Characterization of prepreg and cured epoxy/fiberglass composite material for use in advanced composite piping systems

A company that uses epoxy/fiberglass prepreg material in advanced composite piping systems requested that the NASA/Marshall Space Flight Center (MSFC) use several thermal analysis techniques to characterize the material. Dynamic and isothermal tests by use of the TA Instruments 2920 Differential Scanning Calorimeter (DSC) yielded cure kinetics on the prepreg. The dynamic data showed two exothermic cure reactions for the prepreg, but isothermal data showed that the first cure exotherm was a low temperature event and began to disappear near 105°C. For the second cure exotherm, activation energies (E2) of 79.0 and 87.1 kJ/mol were obtained from the dynamic and isothermal data, respectively. Partial cure of the prepreg for several isothermal cure temperatures and times yielded a glass transition temperature (Tg) versus conversion plot with an approximate gelation point of the prepreg at 63% conversion. At a cure temperature of 135°C and a Tg of 103°C, most of the ultimate cure of the prepreg was achieved. The TA Instruments 983 Dynamic Mechanical Analyzer (DMA) yielded activation energies of cure of 140 (E1) and 50.5 (E2) kJ/mol for the first and second cure reactions, respectively, based on times to gelation at seyeral cure temperatures. A DMA temperature sweep at several fixed frequencies yielded an average activation energy of 357 kJ/mol for the Tg of the epoxy/fiberglass composite in cured sheet form. The fiber filler is a fiberglass mat, and DMA data as well as thermomechanical analysis (TMA) data on the cured sheet material showed a slight dependence on mat direction for the measured properties.