Analysis of voids, interfacial and thermal properties of additively manufactured continuous natural fiber-reinforced biocomposites

The incorporation of continuous natural fibers as reinforcement in Fused Filament Fabrication (FFF) is influenced by the intrinsic characteristics of the printing process. Analyzing the effects of this type of reinforcement is essential for achieving high-performance biocomposites. This study evaluates the impact of heating temperature on fiber and biocomposite properties, the types of voids generated during printing, and the quality of the fiber–matrix interface. Thermal and image analyses were conducted to investigate the fibers’ thermal behavior and the presence of voids. Additionally, a novel methodology was developed to fabricate thermoplastic printed samples reinforced with natural large-diameter yarns for pull-out tests. The results indicate that the natural fibers exhibit suitable thermal stability for FFF applications, with the lignin degradation peak occurring between 294.6 and 366.1 °C, which is above the FFF printing temperature range for PLA (160–220 °C). However, image analysis revealed that larger yarn diameters compromise the interfacial bonding with the matrix material, despite partial impregnation along the perimeter of the yarn. Void content was observed to reach up to 57.0% of the total volume, emphasizing the inadequate material impregnation within the yarn structure. Overall, the findings confirm the potential of utilizing continuous natural fibers as reinforcements in FFF-based composites.