Durability of sandwich structures with a maximized natural raw material basis: comparison of expanded polystyrene, cellulose foam and polylactic acid subjected to UV-rain aging

In this study, alternative core materials to commercial cork were searched for. Additionally, aging of new core materials was studied. Bio-based materials in sandwich structures can be useful for sports equipment, transportation, and furniture with much less impact on the environment in comparison with their synthetic counterparts. In this paper, sandwich panels made of fiber-reinforced polymer (FRP) skins and various sustainable core materials with a core thickness of 6 mm were studied. The core materials were: cork, expanded polystyrene (EPS), cellulose foam, and 3D-printed polylactic acid (PLA) honeycomb lattice. FRP composites made of flax fibre reinforcement and bio-based epoxy resin (30% bio-content) were used to manufacture the skins to compete the glass fibre reinforced rival composite. The experimental analysis of the panel performance focused on the out-of-plane behavior and aging due to conditioning in an ultraviolet (UV) irradiation-rain cabinet. The results showed that under mechanical and environmental loading, the sandwich composite with cellulose foam had comparable or even better mechanical performance under shearing load, including UV-rain effects, than structures with EPS cores. Failure localization was studied using digital image correlation (DIC). The 3D-printed PLA honeycomb sandwich structures had a high absolute flatwise tensile strength and shear strength but also greatest degradation by the UV-rain aging.