Fused Filament Fabrication Using Cellulose Nanofiber Composites: Development of Filament with Higher Fiber Content and Evaluation of Fabricated Objects

Fused filament fabrication is a type of material extrusion process category of additive manufacturing. Because the material is prepared in the form of filaments, a wide variety of materials including composite materials with continuous fibers can be used. With the recent increase in environmental consciousness, the use of biodegradable composites using polylactic acid (PLA) and continuous cellulose nanofiber (CNF) strings has garnered attention from the scientific community. However, the fiber content of the composites remains low, preventing full exploitation of the ultrahigh intrinsic strength of CNFs. In this study, we proposed two methods to increase fiber content. First, we modified the cross-sectional shape of the filament from circular to rectangular to increase the fiber content. Second, we optimized the process parameters during filament fabrication by adjusting the feed rates of continuous CNFs and PLA, resulting in a higher fiber content up to 35%. Following this, filaments with higher fiber content were used in fabrication experiments. Tensile tests of the fabricated specimens showed that the mechanical strength increased with the fiber content. Finally, we present an application example of the developed CNF filament for reinforcing finger orthosis.