First Stratospheric Flight of Preimpregnated Uncured Epoxy Matrix

A cassette with uncured preimpregnated based on carbon fibers and epoxy resin was exposed in the stratosphere (40 km altitude) above the ozone layer for over three days. Temperature variations of -76 degrees C to +32.5 degrees C and pressures up to 2.1 Torr were observed during flight. Analyses of the chemical structures of the composites show that the polymer matrix exposed in the stratosphere becomes crosslinked while the epoxy groups remain active, and the ground control polymer matrix reacted through polymerization reaction of epoxy groups. The space radiation exposures are considered to be responsible for crosslinking of the uncured polymers exposed in the stratosphere. The composites were cured on Earth after landing. Analysis of the cured composites showed that the polymer matrix remains active after exposure in the stratosphere. The results can be used for predicting the curing processes of polymer composites in the space environment during an orbital space flight.