annealing for – A post-print annealing test aimed at fixing weak adhesion in chopped carbon fiber (CCF) thermoplastic FDM prints delivered an awkward split: PETG improved sharply, but PETG-CF got worse, while PLA and PLA-CF barely benefited. The results also showed Z-directio
After a run of videos on poor adhesion between chopped carbon fiber (CCF) additives and thermoplastic filaments used in FDM 3D printing. one piece of feedback kept coming up: post-print annealing might be the missing step. The claim was simple enough to test. and the answers—especially under a scanning electron microscope (SEM)—landed with an uncomfortable mix of “maybe” and “not for this material pair.”.
In the annealing trial. the researcher used PETG and PETG-CF. plus PLA and PLA-CF. each in two versions: annealed and not annealed. Then the parts were pushed through the basics that matter for end users—tensile strength. stiffness. and failure type—along with dimensional accuracy and warping. Only after that came the microscopic look, again using an SEM, this time after annealing. The SEM images themselves showed clear voids after post-annealing, reinforcing the central problem rather than wiping it away.
The testing wasn’t small. A total of 160 samples were examined, with 20 samples per material and annealing state. That scale mattered because the findings weren’t subtle.
The biggest surprise was how much PETG benefits from annealing. Instead of staying fragile, the annealed PETG became much more resilient to breaking. But that improvement didn’t carry over to PLA. Neither PLA nor PLA-CF seemed to see much benefit from annealing. leaving the hoped-for “one fix for all” narrative in tatters.
Then came the most striking result: PETG-CF performed much worse than PETG. In fact, the annealed PETG-CF was worse than both PLA and PLA-CF in the same comparison, turning what looked like a promising path into a dead end for this specific fiber–polymer combination.
Dimensional accuracy told a similar story. Annealing caused expansion in the Z direction, while shrinking the samples in the other directions. The CCF addition prevented much of that shrinking and expansion—offering the first clear benefit for adding carbon fiber into the mix. But the improvement came with a ceiling. Even annealing “at right above the glass transition temperature as is proper,” the practical benefits seemed limited.
When these outcomes are laid beside earlier work that focused on PLA-CF. the case the experiment tries to make gets sharper. If shrinkage during annealing can already be accounted for before printing. then the question becomes why the CCF additive is needed at all. The interface problem—between the chopped carbon fiber and the thermoplastic filament—also doesn’t feel like a mystery when the chemistry is considered. The write-up points out that there’s no real purpose to CCF additives. and that the lack of improvement to the CCF and thermoplastic interface adhesion aligns with how thermoset materials can form bonds with carbon fiber. compared with what thermoplastics can manage.
In the end. the annealing idea didn’t fail across the board—it helped PETG—but the same approach didn’t rescue the carbon-fiber composites. For PETG-CF especially. the results looked like a step in the wrong direction. and the SEM findings of clear voids after annealing made it harder to argue that the core adhesion issue was getting truly solved.
3D printing FDM annealing PETG PLA carbon fiber chopped carbon fiber CCF SEM tensile strength warping dimensional accuracy