Enhancing PET Printability via Solid‐State Polymerization: Structure‐Processing‐Properties Relationships

This paper aims to investigate the impact of solid‐state polymerization (SSP) on the printability of PET for 3D printing. Fused filament fabrication (FFF) and fused granulate fabrication (FGF) technologies were considered. Firstly, the effect of SSP temperature (120°C vs. 200°C) on molecular weight and viscosity was analyzed. It was found that SSP at 200°C (PET SSP 200) significantly increased viscosity from 100 to 400 Pa·s, making it suitable for 3D printing. In contrast, SSP at 120°C had limited effects due to lower reaction kinetics. When filament extrusion was tried, PET SSP 200 generated more stable filaments because of its higher viscosity, while the low‐viscosity virgin PET (PET V) showed irregular flow due to creep and a high crystallization rate, making the filament brittle. Mechanical measurements showed that injection‐molded PET SSP 200 had comparable flexural properties to virgin PET (2.2 GPa modulus and 70 MPa strength), with a threefold increase in Charpy impact strength (143 kJ/m 2 ) due to its higher molecular weight and reduced crystallinity. However, in comparison to injected specimens, FGF printed PET SSP 200 parts exhibited a 20% decrease in flexural modulus (1.8 GPa) and a 45% reduction in strength (46 MPa). This was attributed to porosity and anisotropy of printed parts. Despite these limitations, printed PET SSP 200 retained satisfactory toughness. This study emphasizes the effectiveness of SSP in improving the printability of PET, which opens up promising opportunities for 3D printing of virgin but also recycled PET.