Experimental characterization and molecular dynamics simulation of thermal stability, mechanical properties and liquid oxygen compatibility of multiple epoxy systems for cryotank applications

Abstract

Epoxy resins with high thermal stability, good mechanical properties and liquid oxygen compatibility are primary candidates in large cryogenic engineering projects, particularly for cryotank applications to avoid catastrophic accidents. Herein, an experimental characterization and molecular dynamics modeling are conducted for the thermal stability, mechanical properties and liquid oxygen compatibility of multiple epoxy systems. The multiple epoxy systems are synthesized to achieve a comprehensive evaluation of their thermal stability, room-temperature and cryogenic mechanical properties as well as liquid oxygen compatibility. Concretely speaking, the anti-oxidation properties of the degradation are investigated by thermogravimetric analysis (TGA) and the glass transition temperature (Tg) is measured by the differential scanning calorimetry (DSC). The tensile test and fracture toughness test under room-temperature/cryogenic conditions (90 K) are chosen for determining their mechanical performances. Moreover, limited oxygen index measurements and liquid oxygen impact tests are utilized to characterize the flame retardancy and liquid oxygen compatibility, respectively. In parallel, molecular dynamics models are established to construct the high cross-linking structures and predict thermomechanical properties, which helps reveal the relationship between the molecular structures and macroscopic properties. Finally, the synergistic effects of organic/inorganic flame retardants and polyurethane toughener are proven to be effective to balance the liquid oxygen compatibility and mechanical properties. The valuable and extensive evaluation data in this work could be beneficial to the epoxy resin system design for cryotank applications.