Why Chopped Carbon Fiber in FDM Prints is a Contaminant
A lot of claims have been made about the purported benefits of adding chopped carbon fiber to FDM filaments, but how many of these claims are actually true? In the case of PLA at least, the [I built a thing] channel on YouTube makes a convincing case that for PLA filament, the presence of chopped CF can be considered a contaminant that weakens the part.
Using the facilities of the University of Basel for its advanced imaging gear, the PLA-CF parts were subjected to both scanning electron microscope (SEM) and Micro CT imaging. The SEM images were performed on parts that were broken apart to see what this revealed about the internal structure. From this, it becomes apparent that the chopped fibers distribute themselves both inside and between the layers, with no significant adherence between the PLA polymer and the CF. There is also evidence for voids created by the presence of the CF.
To confirm this, an intact PLA-CF print was scanned using a Micro CT scanner over 13 hours. This confirmed the SEM findings, in that the voids were clearly visible, as was the lack of integration of the CF into the polymer. This latter point shouldn’t be surprising, as the thermal coefficient of PLA is much higher than that of the roughly zero-to-negative of CF. This translates into a cooling PLA part shrinking around the CF, thus creating the voids.
What this means is that for PLA-CF, the presence of CF is by all measures an undesirable contaminant that effectively compromises it as much as having significant moisture in the filament before printing. Although for other thermoplastics used with FDM printing, chopped CF may make more sense, with PLA-CF, you’re effectively throwing away money for worse results.
As also noted in the video, in medical settings, these CF-reinforced FDM filaments aren’t permitted due to the chopped CF fragments. This topic has featured more widely in both the scientific literature and YouTube videos in recent years, with some significant indications that fragments of these chopped fibers can have asbestos-like implications when inhaled. Looking for the thrill of a weird filament? Maybe try one of these.
youtube.com/embed/w7JperqVfXI?…
hackaday.com/2025/12/21/why-ch…
