The present study investigates the feasibility of utilizing polylactic acid (PLA) and PLA-based natural fiber-reinforced composites (NFRCs) in mechanical recycling. A conical twin screw extrusion (CTSE) process was utilized to recycle PLA and PLA-based NFRCs consisting of 90 wt.% PLA and a 10 wt.% proportion of either basalt fibers (BFs) or halloysite nanotubes (HNTs) for up to six recycling steps. The recycled material was then injection molded to produce standard test specimens for impact strength and tensile property analysis. The mechanical recycling of virgin PLA led to significant discoloration of the polymer, indicating degradation during the thermal processing of the polymer due to the formation of chromatophores in the structure. Differential scanning calorimetry (DSC) analysis revealed an increase in glass transition temperature (T_g) with respect to increased recycling steps, indicating an increased content of crystallinity in the PLA. Impact strength testing showed no significant detrimental effects on the NFRCs’ impact strength up to six recycling steps. Tensile testing of PLA/HNT NFRCs likewise did not show major decreases in values when tested. However, PLA/BF NFRCs exhibited a significant decrease in tensile properties after three recycling steps, likely due to a reduction in fiber length beyond the critical fiber length. Scanning electron microscopy (SEM) of the fracture surface of impact specimens revealed a decrease in fiber length with respect to increased recycling steps, as well as poor interfacial adhesion between BF and PLA. This study presents a promising initial view into the mechanical recyclability of PLA-based composites.

In this study, a 3D-printed photocurable resin was developed by incorporating graphene nanoplatelets functionalised with melamine to investigate the thermal, mechanical, fracture and shape memory behaviours. The objective of this work was to produce a printed functionally graded nanocomposite material that has a smart temperature-responsive structure; presents good thermal stability, strength and fracture toughness; and can demonstrate shape-changing motions, such as sequential transformations, over time. The functionalised graphene nanoplatelets were examined via thermogravimetric analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and ultraviolet–visible spectroscopy. Thermogravimetric analysis showed that the degradation temperature of the nanocomposite containing 0.1 wt% of functionalised graphene nanoplatelets at the weight loss of 5% was 304 °C, greater than that of the neat one by 29%. Dynamic mechanical analysis results showed property enhancements of the storage modulus and glass transition temperature. Fracture toughness, tensile strength and impact resistance were improved by 18%, 35% and 78%, respectively. The shape memory tests were performed to obtain the temperature-time recovery behaviour of the 3D-printed structures. The addition of functionalised graphene nanoplatelets demonstrated an enhancement in the shape recovery ratios. Generally, the five subsequent cycles were notably stable with a high recovery ratio of 97–100% for the flat shape and circular shape of the M-GNP specimens. On the other hand, these values were between 91% and 94% for the corresponding neat specimens.

This study explores the use of vat polymerization stereolithography (SLA) for fabricating mold tooling, subsequently utilized in injection molding (IM) and overmolding of tensile specimens and directly compared to those produced using metal molds. The results first find the manufacturing time for an SLA‐fabricated mold is remarkably short, approximately 6 h, presenting a substantial improvement over traditional methods. Mechanical testing revealed that the tensile specimens from the SLA‐fabricated molds exhibited the highest tensile strength among all overmolding batches. This performance was consistent with the tensile bars produced using metal molds, demonstrating the viability of SLA‐fabricated molds for overmolding applications and highlighting the potential of FDM to customize the properties of final products. However, variations in mold types impacted the dimensional tolerance and tensile strength of the final specimens. Metal mold‐fabricated tensile bars exhibited superior dimensional accuracy and maximum tensile strength (50.6–61.7 MPa) compared to those produced with SLA‐fabricated molds (46.9–55.9 MPa). These differences are attributed to the rougher surface finish inherent to the layer‐by‐layer construction of SLA and the internal stresses and defects resulting from lower thermal conductivity and uneven cooling. In conclusion, this study underscores the promising future applications of SLA‐fabricated molds in overmolding, offering reduced manufacturing costs and enhanced design freedom. The findings support the potential of SLA to revolutionize mold fabrication, thereby extending its utility and optimizing the production of polymer components with customized properties. Highlights: SLA molds compared to metal molds for direct injection molding and overmolding. FFF preforms with varied geometries were overmolded to finalize the specimens. Joint configurations in overmolding improved tensile performance. Overmolding showed better dimensional accuracy than FFF specimens. SLA mold preparation significantly reduced manufacturing costs.

The immiscibility of thermoplastic starch (TPS) and polybutylene succinate (PBS) complicates the thermal processing of these materials. This study provides the first comparative assessment of two compatibilizers with differing reaction mechanisms, Joncryl^® ADR 4468 and epoxidized linseed oil (ELO), for the optimization of biobased TPS/PBS blends. A total of 13 batches, varying in compatibilizer and blend composition, were processed via hot melt extrusion and injection molding to produce pellets. Blends were analyzed using tensile and impact testing, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), rheology, and scanning electron microscopy (SEM). The findings suggest that both compatibilizers can improve the compatibility of these blends, as evidenced by higher glass transition temperatures (T_g) compared to the reference batch (100-0-N/A). Joncryl^® ADR 4468 batches exhibit superior tensile strength and Young’s moduli, while ELO batches demonstrate greater elongation at break. The enhanced processability observed in Joncryl^® ADR 4468 is attributed to the increased polymer chain entanglement and molecular weight, whereas ELO facilitates greater chain mobility due to its plasticizing effect. These differences arise from the distinct mechanisms of action: Joncryl^® ADR 4468 promotes chain extension and crosslinking, whereas ELO mainly enhances flexibility through plasticization. Overall, this study provides a comparative assessment of these compatibilizers in TPS/PBS blends, laying the groundwork for future investigations into optimizing compatibilizer concentration and blend composition.

Using 3D-printed (3DPd) polymers and their composites as shape memory materials in various smart engineering applications has raised the demand for such functionally graded sustainable materials. This study aims to investigate the viscoelastic, shape memory, and fracture toughness properties of the epoxy-based ultraviolet (UV)-curable resin. A UV-based DLP (Digital Light Processing) printer was employed for the 3D printing (3DPg) epoxy-based structures. The effect of the hydrothermal accelerated ageing on the various properties of the 3DPd components was examined. The viscoelastic performance in terms of glass transition temperature (T_g), storage modulus, and loss modulus was evaluated. The shape memory polymer (SMP) performance with respect to shape recovery and shape fixity (programming the shape) were calculated through dynamic mechanical thermal analysis (DMTA). DMTA is used to reveal the molecular mobility performance through three different regions, i.e., glass region, glass transition region, and rubbery region. The shape-changing region (within the glass transition region) between the T_g value from the loss modulus and the T_g value from the tan(δ) was analysed. The temperature memory behaviour was investigated for flat and circular 3DPd structures to achieve sequential deployment. The critical stress intensity factor values of the single-edge notch bending (SENB) specimens have been explored for different crack inclination angles to investigate mode I (opening) and mixed-mode I/III (opening and tearing) fracture toughness. This study can contribute to the development of highly complex shape memory 3DPd structures that can be reshaped several times with large deformation.