Preparation of highly conductive reduced graphite oxide/poly(styrene-co-butyl acrylate) composites via miniemulsion polymerization

Polymer/reduced graphite oxide (rGO) composite nanoparticles with a high electrical conductivity were synthesized using the miniemulsion polymerization technique. The rGO was modified with a reactive surfactant, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), to facilitate monomer intercalation into the rGO nanogalleries. The AMPS-modified rGO was emulsified in the presence of styrene (St) and butyl acrylate (BA) monomers, and the stable miniemulsion was polymerized to form poly(St-co-BA)/rGO composite latex nanoparticles. The transition in the composite nanoparticles from an electrical insulator to an electrical conductor occurred at an rGO content of 10 wt% (relative to the monolayer content), yielding an electrical conductivity of 0.49 S/cm. The electrical conductivity of the composite nanoparticles reached 2.22 S/cm at 20 wt% rGO, yielding a much better conductivity than other polymer composites prepared using a GO filler. Importantly, the miniemulsion polymerization method for fabricating poly(St-co-BA)/rGO composite nanoparticles is easy, green, low-cost, and scalable, providing a universal route to the rational design and engineering of highly conductive polymer composites.     

Polymer/graphene oxide (GO) thermoset composites with GO as a crosslinker

Composites have historically been of intense interest due to their potential to replace glass, wood and metal at a fraction of the weight. Of the many choices of fillers, graphene oxide (GO) is generally attractive for its versatility and tunability in terms of surface functionality, size and shape. While the majority of GO has been incorporated into polymers and polymer precursors by physical mixing, this review focuses on research where GO has served as both a property enhancer and multifunctional crosslinker in thermosets. Methods for preparing GO (with and without additional functionalization) and incorporating it appropriately into thermosets are described. A review of characterization techniques, typically applied before and after GO is incorporated into thermosets and analytical methods for confirming important chemical reactions during crosslinking, is also provided. Finally, the resulting composite thermoset properties are surveyed throughout to connect preparation and characterization methods to their potential practical importance.     

Preparation of poly(butylene succinate) vitrimer with thermal shape stability via transesterification reaction

Poly(butylene succinate) (PBS) refers to a high-performance biodegradable polymer employed to substitute petroleum polymers that cause environmental issues. However, PBS exhibits the defect of flowing above the melting point and rapid dripping for its poor melt strength. Accordingly, this study proposed a novel method to fabricate PBS vitrimer by exploiting reactive extrusion technology to mix diepoxide with PBS and then by employing zinc acetate as a catalyst to crosslink the PBS. Therefore, after the reaction extrusion blending, the blend still has a lower viscosity and high processing performance; in the subsequent curing process, the polymer undergoes a transesterification reaction and the viscosity increases. Via transesterification to form a cross-linked network, the storage modulus, and loss modulus of PBS vitrimer at 140°C reach 55,800% and 3500% of pure PBS, respectively. At this time, the crystallinity of PBS vitrimer is still as high as 56.9% (The crystallinity of pure PBS is 47.4%). And the shape stability of PBS at high temperatures was significantly improved. Moreover, PBS vitrimer could still be reshaped after the cross-linking process. This study proposed a facile method to produce PBS materials exhibiting high thermal shape stability.     

Si/SiC coated Cf/SiC composites via tape casting and reaction bonding: The effect of carbon content

In this paper, a novel surface modification method for C_f/SiC composites is proposed. Si/SiC coating on C_f/SiC composites is prepared by tape casting and reaction bonding method. The effects of carbon content on the rheological property of the slurries along with the microstructure of the sintered coatings are investigated. The best result has been obtained by infiltrating liquid silicon into a porous green tape with a carbon density of 0.84 g/cm³. In addition, the effect of sintering parameters on the phase composition of the coatings is studied. Dense Si/SiC coating with high density as well as strong bonding onto the substrate is obtained. This Si/SiC coating exhibits an excellent mechanical property with HV hardness of 16.29±0.53 GPa and fracture toughness of 3.01±0.32 MPa m^1/2. Fine surface with roughness (RMS) as low as 2.164 nm is achieved after precision grinding and polishing. This study inspires a novel and effective surface modification method for C_f/SiC composites.     

Transforming rapeseed oil into fatty acid ethyl ester (FAEE) via the noncatalytic transesterification reaction

A simple methodology for producing biodiesel is presented. The noncatalytic transesterification was carried out via the thermochemical process because the main driving force of biodiesel conversion was temperature rather than pressure. Noncatalytic transformation of rapeseed oil into fatty acid ethyl ester (FAEE) was performed in a continuous flow system under ambient pressure in the presence of activated alumina, charcoal, and carbon dioxide (CO₂). The biodiesel conversion methodology introduced in this work enables the esterification of fatty acids (FFAs), and transesterification of triglycerides to be combined into a single process and leads to a 97.5 (±0.5)% conversion efficiency of biodiesel within 1 min at 420–500^°C. The new process has high potential to achieve a breakthrough in minimizing the cost of biodiesel production owing to its simplicity and technical advantages. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1468–1471, 2013     

Toughening of thermoset/thermoplastic composites via reaction‐induced phase separation: Epoxy/phenoxy blends

Phase morphology and phase separation behavior of amine‐cured bisphenol‐A diglycidyl ether epoxy and phenoxy mixtures have been investigated by means of time‐resolved small angle light scattering, optical microscopy, and scanning electron microscopy. The starting reactant mixtures composed of epoxy, phenoxy, and curing agents such as diaminodiphenyl sulfone (DDS) and methylene dianiline (MDA) were found to be completely miscible. Upon curing with DDS at 180°C, phase separation took place in various epoxy/phenoxy blends (compositions ranging from 10–40% phenoxy), whereas the MDA curing showed no indication of phase separation. The mechanical and physical properties of single‐phase and two‐phase networks were examined, in that the DDS‐cured epoxy/phenoxy blends having a two‐phase morphology showed improved ductility and toughness without significantly losing other mechanical and thermal properties such as modulus, tensile strength, glass transition and heat deflection temperatures. The energy absorbed to failure during the drop weight impact event was also found to improve relative to those of the single‐phase MDA‐cured blend as well as of the neat epoxy. Such property enhancement of the DDS‐cured blends has been discussed in relation to the two‐phase morphology obtained via scanning electron microscopy micrographs of fractured surfaces. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1257–1268, 2000     

Synthesis of high conductivity Polyaniline/Ag/graphite nanosheet composites via ultrasonic technique

A new process for the synthesis of high conductivity polyaniline/Ag/graphite nanosheet (PANI/Ag/NanoG) composites was developed. Graphite nanosheet was prepared by treating the expanded graphite in aqueous alcohol solution using sonication, and a uniform silver film about 470 nm thick was obtained on graphite nanosheet surface via an improved electroless plating method. Then PANI/Ag/NanoG composites were fabricated via in situ polymerization of aniline monomer in the presence of silver coated graphite nanosheet through using ultrasonic technique. The sliver particles and composites were evidenced by scanning and transmission electron microscopy examinations, the results showed that the silver coated graphite nanosheet particles played an important role in forming conducting bridge in polyaniline matrix. According to the electrically test, the conductivity of the PANI/Ag/NanoG composites was dramatically increased compared with pure PANI. From the thermogravimetric analysis, the PANI/Ag/NanoG composites exhibited a beneficial effect on the thermal stability of pure PANI.     

Mechanical properties of polydicyclopentadiene/graphite nanosheet composites prepared by reaction injection moulding

Abstract

Polydicyclopentadiene (PDCPD)/expanded graphite nanosheets treated with silane coupling agent (TEG) composites were prepared by simulating reaction injection moulding. Studies on the mechanical and tribological properties of the composites were carried out. The results showed that TEG of low content had an effect on reinforcing the PDCPD matrix. The incorporation of TEG in PDCPD greatly decreased wear rates and slightly increased friction coefficients under both dry sliding and oil lubricated conditions. The SEM images of the worn surface revealed their wear mechanisms. Unfilled PDCPD was characterised by spalling, with adhesive wear being the major wear form. Polydicyclopentadiene composites were characterised by plastic deformation, fatigue microcracking, spalling and ploughing effect in dry sliding. The wear forms for PDCPD composites under oil lubricated condition were also complicated, and several wear forms such as adhesive, abrasive and fatigue wears co-existed.     

Reactive processing of ethylene-vinyl acetate rubber/polyamide blends via a dynamic transesterification reaction

Dynamic vulcanization process of ethylene-vinyl acetate rubber (EVM) and ternary polyamide copolymer (tPA) blends in the presence of tetraethyloxysilane (TEOS) was investigated. The morphology, crosslink density and mechanical properties of the resultant EVM/tPA thermoplastic elastomers (TPEs) were characterized. The dynamically crosslinked EVM phase was distributed homogeneously in the continuous tPA phase for the EVM/tPA (70/30) TPE, and the phase size of EVM decreased further as the TEOS content increased. The crosslink density reached 3.17 × 10^?5 mol cm^?3, and the tensile strength and the elongation at break were up to 10.6 MPa and 296 %, respectively, when the TEOS content was increased to 8 phr, and the heat oil resistance was accordingly enhanced. As compared to dicumyl peroxide-initiated crosslinking reaction of EVM, the crosslinking reaction of EVM through the transesterification reaction between EVM and TEOS presented lower crosslinking rate constant and activation energy, indicating that the transesterification reaction is more suitable for high temperature dynamic vulcanization processing. The optimized dynamic vulcanization process of EVM/tPA TPEs is useful for developing high-performance TPEs for automotive applications.     

Toughening of epoxy/polycaprolactone composites via reaction induced phase separation

A series of melt processable thermoset/thermoplastic blends were prepared by mixing bisphenol‐A diglycidyl ether (Epon‐828)/diaminodiphenyl sulfone (DGEBA/DDS) system with two grades of polycaprolactone resin. Phase separation behavior of the blends was investigated by means of optical microscopy, microstructure by scanning electron microscopy (SEM), and thermo‐mechanical properties. The toughness of polycaprolactone modified epoxies was measured by instrumented falling weight impact (IFWI) testing. Various blend morphologies were observed depending upon the cured epoxy network/thermoplastic composition. Spinodal decomposition as characterized by modulated structure of unique periodicity and phase connectivity was found to be the probable mechanism of phase separation. SEM examination of fracture surfaces indicated a strong adhesion between the epoxy‐rich and polycaprolactone‐rich phases. Optimum improvement in failure energy was obtained for the compositions containing 10‐20% polycaprolactone without significantly compromising the elastic modulus and the thermo‐mechanical stability of the epoxy. In light of morphological evidences, a possible toughening effect was postulated in terms of tearing of the thermoplastic component and induced plastic deformation of the epoxy matrix.     

Low-frequency plasmonic state and tunable negative permittivity in percolative graphite / barium titanate composites

Percolative composites with negative permittivity have attracted widespread attentions due to their great potential in electromagnetic shielding and microwave devices. Targeting at achieving epsilon-negative properties, the percolative graphite/barium titanate (GR/BaTiO₃) composite is herein designed and prepared using hot-pressing sintered process. It's found that the plasma oscillations of delocalized electrons result in the epsilon negative permittivity behaviors when the GR contents exceeds the 2 wt% (percolation threshold), and frequency dependence of the negative permittivity which is in well agreement with the Drude model. Meanwhile, it's demonstrated that the ac conductivity represents a typical metal-like behavior as the conductive networks formed within the composites by the increasing GR loadings. Moreover, the equivalent circuit analysis reveals the relationships between capacitive-inductive transition and the conversion of permittivity changing from positive to negative. This work provides effective possibility for developing excellent dielectric properties of percolative GR/BaTiO₃ composite for capacitors and coil-less electrical inductors applications.     

High electrical conductive polymethylmethacrylate/graphite composites obtained via a novel pickering emulsion route

In this work, high electrically conductive Polymethylmethacrylate/graphite (PMMA/G) composites with a specific core-shell structure were synthesized via Pickering emulsion (solid-stabilized emulsion) route. The electrical conductivity of the core-shell composites was measured by a four-point probe resistivity determiner and a very high value of 9.8?×?10^?3 S/cm (10¹³ times higher than virgin PMMA) was obtained at 30 wt% graphite. However, the electrical conductivity of the PMMA/G composites gained through traditional blend process was relatively lower and the value only reached 9.4?×?10^?9 S/cm at same graphite loading fraction. Contact angle measurement was applied to determine the surface free energy of the modified graphite which was cladded by Al(OH)₃. The morphology of the core-shell composites was observed by SEM and optical microscopy. Dynamic rheology analysis was employed to study the structural change by the interconnection of the graphite flakes and the formation of the networks in the composites. The interconnected networks of the core-shell composites were more easily constructed when compared with the composites obtained by the traditional blending process.     

Interfacial bonding and optical transmission for transparent fiberglass/poly(methyl methacrylate) composites

Evidence is presented relating the interfacial bonding strength and the optical transmission of transparent glass fiber reinforced PMMA composites. The temperature dependent (20° to 50°C) optical transmission of composites that contained uncoated 13 μm glass fibers and 13 μm glass fibers coated with divinyltetramethyl disilazane or 3-(trimethoxysilyl)propyl methacrylate was found to decrease in the same order as the bond strength of the PMMA/glass fiber interface, namely, trimethoxy silane coated fiber, disilazane coated fiber, and uncoated fiber. SEM photographs showed similar fracture surfaces, clean fiber pull-out, and no apparent bonding of the glass fiber to the PMMA for the composites containing uncoated and disilazane coated fiber, whereas, the composite containing trimethoxy silane coated fiber showed virtually no clean fiber pullout. Additional evidence for differences in the bonding strength is seen in the degradation (penetration of water and fiber whitening) on aging at 23°C in air or water for composites containing uncoated fiber (most degradation), disilazane coated fiber (slight degradation), and trimethoxy silane coated fiber (no degradation). The optical transmission between 20° and 30°C at 600 to 800 nm for the composite containing trimethoxy silane coated fiber decreased the least with increasing temperature (from ∼85% to 70%) while the composite containing uncoated fiber decreased the most (from ∼85% to 32%).     

Electrical conductivity of graphite/polystyrene composites made from potassium intercalated graphite

Composites between graphite and polystyrene have been synthesized starting from potassium intercalated graphite and styrene vapor. This in situ polymerization process can be used to make electrically conductive composites containing well-dispersed thin graphite sheets. The conductivities of the composites increase as the number of ordered carbon layers increases. With only 10% graphite in a polystyrene matrix, an electrical conductivity up to 1.3 × 10⁻¹ S/cm can be obtained. The key is synthesizing a material with at least four ordered graphite layers (a stage IV complex) separated by polystyrene. This composite shows an improvement in conductivity over a control composite made by radical polymerization of styrene containing the same amount of dispersed graphite which had a conductivity of 5.0 × 10⁻³ S/cm. Characterization of the complexes by powder X-ray diffraction, scanning electron microscopy and electrical conductivity is presented.     

Capacitance properties of graphite oxide/poly(3,4‐ethylene dioxythiophene) composites

Poly(3,4‐ethylene dioxythiophene) (PEDOT) and graphite oxide (GO)/PEDOT composites (GPTs) doped with poly(sodium styrene sulfate) (PSS) were synthesized by in situ polymerization in aqueous media. The electrochemical capacitance performances of GO, PEDOT–PSS, and GPTs as electrode materials were investigated. The GPTs had a higher specific capacitance of 108 F/g than either composite constituent (11 F/g for GO and 87 F/g for PEDOT–PSS); this was attributable to its high electrical conductivity and the layer‐within/on‐layer composite structure. Such an increase demonstrated that the synergistic combination of GO and PEDOT–PSS had advantages over the sum of the individual components. On the basis of cycle‐life tests, the capacitance retention of about 78% for the GPTs compared with that of 66% for PEDOT–PSS after 1200 cycles suggested a high cycle stability of the GPTs and its potential as an electrode material for supercapacitor applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Flame retarding effect of graphite in rotationally molded polyethylene/graphite composites

Linear low‐density polyethylene (LLDPE) compounds containing 10 wt % graphite fillers were rotationally molded into flat sheets. Flame retardancy was studied using cone calorimeter tests conducted at a radiative heat flux of 35 kW/m². Only the expandable graphite, an established flame retardant for polyethylene, significantly reduced the peak heat release rate. Compared with the neat polyethylene, it was easier to ignite the LLDPE composites containing carbon black, expandable graphite, and exfoliated graphite. However, rather unexpectedly, the inclusion of flake graphite increased the time to ignition by up to 80%. Simulations conducted with the ThermaKin numerical pyrolysis software suggest that increased reflectivity was mainly responsible for this effect. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41472.     

聚合物/纳米石墨微片复合材料的研究进展

详述了纳米石墨微片（NanoG）的制备工艺、结构特征,重点归纳总结了纳米石墨微片与聚甲基丙烯酸甲酯（PMMA）、聚苯胺(PANI)、聚苯乙烯(PS)以及聚吡咯(PPy)复合材料的复合方法、性能及应用情况。最后对聚合物/纳米石墨微片复合物制备工艺问题,纳米石墨微片在聚合物中的分散性问题以及如何提高聚合物/纳米石墨微片复合物的导电性问题进行了展望,同时提出改性的纳米石墨微片与聚合物复合的应用研究将是一个崭新的研究领域。     

Rheological behavior of cycloolefin copolymer/graphite composites

In this study, morphological and rheological properties of cycloolefin copolymer (COC)/graphite composites prepared in a twin screw extruder by using various amounts of graphite (G) and expanded graphite (EG) were investigated in detail. Rheological behaviors of the samples were measured in a dynamic oscillatory rheometer in the melt state. Rheology data were analyzed in different ways in order to quantify the microstructural features which indicate the solid‐state physical properties of the composite materials. In the linear viscoelastic region, increasing of storage modulus (G′) with the filler amount and the van Gurp‐Palmen plots were used to determine the percolation threshold which is the critical filler amount for the physical network formation by the G sheets. Percolation threshold values were found to be about 21.5 phr and 3.8 phr for the G‐ and EG‐loaded samples, respectively. Microstructures of the samples which include quite higher amount of filler than the percolation were observed in a scanning electron microscopy. It was found that the sheets of pristine G maintained their original stack form while the EG was successfully dispersed in the COC phase and formed three dimensional house‐of‐card structures without a compatibilizer. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

改性石墨/丁腈橡胶复合材料的性能

采用十六烷基三甲基溴化铵、硅烷偶联剂KH 570以及聚乙二醇分别对石墨表面进行了有机改性,通过机械共混法制备了改性石墨/丁腈橡胶复合材料,考察了改性剂种类以及改性石墨用量对复合材料物理机械性能及摩擦性能的影响,并用扫描电子显微镜表征了石墨在橡胶基体中的分散情况及复合材料磨损表面情况。结果表明,随着改性石墨用量的增加(20份以内),复合材料的物理机械性能有所上升,摩擦系数不断下降;3种改性剂中,KH 570改性石墨所制备复合材料的物理机械性能及摩擦性能较优,当添加20份KH 570改性石墨时,其在橡胶基体中分散较好,磨损表面最为光滑、平整,复合材料的物理机械性能最佳,摩擦系数达到最低值(0.7)。