Synergic effects of silica aerogel (SA) particles on tensile behavior of cryo-conditioned epoxy: The role of particle morphology and mixing sequence

Abstract

Cryogenic conditions are of crucial importance for gas storage tanks to provide increased storage density, reduced pressure requirements and minimized energy losses. Incorporation of silica aerogel (SA) particles as a nanostructured material with extremely low density and exceptional thermal insulating properties into epoxy matrices has the potential to facilitate the progress of high performance nanocomposite coatings for advanced cryogenic applications. The objective of this study is therefore to investigate the impacts of particle size, particle content, milling method and mixing sequence on toughness of the cryo-conditioned epoxy coatings. SA particles of varying size (50 μm to 300 μm) were prepared using two different techniques (planetary ball milling vs. 2-blade grinding). Nanocomposite samples were prepared using two distinct mixing sequences, i.e., adding particles (in 0, 0.5, 1 and 1.5%wt.) to epoxy followed by mixing with hardener or adding particles to epoxy/hardener (with 3 or 15 min delay). The nanocomposite samples were subjected to different cryogenic conditions (single 3-h immersion in liquid nitrogen vs. three consecutive 1-h immersions). Mechanical properties of the samples were evaluated by conducting fractography, dynamic mechanical thermal analysis (DMTA) and tensile tests. Large SA particles settled towards the bottom of nanocomposite and resulted in loss of mechanical properties at cryo-conditions. Mixing 1 wt% of optimized SA particles with epoxy/hardener system led to an enhanced tensile strength (26 %), stiffness (3 %) and toughness (71 %) by providing uniform cross-linking reactions and mitigating thermal shock effects at cryo-conditions. Toughening mechanisms included crack deflection, crack pinning, crack arrest and crack branching.