Towards sustainable composite manufacturing: Impact of matrix variants on processing energy and mechanical performance of recycled glass fibre composites

The transition to circular polymer manufacturing requires improved understanding of how recycled feedstock composition influences manufacturing energy demand and final material performance. While recycled fibre-reinforced thermoplastic composites have attracted increasing interest, the connected effects of material composition and processing conditions on specific energy consumption and mechanical properties remain insufficiently quantified. This study presents a systematic correlation-based analysis of post-industrial glass fibre-reinforced polypropylene (GFPP)-reinforced recycled polypropylene (rPP) composites, linking material composition, extrusion and injection moulding parameters, specific energy consumption, and tensile properties. The results show that increasing rPP content increases specific energy consumption by approximately 10%–15%, whereas higher GFPP and additive contents reduce energy demand by up to 12%. Among the processing parameters, higher extruder throughput improves machine efficiency and lowers energy consumption (up to 8%), while increased screw speed increases energy demand (approximately 9%). Tensile strength exhibits a positive correlation with GFPP content and extruder throughput, but decreases with increasing rPP content. These findings demonstrate the trade-offs between material circularity, energy efficiency, and mechanical performance. The novelty of this work lies in the integrated quantitative assessment of material composition, processing conditions, manufacturing energy consumption, and tensile behaviour within recycled fibre-reinforced polypropylene systems. The presented correlations provide practical guidance for optimising composite formulations and processing conditions to support energy-efficient, high-performance, and circular polymer manufacturing.