Combined Effects of Halloysite Nanotubes, Nucleating Agent, and Thermal Annealing on the Printability and Mechanical Performances of 3D-Printable Polypropylene Random Copolymer-Based Composites.

This study developed three-dimensional (3D)-printable polypropylene random copolymer (PPR)-based composites incorporating halloysite nanotubes (HNTs) and a nucleating agent (NA) for extrusion-based additive manufacturing. The combined effects of HNT loading (0-5 wt %), NA incorporation (0.1 wt %), and postprinting thermal annealing on their thermal behavior, crystallization, printability, and mechanical performance were systematically investigated. Thermogravimetric analysis (TGA) demonstrated enhanced thermal stability with HNT addition due to the barrier effect of the aluminosilicate structure. Differential scanning calorimetry (DSC) revealed that HNTs had limited influence on crystallization behavior, whereas NA significantly increased the crystallization and onset temperatures, indicating accelerated crystallization kinetics without altering the dominant α-phase crystal structure, as confirmed by X-ray diffraction (XRD). HNT incorporation improved filament dimensional stability during extrusion, yielding uniform, near-circular cross sections compared to neat PPR, and enhanced build plate adhesion and dimensional stability during printing without external adhesives. Mechanically, HNT addition increased stiffness but reduced impact strength. Postprinting thermal annealing increased melting enthalpy and refined crystalline morphology, resulting in partial recovery of impact strength in HNT-filled samples, although the values remained below that of neat PPR. The combined use of HNT incorporation, nucleation control, and thermal annealing provided an effective strategy to enhance the 3D-printability and mechanical performance of PPR-based composites.