Tiejun Shi

Graphene/polystyrene nanocomposites synthesized via Pickering emulsion polymerization

In this study, graphene/polystyrene nanocomposites were first obtained by Pickering emulsion polymerization technique. The results showed that the thermal, mechanical, and conductivity properties of polystyrene were remarkably improved at low loading of functionalized graphene. In fact, the functionalized graphene could not only be use as an effective solid stabilizer for styrene-in-water Pickering emulsion but also be dispersed homogeneously into the production of polystyrene as highly effective nanofiller using this method. The superior properties of the graphene/polystyrene composites are the result of good dispersion of functionalized graphene in the polystyrene matrix.

Pickering Emulsion Polymerization of Styrene Stabilized by the Mixed Particles of Graphene Oxide and NaCl

A novel method of Pickering emulsion polymerization stabilized by graphene oxide (GO) and the role of adding salt (NaCl) were first described here. The ability of GO lower the interfacial tension and the effect of adding salt (NaCl) on particle adsorption at the oil–water interface were studied. It was found that GO nanosheets adsorbed effectively at the oil–water interface in salt solution and stable Pickering emulsion could be created. After the Pickering emulsion polymerization of styrene, the PS/GO nanocomposites were prepared successfully. The nanocomposites were characterized by transmission electron microscopy (TEM) and atomic force microscopy.

Preparation and properties of amine-functionalized reduced graphene oxide/waterborne polyurethane nanocomposites:

Amine-functionalized reduced graphene oxide (NH2-RGO), with primary amine (—NH2) groups linked onto surfaces by toluene-2,4-diisocynate), was successfully synthesized. Subsequently, the as-prepared NH2-RGO nanoplatelets were covalently incorporated into a waterborne polyurethane (WPU) matrix to fabricate NH2-RGO/WPU nanocomposites by the reaction of —NH2 groups with the isocyanate-terminated polyurethane prepolymer. Electron microscopic observations confirmed that the NH2-RGO nanoplatelets were homogenously dispersed in the WPU matrix. The NH2-RGO/WPU nanocomposites exhibited a significant improvement in their mechanical and thermal properties. The tensile strength and storage modulus of the nanocomposites increased by 73% and 973%, respectively, with the addition of 1.0 wt% NH2-RGO. The thermal degradation temperature was enhanced by about 40°C compared with the neat WPU. Meanwhile, the thermal conductivity increased by about 258%.

Poly (vinyl alcohol)/SiO2 composite microsphere based on Pickering emulsion and its application in controlled drug release

In this paper, with W/O Pickering emulsion stabilized by modified SiO2 nanoparticles as template, PVA/SiO2 composite microspheres with PVA hydrogel cores and shells of SiO2 nanoparticles are successfully fabricated through freezing/thawing method. The final structure and constituents of the products are investigated through SEM, FTIR, and TGA. The PVA/SiO2 composite microspheres obtained are applied as a drug carrier to study their controlled release behaviors and methylene blue is used as a model drug. The effect of PVA concentration, SiO2 nanoparticle concentration, and freezing/thawing cycles on the morphology of products and release behaviors is studied. All release curves are, respectively, fitted by Monoexponential equation, Higuchi equation, Weibull equation, and Hixson-Crowell equation. Weibull equation is found to give the best fit to the release process. The fitted results prove that the drug release from the PVA/SiO2 composite microspheres follows Fick diffusion.

High Concentration and Stable Aqueous Dispersion of Graphene Stabilized by a New Amphiphilic Copolymer

In this study, the new amphiphilic copolymer of sodium-4-styrenesulfonate (SS) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) [poly(SS-co-AMPS)] was prepared and first used as an effective stabilizer to prepare a high concentration and stable aqueous dispersion of graphene. It was found that the high concentration of the stable graphene dispersion can reach up to 12.0 mg/mL using the copolymer as a stabilizer. FT-IR and UV-Vis study show that owing to the coexistence of π-π interaction, hydrophobic attraction, and hydrogen bonding, the poly(SS-co-AMPS) exhibits a high adsorptivity for graphene sheets. In addition, the electrostatic repulsions and stereo-hindrance effect supplied by the sulfonic groups (-SO3−) and the side chain can prevent the π-π stacking of graphene sheets effectively. The morphology of the exfoliated graphene sheets was investigated by atomic force microscopy and transmission electron microscopy with a 3.9-nm average thickness. Furthermore, this polymer-functionalized graphene can also be dispersed very well in polar organic solvents, such as N,N-dimethylmethanamide, acetone, and ethanol, to form stable homogeneous suspensions.

Fabrication and properties of hybrid Mo-CPF/P1B from cardanol

A Mo-CPF/P1B hybrid has been prepared from molybdenum modified cardanol phenolic resin (Mo-CPF) and cardanol benzoxazine with phosphorus (P1B). Cardanol benzoxazine with phosphorus (P1B) has been synthesized from cardanol-allylamine-based benzoxazine (BZc-a) and DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide). Cardanol phenolic resin modified with molybdenum (Mo-CPF) has been synthesized by reacting cardanol-based phenolic resin (CPF) with ammonium molybdate tetrahydrate at 150 °C, where the CPF was synthesized from cardanol and paraformaldehyde in the presence of sodium hydroxide at 65 °C. The synthesized CPF and Mo-CPF were characterized by 1H-NMR and size exclusion chromatography (SEC). Mo-CPF was mixed with P1B, and the mixtures were cured at 110 °C for 4 h and got the Mo-CPF/P1B hybrid. The properties of the Mo-CPF/P1B hybrid were investigated; the results demonstrated that the mechanical and thermal properties, together with flame retardance, were greatly improved. Dynamic Mechanical Analysis (DMA) measurement results indicated that CPF, Mo-CPF and Mo-CPF/P1B could all sustain a large amount of stress and the elongations at break were different. DMA measurements suggested that the Tg of CPF, Mo-CPF and Mo-CPF/P1B was 98 °C, 170 °C and 131 °C respectively. Mo-CPF/P1B exhibited better flame retardance after conjugating with molybdenum and phosphorus. TGA results suggested that Mo-CPF/P1B exhibited better thermal properties. Field emission electron microscopy (FE-SEM) suggested that molybdenum was randomly distributed in Mo-CPF and Mo-CPF/P1B, and EDX indicated that molybdenum and phosphorus were randomly distributed in Mo-CPF/P1B.

Preparation and Characteristics of Graphene Oxide from the Biomass Carbon Material Using Fir Powder as Precursor

Graphene oxide (GO) was successfully prepared from the graphitization carbon based upon biomass material using fir powder as a precursor, which was named as FPGO. As a comparison to verify the successful synthesis of FPGO, GO from expanded graphite (named as EGO) was prepared. FPGO had the typical characteristics of GO, possessing the grossly close nanostructures and comparable element constitutions with EGO. The interlayer spacing of FPGO was 8.5 Å, close to 9.1 Å of EGO. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses indicated five different oxygen-containing functional groups existing between the FPGO nanosheets. The atomic force microscopic image directly observed that the FPGO nanosheets were single-layer thick, and lateral dimensions were in the range of about one to several micrometers in diameter. FPGO had a wrinkled morphology, and the layer structure was intuitively observed by field emissions scanning electron microscope and transmission electron microscope images. The thermogravimetric analysis curves reflected that FPGO had close contents of oxygenated groups with EGO, leaving the same residual carbon element of about 49 wt.% at 900°C.

Synthesis of carbon nanotubes/polyacrylamide nanocomposites with improved load-carrying capacity and antiwear ability

In this study, the functionalized carbon nanotubes (CNTs) were prepared and used for the first time as a high-efficient dispersant for the synthesis of CNTs/polyacrylamide nanocomposites via dispersion polymerization. The results showed that the functionalized CNTs not only could be use as an effective solid stabilizer for dispersion polymerization but also could be homogeneously dispersed into the production of polyacrylamide as nanofillers by this method. Furthermore, the functionalized CNTs/polyacrylamide nanocomposites can be dissolved in water and can effectively improve the load-carrying capacity and antiwear ability of base stock as a good lubricant additive in water-based fluid.

Preparation and characteristics of poly(benzoxazine-urethane)/graphene oxide composites: Toughness, mechanical and thermal properties

ABSTRACT Poly(benzoxazine-urethane)/graphene oxide [poly(Bz-PU)/GO] composites were successfully prepared by blending benzoxazine (Bz) with graphene oxide (GO) and isocyanato (NCO)-terminated polyurethane prepolymer (PU), followed by thermally activated polymerization of the blends. The network was formed via the mutual reaction and intermolecular interaction among the hydroxyl of GO, NCO groups of PU and phenolic hydroxyl of Bz. The toughness shown from SEM images and tensile properties of polybenzoxazine (PBz) plastic composites can effectively be improved by alloying with PU and GO. The onset curing temperature and exothermic peak maximums of the polymerization obtained from differential scanning calorimetry decreased resulted from the GO addition. The thermogravimetric analysis showed that the incorporation of 0.5 wt% of GO slightly improved the thermal stability of poly(Bz-PU)/GO composites. Additionally, the storage modulus improved and the glass transition temperature (Tg) increased gradually as the increasing GO content not beyond a certain amount. Finally, the exothermic peaks of the polymerization were shifted to lower temperature, and the thermal stability increased for the ternary composites as the number average molecular weights (Mn) of polyol decreased.

Comparative studies of flexible aliphatic ternary/binary benzoxazines and their copolymers: Thermal and dynamic mechanical properties

ABSTRACT Aliphatic ternary benzoxazine (Bz) based from triamine with long chain, as well as flexible binary Bz, was successfully synthesized, which was named as BzT and BzD respectively. The corresponding polybenzoxazines (PBz) rooting from BzT and BzD (PBzT and PBzD) respectively and their copolybenzoxazines (co-PBzs) were obtained to improve the mechanical and thermal properties via chemical cross-linking. The onset polymerization temperatures of the copolymers decreased from 189.1°C to 143.9°C, and the exothermic peak temperature reduced significantly from 232.5°C to 217°C as the content of BzT increased from 0 wt% to 100 wt% in the copolymers. The value of char yield at 800°C increased gradually from 21.5 wt% for PBzD to 28.7 wt% for PBzT. The increasing crosslink density resulted higher glass transition temperatures and improved storage moduli in glassy region because of the introduction of BzT.