Research Article Received: 3 August 2025 Revised: 14 September 2025 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/pi.70043 Performance analysis of recycled PET composites reinforced with waste slate dust: physicomechanical and wear properties Aditya Chauhan, a Robert Brüll, b * Subrajeet Deshmukh, b Sampat Singh Bhati, a Kirtiraj K Gaikwad a * and Tej Singh c Abstract In this study, thermoplastic composites were developed from recycled poly(ethylene terephthalate) (rPET) reinforced with waste slate dust (WSD). The composites were processed through twin-screw extrusion followed by injection molding with vary- ing WSD contents (0–20 wt%). The fabricated composites were systematically characterized for their physical, mechanical, slid- ing wear and morphological properties. The composites exhibited a monotonic increase in Young's modulus from 2.14 to 3.00 GPa and flexural modulus from 2.11 to 3.20 GPa. Flexural strength increased modestly from 72.5 to 76.8 MPa, while the tensile strength remained largely unaffected (38.07 MPa for neat rPET versus 37.27 MPa at 20 wt% WSD). In contrast, the elon- gation at break was reduced by ca 36% at 5 wt% and ca 80% at 20 wt%, and impact strength dropped from 19.6 to 10.0 kJ m -2 . Surface hardness increased slightly (76.1 to 78.0), while wear performance improved significantly, with the specific wear rate decreasing by more than 60% at 20 wt% WSD. These findings show the potential of repurposing slate waste as a functional filler for rPET-based composites, thus providing the dual benefit of performance enhancement and circular material utilization. © 2025 Society of Chemical Industry. Keywords: recycled poly(ethylene terephthalate); slate dust; polymer composites; mechanical properties; wear resistance; waste valorization INTRODUCTION The accumulation of solid waste has become one of the most pressing environmental challenges of the 21st century, with plas- tics as dominant contributor. 1 Global plastic production now exceeds 380 million tonnes annually, yet only about 9% is effec- tively recycled. The remainder is either incinerated or landfilled, causing significant ecological and resource concerns. 2,3 Poly(ethylene terephthalate) (PET) is among the most widely used thermoplastics, following polyolefins and polystyrene. 4 It has a semicrystalline structure with high toughness, mechanical strength, chemical resistance and transparency. 5 These properties make PET highly adaptable for a wide range of applications, including food packaging, synthetic fibers, beverage bottles, cas- settes and engineering components. 6,7 However, PET waste is often mismanaged and generates 8% by weight and 12% by vol- ume of total solid waste worldwide. 8 Therefore, recycling PET is essential to mitigate environmental impact and conserve energy since recycled PET (rPET) requires 50–60% less energy than virgin PET production. 9–11 Recycling approaches for PET include thermal (energy recov- ery), biochemical or catalytic depolymerization (to regenerate monomers) and mechanical reprocessing. 12 Among these, mechanical recycling is the most industrially viable due to its lower energy demands and established large-scale infrastruc- ture. 13 PET recycling starts with sorting and separating the waste, followed by washing to remove any impurities. The clean PET is then shredded and ground into flakes or powder, which is further re-extruded to produce granules for making new products. 14 However, recycling of PET is challenging, as reprocessing often leads to the deterioration of its mechanical and chemical proper- ties due to hydrolytic and thermomechanical degradation. 15,16 This involves chain scission and a reduction in PET molecular weight. 17 To maintain the properties of the recyclates, most of the time, additives (copolymers, antioxidants, filler particles, chain extenders, etc.) are introduced to the material during the proces- sing stage. 18,19 These additives can enhance the material through various mechanisms, enabling the recyclate to perform at a level comparable to or exceeding that of the virgin polymer. 20 * Correspondence to: KK Gaikwad, Department of Paper and Packaging Tech- nology, Indian Institute of Technology Roorkee, Roorkee, 247667, India. E-mail: kirtiraj.gaikwad@pt.iitr.ac.in; or R Brüll, Department Material Analysis and Characterization, Division Plastics, Fraunhofer Institute for Structural, Durability and System Reliability LBF, 64289 Darmstadt, Germany. E-mail: robert.bruell@lbf.fraunhofer.de a Department of Paper and Packaging Technology, Indian Institute of Technol- ogy Roorkee, Roorkee, India b Department Material Analysis and Characterization, Division Plastics, Fraun- hofer Institute for Structural Durability and System Reliability LBF, Darmstadt, Germany c Savaria Institute of Technology, Faculty of Informatics, ELTE Eötvös Loránd University, Budapest, Hungary Polym Int 2025 www.soci.org © 2025 Society of Chemical Industry. 1