Glass transition temperature ( T g ) determination of partially cured thermosetting systems

Previous experiments have shown that T g of a partially cured thermosetting system can be measured with conventional thermal scan methods only if no appreciable additional cure occurred during the scan. For high temperature performance systems, the partially cured T g is often at a temperature where kinetics rate is very rapid, causing either an observation of a more advanced cured T g , or only the completely cured system's T g [ T g (∞)]. Two methods to interpolate the T g information in spite of additional cure are presented and illustrated with an epoxy resin as a testing material. The Isocure State Curve method is demonstrated with a two‐step curing experiment with the Torsion Impregnated Cloth Analysis (TICA) technique, which is a forced torsion measurement on the Rheometrics mechanical spectrometer, with the resin impregnated on a glass cloth specimen. The calibration method is demonstrated by the post cure experiments of TICA, using the time to loss modulus maximum, and the softening parameter R as the calibration parameters.