Graphene oxide-anchored reactive sulfonated copolymer via simple one pot condensation polymerization: proton-conducting solid electrolytes

A rapid and efficient post-polymerization functionalization of poly(urea-co-urethane) (PUU) onto the graphene oxide (GO) nanosheets has been developed to produce super-acidic polymer/GO hybrid nanosheets. Thus, the surface of GO nanosheets were functionalized with 3-(triethoxysilyl)propyl isocyanate (TESPIC) from hydroxyl groups to yield isocyanate functionalized graphene oxide nanosheets. Then, sulfonated polymer/GO hybrid nanosheets were prepared by condensation polymerization of isocyanate-terminated pre-polyurea onto isocyanate functionalized graphene oxide nanosheets through the formation of carbamate bonds. FTIR and TGA results indicated that TESPIC modifier agent and poly(urea-co-urethane) were successfully grafted onto the GO nanosheets. The grafting efficiency of poly(urea-co-urethane) polymer onto the GO nanosheets was estimated from TGA thermograms to be 205.9%. Also, sulfonated polymer/GO hybrid nanosheets showed a proton conductivity as high as 3.7 mS cm^?1. Modification and morphology of GO nanosheets before and after modification processes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD).     

Hollow porous carbon microspheres obtained by the pyrolysis of TiO2/poly(furfuryl alcohol) composite precursors

Disordered carbon materials with high porosity were prepared through the pyrolysis of TiO₂/poly(furfuryl alcohol) composites, obtained by the sol-gel method. The composites were prepared starting from titanium tetra-isopropoxide (TTIP) and furfuryl alcohol (FA) as precursors. Two different synthetic procedures for our composites were carried out, based on the addition of furfuryl alcohol (FA) before or after the TiO₂ nanoparticles formation. Also, different TTIP/FA ratio was tested. The hybrid materials obtained by both synthetic routes were pyrolyzed, under argon flow, at 900 °C producing novel TiO₂/carbon composites. All samples were characterized by XRD, FT-IR, DR-FTIR, Raman spectroscopy and TEM. Results indicated the effective FA polymerization on TiO₂ (anatase) nanoparticles, and polymer conversion to disordered carbon after the pyrolysis, simultaneously with TiO₂ anatase-rutile phase transition. The resulting TiO₂/carbon composites were treated with HF solution aiming the oxide dissolution, yielding an extremely porous carbon material as insoluble fraction. The morphology of these porous carbon materials is strongly dependent on the synthetic route adopted for the composite precursor, varying from carbon foam to highly ordered hollow microspheres.     

Synthesis of enhanced hydrophilic and hydrophobic graphene oxide nanosheets by a solvothermal method

We report that the hydrophilic affinity of graphene oxide nanosheets can be significantly increased by reacting with allylamine. High resolution transmission electron microscopy and electron diffraction analysis confirmed that the graphene oxide nanosheets were amorphous in structure. Hydrophobic graphene oxide nanosheets were also prepared via functionalising with phenylisocynate (C₆H₅NCO) through a solvothermal synthesis process. Hydrophobic graphene oxide nanosheets can be used as additives in polymer-based composites and other functional applications.     

Phenolic Thermoset Matrix Reinforced with Sugar Cane Bagasse Fibers: Attempt to Develop a New Fiber Surface Chemical Modification Involving Formation of Quinones Followed by Reaction with Furfuryl Alcohol

Summary: A new chemical modification of sugar cane bagasse fibers for phenolic thermoset composites is presented. It consists in creating quinones in the lignin portions of fiber and react them with furfuryl alcohol to create a coating around the fiber more compatible with the phenolic resins used to prepare polymeric matrix. Sodium periodate was used in suitable conditions to oxidize mainly phenolic syringyl and guaiacyl units of the lignin polymer to create quinones, which were characterized by UV‐visible diffuse reflectance spectroscopy by comparison with model compounds. The reactivity of furfuryl alcohol (FA) with fibers was greatly enhanced after they were oxidized: 13% weight percent gain compared to 2% without oxidation. Chemical analysis of unmodified and FA‐modified fibers have shown an important degradation of hemicelluloses and a slight one of cellulose which almost maintains its crystallinity. A 25% decrease of strength and length properties of the fibers after FA chemical treatment was measured by dynamic mechanical analysis. The lignin‐like proportion of the fiber was greatly enhanced after the FA‐treatment. This was confirmed by thermal analysis, DSC, and TGA experiments, on unmodified and FA‐modified fibers. SEM analysis of the fibers and of phenolic composites with modified fibers have confirmed the FA grafting and shown a better compatibility at the interface between the chemically modified fibers and the phenolic matrix. Nevertheless, the chemical treatment of the fibers decreased the impact strength of the composite, which could be caused by the fiber damage suffered during the chemical modification and for the more intense adhesion at the interface, which in some cases decrease somewhat the impact strength.

Cross photomicrography of FA‐modified sugar cane bagasse fiber (600×).     

Mechanical properties of carbon fiber composites modified with graphene oxide in the interphase

The surface topographies of carbon fibers treated by sizing agents with different graphene oxide (GO) content were investigated by scanning electron microscopy. The surface elements compositions of carbon fibers were determined by X‐ray photoelectron spectrometer. The interfacial properties of composites were studied by interfacial shear strength. The thermo‐mechanical properties of two typical specimens (CF‐G0 and CF‐G1 composites) were investigated by dynamic mechanical thermal analysis. The results showed the introduction of GO sheets on carbon fibers surfaces effectively improved the mechanical properties of carbon fibers/epoxy composites. POLYM. COMPOS., 38:2425–2432, 2017. © 2016 Society of Plastics Engineers     

Sonochemical synthesis and characterization of amine‐modified graphene/conducting polymer nanocomposites

The objective of this work is to modify graphene and study the effect of modification of graphene in thermal and electrical properties of graphene/polypyrrole and graphene/polyaniline nanocomposites. The amine functionalization of graphene was confirmed by Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. The nanocomposites were prepared by insitu oxidative polymerization method using ammonium persulfate as oxidant. Field emission scanning electron microscopy and high‐resolution transmission electron microscopy were used to study the morphology of the nanocomposites which indicates toward the better dispersion of modified graphene within the polymer matrices as compared to unmodified composites. The modification of graphene played an important role in the noticeable improvements in electrical conductivity of the prepared composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

Modification of oil palm empty fruit bunches with maleic anhydride: The effect on the tensile and dimensional stability properties of empty fruit bunch/polypropylene composites

Oil palm empty fruit bunch (EFB)‐filled polypropylene (PP) composites were produced. The EFB filler was chemically modified with maleic anhydride (MAH). The effects of the filler size and chemical modification of EFBs on the tensile and dimensional stability properties of EFB–PP composites were studied. The composites with MAH‐treated EFBs showed higher tensile strengths than those with untreated EFBs. This was attributed to the enhanced compatibility between the MAH‐treated EFBs and PP matrix, as shown in a scanning electron microscopy study. Fourier transform infrared analysis showed evidence of C?C and C?O bonds from MAH at 1630 and 1730 cm^?1, respectively. The MAH‐treated PP composites showed lower water absorption and thickness swelling than those with untreated EFBs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 827–835, 2003     

一种氧化还原石墨烯的稳定水溶液分散体的合成方法

提供了一种在聚苯乙烯磺酸钠（PSS）的帮助下,合成氧化还原石墨烯稳定水溶液分散体的简单方法。这种方法制备的分散体非常稳定,长达几个星期都没有聚集或者沉淀。通过各种方法对材料进行了表征。扫描电子显微镜（SEM）和紫外-可见光吸收光谱的结果表明PSS紧密地包裹住了石墨烯,形成功能化石墨烯;石墨烯的亲水性大大提高。傅里叶变换红外光谱（FTIR）表明O=S=O官能团的存在,说明石墨烯中存在PSS。X射线光电子能谱（XPS）提供了C/S的原子浓度比等,进一步说明了PSS的存在。结果表明,覆盖有PSS的氧化还原石墨烯能够应用于石墨烯的复合材料中。     

The effect of different modified multiwalled carbon nanotubes on tribological behaviors of poly(furfuryl alcohol) composite coatings

Three kinds of modified multiwalled carbon nanotubes (MWNTs) with different length were obtained by grafting carboxylic groups on long MWNTs or copolymer groups on short and long MWNTs. The modified MWNTs were examined by infrared spectroscopy, thermal gravimetric analysis, X‐ray photoelectron spectroscopy, and field emission scanning electron microscopy (FESEM). Afterward, the modified MWNTs were introduced into poly (furfuryl alcohol) (PFA), and the tribological behaviors of the resultant PFA composite coatings were investigated using a ring‐on‐block wear tester under dry friction condition. The dispersion of MWNTs in PFA composites and the worn surfaces were investigated by FESEM. The results indicated that the MWNTs dispersion and the tribological behaviors of PFA composite coatings could be obviously improved by modification with the copolymer. More significantly, under similarly uniform dispersion of MWNTs, the tribological properties of PFA composite coatings with short nanotubes presented better results when compared with those with long nanotubes because of the influence of nanotube length on the degree of modification of the MWNTs surfaces. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Enhanced mechanical and electrical properties of nylon‐6 composite by using carbon fiber/graphene multiscale structure as additive

In order to improve the mechanical properties and electrical conductivity of nylon‐6 (PA6) composites, a highly effective multiscale structure filler comprising poly(diallyldimethylammonium chloride) (PDDA)‐modified graphene and negatively surface‐charged carbon fiber was synthesized in this study. For this, the graphene used a top‐down method for synthesis by exfoliating graphite oxide (GO) through focused solar radiation on it and then modified its surface by using a polyelectrolyte. The carbon fiber (CF) surface was functionalized by an acid oxidation method. The multiscale structure was manufactured via the electrostatic interaction between the positively charged solar graphene (SG) and oppositely charged CF by homogeneous mixing. Scanning electron microscopy (SEM) images of the fracture surface of the PA6 composites exhibited that the carbon fiber/graphene multiscale structure possessed better dispersion and compatibility than those of individual CF and SG did. Thus, the impact strength, bending properties, and electrical conductivity of the PA6 composites were enhanced. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41968.     

Hydrothermal Synthesis of Graphene/Bi2WO6 Composite with High Adsorptivity and Photoactivity for Azo Dyes

Graphene/Bi₂WO₆ composites have been synthesized by hydrothermal reduction at 160°C for 24 h using ethanol as the reducing agent. All as‐prepared composites were characterized using X‐ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, FT‐IR spectroscopy, Raman spectroscopy, scanning electron microscopy, high‐resolution transmission electron microscopy, N₂ adsorption, and photocatalytic activity evaluation. The effective charge separation of graphene/Bi₂WO₆ composites was caused by the electrical conduction of graphene which is the most important factor. The results have proved the formation of interfacial contact between graphene nanosheets and Bi₂WO₆ nanoplates. The adsorptivity for azo dyes was enhanced greatly with the introduction of graphene. The oxy‐functional groups located at the edges of graphene were responsible for the enhanced adsorptivity. As‐prepared graphene/Bi₂WO₆ composites exhibited enhanced light absorption from UV to visible‐light region. In addition, the introduction of graphene would also result in smaller crystalline size and lower crystallinity of Bi₂WO₆. Graphene/Bi₂WO₆ composites containing an appropriate amount of graphene were proved to exhibit higher adsorptivities and photocatalytic activities for azo dyes. High photocatalytic activities of graphene/Bi₂WO₆ composites were considered to be the synergetic effects of high adsorption, high light absorption, and high electrical conduction induced by the introduction of graphene.     

Nanoscale toughening of carbon fiber‐reinforced epoxy composites through different surface treatments

Interests in improving poor interfacial adhesion in carbon fiber‐reinforced polymer (CFRP) composites has always been a hotspot. In this work, four physicochemical surface treatments for enhancing fiber/matrix adhesion are conducted on carbon fibers (CFs) including acid oxidation, sizing coating, silane coupling, and graphene oxide (GO) deposition. The surface characteristics of CFs are investigated by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, interfacial shear strength, and interlaminar shear strength. The results showed that GO deposition can remarkably promote fiber/matrix bonding due to improved surface reactivity and irregularity. In comparison, epoxy sizing and acid oxidation afford enhancement of IFSS owing to effective molecular chemical contact and interlocking forces between the fiber and the matrix. Besides, limited covalent bonds between silane coupling and epoxy matrix cannot make up for the negative effects of excessive smoothness of modified CFs, endowing them inferior mechanical properties. Based on these results, three micro‐strengthening mechanisms are proposed to broadly categorize the interphase micro‐configuration of CFRP composite, namely, “Etching” “Coating”, and “Grafting” modifications, demonstrating that proper treatments should be chosen for combining optimum interfacial properties in CFRP composites. POLYM. ENG. SCI., 59:625–632, 2019. © 2018 Society of Plastics Engineers     

Interpenetrating polymer networks of polyurethane and furfuryl alcohol. I. Morphology and mechanical properties

Polyurethane/furfuryl alcohol (PU/FA) interpenetrating polymer networks (IPNs) were synthesized from furfuryl alcohol using p-toluene sulfonic acid as a catalyst and blocked NCO-terminated PU prepolymer with m-xylylenediamine (MXDA) as a chain extender. From IR spectrum analysis it was found that the major reactions in the PU/MXDA/FA system are the polymerization of PU/MXDA and the self-polymerization of FA. The tensile strengths of PU/FA IPNs that contain 5 p.h.r. PU are greater than those of the pure components. The flexural strength, flexural modulus, Shore D hardness and HDT decrease and the notched Izod impact strength increases with the polyurethane content. The compatibility of the compounds in these PU/FA IPNs was investigated by dynamic mechanical analysis and scanning electron microscopy. It was found that glass transition temperatures are shifted inwardly which indicated that the PU/FA IPNs were semicompatible. It was confirmed from scanning electron micrography that the system was heterogeneous.     

Mechanical and piezo‐resistive properties of styrene–butadiene–styrene copolymer covalently modified with graphene/styrene–butadiene–styrene composites

As novel piezoelectric materials, carbon‐reinforced polymer composites exhibit excellent piezoelectric properties and flexibility. In this study, we used a styrene–butadiene–styrene triblock copolymer covalently grafted with graphene (SBS‐g‐RGO) to prepare SBS‐g‐RGO/styrene–butadiene–styrene (SBS) composites to enhance the organic solubility of graphene sheets and its dispersion in composites. Once exfoliated from natural graphite, graphene oxide was chemically modified with 1,6‐hexanediamine to functionalize with amino groups (GO–NH₂), and this was followed by reduction with hydrazine [amine‐functionalized graphene oxide (RGO–NH₂)]. SBS‐g‐RGO was finally obtained by the reaction of RGO–NH₂ and maleic anhydride grafted SBS. After that, X‐ray diffraction, X‐ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and other methods were applied to characterize SBS‐g‐RGO. The results indicate that the SBS molecules were grafted onto the graphene sheets by covalent bonds, and SBS‐g‐RGO was dispersed well. In addition, the mechanical and electrical conductivity properties of the SBS‐g‐RGO/SBS composites showed significant improvements because of the excellent interfacial interactions and homogeneous dispersion of SBS‐g‐RGO in SBS. Moreover, the composites exhibited remarkable piezo resistivity under vertical compression and great repeatability after 10 compression cycles; thus, the composites have the potential to be applied in sensor production. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46568.     

Improved interfacial properties of carbon fiber-reinforced epoxy composites with Fe2O3/graphene nanosheets using a magnetic field

The performance of carbon fiber-reinforced composites largely depends on the properties of the fiber-matrix interface. Here, to improve the interfacial strength properties of carbon fiber/epoxy composites, we doped different concentrations of Fe₂O₃/graphene nanosheets onto the interfacial region of the carbon fiber composites by nano-coating technology. With the aid of the magnetic field, the arrangement of nanosheets could be controlled in the interface. The nanosheets can be arranged on the carbon fiber surface parallel or perpendicularly with different concentrations. The tensile strength and interfacial shear strength of the modified fiber microcomposites had increased by 22.1 and 44.4% respectively with 1.0 mg/mL Fe₂O₃/graphene nanosheets. The results indicated that the Fe₂O₃/graphene nanosheets have an important influence on the carbon fibers and carbon fibers composites.     

Ultraporous Palladium Supported on Graphene‐Coated Carbon Fiber Paper as a Highly Active Catalyst Electrode for the Oxidation of Methanol

Ultraporous Pd nanocrystals for electrocatalysis applications were fabricated using a direct electrodeposition method on three differing carbon supports: flexible carbon fiber paper (CFP), and CFP modified with either graphene oxide nanosheets or their chemically reduced forms using a simple spray coating technique. The electrocatalytic activity of these electrodes was investigated for the direct electro‐oxidation reaction of methanol in alkaline media. Pd deposited on the CFP modified with reduced graphene oxide (rGO) has excellent poisoning tolerance to carbonaceous species and a significantly better catalytic activity toward methanol oxidation than the other two catalyst support materials. Pd/rGO/CFP in 2.0 M CH₃OH in 2.0 M NaOH yields a specific current density of 241 mAmg^–1 cm^–2 determined at the anodic oxidation peak. It is believed that the collaborative effects due to the three‐dimensional ultraporous Pd nanocrystals and fast electron transfer owing to high conductivity of rGO nanosheets play an important role in enhancing the catalytic performance of Pd/rGO/CFP toward methanol oxidation in alkali media.     

Utilization of multiple graphene nanosheets in fuel cells: 2. The effect of oxidation process on the characteristics of graphene nanosheets

Structural properties of graphene nanosheets that will be used as electrode material in fuel cells were investigated at different oxidation times. As the oxidation time was increased, the strong bonding between graphene layers in graphite was reduced and graphene layers started to exfoliate forming clusters with a few number of graphene layers. The variations in interplanar spacings, layer number and percent crystallinity indicated how stepwise chemical procedure influenced the morphology of graphite. It was possible to produce relatively flat graphene clusters with definite number of layers by controlling the oxidation time. Graphene nanosheets were characterized in detail by scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, and thermal gravimetric analyzer.     

Graphene nanosheets as cathode catalysts for lithium-air batteries with an enhanced electrochemical performance

Graphene nanosheets have been investigated as cathode catalysts for lithium-air batteries with alkyl carbonate electrolyte. Field emission scanning electron microscopy, transmission electron microscope and Raman spectroscopy have confirmed the high quality of the as-prepared graphene nanosheets and the surface analysis has identified the mesoporous characteristic of graphene nanosheets. The electrochemical properties of graphene nanosheets as cathode catalysts in lithium-air batteries were evaluated by a galvanostatic charge/discharge testing. The reaction products on the graphene nanosheets cathode were analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. The graphene nanosheet electrodes exhibited a much better cycling stability and lower overpotential than that of the Vulcan XC-72 carbon. This work demonstrated that graphene nanosheets could be an efficient catalyst for lithium-air batteries.     

Effect of ball milling speed on the quality of Al2O3 stripped graphene in a wet milling medium

Graphene nanosheets (GNSs)/Al₂O₃ composites were synthesized by wet milling. In this study, the effects of wet milling speed on the layer distribution, quality and conversion efficiency of graphene in GNSs/Al₂O₃ composites were studied using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), raman spectroscopy, fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results show that the intensity of graphite peak decreases and the conversion efficiency of graphene increases with the increase of rotational speed in the range of 200–300 rpm, and a small amount of graphene coated Al₂O₃ nanoparticles were found in GNSs/Al₂O₃ composites. The number of layers (≤10 layers) of GNSs gradually increases with the increase of ball milling speed. When the rotational speed is 300 rpm, the graphene conversion efficiency is the highest. At different rotational speeds, graphene defects were the least influential marginal defects. There was no characteristic peak of graphene oxide (GO) appeared in the composite, indicating a small oxidation degree of graphene.