Preparation of polystyrene/graphite nanosheet composite

A new process for the dispersion of graphite in the form of nanosheets in a polymer matrix was developed via in situ polymerization of monomer at the presence of sonicated expanded graphite during sonication. Graphite nanosheets prepared via powdering the expanded graphite had a thickness ranging 30-80 nm and a diameter ranging 0.5-20 μm and was an excellent nanofiller for the fabrication of polymer/graphite conducting nanocomposite. The process fabricated electrically conducting polystyrene/graphite nanosheet nanocomposite films with much lower percolation threshold and much higher conductivities than those of composites made by conventional methods.     

Fabrication of polyethylene/graphite nanocomposite from modified expanded graphite

A novel process was employed to fabricate a polymer/expanded graphite nanocomposite by modifying the conducting filler expanded graphite (EG) with unsaturated polyester resin (UPR). The modified expanded graphite (MEG) was prepared from EG in which the graphite nanosheets, already present in EG, were wrapped and isolated by the UPR during processing. The as‐prepared MEG was reduced to powder form to improve its dispersion in the matrix. MEG powders were embedded into a high‐density polyethylene (HDPE) matrix via melt‐extrusion in a single‐screw extruder to prepare the conducting composite. The as‐prepared HDPE/EG conducting composite exhibited a low percolation threshold of ～5.7 wt% due to the high aspect ratio of graphite nanosheets. Mechanical properties such as the tensile and impact strength were also studied. Scanning electron microscopy was used to characterize the microstructure of EG, MEG powder and the resulting nanocomposites. Copyright © 2006 Society of Chemical Industry     

Preparation of graphene nanosheet/polymer composites using in situ reduction-extractive dispersion

Graphene nanosheet/polymer composites were prepared using in situ reduction-extractive dispersion technology. The morphology and microstructure of the composites were examined by scanning electron and optical microscopy. The results indicate that graphene nanosheets from the reduction of graphite oxide are about 5 nm thick and 1-3 μm in diameter. Reduction-extractive dispersion technology can effectively promote the dispersion of graphene nanosheets and consequently an excellent conductive network is formed in the matrix. The percolation threshold of the composite is about 0.15 vol.%. When the graphene nanosheet content is lower than 1.5 vol.%, the conductivity of the composites is 3-5 orders of magnitude higher than that of composites filled with graphite nanosheets from expanded graphite.     

丁腈橡胶/膨胀石墨导电纳米复合材料的制备和性能

采用熔融插层法制备了丁腈橡胶/膨胀石墨纳米复合材料。扫描电镜(SEM)研究表明,超声处理后的膨胀石墨薄片厚度为纳米级。透射电镜(TEM)研究证实,膨胀石墨确以纳米级尺寸分散在橡胶基体中。力学性能研究表明,填加5份膨胀石墨时,纳米复合材料的拉伸强度最大,为28·4MPa,是不含膨胀石墨的复合材料的1·8倍。导电性能研究显示,填加10份膨胀石墨时,纳米复合材料的表面电导率和体积电导率分别为1·1×10-9S/cm和1·2×10-9S/cm,是不含膨胀石墨的复合材料的100倍和43倍。     

Preparation of polystyrene–graphite conducting nanocomposites via intercalation polymerization

In situ polymerization of styrene was conducted in the presence of expanded graphite obtained by rapid heating of a graphite intercalation compound (GIC), to form a polystyrene–expanded graphite conducting composite. The composite showed excellent electrically conducting properties even though the graphite content was much lower than in normal composites. The transition of the composite from an electrical insulator to an electrical semiconductor occurred when the graphite content was 1.8 wt%, which is much lower than that of conventional conducting polymer composites. TEM, SEM and other studies suggest that the graphite was dispersed in the form of nanosheets in a polymer matrix with a thickness of 10–30 nm, without modification of the space between carbon layers and the structure of the graphite crystallites. The composite exhibited high electrical conductivity of 10^?2 S cm^?1 when the graphite content was 2.8–3.0 wt%. This great improvement of conductivity could be attributed to the high aspect ratio (width‐to‐thickness) of the graphite nanosheets. The rolling process strongly affected the conductivity and the mechanical properties of the composite. © 2001 Society of Chemical Industry     

Material characterization of graphite nanosheet composites

Three sets of expanded graphite‐filled polymers, having three different particle sizes, were reinforced with 1–5% by weight. The structural, mechanical, electrical, and thermal properties of these composites were studied and compared. After dispersion, the particles were reduced to nanometer size through exfoliation, sonication, and high‐shear strain rate mixing, which further breaks and delaminates them. In addition, scanning electron microscope characterizations were performed. The expanded graphite‐filled polymer material could be tailored to be high conducting. Compared with the pure polymer, the polymers filled with 5 wt% expanded graphite have seen a significant reduction in electrical resistivity by orders. The thermal expansion coefficient and water absorption for the weight containing 5 wt% expanded graphite has also been drastically improved, decreasing with the weight percentage of graphite content. Compression and impact tests were conducted. The influence of dispersion on the material behavior was studied. Some fracture modes associated with the layered microstructures of the graphite nanosheets were observed. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

环氧树脂/镀银纳米石墨微片导热复合材料的制备与性能

以膨胀石墨为原料,采用超声分散法和化学镀法制得镀银纳米石墨微片,然后将其填充在环氧树脂基体中制备环氧树脂/镀银纳米石墨微片复合材料。结果表明,银粒子均匀镀覆在纳米石墨微片上,银层厚度为100 nm,有利于在环氧树脂基体中形成导热通路;与环氧树脂相比,环氧树脂/镀银纳米石墨微片复合材料的力学性能和热导率能都得到提高;当镀银纳米石墨微片含量为3 %时,复合材料的热导率为1.827 W/(m·K),比纯环氧树脂热导率提高了近5倍。     

Dispersion of graphite nanosheets in a polymer matrix and the conducting property of the nanocomposites

Poly(methyl methacrylate)(PMMA)/expanded graphite composite has been made via an in situ polymerization of methyl methacrylate(MMA) in the presence of expanded graphite obtained by rapid heating of the graphite intercalation compound (GIC). The composite was then blended with poly(vinyl chloride) (PVC) to form an electrically conducting composite. SEM, TEM and XRD showed that the graphite had been dispersed throughout the polymer matrix in the form of nanosheets with thicknesses of about 20 nm. The resulting composite showed excellent electrical conductivity despite a low concentration of graphite. The transition from an electrical insulator to an electrical semiconductor for the composite occurred when the graphite content was 3.5 wt%, much lower than that of conventional conducting polymer composites. Conductivity reached a maximum of 10^?4 s/cm at a graphite concentration of 5.0 wt%. This improvement of conductivity could be attributed to the high aspect ration (width‐to‐thickness) of the graphite nanosheets dispersed in the polymer matrix.     

In situ vacuum exfoliation plus microwave curing: A facile and green technique for preparing polymeric composites with very good dispersion based on expanded graphite

Functional polymeric composites based on expanded graphite (EG) have obtained wide attentions worldwide owing to their great potential in many fields. Poor dispersion is the main problem limiting the full exploitation of outstanding properties of these composites. To solve the problem, a facile and green method, named as in situ vacuum exfoliation plus microwave curing (VEMC) technique, is developed. The biggest merit of the VEMC process is that worm‐like EG particles are directly used to prepare composites, and no solvent or other chemical is needed, so the chemical structure and original advantages of exfoliatable fillers can be fully utilized in the composites. A series of composites based on EG particles and epoxy (EP) resin, coded as new‐EG/EP, were fabricated using the VEMC technique. Interestingly, worm‐like EG particles are found to be in situ exfoliated into nanosheets, and these sheets are well dispersed in the resin. Compared with the composites prepared using traditional processes, new‐EG/EP composites have much higher dielectric constants, demonstrating that the VEMC technique is efficient to prepare composites with good dispersion based on exfoliatable fillers. POLYM. COMPOS., 36:385–388, 2015. © 2014 Society of Plastics Engineers     

Preparation and characterization of high‐density polyethylene/expanded graphite conducting masterbatch

High level of expanded graphite (EG) was melt‐blended with high‐density polyethylene to prepare electrical conducting masterbatch. Some factors such as processing temperature, EG contents, treating time were discussed for the effect on electrical and mechanical properties of composites. Results showed that EG tends to reunite while the content of EG is higher than 60% because of the large aspect ratio and surface area of EG nanosheets. In addition, increasing processing temperature and mixing time appropriately could enhance the dispersion of EG, leading to improvement in electrical and mechanical properties. Scanning electron microscopy (SEM) measurements were used as an assistant analysis to study the microstructure of composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and characterization of a PMMA/Ce(OH)3, Pr2O3/graphite nanosheet composite

An easy process for the synthesis of poly(methyl methacrylate)/Ce(OH)₃, Pr₂O₃/graphite nanosheet (PMMA/Ce(OH)₃, Pr₂O₃/NanoG) composite was developed. Graphite nanosheets (NanoG) were prepared by treating the expanded graphite with sonication in aqueous alcohol solution. The PMMA/Ce(OH)₃, Pr₂O₃/NanoG composites were prepared via in situ polymerization of MMA monomer in the presence of graphite nanosheets and Ce(OH)₃, Pr₂O₃ through reverse micelle template, in which the methyl methacrylate was designated as the oily phase. The composites were then dispersed with chloroform and coated on glass slides to form films. Scanning and transmission electron microscopy were used to characterize the structure and dispersion of the graphite nanosheets and the composites. The results showed that the high-aspect-ratio structure of the nanosheets played an important role in forming a conducting network in the PMMA matrix. From thermogravimetric analysis, the introduction of graphite nanosheets and inorganic nanopartices exhibited a beneficial effect on the thermal stability of PMMA.     

Resin infusion of triaxially braided preforms with through‐the‐thickness reinforcement

Vacuum assisted resin transfer molding (VARTM) has shown potential to significantly reduce the manufacturing cost of high‐performance aerospace composite structures. In this investigation, high fiber volume fraction, triaxially braided preforms with through‐the‐thickness stitching were successfully resin infiltrated by the VARTM process. The preforms, resin infiltrated with three different resin systems, produced cured composites that were fully wet‐out and void free. A three‐dimensional finite element model was used to simulate resin infusion into the preforms. The predicted flow patterns agreed well with the flow patterns observed during the infiltration process. The total infiltration times calculated using the model compared well with the measured times.     

熔融挤出制备HDPE/纳米石墨薄片导电塑料研究

采用苯乙烯-丙烯腈共聚(AS)树脂对纳米石墨薄片(GN)进行包裹改性,制备成GN母料,并将它与高密度聚乙烯(HDPE)树脂进行混合挤出,制备了HDPE/GN复合材料,其渗滤阀值质量含量为14%。讨论分析了复合体系在加工过程中导电性能及其变化特征,研究了所制备的复合材料力学性能与石墨含量的关系。     

Mechanical and functional properties of composites based on graphite and carboxylated acrylonitrile butadiene rubber

In this study, carboxylated acrylonitrile butadiene rubber (xNBR)/expanded graphite (EG) nanocomposites were prepared with a latex compounding technique by ultrasonic stirring. The dispersion of EG in the xNBR matrix was investigated with transmission electron microscopy, scanning electron microscopy, and X‐ray diffraction analysis. EG could be exfoliated into lots of nanosheets dispersing in the xNBR matrix. More EG loading resulted in the presence of a few incompletely exfoliated agglomerates. The mechanical properties (hardness, tensile modulus, and tensile strength) of the xNBR/EG composites were determined. Dynamic mechanical thermal analysis was also performed, and it showed that the nanosheets of EG somewhat immobilized the motion of rubber macromolecular chains and led to the shifting and broadening of the tan δ peak toward higher temperatures. Many other functional properties of EG‐filled xNBR composites were studied, and it was established that the composites had excellent electrical conductivity as well as gas‐barrier and wear properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of graphite nanosheets in different solvents by sand milling and their enhancement on tribological properties of lithiumbased grease

Graphite nanosheets with the average thicknesses ranging from 24.4 to 48.9 nm were prepared with the use of expanded graphite as the raw material by sand milling in deionized water, anhydrous ethanol, glycerol, and 1,4-butanediol, respectively. Anhydrous ethanol favored the formation of graphite nanosheets with a smaller average thickness. When the graphite nanosheets with the content of 2 wt% were added in lithium-based grease, the average friction coefficient decreased by 27% as compared with the pure lithium-based grease. The weld point and load wear index were 1.6 and 1.4 times those of the pure lithium-based grease, respectively. The tribological properties of the graphite nanosheet-containing lithium-based grease were comparable with those of the graphene-containing lithium-based grease.     

Preparation of polypropylene/graphite nanocomposite with the aids of rotating solid‐state mixing and dynamic packing injection molding

In this work, to achieve good dispersion state of graphite in the nonpolar intractable polymer, polypropylene (PP), two specific compounding/molding techniques, rotating solid‐state mixing (RSSM), and dynamic packing injection molding (DPIM), were used during the preparation of PP/graphite nanocomposite. The enhanced dispersion/exfoliation of graphite substance in PP matrix induced by RSSM and/or DPIM treatment was well identified by a combination of polarized optical microscopy, wide‐angle X‐ray diffraction, and scanning electronic microscopy. A comparative analysis indicated that RSSM mainly pulverizes graphite pristine‐particles into tactoids with significantly decreased diameter‐size, while DPIM offers strong melt shear force for exfoliating graphite tactoids into nanosheets whose thicknesses are about tens nanometers and length of 1 micron. Uniform dispersion of graphite nanosheets leaded to substantial increase in heterogeneous crystallization rate and mechanical properties. Our present study proposes a facile effective approach for large‐scale preparation of polymer/graphite nanocomposite with high‐performances. POLYM. COMPOS., 35:1943–1951, 2014. © 2014 Society of Plastics Engineers     

Electrical,mechanical, and thermal properties of exfoliated graphite/phenolic resin composite bipolar plate for polymer electrolyte membrane fuel cell

Exfoliated graphite (EG) was synthesized from natural flake graphite by acid treatment followed by microwave irradiation. A maximum expanded volume of 560 mL/g was achieved for this exfoliation of graphite. EG/phenolic resin composite bipolar plates for polymer electrolyte membrane fuel cell were fabricated with a high loading of EG by compression molding. The composites possess low density, high electrical conductivity, high thermal stability, and high compressive strength. The composite bipolar plates were also characterized by X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and so on. The composite prepared with 50 wt% of EG has shown the desired properties for bipolar plate as per the US Department of Energy (DOE‐2015) targets. As a result, the EG–resin composites can be used as bipolar plates for polymer electrolyte membrane fuel cell applications. POLYM. ENG. SCI., 55:917–923, 2015. © 2014 Society of Plastics Engineers     

Performance of graphite filled composite based on benzoxazine resin

In this study, we aimed to prepare and characterize graphite filled composites based on benzoxazine resin for the bipolar plate in fuel cell. Three kinds of graphite (synthetic graphite, natural graphite, and expanded graphite) were used for the preparation of the graphite filled composites. The composites were prepared by means of the compression molding of mixtures of graphite and benzoxazine resin. The properties of the graphite filled composites based on benzoxazine resin were estimated by mechanical property, gas permeability, and electrical conductivity. As a result, it was found that graphite filled composites based on benzoxazine resin showed good gas impermeability, electrical conductivity and mechanical property compared with those of the graphite filled composites based on the conventional phenolic resin. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Silicone rubber/graphite nanosheet electrically conducting nanocomposite with a low percolation threshold

A novel electrically conductive nanocomposite was successfully fabricated by dispersing homogeneously conductive graphite nanosheets (GN) in an insulating silicone rubber (SR) matrix. GN were prepared by powdering expanded graphite with sonication in aqueous alcoholic solution. The particular geometry of GN 30–80 nm in thickness with high aspect ratio contributes to the advantage of forming the conducting network, so that the percolation threshold of SR/GN nanocomposite is about 0.009, much lower than that of composites with conventional graphite. The SR/GN nanocomposite presents a remarkable piezoresistive behavior under much low pressure, related to the low elastic modulus of the composite. The elastic modulus of the nanocomposite with various GN content and at the different speed of compression was discussed. POLYM. COMPOS., 28:493–498, 2007. © 2007 Society of Plastics Engineers     

Simultaneously improved toughness and dielectric properties of epoxy/graphite nanosheet composites

Very thin graphite nanosheets are obtained using an ultrasonic irradiation method, and epoxy/graphite nanosheet composites with different filler content are fabricated using the diglycidylether of bisphenol A epoxy matrix. An investigation of structural characteristics and mechanical and dielectric properties of the nanocomposites is carried out. SEM micrographs shows that the thickness of a single layer graphite nanosheet is about 20 nm whereas FTIR studies indicates that the surfaces of the graphite nanosheets are enriched with hydroxyl and carbonyl groups. The dielectric constants of the composites are increased with increases in graphite nanosheet content lower than 3.5 wt%, and are still higher than 100 in the high frequency range with 3.5 wt% graphite filler content. The tensile strength and storage modulus of the composites increase with increasing nanosheet concentration. These epoxy/graphite nanosheet composites, which show both high dielectric constant and toughness, could have potential application in embedded capacitor technology. POLYM. ENG. SCI., 50:1734–1742, 2010. © 2010 Society of Plastics Engineers