Feasibility of Ethylene‐Vinyl Acetate ( EVA ) for Additive Manufacturing of Mouthguards: Influence of Natural Fiber and Polymer Reinforcement

OBJECTIVES: This study aimed to evaluate the feasibility of using ethylene-vinyl acetate (EVA) for extrusion-based additive manufacturing, focusing on its potential application in mouthguard fabrication. Additionally, the influence of reinforcement with ramie fiber and polycyclohexylene dimethylene terephthalate (PCT) on the mechanical and structural properties of EVA-based composites is evaluated. MATERIALS AND METHODS: EVA served as the polymer matrix and combined with two reinforcing phases: Short ramie fibers (Boehmeria nivea) and PCT copolyester. Composites were prepared with reinforcement contents of 10%, 20%, 30%, 40%, and 50% (w/w). The materials through density apparent measurements, tensile testing, and morphological analysis using scanning electron microscopy (SEM) to evaluate the influence of reinforcement on mechanical performance and structural behavior. RESULTS: Neat EVA exhibited high ductility but limited tensile strength, which may restrict its direct use in extrusion-based additive manufacturing. The incorporation of PCT increased tensile strength to higher concentrations, reaching 9.3 MPa at 50% reinforcement, although with a significant reduction in elongation. Ramie fiber reinforcement produced a more pronounced improvement in mechanical performance, with tensile strength reaching 19 MPa at 40% fiber content while maintaining part of the material's ductile characteristics. SEM analysis revealed biphasic morphology in EVA/PCT blends and a homogeneous fiber distribution in EVA/ramie composites. CONCLUSION: The results indicate that neat EVA alone may not provide sufficient mechanical stability for additive manufacturing processes. However, reinforcement with ramie fiber or PCT significantly improves the mechanical performance of EVA-based composites. Among the evaluated formulations, ramie fiber reinforcement showed the most favorable balance between strength and ductility, suggesting potential for the development of flexible materials suitable for additive manufacturing and future application in customized mouthguard fabrication.