Study on PA11 in FFF: Less warping thanks to bamboo charcoal and glass fiber reinforcement

In 3D printing using fused filament fabrication, dimensional stability often determines the practical suitability of a component. Polyamides tend to warp, which can limit dimensional accuracy and reproducibility. PA11 is considered a bio-based, technically resilient plastic, but exhibits typical weaknesses in the FFF process. The study “Bio-derived PA11/bamboo charcoal/glass fiber composites for fused filament fabrication, warpage control, strength, and flame retardancy” therefore focuses on PA11 composites with bamboo charcoal (BC, 0 to 5 percent by weight) and optionally 30 percent by weight glass fiber (GF) and examines their influence on the process and component properties.

For processing, the authors dried PA11 and PA11 with 30 percent GF at 80 degrees Celsius for 12 hours. They then mixed the components in a ball mill and extruded filament on a Filabot EX2 at 180 to 190 degrees Celsius. Printing was performed on an Original Prusa MK4S with a 0.4 mm nozzle, 0.3 mm layer height, 80 mm/s, 100 percent infill, 245 degrees Celsius nozzle temperature, and 90 degrees Celsius bed temperature.

In the warpage test, the corner lift of PA11 was 3.81 mm. With 3 percent BC, it dropped to 2.58 mm. The hybrid mixture of 3 percent BC and 30 percent GF reduced warpage to around 0.1 mm. According to the authors, this corresponds to a warpage reduction of about 97 percent. SEM images show BC particles in the matrix and glass fibers as load-bearing reinforcement.

At the same time, other characteristic values shift. The water contact angle increases from around 62 degrees for PA11 to around 78 degrees for the hybrid, which the authors classify as higher hydrophobicity, with a 34 percent increase in their summary. In terms of fire behavior, the horizontal burning rate decreases by up to 61.9 percent compared to PA11, the LOI reaches 29.1 percent by volume, and UL-94 improves to V-2. Mechanically, the study cites a tensile strength of 76.5 MPa and a modulus of elasticity of 7.85 GPa for the hybrid at 23 degrees Celsius, and 39.8 MPa and 2.55 GPa at 90 degrees Celsius. For the bending test, the authors highlight a three to four times higher performance.

In addition, the study describes a meta-structured “meta-bio-composite” geometry with virtually zero stiffness and an almost constant force response, which is designed for overload protection and achieves a specific energy absorption of up to 655 J/kg at 50 percent compression.