Investigation of recovery behavior on 3D-printed continuous plant fiber-reinforced composites

The mechanical properties and accuracy of 3D-printed composites can be significantly affected by printing parameters. This work discovered a noteworthy recovery phenomenon during 3D printing of continuous flax fiber-reinforced composites (CFFRCs). The yarn count and printing speed are the critical factors that influence the recovery behavior, which, in turn, affects the thickness, the fiber volume fraction, and the void content of CFFRCs, ultimately impacting the mechanical properties. Smaller yarn counts have a greater effect on the recovery behavior of CFFRCs. Increasing the printing speed from 5 mm/s to 15 mm/s leads to the loss of tensile properties and flexural modulus in CFFRCs up to 30 % and 58 %, respectively. The recovery mechanism of the CFFRCs is further elucidated with the observation of temperature distribution during the printing process. This indicates that recovery is more likely to occur in the compressed yarn with a twisted structure when the deposited thermoplastic matrix exceeds the glass transition temperature. The results and findings have the potential to enhance the process optimization of 3D-printed continuous plant fiber composite parts, ensuring high mechanical properties and dimensional precision.