Keqing Zhou

Combination effect of MoS2 with aluminum hypophosphite in flame retardant ethylene-vinyl acetate composites

A series of flame retardant ethylene-vinyl acetate (EVA) composites, with different aluminum hypophosphite (AHP), melamine cyanurate (MCA) and MoS2 content, has been prepared. The synergistic flame retardant effects of MoS2 with AHP and MCA in EVA/AHP/MCA blends have been studied by limiting oxygen index (LOI), UL-94 tests, cone calorimetry tests, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The LOI and UL-94 results show that when 2 wt% AHP/MCA is substituted with MoS2 (total content of the flame retardant system is 30 wt%), the LOI value can be raised to the maximum value of 38.5 among all of the samples. The data obtained from the cone test show that the heat release rate (HRR) and total smoke production (TSP) values of the EVA/AHP/MCA/MoS2 sample are decreased compared with EVA/AHP/MCA composites. From the TGA measurement, with the incorporation of AHP, MCA and MoS2, the thermal stability of the composites and char residue yield is increased obviously. Residue analysis shows that the presence of MoS2 in EVA/AHP/MCA composites promotes the formation of a compact protective char layer resulting in the improvement of thermal stability and flame retardant properties combined with the physical barrier effect of MoS2 nanosheets. The incorporation of MoS2 also enhances the mechanical properties of the flame retardant EVA composites.

Facile synthesis and characterization of a novel silica-molybdenum disulfide hybrid material

To improve the dispersion of MoS2 in polymer matrix, a facile synthesis approach was developed in this study through a synergetic effect between two kinds of nanofillers with different dimensionality. The nanohybrids based on two dimensional (2D) MoS2 and 0D silica nanospheres were fabricated by in situ growth method without any surfactants. Characterizations of the hybrid materials were done by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Solid-state 29Si nuclear magnetic resonance (NMR) spectra, transmission electron micrographs (TEM) and scanning electron microscopy (SEM). The TEM and SEM results demonstrated that the dispersibility of MoS2 was greatly improved and the agglomeration was suppressed, with the introduction of silica nanospheres.

Synthesis and characterization of Cu–MoS2 hybrids and their influence on the thermal behavior of polyvinyl chloride composites

In this work, Cu–MoS2 hybrids were synthesized by a facile wet chemical method. The structure and morphology of the synthesized hybrids were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy measurements. Subsequently, the hybrids were introduced into a polyvinyl chloride matrix to act as a thermal stabilizer. The hybrids were well dispersed in the matrix and no obvious aggregation was observed. The obtained nanocomposites exhibited significant improvements in thermal stability and inhibited the release of pyrolysis products effectively, which were mainly attributed to the enhancement of char formation, a physical barrier effect of the MoS2 nanosheets and an inhibition effect of the Cu nanoparticles.

The influence of a novel two dimensional graphene-like nanomaterial on thermal stability and flammability of polystyrene

Significant improvements in thermal stability and fire resistance properties of polymer materials with nanofillers at low loadings hold tremendous promise for fire safety materials. In this study, a novel two dimensional (2D) graphene-like nanomaterial (VOP) was synthesized by a simple refluxing method and then modified with typical organic surfactants. Subsequently, the novel graphene-like nanomaterials were incorporated into polystyrene (PS) matrix for reducing fire hazards. The SEM and TEM images indicated that the VOP nanosheets were well dispersed throughout the matrix without obvious aggregates, leading to remarkable improvements of thermal stability and fire safety properties. With the loading of 1wt% modified VOP, the T5%, T10%, T50% and Tmax values were increased by 15, 22, 29 and 33°C, respectively. In addition, the presence of VOP nanosheets decreased the decomposition rate of PS and increased the amount of char residues. Furthermore, the peak heat release rate and total heat release of PS composites was decreased by 48.3% and 43.6%, respectively, compared to that of neat PS. The well dispersion, physical barrier effect and catalytic carbonization effect of VOP nanosheets were the main causations for the reduction of fire hazards.

Ultrathin 2D VOPO4 nanosheets: a novel reinforcing agent in polymeric composites

In the present work, ultrathin VOPO4 nanosheets were prepared through simple ultrasonication in 2-propanol, starting from bulk VOPO4·2H2O chunks. Subsequently, the ultrathin VOPO4 nanosheets were incorporated into poly(vinyl alcohol) (PVA) matrix as reinforcing agents based on a solution casting method. The ultrathin VOPO4 nanosheets were homogeneously dispersed in PVA matrix and no obvious aggregation was observed, leading to remarkable improvements of thermal stability, flame retardancy, and mechanical properties. With the incorporation of 3.0 wt% VOPO4 nanosheets into PVA, the initial decomposition temperature (Tonset)and half weight loss temperature (T50%) increased by 45 °C and 139 °C, respectively. In addition, the presence of ultrathin VOPO4 nanosheets decreases the decomposition rate of PVA and increases the amount of char residues. Furthermore, the peak heat release rate and the tensile strength of PVA films was decreased by 67% and improved by 45%, respectively, compared to that of neat PVA. These remarkably enhanced properties were mainly attributed the well dispersion, physical barrier effect and catalytic carbonization effect of the ultrathin VOPO4 nanosheets.

Morphology, thermal and mechanical properties of poly (ε-caprolactone) biocomposites reinforced with nano-hydroxyapatite decorated graphene

In this work, hydroxyapatite (HAP) nanorods decorated on graphene nanosheets (HAP-Gs) was synthesized by a hydrothermal method. The structure, elemental composition and morphology of the HAP-Gs hybrids were characterized by X-ray diffraction, Fourier transform infrared and Transmission electron microscopy. Subsequently, the hybrids were incorporated into poly (ε-caprolactone) (PCL) via a solution blending method. Optical images and scanning electron microscopy observation revealed not only a well dispersion of HAP-Gs hybrids but also a strong interfacial interaction between hybrids and PCL matrix. The influence of HAP-Gs hybrids on the crystallization behavior, crystal structure, thermal stability, mechanical properties and biocompatibility of the PCL nanocomposites was investigated in detail. The results showed that the crystallization temperature of PCL was enhanced obviously, but the crystal structure was not affected by the incorporation of HAP-Gs hybrids. The mechanical properties of PCL bionanocomposites were improved obviously.

Construction of sandwich-structured CoAl-layered double hydroxide@zeolitic imidazolate framework-67 (CoAl-LDH@ZIF-67) hybrids: towards enhancing the fire safety of epoxy resins

In this work, sandwich-like structured CoAl-LDH@ZIF-67 hybrids were constructed by in situ growth of nanosized ZIF-67 crystallites on CoAl-LDH nanoplates. The structure and morphology of CoAl-LDH@ZIF-67 hybrids were represented by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). Accordingly, the hybrids were introduced into epoxy resins to explore their effect on the thermal and fire safety properties of epoxy composites. With the introduction of 2% CoAl-LDH@ZIF-67 hybrids, the T10%, T50% and Tmax values were decreased to some extent and the char residue yield was higher than that of pristine epoxy. The peak heat release rate (PHRR) of epoxy composites declined by 26.4%, in comparison with those of pure epoxy. Moreover, the quantity of smoke produced, toxic CO released and CO2 produced were suppressed markedly and decreased by 16.7%, 59.8% and 32.2%, respectively. A possible mechanism for improving fire safety was put forward based on the analysis of the carbon residues.