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Abstract: This study explores the potential of hydrothermally treated waste glass for producing foamed glass using a carbonaceous foaming agent (glycerol) in an air atmosphere. The objective was to assess the feasibility of this alternative route for producing sustainable, lightweight materials with reduced energy and material inputs by repurposing cathode ray tube panels (CRT), flint glass (FG), and mixed-color container glass (MCG). Investigated glass powders were treated in a saturated steam atmosphere inside a pressure vessel and characterized using Xray diffraction and Fourier-transform spectroscopy to identify structural changes. The foaming behavior of hydrothermally treated waste was analyzed through heating stage microscopy and thermogravimetric analysis coupled with mass spectrometry. The foamed glass samples were further assessed for density and thermal conductivity. The results demonstrate that hydrothermal treatment significantly influences the foaming process. Glass powders with higher content of structurally bonded water exhibit lower sintering temperature and pronounced expansion after the hydrothermal treatment. A higher hydration level reduced the onset foaming temperature and facilitated higher expansion. Additionally, combining hydrothermally treated powders with glycerol as a foaming agent enabled effective expansion, even in an air atmosphere, achieving density as low as 108 kg m-3. The results of this study suggest that hydrothermal treatment of waste glasses enables the implementation of carbonaceous foaming agents in the air atmosphere and could thus offer an alternative route for the foaming of glass.
Keywords: foamed glass, waste glass, hydrothermal treatment
Published in DiRROS: 18.11.2025; Views: 282; Downloads: 97
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Abstract: Polyurethane foam (PUR) is a lightweight, thermally insulating, widely used, and highly flammable material that has after its use an adverse effect on the environment, i.e., PUR disposal is considered hazardous. Its flammability can be mitigated using various fire retardants, but they do not change the hazardous nature of waste PUR. Therefore, in the current study, waste PUR with and without flame retardants based on N and P was incorporated into a geopolymer, the alkali-activated material (AAM) based solely on metakaolin, to evaluate the potential recycling route of waste PUR while taking into account its flammability, so it can enter safely into the circular economy through the building industry. To enhance the mechanical properties of the composite, a fresh mixture was irradiated with microwaves. However, the irradiation of geopolymer containing PUR negatively influenced mechanical performance, which led to the evaluation of the behaviour of the complex dielectric constant of PUR and fire retardants. Materials and composites were evaluated regarding their chemistry, mineralogy, microstructure, and porosity to connect the structure with extrinsic properties like geometrical density, thermal conductivity, and fire properties. Nonetheless, positive influences of PUR being encapsulated in the geopolymer were lowered density (from 1.8 to 1.6 kg/l) and improved thermal insulation ability (from 940 to 860 mW/(m·K)) of the composites: with the inclusion of <5 % of PUR, thermal insulation improved by nearly 10 %. However, the contribution of PUR to the composite originated from its skeleton, which has more than 15 times bigger geometrical density (0.81 kg/l) compared to the density of the skeleton (0.047 kg/l). This offers an open field for further advancements of thermal properties, but would also lead to a decrease of the compressive strength, which was already lowered from 90 MPa for 30 % with <5 % of added grated PUR. Furthermore, the flammable nature of PUR and its other drawbacks can be controlled by permanent embedding in the noncombustible structure of geopolymer, making the envelope of sustainable buildings green and safer. Overall, including grated waste PUR in geopolymer represents a promising, easy, cost-effective recycling path with low energy consumption, where the composite cannot develop fire on a scale of pure PUR, even in the worst-case scenario, but only if the composite is designed in a way, that flammable materials cannot join flames during their combustion. This paper gives prospects to other flammable waste materials to be safely used in the circular economy, and to porous materials to shape properties of the composite by their intrinsic and/or extrinsic properties.
Keywords: waste polyurethane foam, polymeric flame retardants, alkali activated material, metakaolin, microwave irradiation, thermal-fire behaviour, mechanical strength
Published in DiRROS: 01.03.2024; Views: 3180; Downloads: 1657
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