Assessment of controllable shape transformation, potential applications, and tensile shape memory properties of 3D printed PETG

Abstract

In this research, for the first time, highly controllable self-coiling and tensile shape memory behaviors of the 3D printed (Poly-Ethylene Terephthalate Glycol) PETG thermoplastic structures, as a novel shape memory polymer (SMP), are introduced. The results showed that the maximum printing-induced pre-strain of the PETG is stored in the first printed layer. Manipulating the infill printing direction of the 3D printed PETG strip provides different controllable shape transformation modes, including bending and spiraling. The wall effect experiments indicated that the shape transformation related to the infill pattern weakens by increasing the wall size. Employing a cross printing pattern resulted in the strip's more intense self-spiraling behavior, making the final shape transformation mode less influenced by the wall size. The shape transformation of the planar rectangular surfaces printed with single and cross printing patterns caused a self-tubing shape transformation in half and full tubes, respectively. Mechanical and biomedical potential applications of the PETG 3D printed parts' shape transformation are defined as a self-deployable spiral stent, self-conforming supporting splint, mechanical fastening, and self-locking planarly printed gripper to grab spherical, slippery, and soft objects that are hard to grab. The tensile shape memory test was done on a dog-bone tensile sample printed with a cross pattern to evaluate the effect of the first layer's printing direction, programming temperature, and strain rate on the tensile shape memory performance. Hot programmed samples (Tg+10 °C) exhibited a higher shape fixity and weaker strain recovery than warm programmed samples (Tg). Warm programmed samples showed full strain recovery with a considerable downward self-bending in their recovered shape, but hot programmed samples did not show any curvature. This behavior intensifies by increasing the stretching percentage. Also, changing the first printed layer's direction from the longitudinal to the transverse condition prevented the from self-bending during the recovery process. A twentyfold increase in the deformation speed for the warm programming condition resulted in a doubled gentler undesired self-bending and a 14.3% higher shape recovery.