Direct ink writing of surface-modified flax elastomer composites

Compared with synthetic fibers, natural fibers exhibit high specific mechanical strength, excellent thermal and acoustic insulation, and super biodegradability. These characteristics made them potential materials for green, sustainable, and inexpensive manufacturing of the next-generation composite components. This work focuses on addressing the material extrusion challenge in 3D printing natural fibers using direct ink writing technique. Flax fiber, a common natural fiber, is studied. Influence of the layered structure of the flax fiber on the printability in direct ink writing process is investigated. Techniques. It is found that the outer layer of the fiber can be controllably removed by the sonication process and the processed fiber can be dispersed uniformly in the elastomer to form a homogeneous ink, which overcomes the tip clogging issue in extrusion-based 3D printing techniques. To understand and quantify the influence, rheological properties are characterized. Additionally, the printability is investigated. Furthermore, mechanical behaviors of the 3D printed flax-fiber elastomer composites are analyzed. It was found that with an addition of only 0.2 wt% surface-modified flax fibers, the tensile properties could be increased over 100%, which is comparable to or even higher than other synthetic fiber-based composites with much higher fiber loading fractions. The findings in this study indicate a novel and sustainable method to engineer composites using direct ink writing technique. The high degree of property tunability and material biocompatibility indicate great promise of applications of the 3D printed fiber-elastomer composites in many fields, such as soft robotics, biomedical devices, and flexible wearable electronics.