Chemical recycling of polyethylene terephthalate wastes into monomers for utilization as binding agents in ceramic floor tiles

Abstract

The accumulation of plastic waste, particularly polyethylene terephthalate (PET), presents a growing environmental threat due to its non-biodegradable nature and limited recycling efficiency using conventional methods. This research explores a sustainable solution by chemically recycling PET plastic waste into monomers and integrating them as binding agents in ceramic floor tile production. Two chemical recycling techniques, glycolysis and ammonolysis, were used to depolymerize PET wastes into functional monomers, Bis(2-hydroxyethyl) terephthalate (BHET) and terephthalamide derivatives, respectively. These monomers were then incorporated into clay-based ceramic tile formulations using a fixed clay mass of 200 g and varying monomer volumes from 50 to 90 ml. This study involved the production and testing of both monomer samples and ceramic tile samples. Key properties such as thermal conductivity, water absorption, density, specific gravity, flexural strength, and compressive strength were characterized according to relevant ASTM and ISO standards. To further understand the structural integration and chemical composition of the tiles, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDX) were also conducted. FTIR analysis revealed the presence of functional groups such as hydroxyl (-OH), carbonyl (C=O), and ester groups, confirming the successful incorporation of PET-derived monomers into the ceramic matrix. SEM images displayed a more compact and homogenous microstructure in tiles produced using glycolyzed PET monomers, while EDX analysis confirmed the elemental composition, including the distribution of Si, Al, Fe, and traces of carbon indicative of monomer integration. These findings provided insight into the microstructural and molecular interactions between the recycled PET waste monomers and ceramic components. Results indicated that tiles made using glycolysis-based monomers exhibited better mechanical and thermal properties than those from ammonolysis, with compressive strengths reaching 34.25 MPa and flexural strengths exceeding 14 MPa at optimal monomer volume. Water absorption rates declined with increasing monomer content, indicating reduced porosity and improved structural integrity. Both glycolysis and ammonolysis were effective in producing high-performance tiles; however, glycolysis showed superior compatibility with the ceramic matrix due to better polymer dispersion. This work not only demonstrated the feasibility of using recycled PET wastes in ceramic tile production but also contributes to sustainable materials innovation by diverting plastic waste from landfills and reducing reliance on traditional petrochemical-based binder