Utilizing reactive extrusion additive manufacturing (REAM) to produce composite parts is a relatively unexplored area of research. The introduction and effectiveness of continuous fiber reinforcement in additive manufacturing requires a delicate balance of process parameters, including line spacing, layer height, deposition rate, and nozzle design. This study established the baseline parameters needed to produce REAM composite samples using two two-part reactive polymer resin systems and two reinforcing fibers. A venturi nozzle with internal agitation nodes was developed to introduce the continuous fiber to the REAM process and improve fiber wet-out. Material characterization revealed tensile modulus and strength increases of 1219% and 276%, respectively, for a composite containing 8.29% glass fiber—the highest fiber volume percentage achieved in this study. A basalt composite with 2.19% fiber and 13.2% voids by volume—the highest void percentage found—had a flexural strength of 35.3 MPa, a 233% increase compared to its unfilled resin system. Material characteristics, including fiber tow size, fiber sizing, resin viscosity, and resin gel time, contributed to overall composite and process performance. These findings and the processes developed in this study provide a foundation for future research aimed at improving the quality, performance, and complexity of REAM composites.

Natural fiber-reinforced composites improve environmental sustainability, and their use is increasing as environmental awareness grows. Natural fibers, such as hemp and flax, are renewable resources. They offer several advantages, including abundant availability, low cost, and high biodegradability. Three-dimensional printing has introduced a novel approach for advancing natural fiber-based composites. However, there is a significant lack of research on the 3D printing of continuous hemp and flax fiber-reinforced thermoset composites. This research investigates the fabrication of hemp and flax fiber-reinforced thermoset composites using a UV-light-assisted 3D printing process. Both printed composites achieved a fiber volume fraction of approximately 13%. The tensile strength of hemp and flax fiber-reinforced composites was found to be 32.3 ± 3.5 MPa and 61.1 ± 4.2 MPa, respectively. Moreover, the flexural strengths of hemp and flax fiber-reinforced composites were 81.8 ± 13.5 MPa and 85.3 ± 23.1 MPa, respectively. Thus, this study may open research pathways for utilizing natural fiber-reinforced thermoset composites with improved biodegradability and renewability.