Fused Granulate Fabrication of Virgin and Reprocessed PLA/Silicon Dioxide Nanocomposites: Processing, Mechanical Integrity, and Soil Microbial Respiration Response

Abstract

This study evaluates processing via fused granulate fabrication (FGF) of nanocomposites based on virgin polylactic acid (PLA) and thermomechanically reprocessed polylactic acid (rPLA), incorporated with 0 wt%, 5 wt%, and 10 wt% of silicon dioxide (SiO2) nanoparticles. Rheological analysis revealed that rPLA exhibited a 42.4 % increase in melt flow rate compared to PLA, which can be attributed to thermomechanical chain scission occurring during reprocessing. At 10 wt% filler loading, the tensile strength along the XZ build direction tended to decrease. Scanning electron microscopy analysis suggests that this trend is related to nanoparticle agglomeration. Thermogravimetric analysis showed that adding 5–10 wt% SiO2 restored the lower initial thermal degradation onset of rPLA (𝑇�5%loss=313°C) to values equal to or exceeding PLA (323–324°C), while overall crystallinity remained near 0% owing to rapid convective cooling during FGF printing. Short-term soil respirometry trials using extruded granule samples revealed that rPLA exerted a temporary respirometric inhibition, reducing soil basal respiration by 22.5%. The incorporation of 10 wt% SiO2 recovered 96.3% of the native soil metabolic activity by increasing extruded granules surface wettability and water availability at the particle interface. These findings demonstrate that the control of SiO2 loading enables the tuning of mechanical performance, establishing a framework for sustainable, large-format PLA components with tailored end-of-life properties.