Handai Liu

Foam 3D printing offers a promising route for producing lightweight structures, although the cell morphology and mechanical performance of printed polypropylene remain highly sensitive to processing conditions. This study investigates the effects of printing temperature, printing speed, and nozzle diameter on the foaming behavior and property retention of polypropylene containing a chemical foaming agent using a Taguchi L9 design. Printing temperatures of 220°C–240°C, speeds of 40– 80 mm/s, and nozzle diameters of 0.4–0.8 mm were evaluated through density, hardness, tensile, and flexural testing, scanning electron microscopy, and differential scanning calorimetry. Printing temperature had the greatest influence on density, contributing 34% of the observed variation, and affected hardness and cell morphology. Nozzle diameter was the dominant factor affecting mechanical performance and contributed 59.1% to flexural strength variation. The 0.8 mm nozzle was associated with a more stable cellular structure at high temperatures, while printing speed showed a smaller overall contribution. The preferred conditions identified from the main effect analysis provide practical guidance for selecting printing parameters within the ranges investigated. These findings provide a quantitative basis for balancing lightweight design and mechanical performance.

Compatibilizers that enhance sustainability and improve the miscibility of polymer blend components have garnered significant attention. This study investigates the difference between the synthetic chain extender Joncryl^® ADR 4468 and the natural epoxidized linseed oil (ELO) Merginat 8510100 as compatibilizers for thermoplastic starch/poly (butylene succinate) (TPS/PBS) blends. Blends containing 40% TPS and 60% PBS were prepared with 1, 3, and 5 phr of each compatibilizer, along with a reference with no additives. The properties of these blends were evaluated using tensile testing, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), rheology, and scanning electron microscopy (SEM). The findings indicate that while Joncryl^® ADR 4468 significantly improved tensile strength, it also resulted in a brittle fracture. In contrast, ELO batches exhibited greater ductility, albeit with lower tensile strength. These differences are attributed to the chain extension and minor cross-linking effects of Joncryl^® ADR 4468, compared to the increased chain mobility arising from ELO’s plasticizing and compatibilizing actions. Supporting evidence for these observations includes increased cold crystallization temperature (T_cc) and melting temperature (T_m), greater storage modulus along with higher complex viscosity, strengthened interfacial adhesion, and fewer morphological defects in Joncryl^® ADR 4468 blends. These results highlight the importance of selecting an appropriate compatibilizer based on specific application requirements. Overall, this study addresses the knowledge gap regarding the loadings of Joncryl^® ADR 4468 and ELO in TPS/PBS blends and provides a basis for further optimization strategies, such as the incorporation of binary compatibilizers, alternative grafting-based compatibilizers, and twin-screw blending modifications.

Poly(L-lactic acid) (PLLA) and iron (Fe) are popular bioresorbable material candidates for biomedical implants. However, PLLA coronary stents are relatively too thick compared to metallic stents when providing the same mechanical strength, while iron degrades too slowly. Recent studies show that PLLA coatings can enhance iron’s corrosion rate, and iron has strong mechanical strength, making PLLA–Fe composites ideal for bioresorbable implants. Although PLLA coatings on iron samples have been studied, research on embedding iron wires in relatively thick PLLA matrices is limited. Moreover, no studies have yet explored 3D-printed metal wire-reinforced PLLA monofilaments for biomedical applications. To address these research gaps and investigate the in vitro degradation profile of PLLA/Fe wire monofilaments for bioresorbable stents, this study first developed a novel polymer filament–metal wire coextrusion 3D printer for printing PLLA/Fe wire monofilaments. In vitro degradation tests were then conducted on both PLLA/Fe and neat PLLA monofilaments at 50 °C. Thereafter, characterizations, including mass loss, pH, surface appearance and morphology, tensile tests, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC), were performed. Results indicated that the overall degradation rate of PLLA/Fe monofilaments was higher than that of PLLA counterparts, while the degradation rate of PLLA matrix was not affected by the embedded iron wire according to molecular weight analysis. Notably, the Young’s modulus and stiffness of PLLA monofilaments were significantly improved by the iron wires during the early stages of degradation, but the reinforcement in tensile strength was negative after immersion due to the poor embedding quality of the iron wires in the PLLA monofilaments. With future improvement of the embedding quality of iron wire, the 3D-printed PLLA/Fe wire composites can have great potential in the development of biomedical devices using the novel 3D printing method, including most types of stents and bone scaffolds.