3D printing-enabled self-assembling β-nucleating agent alignment: Structural evolution and mechanical performances.

Achieving good alignment of fillers within the composites is critical towards developing the high performance of the final 3D printed objects. Herein, flow-induced the alignment of self-assembling β-nucleating agent (SANA β) within the isotactic polypropylene (iPP) matrix was achieved via fused deposition modeling (FDM) process. The influence of printing speed on the alignment of SANA β , crystalline structure, and mechanical properties of FDM printed samples were investigated. Due to the converging nozzle effect, SANA β fibers were fragmented from 26.13 μm to 9.98 μm in length, generating more oriented templates and further preferentially aligned along the printing direction to trigger the iPP crystallization. As a result, the crystal morphology of the printed sample was transformed from α-form to β-form hybrid shish-kebab structure. Highly oriented β-crystal was observed in iPP/SANA β (FT) samples, as evidenced by 2D-WAXD. 2D-SAXS results revealed the formation of plenty of oriented lamellae in FT samples, which were arranged perpendicular and parallel to the printing direction. The aligned SANA β also contributed to maintaining a high β-crystal content to overcome the shortcomings of rapid decrease of β-crystal for iPP at a high printing speed. Benefiting from this, with the increasing printing speed, compared with elongation at break of iPP samples decreased from 241.36% to 61.32%, those of FT sample increased dramatically from 305.07% to 390.23% but with a slight fade of less than 1% in the tensile strength. Additionally, the as-printed honeycomb array structure of FT sample presented superior energy absorption capacity and thus could function as loading-bear objects, highlighting the advantages of the alignment of self-reinforcing β-form hybrid shish-kebab. Due to the alignment of β-nucleating agent induced by the FDM process, β-form shish-kebab crystals were formed in the printed parts with superior energy absorption capacity but without sacrificing tensile strength. [Display omitted] • Self-assembling β-nucleating agent (SANA β) was fragmented from 26.13 to 9.98 μm in length during FDM process. • More SANA β were generated, aligned, and functioned as oriented templates to trigger the iPP crystallization. • β-form hybrid shish-kebab crystals were formed, where SANA β was acted as the "shish" and β-lamellae was acted as the "kebab". • The aligned SANA β contributed to maintaining a high β-crystal content even at a high printing speed. • The resultant samples presented superior energy absorption capacity without sacrificing tensile strength. [ABSTRACT FROM AUTHOR]