Impact of Waste‐Derived Slate Dust on Structural, Thermal, and Thermomechanical Behavior of Recycled Poly(Ethylene Terephthalate)

ABSTRACT Recycled polyethylene terephthalate (rPET) is widely considered a sustainable alternative to virgin polyethylene terephthalate (PET). Nevertheless, its application in value‐added processes is frequently restricted due to property degradation occurring during recycling. This study investigates the use of slate dust (SD) as a reinforcing filler and its effects on the structural, thermal, and thermomechanical properties of rPET. Twin‐screw extrusion and injection molding were used to prepare composites with up to 20 wt% of SD. Gel permeation chromatography, Fourier transform infrared spectroscopy, and x‐ray diffraction confirmed that SD maintains chemical inertness during processing, with no detectable molecular degradation due to the filler. With a 20 wt% SD content, the thermal conductivity of rPET increased by approximately 41%, from 0.267 to 0.377 W/mK. Additionally, the crystallization temperature increased by 5°C, indicating the filler's nucleating effect. Dynamic mechanical analysis (DMA) indicates a ~39% increase in storage modulus at room temperature. To further explore the filler‐matrix interaction, Cole‐Cole plots and C‐factor, reinforcement efficiency, degree of entanglement, and adhesion‐related factors (A and B factors) were calculated from the DMA results. This study promotes waste valorization strategies by using slate waste as a filler and enhancing rPET to develop recycled polymer composites aligned with circular economy principles.