Tuneable Mechanics in 3D Printing: Molecular Design of UV-Curable Bio-based Oligoesters

Abstract

Digital Light Processing (DLP) is a 3D printing technology that enables the fabrication of complex, high-resolution structures; however, the mechanical properties of DLP-printed objects are often limited by the resins used. This study focuses on developing and characterizing bio-based polyester UV-curable resins with tuneable mechanical properties optimized for DLP 3D printing. Bio-based polyester resins were synthesized by direct esterification polycondensation reaction of itaconic and/or succinic acids with 1,2-propane-, 1,4-butane-, and/or 1,8-octanediols followed by blending with triethylene glycol dimethacrylate. The bio-renewable nature of the resin components provides several advantages over traditional petroleum-derived resins. The diacid and diol monomers come from renewable feedstocks such as corn, soybean, and vegetable oils rather than finite fossil fuel reserves. Furthermore, bio-renewable materials lower dependence on petrochemicals and increase the sustainability of 3D printing. The effects of diacid structure and diol chain length on resin properties were systematically investigated. Chemical characteristics were investigated by NMR and FTIR and suggested successful synthesis of the desired bio-based polyesters. By varying the molecular design, diacid, and diol building blocks, the molecular weight, crosslink density, and mechanical performance were tailored. The liquid resins were characterized by gel permeation chromatography and rheological measurements, and solid UV-cured objects were characterized by static and dynamic tensile testing. Rheological studies confirmed all resin formulations displayed shear-thinning behaviour ideal for DLP printing. Mechanical testing revealed that varying diacid and diol components could modulate tensile elastic modulus and elongation at break from 0.1-1.0 GPa and 3.5-8.5%, respectively. Printability was assessed by printing a resolution test structure on a DLP 3D printer equipped with a 405 nm LED source. This ability to tailor the properties of bio-based polyester resins by molecular design provides an avenue for fabricating high-performance DLP-printed objects targeted for specific applications ranging from prototypes to end-use products.