4D printing and annealing of PETG composites reinforced with short carbon fibers

In this study, for the first time, post-heat treatment was applied to improve the stress recovery of short carbon fiber reinforced PETG (SCFRPETG). PETG and SCFRPETG composite were printed under optimal conditions, and constrained and free shape memory cycles were applied under compression and three-point bending loadings to assess shape and stress recovery. The results of the free shape memory test for both vertical and horizontal patterns showed that PETG composite also has a higher shape memory effect (SME) compared to PETG. The SME was significantly improved by performing heat treatment. The stress recovery values for pure PETG, reinforced PETG before and after annealing are 2.48 MPa, 3.04 MPa and 3.18 MPa, respectively. It showed that the addition of 1.5% carbon fiber increases the stress recovery by 22%. The increasing trend reaches 28% by performing post-heat treatment. Additionally, altering the printing pattern affects the programming and stress recovery values. For the SCFRPETG composite samples before and after annealing, changing the printing pattern from horizontal to vertical, resulted in a 16% and 7% increase in recovery stress, respectively. SEM results confirm that the annealing process removes the layered structure, micro-holes caused by shrinkage and 4D printing mechanism. Using the controlled heat treatment method can be a practical solution to solve the problem of adhesion and reduce the anisotropy of FDM 3D printed layers.