Sustainable fused granulate fabrication: the effects of multiple recycling processes on mechanical properties of recycled polycarbonate

This study explores the potential of polycarbonate (PC) using a novel 3D printing technique such as fused granulate fabrication (FGF), focusing on the effects of multiple recycling cycles on thermal stability, mechanical properties and microstructural integrity. Thermal stability analysis of FGF-printed recycled polycarbonate (rPC) shows a 12.5 % decrease in glass transition temperature (T_g) and slight degradation in onset degradation temperature T_onset after 10 recycling cycles. FTIR spectra shows initial improvements in the rPC structure after the 1^st cycle, followed by degradation in subsequent cycles, confirming chain scission and reduced functional groups. Mechanical testing indicates that tensile strength increases from 54.96 MPa at the 1^st cycle–68.59 MPa at the 3^rd cycle due to improved polymer chain alignment but reduced significantly to 27.31 MPa by the 10^th cycle due to degradation. The maximum flexural strength of 76.4 MPa was oberved at the 3^rd cycleand then begins to decline from the 5^th onwards. Impact strength shows a steady decrease, from 3.29 kJ/m² at the 1^st cycle–2.4 kJ/m² at the 10^th cycle, reflecting molecular breakdown and reduced ductility. Fracture surface analysis reveals a transition from ductile to brittle failure as the number of recycling cycles increased. In terms of 3D printing efficiency, FGF significantly reduced printing time compared to fused filament fabrication (FFF), with up to an 84 % time saving, demonstrating the FGF potential as a cost-effective and sustainable alternative for rPC. These results contribute to comprehensively understanding the trade-offs and benefits of using rPC in Additive Manufacturing, providing insights into the sustainable use of rPC for FGF-printed products.