Ming-Bo Yang

Efficient electromagnetic interference shielding of lightweight graphene/polystyrene composite

A combination of high-pressure compression molding plus salt-leaching was first proposed to prepare porous graphene/polystyrene composites. The specific shielding effectiveness of the lightweight composite was as high as 64.4 dB cm3 g−1, the highest value ever reported for polymer based EMI shielding materials at such a low thickness (2.5 mm).

Functionalized graphene oxide with ethylenediamine and 1,6-hexanediamine

Abstract Graphene oxide (GO) obtained by Hummers method was functionalized by ethylenediamine (EA) and 1,6-hexanediamine (HA) in N, N-dimethyl formamide using 1, 1, 3, 3-tetramethy-luronium hexafluorophosphate as a coupling agent. The functionalized GO was characterized by elemental analysis, FT-IR, XRD, XPS, TGA, SEM and TEM. Results showed one carbon atom in nine to ten of the carbon atoms in GO was functionalized by an amine group. The thermal stability of the GO functionalized by HA was much higher than the one functionalized by EA. However, the former was less dispersible in N, N-dimethyl formamide than the latter.

Tensile properties of poly(ethylene terephthalate) and polyethylene in-situ microfiber reinforced composite formed via slit die extrusion and hot-stretching

This article dealt with the tensile properties of in-situ microfiber-reinforced composite (MRC) based on poly(ethylene terephthalate) (PET) and polyethylene (PE). The MRC was prepared through slit die extrusion and hot-stretching, followed by injection molding at the processing temperature of PE matrix, far below the melting temperature of PET in order to maintain the formed microfibers. As expected, the tensile modulus and strength of PET/PE MRC can be significantly elevated at some composition. On the other hand, the reinforcement is heavily dominated by PET concentration; neither low nor high PET content was desirable for reinforcement. Results from elongation tests showed that the ultimate elongation between the samples with mincrofiers and spherical particles at some PET concentrations was extremely different, which was illustrated by the model proposed in which great slippage between the particles and the matrix occurred for the system with spherical particles, whereas there was no slippage between the microfibers and the matrix for MRC.

Polymorphism of racemic poly(L-lactide)/poly(D-lactide) blend: effect of melt and cold crystallization.

The crystallization and melting behaviors and crystalline structure of melt and cold crystallized poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blend were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), respectively. The isothermal crystallization kinetics during the melt and cold crystallization process were analyzed using the Avrami equation. The overall crystallization rate constant (k) of cold crystallization is much higher than that of melt crystallization. Moreover, k as a function of crystallization temperature shows different trends in melt and cold crystallization, indicating different crystallization mechanisms in the melt and cold crystallization. The polymorphic crystallization of homocrystallites (the transition crystallization temperature from δ to α form) is not altered by either the equimolar blending of PLLA and PDLA or the type of crystallization procedures, while the crystallization window for exclusive stereocomplex crystallites is widened from 170 °C for melt crystallization to 170-200 °C for cold crystallization. The stereocomplex crystallites are hard to form in both melt and cold crystallization at crystallization temperatures of 90 and 100 °C, and the crystallinity of stereocomplex crystallites for cold crystallization is higher than that of melt crystallization at temperatures above 110 °C. Especially, a pure and significantly higher crystallinity of stereocomplex crystallites can be achieved at 170-200 °C by cold crystallization. The results provide a huge possibility to control stereocomplex crystallization to enlarge its applications.

Self-assembled high-strength hydroxyapatite/graphene oxide/chitosan composite hydrogel for bone tissue engineering

Graphene hydrogel has shown greatly potentials in bone tissue engineering recently, but it is relatively weak in the practical use. Here we report a facile method to synthesize high strength composite graphene hydrogel. Graphene oxide (GO), hydroxyapatite (HA) nanoparticles (NPs) and chitosan (CS) self-assemble into a 3-dimensional hydrogel with the assistance of crosslinking agent genipin (GNP) for CS and reducing agent sodium ascorbate (NaVC) for GO simultaneously. The dense and oriented microstructure of the resulted composite gel endows it with high mechanical strength, high fixing capacity of HA and high porosity. These properties together with the good biocompatibility make the ternary composite gel a promising material for bone tissue engineering. Such a simultaneous crosslinking and reduction strategy can also be applied to produce a variety of 3D graphene-polymer based nanocomposites for biomaterials, energy storage materials and adsorbent materials.

Morphology of in situ poly(ethylene terephthalate)/polyethylene microfiber reinforced composite formed via slit-die extrusion and hot-stretching

This article introduced the morphologies of in situ microfiber reinforced composite (MRC) based on poly(ethylene terephthalate) (PET) and polyethylene (PE). The PET/PE MRC was prepared through slit-die extrusion and hot-stretching, followed injection molding at the processing temperature of PE matrix, far below the melting temperature of PET in order to maintain the microfibers. Morphological observation indicated that the PET microfibers could be achieved by the way used in this study, and the microfiber characteristics, such as diameter, diameter distribution, were mainly dominated by PET content at a fixed hot-stretching ratio (HSR) of 19.17. Increasing the PET content the fiber diameter became bigger and the diameter distribution wider, but the minimum fiber diameter always remained constant.

Poly(ethylene terephthalate)/polyethylene composite based on in-situ microfiber formation

Poly(ethylene terephthalate) (PET) microfiber was in-situ formed by compounding PET with polyethylene (PE) through a single screw extruder of a Haake rheometer system, where a rod die with comparatively smaller diameter (2.1 mm) was used, and the extrudate was drawn in a certain drawing ratio (3.1:1) and quickly cooled in cold water. Subsequently, the in-situ PET/PE composite was injection molded into specimens at temperatures that were lower than the melting temperature of the PET to keep the original shape of the PET fibers. The result from morphology observations of the composite showed that when the die diameter of the extruder is 2.1 mm and the drawing ratio of the extrudate is 3.1:1, PET was more or less changed into microfibers. The PET almost changed into fibers when the concentration was 15 wt%; concentrations below and above which decreased the fiber content. For the PET/PE blend prepared by conventional mixing technology, the dispersed PET formed spheres and no microfibrilar structure were found. The reinforcing effect of the PET fibers on the corresponding composite was significant at 15 wt% PET concentration observed from the correlation between the PET content and the tensile properties of the PET/PE in-situ composite. Besides, in general, the tensile strength and modulus of the composite increased with the PET concentration, and was higher than the conventional PET/PE blend without microfibers.

A new approach to construct segregated structures in thermoplastic polyolefin elastomers towards improved conductive and mechanical properties

Aiming at improved electrical conductive performance and simultaneously enhanced mechanical properties, a novel segregated structure was constructed for poly(ethylene-co-octene) (POE)/multi-walled carbon nanotube (MWCNT) elastomeric conductive composites with chemically cross-linked POE granules. Structural examination revealed the formation of unique phase morphologies with a stable segregated structure, in which the uncross-linked POE/MWCNT phase localized out of the cross-linked granules. With such a novel segregated structure, a percolation threshold as low as 1.5 vol% of MWCNTs was observed, which is significantly lower than the melt compounded POE/MWCNT composites; the stress at 100% and 300% stretching increased for more than 12% and 30%, respectively, and the tensile modulus inherent to the matrix elastomer was maintained. The elastic recovery of the composite with such a novel segregated structure was more than 85% and 65% after large strains up to 100% and 300%, respectively, always higher than the melt compounded POE/MWCNT composites. The Shore A hardness of the elastomeric conductive composites with cross-linked POE granules was also lower, showing better elasticity of POE/MWCNT composites with such a novel segregated structure. All these results demonstrated that the elastomeric POE/MWCNT conductive composites with such a novel segregated structure exhibited greatly reduced percolation thresholds with enhancement in mechanical properties, which provides a new way for the preparation of elastomeric conductive composites with simultaneously improved electrical performance and mechanical properties.

Morphology-tensile behavior relationship in injection molded poly(ethylene terephthalate)/polyethylene and polycarbonate/polyethylene blends (I) Part I Skin-core Structure

The skin-core structure of injection molded poly(ethylene terephthalate) (PET)/polyethylene (PE) and polycarbonate (PC)/PE blends was investigated. The results indicate that both shape and size of the PET and PC phases depended not only on the nature properties of PET/PE and PC/PE blends, but also on the injection molding parameters such as injection speed and the positions in the molded bars. The morphology in the section perpendicular to the melt flow direction included four layers, surface, sub-skin, intermediate layers as well as core zone. The surface layer was ignored in the present study. The sub-skin layer contained more or less fibrous structure and its thickness gradually decreased along the molded bar from the gate toward the non-gate end. At the same injection speed, the concentration of the injection-induced fibers in PC/PE blend was much higher than that in PET/PE blend. In the core region, the dispersed phase was mainly composed of spherical particles whose diameter increased along the melt flow pathway. Between these two layers, there was an intermediate layer where the dispersed particles mainly assumed the form of fibers, ellipsoids or spheres. Generally, no matter whether the dispersed particles were elongated or not during injection molding, the PET particles were larger than PC ones.

Towards balanced strength and toughness improvement of isotactic polypropylene nanocomposites by surface functionalized graphene oxide

Balanced stiffness and toughness is always the goal of high-performance general plastics for engineering purposes and the interfacial crystalline structure control has been proved to be an effective way to approach this goal. In this work, a kind of novel β-nucleating agent (β-NA) for isotactic polypropylene (iPP), one of the most rapidly developing general plastics, was supported onto the surface of octadecylamine functionalized graphene oxide (GO-D), and the effects of functionalized graphene oxide (GO) on the crystallization behavior, crystalline structures and mechanical properties of iPP composites were studied. The presence of the octadecyl chain changes the hydrophilic GO to be hydrophobic, and further supporting of β-NA onto GO-D (GO-N) does not change its solubility in xylene. The hydrophobic nature of octadecyl chains on the GO-D and GO-N surfaces leads to improved interfacial adhesion with the non-polar iPP matrix. At the same time, GO-N exhibits high efficiency in inducing the formation of β-crystals of iPP. The relative content of β-crystals, kβ, reaches a value as high as 73.6% at a loading of 0.1 wt% GO-N, resulting in a maximum increase in impact strength by almost 100% and a simultaneous improvement of the tensile strength by about 30%. This work provides a potential industrializable technique for high-performance iPP nanocomposites.