Nguyen Dang Luong

Graphene/cellulose nanocomposite paper with high electrical and mechanical performances

Graphene/cellulose nanocomposite paper with high mechanical and electrical performances was reported in this study by combining reduced graphene oxide sheets (RGO) and amine-modified nanofibrillated cellulose (A-NFC) in a well-controlled manner. By adjusting the GO content, various graphene/cellulose nanocomposites with 0.1–10 wt% content of graphene were obtained. The RGO/A-NFC nanocomposite synthesized by the developed method exhibits an electrical percolation threshold of 0.3 wt% with an electrical conductivity of 4.79 × 10−4 S m−1, which is well above the antistatic value. Furthermore, with 10 wt% of graphene, a high conductivity of 71.8 S m−1 was measured for the nanocomposite. Moreover, it was found that on addition of only 0.3 wt% of graphene, the tensile strength increased by 1.2 fold and 2.3 folds compared to that of the neat cellulose and graphene oxide paper, respectively, revealing an excellent reinforcement of graphene sheets. Moreover, the elongation at break of the composite with graphene content was 8.5%, which is similar to that of A-NFC paper and much higher than that of GO paper. It is noteworthy to mention that with 5 wt% of graphene, the RGO/A-NFC composite paper showed a significantly enhanced tensile strength of 273 MPa that is 1.4 fold and 2.8 folds higher than that of the cellulose papers and graphene oxide paper, respectively. Such a high enhancement of electrical and mechanical properties in cellulose paper by graphene has never been reported before for any carbon-based material/cellulose composite paper.

Graphene oxide porous paper from amine-functionalized poly(glycidyl methacrylate)/graphene oxide core-shell microspheres

Various functional materials, such as metal nanoparticles, carbon nanotubes and conducting polymers were coated on polymer microspheres finding various uses in electronic and biomedical applications. Herein, we demonstrate that single graphene oxide (GO) sheets could be easily wrapped on amine-functionalized poly(glycidyl methacrylate) (PGMA-ed) microspheres (∼2.5 μm in diameter) to form a PGMA-ed/GO core-shell structure with a thickness of ca. 50 nm. Subsequently, the synthesized GO-skin microspheres were consolidated by heating them to 60 °C to form a robust self-standing paper through the formation of electrostatic and van der Waals attractive forces between the very large surfaces of the GO, together with the formation of hydrogen bonding during the dewatering and drying processes, where the GO skins are interconnected to provide an electrical path and mechanical skeletal structure. When a stabilized GO dispersion was added to the PGMA-ed microspheres, the GO sheets were uniformly self-assembled on the PGMA-ed microsphere surfaces, seemingly through dipole–dipole interactions and amine–epoxide chemical reactions. This approach provides a simple route for the large volume production of PGMA-ed/GO core-shell microspheres and large-sized self-standing paper that may find various uses in optoelectronic device materials and porous membrane applications.

Synthesis of Lignin-Based Thermoplastic Copolyester Using Kraft Lignin as a Macromonomer

Lignin-based thermoplastic copolyester was synthesized for eco-friendly polymers and composite applications using lignin as a macromonomer to form a high molecular weight polymer. Kraft lignin was polymerized with sebacoyl chloride in the presence of triethylamine in N,N-dimethylacetamide (DMAc), and the molecular weight of the synthesized polymer was controlled by the polymerization temperatures and [COCl]/[OH] ratios providing up to 39 000 corresponding to 4–5 repeating units of lignin macromonomers. The glass transition temperature of the synthesized polymer was difficult to measure due to the random distribution of functional groups and irregular configurational or conformational arrangement of natural lignin. Therefore, the complex electric modulus (CEM) technique was used to determine the glass transition of the synthesized polymer to give around 70°C measured by the peak of the imaginary part of CEM. The synthesized lignin-copolyester exhibited good thermal stability up to 200°C in TGA analysis and, thus, it was possible to shape the synthesized polymer using the solvent casting or hot-melt processing techniques at 120°C–140°C without generating odor, fume or irritation. Although the molecular weight should further be increased in the future, the developed methodology may help to exploit new applications for eco-friendly sustainable materials in various fields.

Functional Graphene by Thiol‐ene Click Chemistry

Abstract Thiol‐ene click reaction was successfully employed for chemical modification of graphene oxide (GO) by one‐step synthesis. Herein, 2,2‐azobis(2‐methylpropionitrile) (AIBN) was used as thermal catalyst and cysteamine hydrochloride (HS−(CH2)2−NH2HCl) was used as thiol‐containing compound, which is incorporated to GO surface upon reaction with the C=C bonds. The hydrochloride acts as protecting group for the amine, which is finally eliminated by adding sodium hydroxide. The modified GO contains both S‐ and N‐containing groups (NS‐GO). We found that NS‐GO sheets form good dispersion in water, ethanol, and ethylene glycol. These graphene dispersions can be processed into functionalized graphene film. Besides, it was demonstrated that NS‐GO was proved to be an excellent host matrix for platinum nanoparticles. The developed method paves a new way for graphene modification and its functional nanocomposites.

Poly(3,4-ethylenedioxythiophene) Vapor-Phase Polymerization on Glass Substrate for Enhanced Surface Smoothness and Electrical Conductivity

ConclusionsPyridine was found to give a significant effect on generating well-defined PEDOT films in vapor-phase polymerization. This additive was utilized for not only controlling polymerization rate but also stabilizing cation radicals of both EDOT and oligomeric chains during the vapor-phase reaction. At an appropriate pyridine concentration, the highconductivity and smooth PEDOT film was synthesized as a promising thin-film coating for optoelectronic applications.

Crosslinked nanofibrillated cellulose: poly(acrylic acid) nanocomposite films; enhanced mechanical performance in aqueous environments

Nanofibrillated cellulose (NFC) was compounded with poly(acrylic acid) (PAA) via solvent casting. Nanocomposite films were thermally-crosslinked to allow the formation of ester bonds between NFC and PAA, as confirmed by 13CNMR and infrared spectroscopy. The network morphology of the cellulose nanofibrils was left intact by the introduction of PAA and crosslinking. Water absorption and swelling was diminished by the introduction of crosslinking, due to the reduced number of vacant hydroxyl and carboxyl groups available to interact with water molecules. Crosslinking with PAA increased the activation energy required for thermal degradation. PAA effectively reinforced NFC, increasing Young’s modulus, tensile strength and glass transition temperature. Crosslinking imparted restraints on segmental motion of polymer chains, further enhancing the thermomechanical properties and retaining elasticity. Wet-strength properties were enhanced due to the reduced hydrophilicity of crosslinked nanocomposite films.

Thermoresponsive xylan hydrogels via copper-catalyzed azide-alkyne cycloaddition

In the present work, hydrogels of birch wood xylan and thermoresponsive poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (PEG-PPG-PEG) were prepared using copper catalyzed alkyne-azide cycloaddition (CuAAC) in aqueous reaction conditions. First, reactive azide groups were introduced on the backbone of xylan by etherification of 1-azido-2,3-epoxypropane in alkaline water/isopropanol-mixture at ambient temperature, providing degree of substitution (DS) values up to 0.28. On the second step, the azide groups were reacted with propargyl bifunctional PEG-PPG-PEG utilizing CuAAC, leading to formation of crosslinked hydrogels. The novel xylan derivatives were characterized with liquid and solid state nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR) and elemental analysis (EA). The temperature controlled swelling behavior of the developed hydrogels was evaluated in the range of 7-70 °C by water absorption and compressive stress-strain measurements, which showed a reduction in water content and change in stiffness with increasing temperature. The morphology of the hydrogels at different temperatures was studied by scanning electron microscopy (SEM), which showed a reduction in pore size with increasing temperature.

Facile transformation of nanofibrillar polymer aerogel to carbon nanorods catalyzed by platinum nanoparticles

A facile and large-volume production route was developed for synthesizing well-developed carbon nanorods containing highly loaded platinum (Pt) nanoparticles through platinum-catalyzed pyrolysis of a nanofibrillar polymer aerogel. Containing a high electron-rich oxygen density in the polymer molecules, the micro-sized cellulose diacetate (CDA) fibrils were separated into nano-sized fibrils (20–50 nm in diameter) to give a three-dimensionally connected nanofibrillar structure. Using this CDA aerogel structure as an effective nanoreactor, the platinum nanoparticles were in-situ synthesized as anchored on the selective sites of the CDA nanofibril surface in the form of crumpled sheet in the size of 10–30 nm (10.9 wt%). After pyrolysis at 600 °C, the CDA/Pt nanofibrils were converted into Pt-carbon nanorods (150 to 200 nm diameter and 1 to 3 μm length) via the coalescence of the CDA nanofibrils and the subsequent Pt-catalyzed decomposition reaction. A high loading content of Pt was achieved at 56 wt% and the Pt-carbon nanorods exhibited mesoporous characteristics in the N2 desorption isotherm with a BET surface area of 311 m2 g−1.

In situ fabrication of platinum/graphene composite shell on polymer microspheres through reactive self-assembly and in situ reduction

We present a simple method to fabricate a uniform-sized graphene–metal–polymer composite microsphere of core–shell structure. On the surface of amine-functionalized polymer microsphere, graphene oxide (GO) sheets were affixed to give a core–shell structure by self-assembly process followed by the immobilization of platinum (Pt) ions to the assembled GO shell. Subsequently, they were chemically reduced in situ converting both GO and Pt ions to reduced GO (RGO) and Pt nanoparticles (NPs), respectively. As a result, a robust RGO-Pt composite shell, composed of RGO sheets and well-distributed Pt NPs, was fabricated on the microsphere surface. Meanwhile, the insulative GO shell was converted to the conductive RGO-Pt shell giving 24.0 S m−1 of electrical conductivity. We demonstrated that the electrical property of the shell was significantly improved by the incorporation of Pt NPs.

Elastic, crosslinked poly(acrylic acid) filaments: nanocellulose reinforcement and graphene lubrication

Hybrid monofilaments of poly(acrylic acid) (PAA) and 1,6-hexanediol diglycidyl ether (16DGE), compounded with nanofibrillated cellulose (NFC) and graphene, were thermally crosslinked and subsequently spun from aqueous solution. Crosslinking, in the form of ester linkage formation, between PAA and 16DGE was successfully achieved via thermal induction. The monofilaments were elastic and flexible in nature, displaying remarkable elongation and work-to-break values (up to nine times higher than pure PAA–16DGE filaments). This unique behaviour derives from a synergy between the fillers; namely the reinforcing ability of cellulose nanofibrils and the lubricating effect of graphene.