Sustainable recycling of ABS: comprehensive thermophysical characterisation in filament- versus granules-based 3D printing pathways across multiple reprocessing cycles

Purpose: This study aims to evaluate and compare the recycling performance and sustainability of acrylonitrile butadiene styrene (ABS) plastic waste using two additive manufacturing pathways � filament- and granule-based three-dimensional (3D) printing � across multiple successive recycling cycles, through comprehensive thermophysical characterization and carbon footprint assessment. Design/methodology/approach: Recycled ABS granules is processed using two pathways: (i) extrusion into filaments followed by 3D printing and (ii) direct granule-based 3D printing. Specimens are fabricated across three reprocessing cycles involving repeated shredding and reprinting. The printed specimens are evaluated and compared for tensile strength using a universal testing machine (UTM), fracture morphology via scanning electron microscopy (SEM), rheological behavior through melt flow index (MFI), chemical structure using Fourier transform infrared spectroscopy (FTIR) and thermal degradation via thermogravimetric analysis (TGA). Additionally, carbon emissions, energy consumption and costs are assessed. Findings: Granule-based 3D-printed parts outperformed filament-based counterparts, exhibiting approximately 5% higher tensile strength in the first cycle and up to approximately 20% higher strength after three cycles. MFI increased moderately (approximately 27%) for granule-based prints but sharply (approximately 124%) for filament-based prints beyond the third cycle, indicating more severe polymer degradation in the latter. FTIR showed weakening of chemical bonds, notably C?=?N (2238?cm?1), indicating reduced thermal stability and hardness. Thermal stability declined slightly across cycles, with onset degradation temperatures dropping from 415�C to 405�C (granule-based) and 403�C (filament-based). Life cycle assessment revealed that granule-based printing saved approximately 6.2?kg CO2 per kg of plastic, consumed 1.05?kWh less energy, and was nearly 10� more cost-effective than commercial filament printing. Overall, granule-based 3D printing proved more effective for recycling, offering better mechanical strength, chemical retention, thermal stability and sustainability. Originality/value: This study presents a comprehensive comparative assessment of filament- and granule-based 3D printing using recycled ABS, addressing a critical gap in previous studies that often focus on a single recycling pathway, only one reprocessing cycle or limit comparisons to mechanical properties. By evaluating thermal, chemical and environmental performance across multiple recycling cycles, this study provides a thorough assessment of recycling performance via 3D printing. It quantitatively and qualitatively establishes the practical advantages of direct granule-based printing over filament-based printing for decentralized recycling systems. These findings contribute to advancing sustainable and circular economy practices in additive manufacturing.