGO and GO increases, the strong interactions between the rGO or GO and PI lead to contact that enhances its thermal conductivity. However, the rGO and GO have different effects on the films flexibility and thermal conductivity and the differences will be described in the article.     

Rheological behavior ‐ Electrical and thermal properties of polypyrrole/graphene oxide nanocomposites

Polypyrrole/graphene oxide (Ppy/GO) nanocomposites were synthesized via in situ polymerization of pyrrole in the presence of GO at various proportions (1–5%). They were characterized to determine their electrical, thermal, and rheological properties by various techniques. The aim of this study was to determine the rheological behavior of Ppy/GO nanocomposite at different mass ratios (100 : 1, 100 : 2, 100 : 3, 100 : 4, and 100 : 5%) and temperature (25–180°C) using a rotational mode in cone‐plate method. The shear stress (τ Pa) and viscosity (η Pa s) values of the nanocomposites increased with the increase in GO mass ratio added to Ppy, which was accompanied by an increased flexibility of the nanocomposites due to the higher aspect ratio of the GO sheet. Hence, it is suggested that the GO sheets are effective for the reinforcement of Ppy thereby significantly improvising its thermal stability, electrical conductivity, and rheological properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40642.     

Preparation and mechanical properties of Si3N4 nanocomposites reinforced by Si3N4@rGO particles

A new type of reduced graphene oxide-encapsulated silicon nitride (Si₃N₄@rGO) particle was synthesized via an electrostatic interaction between amino-functionalized Si₃N₄ particles and graphene oxide (GO). Subsequently, the Si₃N₄@rGO particles were incorporated into a Si₃N₄ matrix as a reinforcing phase to prepare nanocomposites, and their influence on the microstructure and mechanical properties of the Si₃N₄ ceramics was investigated in detail. The microstructure analysis showed that the rGO sheets were uniformly distributed throughout the matrix and firmly bonded to the Si₃N₄ grains to form a three-dimensional carbon network structure. This unique structure effectively increased the contact area and load transfer efficiency between the rGO sheets and the matrix, which in turn had a significant impact on the mechanical properties of the nanocomposites. The results showed that the nanocomposites with 2.25 wt.% rGO sheets exhibited mechanical properties that were superior to monolithic Si₃N₄; the flexural strength increased by 83.5% and reached a maximum value of 1116.4 MPa, and the fracture toughness increased by 67.7% to 10.35 MPa·m^1/2.     

The mechanism of the reaction of graphite oxide to reduced graphene oxide under ultraviolet irradiation

Under ultraviolet (UV) irradiation, the formation and reduction mechanism of reduced graphene oxide (rGO) layers prepared from graphite oxide (GO) sheets have been investigated. The effects of hydroxyl free radicals (HO), hydroxide ions (OH⁻) or hydrazine molecules (N₂H₄) are considered. It has been demonstrated that the HO radicals, UV-induced from H₂O₂ molecules in aqueous solution, cannot reduce GO into rGO, but to some extent oxidize and damage the GO structure, simultaneously accompanied by a slight increase of acidity, possibly because of a release of H⁺ from H₂O₂ and GO during the reaction. The existence of OH⁻ ions or N₂H₄ instead of H₂O₂ molecules enables GO sheets to be quickly reduced into rGO due to the effect of photo-induced electrons on the GO sheets. The electrons are photogenerated mainly from OH⁻ or N₂H₄ in a GO aqueous dispersion. Because GO in diluted N₂H₄ aqueous solution can be photo-reduced almost completely within half an hour at room temperature, it is inferred that many more electrons are generated from N₂H₄ than from OH⁻.     

Preparation and characterization of reduced graphene oxide-reinforced boron carbide ceramics by self-assembly polymerization and spark plasma sintering

A self-assembly polymerization process was used to prepare graphene oxide/boron carbide (GO/B₄C) composite powders, spark plasma sintering (SPS) was used to fabricate reduced graphene oxide/boron carbide (rGO/B₄C) composites at 1800 °C and 30 MPa with a soaking time of 5 min. The effects of rGO addition on mechanical properties of the composites, such as Vickers hardness, flexural strength and fracture toughness, were investigated. The results showed that GO/B₄C composite powders were successfully self-assembled and a network structure was formed at high GO contents. The flexural strength and fracture toughness of rGO/B₄C composites were 643.64 MPa and 5.56 MPa m^1/2, respectively, at 1 and 2.5 wt.% rGO content, corresponding to an increase of 99.11% and 71.6% when compared to B₄C ceramics. Uniformly dispersed rGO in rGO/B₄C composites played an important role in improving their strength and toughness. The toughening mechanisms of rGO/B₄C composites were explained by graphene pull-out, crack deflection and bridging.     

一段混炼时间对石墨烯/天然橡胶/溶聚丁苯橡胶复合材料性能的影响

采用一段密炼和二段开炼的两段混炼工艺制备氧化石墨烯(GO)/天然橡胶(NR)/溶聚丁苯橡胶(SSBR)和还原氧化石墨烯(rGO)/NR/SBR复合材料,研究一段混炼时间对GO/NR/SSBR和rGO/NR/SSBR复合材料性能的影响。结果表明:随着一段混炼时间的延长,GO/NR/SSBR和rGO/NR/SSBR复合材料的Fmax和FL增大,t90缩短;邵尔A型硬度、300%定伸应力、拉伸强度和撕裂强度呈先增大后减小的趋势,导电性能和导热性能呈先提高后降低的趋势,气密性能呈先提高后平稳再降低的趋势。     

Effect of annealing temperature and graphene concentrations on photovoltaic and NIR-detector applications of PbS/rGO nanocomposites

The effect of annealing temperature on photovoltaic and near-infrared (NIR) detector applications of PbS nanoparticles (NPs) and PbS/graphene nanocomposites was investigated. The products were synthesized by a simple co-precipitation method and graphene oxide (GO) sheets were used as graphene source. Several characterization techniques were used to show transfer of the GO into reduced graphene oxide (rGO) during the synthesis process. In addition, the effect of graphene concentrations on morphology, structure, photovoltaic, and detector parameters of the samples were studied. Transmission electron microscope (TEM) images showed that, the PbS NPs were agglomerated, while, the PbS/rGO nanocomposites were dispersed completely after annealing under H₂/Ar gas atmosphere. UV–visible spectrometer showed an absorption peak for all samples in the near infrared red (NIR) region of the electromagnetic spectrum. The results indicated that, photocurrent intensity, responsivity of the samples to an NIR source, and solar-cell efficiency were affected by annealing of samples and graphene concentrations.     

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.