Enhanced mechanical performance of mSLA-printed biopolymer nanocomposites due to phase functionalization

Functionalized phases can effectively increase the mechanical properties of nanocomposites through interfacial bonding. This work demonstrates masked stereolithography (mSLA) of biopolymer-based nanocomposites and the improvement of their mechanical properties by the functionalization of both polymer matrix and nanoparticles with methacrylate groups. 3D printable nanocomposite inks were prepared from plant-derived acrylated epoxidized soybean oil (AESO), polyethylene glycol diacrylate (PEGDA), and nano-hydroxyapatite (nHA). Both AESO and nHA were further functionalized with additional methacrylate groups. We hypothesized that the additional functionalization of AESO and surface functionalization of nHA would improve the tensile strength and fracture toughness of these nanocomposites by increasing the degree of crosslinking and the strength of the interface between the matrix and nanoparticles. Curing efficiency, rheology, and print-fidelity of the nanocomposites were evaluated. Mechanical test specimens were prepared by mSLA-based 3D printing. Tensile mechanical properties, Poisson's ratio, and Mode-I fracture toughness were measured by following ASTM standards. Fracture surfaces of the tested specimens were studied using scanning electron microscopy. Thermomechanical behavior, especially glass transition temperature (T_g), was studied using dynamic mechanical analysis (DMA). Functionalized AESO (mAESO) improved rheological, tensile, and fracture mechanical properties. For instance, by replacing AESO with mAESO, tensile strength, Young's modulus, fracture toughness (K_1c), and T_g increased by 33%, 53%, 40%, and 38% respectively. In addition, the combination of both functionalized nHA and mAESO improved the fracture toughness of the 10% volume fraction nHA nanocomposites but made them less extensible presumably due to reduced chain mobility due to greater crosslinking.