Mechanical and volumetric expansion of expandable polystyrene subjected to fuel material for self-sealing composite coating applications

Expandable polystyrene is widely used in several industries as a sealing medium due to its desirable mechanical properties, durability, and high-volume expansion. In particular, it has been employed as embedded beads in emerging composite self-sealing coatings for fuel tank applications. To optimize the performance of these composite coatings and support modeling and simulation (M&S) efforts, fundamental mechanical data of the expandable beads is essential. Yet, such data is currently lacking in the literature. This experimental study investigates the volumetric expansion, surface morphology, and mechanical properties of polystyrene beads before and after exposure to Jet-A fuel. The volumetric expansion of beads was measured using an optical microscope, where their surface behavior was assessed before and after fuel exposure to evaluate changes in morphology. Results showcase a considerable mean swelling ratio of approximately 12. Scanning electron microscopy (SEM) analysis revealed an adhesiveness effect among the beads following fuel exposure, contributing to their sealing behavior. In addition, to investigate the mechanical properties of the beads before and after exposure, a flat-tip micro-indentation technique was employed. The results showed that the expanded beads underwent significantly greater deformation and a drop in stiffness (more than 16-fold) compared to their dry counterparts. Both dry and expanded beads exhibited creep behavior, with the expanded beads demonstrating a higher degree of creep (approximately 12 times higher). These findings provide both qualitative and quantitative insights into the volumetric and mechanical changes of the expandable beads at room temperature subjected to fuel.