Epoxy Composites Enabled by Graphene-Related Materials: Properties and Hazard Assessment of the Aerosols Released by Abrasion and Combustion
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Autor(in)
Datum
2021Typ
- Doctoral Thesis
ETH Bibliographie
yes
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Abstract
Graphene-related nanomaterials, GRMs, such as graphene nanoplatelet (GNP), graphene oxide (GO), reduced GO (rGO), etc. have a number of applications in various fields such as composite materials, filtration, catalysis, and electronics. Due to the reinforcement, flame retardancy and electrical conductivity properties, GRMs have been explored as nanofillers in polymer composites. An increasing production volume of the GRMs and the GRM-containing composites in the market has brought attentions to their potential risks to humans and the environment. The exposure of GRMs or particles released from GRM-containing composites is possible during the production, the use phase, or the end-of-life of the GRMs and the GRM-containing composites. However, there are still a number of polymer systems that have not been investigated. Moreover, there are limited data about the toxicity of the aerosols released from GRMs-containing composites. Therefore, this thesis focused on three main goals. First, to manufacture the GRM-containing epoxy composites and characterize their mechanical reinforcement and the flame retardancy properties. Second, to analyze the physical and chemical properties, the released fraction of GRMs from the composites, and the in vitro toxicity of the released particles from the GRM-containing epoxy composites induced by an abrasion process, which resembled one of the release scenarios by mechanical force during the use phase of the composites. Finally, to investigate the released aerosols from the combustion, which was one of the scenarios that can take place at the end-of-life of the materials, of the GNP-reinforced epoxy composite (EP- GNP) as compared to pure epoxy (EP) in terms of the physicochemical properties and the potential adverse effects.
The mechanical reinforcement, flame retardancy, and electrical properties of the epoxy nanocomposites filled with GNP and phosphorous flame retardant, 9,10- dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as fillers in epoxy composites (diglycidyl ether of bisphenol A and polyetheramine system) were investigated (Chapter 2). The homogeneous dispersion of GNP (0.1 – 5 wt %) was achieved by using high speed mixer followed by the three-roll milling process, while DOPO (3 – 30 wt %) was incorporated into the epoxy resin by heated stirring. The three-point bending test was carried out to evaluate the flexural modulus and flexural strength of the fabricated epoxy composites. The flame retardancy properties were tested using a cone calorimeter. The electrical properties were assessed based on corona discharge test and electrical resistance. Increasing the loading of GNP until 1 wt % and DOPO until 10 % could improve the mechanical properties of the epoxy composites, whereas higher loadings could reduce the flexural strengths of the composites. The combination of GNP and
DOPO could enhance the flame retardancy, based on flame retardancy index (FRI), of the epoxy composites compared to using GNP or DOPO alone. The formulation leading to an improvement in both mechanical properties and flame retardant efficiency of the nanocomposite was 0.5 wt % GNP and 10 wt % DOPO, which did not alter the insulating property of the epoxy resin since the percolation threshold was at 1.6 wt % GNP. The structure–property relationship of the additive-filled epoxy composites obtained from this study can be used as a property constraining guidance to manufacture the composites.
The characterization and the in vitro toxicity of the pristine GRMs and the released particles from abrasion of their epoxy composites were determined (Chapter 3). GRMs used in this study included GNP, GO and rGO. The lateral dimension, C/O ratio, thickness, and surface functionality of each GRM were thoroughly characterized. The particle size distributions of the released particles by abrasion measured by a scanning mobility particle sizer and an aerodynamic particle sizer revealed that the abraded particles were in a respirable size range. Since the GRMs that were embedded in the epoxy composite may be released by abrasion and may cause negative health impacts, the released fractions of GRMs were quantified using a lead-labelling method combined with an inductively coupled plasma-optical emission spectrometry. The re- leased fractions of GRMs ranged from 52 % to 92%, depending on the type and size of the GRMs. Raman mapping spectroscopy revealed the defects on the graphitic layers on the GRMs in the abraded particle suggesting that GRMs may be transformed during the fabrication and abrasion process. For in vitro toxicity analysis, human macrophages exposed to the suspensions (5 to 40 μg/mL) of GRMs and particles released from abrasion of GRM-epoxy composites were assessed for several toxicity endpoints including the change in cell morphology, cell viability, oxidative stress, and (pro-) inflammatory responses after 24 h and 48 h. The pristine GRMs could cause dose-dependent oxidative responses, while only large GNP could cause cell death. None of the abraded particles induced negative impacts on cells.
A combustion platform has been established to characterize the fire behavior, emissions from combustion and their potential hazards of the EP-GNP compared to EP (Chapter 4). The particle size distributions of the emissions were measured on-line using an aerodynamic particle sizer and a fast mobility analyzer. The emitted particles were collected for further characterization. Raman spectroscopy and X-ray diffraction analysis of both airborne fraction and char residue demonstrated that GNP was only present in the char residues, not in the airborne fraction. The airborne particulate emissions from EP-GNP revealed higher polycyclic aromatic hydrocarbon concentrations, analyzed by gas chromatography-mass spectrometry, as compared to those from EP. The human alveolar epithelium cells were directly exposed to the emissions at air- liquid interface conditions and the biological effects were evaluated at 24 h and 96 h after exposure. The toxicity endpoints included the change in cell morphology, cell viability, (pro-) inflammatory responses, and the expression of oxidative stress genes (SOD2 and HMOX1) and aryl hydrocarbon receptor (AhR) gene (CYP1A1), which is responsible for the polycyclic aromatic hydrocarbon metabolism. The emissions from EP combustion induced the pro- inflammatory response (MCP-1 and GM-CSF) and the activation of AhR, but did not cause any effects on cell morphology, cell viability nor oxidative stress genes. Despite a transient decrease in mitochondrial activity at 24 h caused by EP-GNP, but not EP, the emissions from EP-GNP did not induce any additional adverse cell effects in comparison to those from EP.
In conclusions, the results from these studies improve the understanding about the role of GRMs to enhance the mechanical strength and the flame retardancy properties of epoxy composites and the physicochemical characteristics and potential hazards of aerosols released from the abrasion and combustion of the GRM-reinforced epoxy composites. These results revealed that the GRMs can be used as nanofillers in epoxy composites mainly due to their beneficial effects, and the limited in vitro toxicity is auxiliary. Mehr anzeigen
Persistenter Link
https://doi.org/10.3929/ethz-b-000511697Publikationsstatus
publishedExterne Links
Printexemplar via ETH-Bibliothek suchen
Beteiligte
Referent: Wang, Jing
Referent: Wick, Peter
Referent: Buerki-Thurnherr, Tina
Referent: Chortarea, Savvina
Referent: Yao, Maosheng
Verlag
ETH ZurichOrganisationseinheit
03887 - Wang, Jing / Wang, Jing
ETH Bibliographie
yes
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