Zhou Gui

Preparation and thermal stability of polypropylene/montmorillonite nanocomposites

Two different methods were used to prepare polypropylene/clay nanocomposites. One was from pristine montmorillonite and a reactive compatibilizer hexadecyl trimethyl ammonium bromide (C6); the other is from different organophilic montmorillonites (OMT). The nanocomposites structures are demonstrated by X-ray diffraction (XRD) and transmission electron microscopy (TEM); The thermal properties of the nanocomposites were investigated by thermogravimetric analysis (TGA). It is shown that different methods and organophilic montmorillonites influence the morphology and thermal stability of polypropylene/clay nanocomposites.

Preparation of poly(vinyl alcohol) nanocomposites with molybdenum disulfide (MoS2): structural characteristics and markedly enhanced properties

As a graphene-like layered nano-material, molybdenum disulfide (MoS2) has gained much attention from the materials fields. In our research, MoS2/poly(vinyl alcohol) (PVA) nanocomposites are prepared by solvent blending method. The morphology, thermal properties, fire resistance properties and mechanical properties of the PVA/MoS2 nanocomposites are studied. MoS2 is homogeneously dispersed and partially exfoliated in the PVA matrix as indicated by X-ray diffraction (XRD) pattern, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) characterization. The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results indicate improved the thermal decomposition temperature and the glass transition temperature (Tg). The thermal degradation temperature is increased by 20–40 °C. Meanwhile, the peak of heat release rate (pHRR) and total heat release (THR) are decreased by 33% and 20%, respectively. Storage modulus at 40 °C is increased by 28%, and the tensile strength is increased by 24% upon addition of 1 wt% and 5 wt% MoS2. The improvements in the thermal properties, fire resistance properties and mechanical properties of PVA nanocomposites are attributed to the good dispersion of MoS2, physical barrier effects of MoS2 and strong interactions between PVA and MoS2.

Superconductivity at 5 K in alkali-metal-doped phenanthrene

Organic superconductors have π-molecular orbitals, from which electrons can become delocalized, giving rise to metallic conductivity due to orbital overlap between adjacent molecules. Here we report the discovery of superconductivity at a transition temperature (T(c)) of ~5 K in alkali-metal-doped phenanthrene. A 1-GPa pressure leads to a 20% increase of T(c), suggesting that alkali-metal-doped phenanthrene shows unconventional superconductivity. Raman spectra indicate that alkali-metal doping injects charge into the system to realize the superconductivity. The discovery of superconductivity in A(3)phenanthrene (where A can be either K or Rb) produces a novel broad class of superconductors consisting of fused hydrocarbon benzene rings with π-electron networks. An increase of T(c) with increasing number of benzene rings from three to five suggests that organic hydrocarbons with long chains of benzene rings are potential superconductors with high T(c).

Preparation and flammability of ethylene-vinyl acetate copolymer/montmorillonite nanocomposites

Abstract Ethylene-vinyl acetate copolymer (EVA)/montmorillonite (MMT) nanocomposites have been prepared using direct melt intercalation by blending EVA and pristine MMT with two different particle sizes: MMTa (average size 38 μm) and MMTb (average size 48 μm). Their structures and flammability properties were characterized by X-ray diffraction (XRD), high resolution electron microscopy (HREM) and Cone Calorimetry. XRD and HREM show that an intercalated structure is formed. The heat release rate (HRR) of the nanocomposite is 40% lower than that of pure EVA and 34% lower than that of the microcomposite. The microcomposite behaves very similarly to the pure EVA. The HRR of nanocomposite loaded with 5% MMTa is lower than that of the nanocomposite loaded with 5% MMTb

The influence of titanate nanotube on the improved thermal properties and the smoke suppression in poly(methyl methacrylate).

The well-dispersed poly(methyl methacrylate)/titanate nanotube (PMMA/TNT) composites were synthesized by in situ polymerization of methyl methacrylate (MMA) in ethanol solution. Thermal stability and the glass transition temperature of the composites are significantly enhanced with a proper amount of TNTs. The comparison between PMMA/TNTs and PMMA/TiO(2) composites suggests the formation of network in PMMA/TNTs composite. The coaction of dehydration and the network is believed to be the crucial factor which improves the thermal properties. TG-FTIR analysis shows that the amount of organic volatiles of PMMA is significantly reduced and the non-flammable CO(2) is generated after incorporating TNTs. It implies the reduced toxicity of the volatiles. The possible mechanism of the smoke suppression is proposed as the dehydration and adsorption effect of TNTs.

MoS2 Nanolayers Grown on Carbon Nanotubes: An Advanced Reinforcement for Epoxy Composites

In the present study, carbon nanotubes (CNTs) wrapped with MoS2 nanolayers (MoS2-CNTs) were facilely synthesized to obtain advanced hybrids. The structure of the MoS2-CNT hybrids was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy measurements. Subsequently, the MoS2-CNT hybrids were incorporated into EP for reducing fire hazards. Compared with pristine CNTs, MoS2-CNT hybrids showed good dispersion in EP matrix and no obvious aggregation of CNTs was observed. The obtained nanocomposites exhibited significant improvements in thermal properties, flame retardancy and mechanical properties, compared with those of neat EP and composites with a single CNT or MoS2. With the incorporation of 2.0 wt % of MoS2-CNT hybrids, the char residues and glass transition temperature (Tg) of the EP composite was significantly increased. Also, the addition of MoS2-CNT hybrids awarded excellent fire resistance to the EP matrix, which was evidenced by the significantly reduced peak heat release rate and total heat release. Moreover, the amount of organic volatiles from EP decomposition was obviously decreased, and the formation of toxic CO was effectively suppressed, implying the toxicity of the volatiles was reduced and smoke production was obviously suppressed. The dramatically reduced fire hazards were generally ascribed to the synergistic effect of MoS2 and CNTs, containing good dispersion of MoS2-CNT hybrids, catalytic char function of MoS2 nanolayers, and physical barrier effects of MoS2 nanolayers and CNT network structure.

Influence of g-C3N4 nanosheets on thermal stability and mechanical properties of biopolymer electrolyte nanocomposite films: a novel investigation.

A series of sodium alginate (SA) nanocomposite films with different loading levels of graphitic-like carbon nitride (g-C3N4) were fabricated via the casting technique. The structure and morphology of nanocomposite films were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis results suggested that thermal stability of all the nanocomposite films was enhanced significantly, including initial thermal degradation temperature increased by 29.1 °C and half thermal degradation temperature improved by 118.2 °C. Mechanical properties characterized by tensile testing and dynamic mechanical analysis measurements were also reinforced remarkably. With addition of 6.0 wt % g-C3N4, the tensile strength of SA nanocomposite films was dramatically enhanced by 103%, while the Youngs modulus remarkably increased from 60 to 3540 MPa. Moreover, the storage modulus significantly improved by 34.5% was observed at loadings as low as 2.0 wt %. These enhancements were further investigated by means of differential scanning calorimetry and real time Fourier transform infrared spectra. A new perspective of balance was proposed to explain the improvement of those properties for the first time. At lower than 1.0 wt % loading, most of the g-C3N4 nanosheets were discrete in the SA matrix, resulting in improved thermal stability and mechanical properties; above 1.0 wt % and below 6.0 wt % content, the aggregation was present in SA host coupled with insufficient hydrogen bondings limiting the barrier for heat and leading to the earlier degradation and poor dispersion; at 6.0 wt % addition, the favorable balance was established with enhanced thermal and mechanical performances. However, the balance point of 2.0 wt % from dynamic mechanical analysis was due to combination of temperature and agglomeration. The work may contribute to a potential research approach for other nanocomposites.

Halogen-free flame retardation and silane crosslinking of polyethylenes

Halogen-free flame-retarded and silane crosslinkable polyethylenes have been prepared by a melt process using magnesium hydroxide (MH) as a flame retardant. The effects of silane concentration, peroxide concentration, etc. on the silane grafting on linear low density polyethylenes were investigated. The thermal analysis of the silane crosslinked polyethylenes was performed by thermogravimetry (TG), and its results show that silane crosslinking provides an increase in the thermal stability of polyethylenes. The combustion characteristics of the silane crosslinked polyethylenes containing MH have also been studied using limiting oxygen index (LOI) and the Cone Calorimeter. The rate of heat release and smoke emission of the silane crosslinked polyethylenes decrease, and LOI, the time to ignition and the residue after combustion increase as MH content increases.

Preparation and characterization of polystyrene/graphite oxide nanocomposite by emulsion polymerization

Polystyrene intercalated graphite oxide (GO) nanocomposite was prepared by emulsion polymerization reaction and characterized by X-ray diffraction (XRD), high resolution electron microscopy (HREM), and thermogravimetric analysis (TGA). It was shown that polystyrene can be intercalated into the interlayer space of GO and form exfoliated and intercalated nanocomposites. The thermal analysis demonstrated that the presence of GO enhances the char residue of the nanocomposite.

Ternary graphene–CoFe2O4/CdS nanohybrids: preparation and application as recyclable photocatalysts

Graphene (Gr)-based binary Gr–CoFe2O4 and Gr–CdS or ternary Gr–CoFe2O4/CdS nanohybrids were prepared via a facile solvothermal strategy. It was encouraging to find that the ternary Gr–CoFe2O4/CdS nanohybrids exhibited the highest photocatalytic degradation ability (80%) among all the photocatalysts. The significant enhancement in photodegradation under 40 W daylight lamp irradiation was attributed to graphene acting as a “bridge”, where electrons generated from CoFe2O4 were transferred to CdS by graphene and finally led to separation of electrons and holes. Interestingly, neat CoFe2O4 resulted in increasing concentration of methylene blue (MB) as the irradiation time increased. The phenomenon was ascribed to adsorption of MB molecules on CoFe2O4 in the dark and desorption from the photocatalyst during irradiation, confirmed by our ingenious experiment. Digital photos of the Gr–CoFe2O4/CdS hybrids in an external magnetic field indicated that the ternary photocatalyst could be easily separated from aqueous solution. The recycle measurements of the photocatalyst revealed that the ternary nanohybrids exhibited acceptable photocatalytic stability due to unstable decoration. This work would provide a new insight into the construction of visible light-responsive and magnetic separable photocatalysts with high performances.