Separation of gelation from vitrification in curing of a fiber-reinforced epoxy composite

Prepregs of a mixture of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM) and the tetrafunctional amine 4,4'-diaminodiphenylsulfone (DDS) were characterized with temperature-modulated DSC (TMDSC) as well as dynamic mechanical analysis (DMA). The baseline shift of the glass transition was separated from the curing exotherm. by using temperature-modulated and step scan DSC temperature scans. Likewise, the baseline shift in heat capacity due to vitrification was isolated using TMDSC isotherms. Using the TMDSC glass transition temperature, degree of conversion, and vitrification results, combined with the gelation data generated from DMA, a time-temperature-transformation MM diagram was constructed, providing information necessary for optimization of industrial processing of the epoxy prepreg. Thus, effects of storage, preprocessing, and postprocessing on the overall curing process are taken into account.