부산대학교 도서관

In this work, for the first time, PET-G commercial filament is employed for 4D printing of novel tailormade self-morphing samples. PET-G was found to be an amorphous shape memory polymer (SMP) with net points of tight-knitted physical entanglements decelerating the stress relaxation. Physical aging as a novel post-treatment on 4D printed parts is investigated to control the self-morphing and shape memory performance. Printing parameters and programing conditions had a significant effect on the self-morphing behavior as well as shape and stress recovery. Birefringence studies using polarized light microscopy (PLM) revealed that the fused deposition modeling (FDM) process induces a higher pre-strain in the bottom layers than in the top ones, resulting in a downward self-bending. Physical aging improved the yield stress, which was significantly ameliorated for samples with a lower degree of molecular orientation. The sample physically aged for 120 h at 55 °C showed no self-bending like sample printed with ±45 raster angles. It was revealed that lower printing temperatures and higher printing speeds enhance the self-bending and shape recovery characteristics. All shape fixity ratios were higher than 82%, with a maximum of 95.83% for samples printed with ±45 raster angles. The sample with the highest self-bending exhibited the maximum recovered stress of 1.24 MPa. A tenfold increase in load holding time showed a decreased stress recovery ratio by 47% for a programming temperature of 75 °C. Samples programmed at 90 °C exhibited a weak shape memory performance, but did not significantly change the stress recovery ratio at a longer load holding time.