Comparative Analysis of Mechanical and Thermal Properties of Virgin and Recycled Polyethylene Terephthalate for Fibre Production

Polyethylene terephthalate recycling from post-consumer bottles represents a significant source of raw material for synthetic fibre production in emerging economies. This study conducts a comparative analysis of the mechanical and thermal properties of virgin and recycled polyethylene terephthalate pellets sourced from a recycling facility in Onitsha, Anambra State, South East Nigeria, evaluating their suitability for fibre-grade applications. Both virgin and recycled material were characterised for intrinsic viscosity, melting point, crystallisation temperature, tensile strength, elongation at break, and melt flow index. Thermogravimetric analysis assessed thermal stability and degradation onset temperatures. Colour measurement using a spectrophotometer quantified yellowness index differences between virgin and recycled grades. Results show intrinsic viscosity reduction in recycled material from 0.85 to 0.71 dL/g, indicating chain scission from mechanical and thermal reprocessing. Melting point and crystallisation temperature remained largely unchanged, confirming similar crystalline structure between grades. Tensile strength of recycled material was 91 percent of virgin values, while elongation at break declined by 18 percent. Yellowness index was significantly elevated in recycled material, a critical aesthetic limitation for light-coloured fibre production. Melt flow index increased in recycled material, confirming molecular weight reduction. The study concludes that single-cycle recycled polyethylene terephthalate is technically suitable for blending with virgin material in fibre production at up to 30 percent recycled content without major quality compromise, supporting sustainable fibre manufacturing practices in South East Nigeria. Keywords: recycled PET, polyethylene terephthalate, fibre production, intrinsic viscosity, mechanical properties