Development of a phase diagram to control composite manufacturing using Raman spectroscopy

Fiber reinforced epoxy resins manufactured in autoclaves are expected to continue to dominate the composites market through 2010. However, the ability to obtain consistent mechanical properties from product-to-product remains difficult. This is largely due to the inability to monitor and control epoxy cure, loosely defined as the process of chain extension and cross-linking. Current autoclave process control employs a heat schedule based on a time-temperature-transformation (TTT) phase diagram that is determined by dynamic mechanical rheology. The phase diagram defines epoxy cure in terms of gelation and vitrification. We have been using an FT-Raman spectrometer to develop correlations between molecular (chain extension and cross-linking) and macroscopic (gelation and vitrification) data. The basis of a TTT phase diagram using Raman kinetic data for process control will be presented for several reactions.