Journal of Manufacturing and Materials Processing

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 (${\mathrm{SiO}}_2$) 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% ${\mathrm{SiO}}_2$ restored the lower initial thermal degradation onset of rPLA ( ) to values equal to or exceeding PLA ( ), 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% ${\mathrm{SiO}}_2$ 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 ${\mathrm{SiO}}_2$ loading enables the tuning of mechanical performance, establishing a framework for sustainable, large-format PLA components with tailored end-of-life properties.

Conventional operator-guided press straightening of round bars relies on operator experience and repeated trial pressing. This study proposes a local deflection control strategy that combines measurement, rotational alignment, model-based reverse bending, and remeasurement after unloading. A circular-arc approximation relates local deflection to full-length straightness. A conditional deflection superposition relationship is derived for initially curved bars under three-point bending and used with a finite difference model to predict pressing displacement. Finite element simulations assess the superposition relationship and the load–displacement response. In the investigated superposition cases, seven of eight relative errors are below 4%, with a maximum of 5.81%. The calculated load–displacement curves agree with the finite element results for both materials. Experiments on GCr15 and 60Si2Mn bars with a diameter of 20 mm and a length of 1.5 m demonstrate full-length straightness below 1‰ for the reported cases. These results demonstrate the feasibility of the prediction-and-feedback strategy for the tested single-peak bars.

This article investigated the effect of screw speed on the molecular weight of starch during thermoplastic starch (TPS) preparation, as well as the effect of this molecular weight on the 3D printing process, interlayer adhesion, molecular orientation, molecular forces, relative crystallinity, and dry mechanical properties of PLA/TPS stents. The increase in screw speed during the preparing of TPS was found to reduce the molecular weight of starch. The reduction in molecular weight of starch was beneficial for the extrusion of filaments and enhanced continuity and uniformity in the lines of 3D-printed stents but reduced the interlayer adhesion of 3D-printed stents. The molecular orientation of stents diminished with decreasing starch molecular weight, leading to a reduction in molecular forces and short-range ordering. This decline was detrimental in terms of enhancing both axial and radial compression characteristics of 3D-printed stents. Considering the influence of starch molecular weight on both the 3D printing process and molecular conformation, the mechanical properties of the 3D-printed PLA/TPS stent were optimized when the screw speed for preparing TPS was set to 160 r/min. The findings will offer theoretical support for the advancement of 3D-printed stents.