Multimaterial 3D printing of structured surfaces for increased hydrophobicity of biocomposite materials

• Incorporation of biofillers leads to increased hydrophilicity • 3D printing is capable of creating intricate, hydrophobic surface patterns • Multimaterial 3D printing allows for a patterned layer to be added to a biocomposite • Compatibility between different materials during and post printing was observed Material extrusion 3D printing is an up-and-coming additive manufacturing method that is continuously being explored for its many benefits including rapid prototyping, high degree of customizability, and low material waste production, among others. One of the most widely used materials in material extrusion 3D printing is polylactic acid (PLA) due to its ease of printability and bio-origins. Recently, new biofiller reinforced PLA biocomposite filaments have begun being sold commercially, but the introduction of the biofiller creates problems of increased hydrophilicity and hygroscopicity. In this study, a possible solution to this problem was explored by using multimaterial 3D printing to add a thin, structured outer layer to the biocomposite in either pure PLA or TPU. This layer helps limit any external moisture from coming into contact with the underlying biocomposite by creating a barrier with increased hydrophobicity. A grid, triangle, and honeycomb pattern were each tested at 50%, 75%, and 100% pattern densities for each material. It was found that, along with the pattern that was printed, the filament deposition process created additional roughness that influenced the way the water droplets interacted with the surface. All the patterned surfaces displayed a higher water contact angle than when the material was printed in a flat manner. Additionally, factors that influence the feasibility of using this outer structured layer to improve the surface hydrophobicity of biocomposite parts were explored, including material compatibility and adhesion.