R. Sheley, J. Tate, S. Shendokar, M. Khaleghian
Texas State University,
United States
Keywords: stereolithography (SLA), additive manufacturing, coefficient of thermal expansion,, polyhedral oligomeric silsesquioxane (POSS), hexagonal boron nitride (h-BN), silicon carbide (SiC)
Summary:
Stereolithography (SLA) enables the fabrication of intricate polymer structures with metal coatings for high-performance applications, yet polymer–metal assemblies frequently experience thermal mismatch due to the high coefficient of thermal expansion (CTE) of conventional resins. This study focuses on the formulation of epoxy-based hybrid nanocomposites with tailored thermal and mechanical properties designed for precision additive manufacturing. The matrix system employs bisphenol A epoxy diacrylate (EBECRYL® 3700) as the oligomer and trimethylolpropane triacrylate (TMPTA) as a reactive diluent, activated by phosphine oxide photoinitiators—diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) and bis (2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO). Two multifunctional nanocomposite formulations were developed using functionalized hexagonal boron nitride (h-BN) as the primary filler for CTE reduction. Secondary reinforcements were incorporated to target specific performance enhancements: polyhedral oligomeric silsesquioxane (POSS) to improve fracture resistance and dimensional integrity, and silicon carbide (SiC) to augment stiffness. Homogeneous nanoparticle dispersion was achieved through sequential ultrasonic mixing and three-roll milling. Test specimens fabricated via SLA printing were characterized by tensile and flexural testing for mechanical performance, differential scanning calorimetry (DSC) for glass transition temperature, and thermomechanical analysis (TMA) for CTE evaluation. The hybrid systems exhibited synergistic effects between h-BN and the secondary nanofillers, resulting in reduced thermal expansion, restricted molecular mobility, and elevated crosslink density. Enhanced thermal and mechanical stability confirmed the effectiveness of the dual-filler approach. These results demonstrate a clear correlation between formulation design and property optimization, supporting the development of dimensionally stable SLA nanocomposites for aerospace, microelectronic, and optical applications where thermal reliability and precision are essential.