The preparation of high performance and conductive poly (vinyl alcohol)/graphene nanocomposite via reducing graphite oxide with sodium hydrosulfite

Sodium hydrosulfite is used to reduce graphite oxide in current study. The preparation of poly (vinyl alcohol) (PVA)/graphene nanocomposites is realized using two simple steps: the synthesis of PVA/graphite oxide (GO) nanocomposites film and immersion of such a film in the reducing agent aqueous solution. This method prohibits the agglomeration of GO during direct reduction in PVA/GO aqueous solution, and opens a new way to scale up the production of graphene nanocomposites using a simple reducing agent. A 40% increase in tensile strength and 70% improvement in elongation at break have been obtained with only the addition of 0.7 wt.% of reduced graphite oxide. Furthermore, a good level of conductivity and a variation in the surface property of the prepared films have been observed for the composites containing graphene.     

Highly conductive graphene oxide/polyaniline hybrid polymer nanocomposites with simultaneously improved mechanical properties

Graphene oxide (GO) was added to a polymer composites system consisting of surfactant-wrapped/doped polyaniline (PANI) and divinylbenzene (DVB). The nanocomposites were fabricated by a simple blending, ultrasonic dispersion and curing process. The new composites show higher conductivity (0.02–9.8 S/cm) than the other reported polymer system filled with PANI (10⁻⁹–10⁻¹ S/cm). With only 0.45 wt% loading of GO, at least 29% enhancement in electric conductivity and 29.8% increase in bending modulus of the composites were gained. Besides, thermal stability of the composites was also improved. UV–Vis spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) revealed that addition of GO improves the dispersion of PANI in the polymer composite, which is the key to realize high conductivity.     

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (T_g) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T_5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10⁻² S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K.     

Crystallization,mechanical performance and hydrolytic degradation of poly(butylene succinate)/graphene oxide nanocomposites obtained via in situ polymerization

Poly(butylene succinate) (PBS)/graphene oxide (GO) nanocomposites were fabricated via in situ polymerization with very low GO content (from 0.03 to 0.5 wt%). The microstructures of the nanocomposites were characterized with Raman spectroscopy, fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), sedimentation experiments and atomic force microscopy (AFM). The results showed that PBS chains have been successfully grafted onto GO sheets during in-situ polymerization, accompanied by the thermo-reduction from GO to graphene. The grafted GO displayed a great nucleating effect on PBS crystallization, resulting in largely improved crystallization temperature and decreased spherules size. A simultaneous enhancement in tensile strength and elongation was achieved for PBS/GO nanocomposites fiber. Meanwhile, increase in hydrolytic degradation rate was also observed for these nanohybrids. Our result indicates that using very low content GO is a simple way to achieve good dispersion yet with remarkable property enhancement for polymer/GO nanocomposites.     

Fabrication of microwave exfoliated graphite oxide reinforced thermoplastic polyurethane nanocomposites: Effects of filler on morphology,mechanical, thermal and conductive properties

Different formulations of microwave-exfoliated graphite oxide (MEGO) based thermoplastic polyurethane (TPU) nanocomposites were successfully prepared via melt blending followed by injection molding. The spectroscopic study indicated that a strong interfacial interaction had developed between the MEGO and the TPU matrix. The microscopic observations showed that the MEGO layers were homogeneously dispersed throughout the TPU matrix. Thermal analysis indicated that the glass transition temperatures (T_g) of the nanocomposites increased with increasing MEGO content and their thermal stability improved in comparison with pure TPU matrix. The mechanical properties of nanocomposites improved substantially by the incorporation of MEGO into the TPU matrix. Electrical conductivity test indicated that a conductivity of 10⁻⁴ S cm⁻¹ was achieved in the nanocomposite containing only 4.0 wt.% of MEGO.     

A study on the preparation of highly conductive graphene

The effects of the washing conditions of graphite oxide (GO) and pyrolysis times on the thermal reduction of graphene are discussed in this article. Graphene samples that had been pyrolyzed for 30 s and 5 min remained homogeneous in N,N-Dimethylformamide (DMF) for one month, whereas those samples that had been pyrolyzed for 20 and 40 min precipitated after one day. The conductivity of graphene increased with pyrolysis time. The resistivity of graphene thermally post-treated for 40 min reached 0.01 Ωcm. Whether or not GO was washed with deionized water had little effect on the structure and electric properties of graphene.     

Preparation and thermomechanical properties of Ag-PVA nanocomposite films

Metal–polymer hybrid nanocomposites have been prepared from an aqueous solution of polyvinyl alcohol (PVA) and silver nitrate (AgNO₃). The silver nanoparticles were generated in PVA matrix by the reduction of silver ions with PVA molecule at 60–70 °C over magnetic stirrer. UV–vis analysis, X-ray diffraction studies, transmission electron microscopy, scanning electron microscopy and current–voltage analysis were used to characterize the nanocomposite films prepared. The X-ray diffraction analysis reveals that silver metal is present in face centered cubic (fcc) crystal structure. Average crystallite size of silver nanocrystal is 19 nm, which increases to 22 nm on annealing the film at 150 °C in air. This result is in good agreement with the result obtained from TEM. The UV–vis spectrum shows a single peak at 433 nm, arising from the surface plasmon absorption of silver nanocolloids. This result clearly indicates that silver nanoparticles are embedded in PVA. An improvement of mechanical properties (storage modulus) was also noticed due to a modification of PVA up to 0.5 wt% of silver content. The current–voltage (I–V) characteristic of nanocomposite films shows increase in current drawn with increasing Ag-content in the films.     

Hydrolytic dehydrogenation of ammonia borane catalyzed by poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets supported Ag0.3Co0.7 nanoparticles

Poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets (PAMAM/rGO) composite was selected as a carrier of heterogeneous Ag_0.3Co_0.7 nanoparticles in order to obtain an excellent catalyst for ammonia borane (AB) hydrolysis. During the synthetic processes, GO could easily assembled with PAMAM by the electrostatic and hydrogen-bonding interactions. Structural characterization revealed that Ag_0.3Co_0.7 bimetallic nanoparticles with uniform size distribution of 5 nm are well dispersed on PAMAM/rGO composite architecture. Ag_0.3Co_0.7@PAMAM/rGO was found to be a highly active and reusable catalyst in hydrogen generation from the hydrolysis of AB with a turnover frequency value (TOF) of 19.79 mol_H2 min^–1 mol_M^–1 at 25.0 ± 0.1 °C and retained 75.4% of their initial activity with a complete release of hydrogen in five runs. The relatively high TOF value and low apparent activation energy (34.21 kJ mol^–1) make these Ag_0.3Co_0.7@PAMAM/rGO NPs as a high-efficient catalyst for catalytic dehydrogenation of AB facilitating the development of practically applicable energy storage materials.     

Strong and optically transparent biocomposites reinforced with cellulose nanofibers isolated from peanut shell

Cellulose nanofibers–reinforced PVA biocomposites were prepared from peanut shell by chemical–mechanical treatments and impregnation method. The composite films were optically transparent and flexible, showed high mechanical and thermal properties. FE-SEM images showed that the isolated fibrous fragments had highly uniform diameters in the range of 15–50 nm and formed fine network structure, which is a guarantee of the transparency of biocomposites. Compared to that of pure PVA resin, the modulus and tensile strength of prepared nanocomposites increased from 0.6 GPa to 6.0 GPa and from 31 MPa to 125 MPa respectively with the fiber content as high as 80 wt%, while the light transmission of the composite only decreased 7% at a 600 nm wavelength. Furthermore, the composites exhibited excellent thermal properties with CTE as low as 19.1 ppm/K. These favorable properties indicated the high reinforcing efficiency of the cellulose nanofibers isolated from peanut shell in PVA composites.     

Chemical functionalization of graphene oxide for improving mechanical and thermal properties of polyurethane composites

Graphene oxide (GO) was chemically functionalized to prepare polyurethane (PU) composites with improved mechanical and thermal properties. In order to achieve a well exfoliated and stable GO suspension in an organic solvent (dimethylformamide, DMF), 4, 4′-methylenebis(phenyl isocyanate) and polycaprolactone diol, which were the two monomers for synthesizing PU, were selectively used to functionalize GO. The obtained functionalized GO (FGO) could form homogeneous dispersions in DMF solvent and the PU matrix, as well as provide a good compatibility with the PU matrix. The most efficient improvement of mechanical properties was achieved when 0.4 wt.% FGO was added into the PU matrix, showing increases in the tensile stress, elongation at break and toughness by 34.2%, 27.6%, and 64.5%, respectively, compared with those of PU. Regarding the thermal stability, PU filled with 1 wt.% FGO showed the largest extent of improvement with T_2% and T_50% (the temperatures at which 2% and 50% weight-loss happened) 16 °C and 21 °C higher than those of PU, respectively. The significant improvement in both mechanical properties and thermal stability of FGO/PU composites should be attributed to the homogeneous dispersion of FGO in the PU matrix and strong interfacial interaction between them.     

Effect of reduced graphene oxide (rGO) on structural,optical, and dielectric properties of Mg(OH)2/rGO nanocomposites

In this paper, we report the synthesis of Mg(OH)₂ NPs and Mg(OH)₂–rGO nanocomposites (NCs) by microwave assisted co-precipitation method. The crystal phase, structural morphology and functional groups of the as-synthesized samples were analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR). Raman spectroscopy was used to study the defects in the samples. Raman spectroscopy and the SEM results validate the growth of Mg(OH)₂ NPs on the rGO nanosheets. The chemical composition of the prepared samples was analyzed by EDAX. Optical properties of the as-synthesized samples were studied by UV–visible spectroscopy and the energy band gap was calculated by Tauc relation which shows a decrease in band gap with an increase in the amount of Graphene Oxide (GO) in the NCs. The dielectric properties were studied as a function of frequency over a range of 50 Hz to 5 MHz at room temperature. The value of dielectric constant decreases with an increase in frequency, this could be due to the existence of a polarization process at the border of the rGO sheets and Mg(OH)₂ NPs. The value of dielectric loss shows a decreasing trend with an increase in frequency whereas the larger value of AC conductivity in Mg(OH)₂–rGO NCs as compared to Mg(OH)₂ NPs approves the restoration of sp² network in the graphene sheets.     

Enhanced stress transfer and thermal properties of polyimide composites with covalent functionalized reduced graphene oxide

This work prepares (3-aminopropyl) trimethoxysilane (APTMS)-functionalized reduced graphene oxide (APTMS-rGO)/polyimide (PI) composite (APTMS-rGO/PI) through in-situ polymerization. NH₂-functionalized rGO coupled by APTMS demonstrates the good reinforced efficiency in mechanical and thermal properties, which is ascribed to the covalent-functionalized PI matrix by APTMS-rGO sheets. The uniform dispersion of APTMS-rGO increases the glass transition temperature (Tg) and the thermal decomposition temperature (Td), exhibiting 21.7 °C and 44 °C improvements, respectively. The tensile strength of the composites with 0.3 wt% APTMS-rGO is 31% higher than that of neat PI, and Young’s modulus is 35% higher than that of neat PI. Raman spectroscopy show the obvious G band shift, and also clearly demonstrates the enhanced interfacial interaction between rGO nanofillers and PI matrix. The high mechanical property of the APTMS-rGO/PI composites is attributed to the covalent functionalized GO by NH₂ groups and its good dispersion in comparison with GO.     

Functional shape memory composite nanofibers with graphene oxide filler

In the present study, we prepared a series of graphene oxide (GO) filled shape memory polyurethane (SMPU) nanofibers and systematically investigated the morphological, thermal and mechanical properties, surface wettability, and the shape memory effect (SME) followed by the proposed programming model. The results show that GO can be well dispersed within the SMPU matrix, and the introduction of GO significantly improves the mechanical strength, surface wettability, and thermal stability of the SMPU. Compared with pristine SMPU nanofibrous mats, the prepared SMPU/GO nanofibrous mats have better SME and lower thermal shrinkage. When the loading amount of GO increased to 4.0 wt%, the thermal shrinkage ratio (R_ts) of composite nanofibrous mats could be as low as 4.7 ± 0.3%, while the average fixation ratio (R_f) and recovery ratio (R_r) could be as high as 92.1% and 96.5%, respectively. The study indicates that GO is a desirable reinforcing filler for preparing shape memory nanofibers with improved properties.     

Starch/polylactide sustainable composites: Interface tailoring with graphene oxide

The high production cost of polylactide (PLA) can be effectively reduced by simply mixing with starch, unfortunately a trade-off of its mechanical properties. In this paper, we reported a new strategy in which graphene oxide (GO) was used as a compatibilizer to bridge PLA and starch. The native starch was first cationized and then encapsulated with GO by electrostatic force between the negatively charged GO and the positively charged cationic starch. The encapsulating GO was reduced by the quaternary ammonium ions on the cationic starch, which converted the surface of the starch from hydrophilic to hydrophobic. Due to the amphipathicity approximation between PLA and starch, a good dispersion as well as a strong interfacial adhesion was achieved. The PLA composite reinforced with GO encapsulated starch exhibited much higher yield strength than that of pure PLA, increasing from 36.64 MPa up to 41.40 MPa.     

Isolation of nanofibers from soybean source and their reinforcing capability on synthetic polymers

The focus of this work is to study nanofibers in three different polymers: polyvinyl alcohol (PVA), polypropylene (PP) and polyethylene (PE). The nanofibers were isolated from a soybean source by combining chemical and mechanical treatments. Isolated nanofibers were shown to have diameter between 50 and 100 nm and the length in micrometer scale which results in very high aspect ratio. The mechanical properties demonstrated an increase in tensile strength from 21 MPa of PVA/UNF5 (untreated-fiber (5 wt%) reinforced PVA) and 65 MPa of pure PVA to 103 MPa of PVA/SBN5 (nanofiber (5 wt%) reinforced PVA). The increased stiffness of PVA/SBN5 nanocomposites was also very promising; it was 6.2 GPa compared to 2.3 GPa of pure PVA and 1.5 GPa of PVA/UNF5. In solid phase melt-mixing, nanofiber was directly incorporated into the polymer matrix using a Brabender. The nanofiber addition significantly changed the stress–strain behavior of the composites: modulus and stress were increased with coated nanofibers by ethylene–acrylic oligomer emulsion as a dispersant; however, elongation was reduced. The dynamic mechanical analysis showed the addition of the soybean nanofiber (SBN) improved the thermal properties for PVA and how the addition of different contents of SBN influenced the tan δ peak and storage modulus of PVA.     

Free-standing functional graphene reinforced carbon films with excellent mechanical properties and superhydrophobic characteristic

In this work, we reported a simple method to fabricate novel free-standing stiff carbon-based composite films with excellent mechanical properties and superhydrophobic behaviors. The free-standing stiff carbon composite films based on reduced graphene oxide/glassy carbon (rGO/GC) were prepared by the combination of in-situ polymerization and carbonization process. The obtained composite films exhibited excellent mechanical properties by the addition of rGO nanosheets. It was found that incorporating 0.5 wt.% of rGO sheets in GC precursors resulted in enhancements of 99% in strength (202.6 MPa) and 184% in modulus (33.8 GPa), respectively. More interestingly, carbon nanoarrays were uniformly grown on the surface of composite films by the incorporation of rGO sheets. Superhydrophobic surfaces of carbon films were subsequently formed through functionalizing carbon nanoarrays with Trichloro(1H, 1H, 2H, 2H-perfluorodecyl)silane. Contact angle (CA) analysis suggested that superhydrophobic surfaces with a CA as high as 155° could be formed through optimizing the fabrication process.     

Effects of post-annealing on the microstructure and mechanical properties of friction stir processed Al–Mg–TiO2 nanocomposites

Aluminum matrix nanocomposites were fabricated via friction stir processing of an Al–Mg alloy with pre-inserted TiO₂ nanoparticles at different volume fractions of 3%, 5% and 6%. The nanocomposites were annealed at 300–500 °C for 1–5 h in air to study the effect of annealing on the microstructural changes and mechanical properties. Microstructural studies by scanning and transmission electron microscopy showed that new phases were formed during friction stir processing due to chemical reactions at the interface of TiO₂ with the aluminum matrix alloy. Reactive annealing completed the solid-state reactions, which led to a significant improvement in the ductility of the nanocomposites (more than three times) without deteriorating their tensile strength and hardness. Evaluation of the grain structure revealed that the presence of TiO₂ nanoparticles refined the grains during friction stir processing while the in situ formed nanoparticles hindered the grain growth upon the post-annealing treatment. Abnormal grain growth was observed after a prolonged annealing at 500 °C. The highest strength and ductility were obtained for the nanocomposites annealed at 400 °C for 3 h.     

Graphene–ZnS quantum dot nanocomposites produced by solvothermal route

Graphene–ZnS (G–ZnS) quantum dots nanocomposites were prepared by one pot solvothermal route. Graphite oxide (GO) was well dispersed in dimethyl sulfoxide (DMSO) solution of ions Zn²⁺, where DMSO acts as a sulphide source as well as reducing agent, resulting in the formation of graphene–ZnS quantum dot nanocomposites and simultaneous reduction of GO to graphene nanosheets. The size of the ZnS QDs in G–ZnS is around 10 nm, and the large 2D flexible atom-thin layer of graphene makes it easier to control the distribution of ZnS. The resulting G–ZnS QDs display a well-defined excitonic emission feature by luminescence analysis.     

Improved cryogenic interlaminar shear strength of glass fabric/epoxy composites by graphene oxide

The cryogenic interlaminar shear strength (ILSS) at cryogenic temperature (77 K) of glass fabric (GF)/epoxy composites is investigated as a function of the graphene oxide (GO) weight fraction from 0.05 to 0.50 wt% relative to epoxy. For the purpose of comparison, the ILSS of the GF/epoxy composites is also examined at room temperature (RT, 298 K). The results show that the cryogenic ILSS is greatly improved by about 32.1% and the RT ILSS is enhanced by about 32.7% by the GO addition at an appropriate content of 0.3 wt% relative to epoxy. In addition, the ILSS of the composite at 77 K is much higher than that at RT due to the relatively strong interfacial GF/epoxy adhesion at 77 K compared to the RT case.     

Synergistic effect of organic and inorganic nano fillers on the dielectric and mechanical properties of epoxy composites

Titanium oxide TiO₂/epoxy and TiO₂ with detonation nano-diamond (DND)/epoxy nanocomposites were prepared by using ultrasonication method. TiO₂ and DND particles as reinforcement species and epoxy as matrix were used to produce nanocomposites. The addition of DND particles into TiO₂/epoxy composite improved the dielectric and mechanical properties of nanocomposites in significant amount. The dielectric properties of TiO₂-DND/epoxy nanocomposite demonstrated increase in permittivity and conductivity after addition of the DND particles. The maximum and minimum reflection losses of TiO₂-DND/epoxy nanocomposite for 0.6 and 0.2 wt% DND loading were detected at ?14.5 and ?1.3 dB, respectively. The flexural and tensile strength of TiO₂-DND/epoxy nanocomposites with the addition of 0.4 wt% DNDs were enhanced to 220% and 223%, respectively. Additionally, the energy to break and percent break strain were 3.9 J and 3.86, respectively for 0.4 wt% DND loading in TiO₂-DND/epoxy nanocomposite. Therefore, the present work findings claim that DND particles are well suitable to enrich the dispersion of TiO₂ nanoparticles in epoxy matrix, which develops a strong load transfer interface between the nanoparticles and epoxy matrix and consequently leads to superior properties.