Design of Graphene Hybrids and Investigation on Smoke Toxicity Suppression

石墨烯雜化材料的設計及其抑煙減毒的研究

Student thesis: Doctoral Thesis

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Award date1 Aug 2019

Abstract

As a thermosetting polymer, epoxy resin (EP) is widely used in coatings, electronic materials, adhesives, and fiber reinforced composites because of its excellent mechanical properties, high adhesion strength, good heat resistance, and high electrical resistance. However, it is highly flammable and large amounts of smoke and toxic gases are released during its combustion, significantly limiting its application. Notably, the fire hazards of EP materials, including flammability and generation of smoke and toxic gaseous products, are being increasingly realized. In this study, graphene hybrid materials had been incorporated into EP to reduce its flame retardancy and toxicity of the released flue gas. Firstly, from the perspective of passive protection, a series of graphene hybrid materials were synthesized and incorporated into EP to improve its fire safety. Secondly, from the perspective of active protection, to further reduce the yield of the toxic gas carbon monoxide (CO), the most harmful toxic fire gases, we synthesized metal compounds/graphene aerogels catalysts, which catalytically oxidized CO, via Joule heating (intrinsic property of graphene aerogel).

1. A novel mesoporous SiO2-graphene (SiO2-GNS) hybrid was successfully synthesized by a one-pot hydrothermal method using tetraethyl orthosilicate and graphene oxide (GO) as the initial materials. Subsequently, the SiO2-GNS hybrid was added into EP resin and the fire behavior of the composite was investigated. Notably, the incorporation of SiO2-GNS into EP resin reduced the flammability (including peak of heat release rate, total heat release, smoke production rate, total smoke production, and production rate). Moreover, a possible flame retardancy mechanism was proposed on the basis of the char residue analysis results. The enhanced flame retardancy of the EP/SiO2-GNS nanocomposites was attributed to the barrier effect of GNS as well as the labyrinth effect of SiO2-GNS in EP resin.

2. Two types of bimetal oxide hybrids: SnO2 nanowires-decorated MnO2 nanosheets and Mn-Cu2O were prepared and respectively incorporated into EP to improve its flame retardancy and smoke suppression performances during combustion. The incorporation of the bimetal oxide hybrids resulted in an enhancement in the char yield and decrease in the maximum mass loss rate of EP. In addition, the peak of heat release rate and total heat release values for EP/bimetal oxide hybrids were significantly lower than those for neat EP. Moreover, the amount of organic volatiles of EP significantly reduced and the release of toxic CO was suppressed after the incorporation of the bimetal oxide hybrids, as confirmed by the thermogravimetry infrared (TG-IR) spectroscopy results. The addition of metal oxide led to an increase in the char yield and the formation of compact char layers, which slowed down the heat and mass transfer between gas phase and condensed phase. The enhanced flame retardancy and smoke suppression performances of the EP nanocomposites were attributed to synergism between the catalytic effect of the bimetal oxide hybrids.

3. Metal oxide/reduced GO (MO-rGO) hybrids were synthesized and incorporated into EP to improve its flame retardancy and smoke suppression performances during combustion. The structure and morphology of the synthesized hybrids were characterized by X-ray diffraction, Transmission electron microscopy, and Raman spectroscopy. Thermogravimetric analysis was performed to simulate and study the influence of the MO-rGO hybrids on the thermal degradation of EP during decomposition. The EP/MO-rGO nanocomposites showed significantly improved flame retardancy and fire toxicity, compared to neat EP and nanocomposites with either rGO or MO. The improvement in the fire safety of EP resin was attributed to the physical barrier of rGO and the catalytic action of MO.

4. Graphene aerogels were prepared by one-step reduction and self-assembly of GO using ethylenediamine, followed by freeze-drying and thermal reduction. Direct resistive heating of graphene aerogels was demonstrated. The morphology and electrothermal performance of the graphene aerogels Joule heaters were studied using a scanning electron microscope and an infrared camera. Their performances were investigated by measuring their thermal resistance and heating/cooling characteristics. The prepared graphene aerogels exhibited excellent performances, making them highly suitable for application in local gas heaters, catalysis, and regeneration of solid adsorbents.

5. Two different metal compounds/monolithic graphene aerogels catalysts, Ag/graphene aerogels catalysts, and Cu/graphene aerogels catalysts (derived from Cu-BTC/graphene aerogels) were prepared. Notably, electric currents directly passed through the monolithic graphene aerogels catalyst, generating Joule heating and bringing the catalysts to the target temperature. The catalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, inductively coupled plasma optical emission spectroscopy, and X-ray photoelectron spectroscopy. The complete CO conversion temperature for the graphene aerogels/Ag-6 wt% was 185 °C. Moreover, Cu/graphene aerogel-2 exhibited high catalytic performance and long-term stability, achieving complete CO conversion at 210 °C. The Joule heating catalytic system can be effectively used for personal protective equipment for fire emergency rescue applications.

    Research areas

  • Hybrids, Polymer nanocomposites, Fire safety, Graphene aerogels, Carbon monoxide oxidation, Joule Heating