Infiltration-Assisted Mechanical Strengthening of 3D-Printed Polypropylene Lattice and Thin-Walled Tube Structures

This study presents a viscosity-controlled epoxy infiltration strategy to mitigate common production defects, such as interlayer bond weaknesses, step gaps, and surface roughness, in 3D-printed polypropylene lattice and tube structures. To address these issues, epoxy resin infiltration was applied at four distinct viscosity levels. The infiltration process, facilitated by ultrasonic assistance, improved epoxy penetration into the internal structure. The results indicate that this method effectively reduced micro-voids and surface irregularities. Variations in epoxy viscosity significantly influenced the final internal porosity and the thickness of the epoxy film formed on the surface. These structural changes directly affected the energy absorption (EA) and specific energy absorption (SEA) of the specimens. While performance was enhanced across all viscosity levels, the medium-viscosity specimens (L-V2 and L-V3), with a mass uptake of ~37%, yielded the most favorable outcome, achieving high SEA (0.84 J/g) and EA (252 J) values. This improvement was mainly attributed to the epoxy filling internal voids and defects. Mechanical test results were further supported by SEM observations and validated through statistical correlation analyses. This work constitutes one of the first comprehensive studies to employ epoxy infiltration for defect mitigation in 3D-printed polypropylene structures. The proposed method offers a promising pathway to enhance the performance of lightweight, impact-resistant 3D-printed structures for advanced engineering applications.