Toward circular, value-added recycling of modified-poly(ethylene terephthalate): Microstructure and performance across multiple fused particle fabrication cycles

Dimensional instability remains a principal concern in extrusion-based additive manufacturing, driven by volumetric shrinkage stemming from microstructural changes, especially throughout closed-loop recycling of semicrystalline polymers such as poly(ethylene terephthalate) (PET). The present study investigates the microstructural evolution and corresponding volumetric shrinkage of modified-PET (mPET) quantifying key microstructural contents ( i.e. , degree of crystallinity, and mobile and rigid amorphous fractions) across 4 fused particle fabrication cycles for the first time. The results reveal proto-spherullite formation in recycled mPET microstructure and associated microstructural changes that cause progressive volumetric shrinkage. The degree of crystallinity and rigid amorphous content are found to vary as a function of the FPF cycle number. Notably, recycled mPET exhibited an increase in density from 1.23 to 1.30 g/cm³ and volumetric shrinkage from 0 to 4.8 % following 4 FPF cycles. The study observations have important implications for predicting dimensional accuracy in 3D-printed parts manufactured from both virgin and recycled semicrystalline polymers using extrusion-based additive manufacturing.