Fabrication of Ce-doped MnO2 decorated graphene sheets for fire safety applications of epoxy composites: flame retardancy, smoke suppression and mechanism

Ce-doped MnO2–graphene hybrid sheets were fabricated by utilizing an electrostatic interaction between Ce-doped MnO2 and graphene sheets. The hybrid material was analyzed by a series of characterization methods. Subsequently, the Ce-doped MnO2–graphene hybrid sheet was introduced into an epoxy resin, and the fire hazard behaviors of the epoxy nanocomposite were investigated. The results from thermogravimetric analysis exhibited that the incorporation of 2.0 wt% of Ce-doped MnO2–graphene sheets clearly improved the thermal stability and char residue of the epoxy matrix. In addition, the addition of Ce–MnO2–graphene hybrid sheets imparted excellent flame retardant properties to an epoxy matrix, as shown by the dramatically reduced peak heat release rate and total heat release value obtained from a cone calorimeter. The results of thermogravimetric analysis/infrared spectrometry, cone calorimetry and steady state tube furnace tests showed that the amount of organic volatiles and toxic CO from epoxy decomposition were significantly suppressed after incorporating Ce–MnO2–graphene sheets, implying that this hybrid material has reduced fire hazards. A plausible flame-retardant mechanism was hypothesized on the basis of the characterization of char residues and direct pyrolysis-mass spectrometry analysis: during the combustion, Ce–MnO2, as a solid acid, results in the formation of pyrolysis products with lower carbon numbers. Graphene sheets play the role of a physical barrier that can absorb the degraded products, thereby extend their contact time with the metal oxides catalyst, and then promote their propagate on the graphene sheets; meanwhile pyrolysis fragments with lower carbon numbers can be easily catalyzed in the presence of Ce–MnO2. The notable reduction in the fire hazards was mainly attributed to the synergistic action between the physical barrier effect of graphene and the catalytic effect of Ce–MnO2

Flexibility improvement of poly(lactic acid) by stearate-modified layered double hydroxide.

Poly(lactic acid)/layered double hydroxide (PLA/LDH) nanocomposites were prepared from PLA and stearate-Mg3Al LDH via a solution casting method. The anionic clay Mg3Al LDH was prepared first by coprecipitation method from nitrate salts solution at pH 9 and then modified by stearate anions through an ion exchange reaction. This modification increased the basal spacing of the synthetic clay from 8.72 to 31.68 Å. The presence of stearate ions in the synthesized Mg3Al LDH was shown by the stearate-Mg3Al LDH infrared spectrum. When the stearate-Mg3Al LDH at the low concentration was dispersed in the PLA matrix, its layers were largely delaminated. The presence of 1.0 wt % of the stearate-Mg3Al LDH in the PLA improved drastically (of around 650%) of its elongation at break but retained its tensile strength and modulus as compared to those of the pure PLA

Effect of multilayered nanostructures on the physico-mechanical properties of ethylene vinyl acetate-based hybrid nanocomposites.

Exfoliated graphene oxide (GO) and Mg-Al-layered double hydroxides (LDHs) nanostructures (LDHs@GO)-filled ethylene vinyl acetate (EVA)-based hybrid nanocomposites were prepared by solution reflux technique followed by injection molding. The physico-mechanical (including morphological, thermal, and mechanical) properties of LDHs@GO-based-layered nanostructures and EVA/LDHs@GO (0-1 wt%)-based hybrid nanocomposites were analyzed by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, wide and low angle X-ray diffraction spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and mechanical (tensile and elongation at break) testing. The morphological studies revealed that LDHs sheets were homogeneously inserted in between GO sheets, while LDHs@GO-based-layered nanostructures were found to be easily exfoliated in EVA/LDHs@GO hybrid nanocomposites up to 0.7 wt% loading after which agglomeration occurred. The thermal stability of the hybrid nanocomposites was found to be improved at highest LDHs@GO loading of 0.7 wt%. Mechanical properties (tensile strength and elongation at break) of the hybrid nanocomposites were observed to be enhanced by 70 and 80%, respectively, at LDHs@GO loading of 0.7 wt% and highest values of mechanical properties were obtained. Though, the morphological, thermal, and mechanical properties of the composites were improved, the FTIR analysis did not reveal any chemical interaction between EVA and the LDHs@GO-based-layered nanostructures. From the overall results, it is obvious that a significant synergism was observed in terms of morphological, thermal, and mechanical properties of EVA/LDHs@GO hybrid nanocomposites with optimum (less than 1 wt%) loading of LDHs@GO-based-layered nanostructures