THERMAL AND MECHANICAL CHARACTERIZATION OF HIGH-PERFORMANCE EPOXY SYSTEMS WITH EXTENDED CURE TIMES

Five epoxy resins of different chemistry and functionality were cured with DDS (4,4'-diaminodiphenyl sulfone) using 2, 8 and 14 h curecycles . Both Differential Scanning Calorimetry (DSC) and Thermomechanical An alysis (TMA) were used to characterize reaction behavior and cured pro perties of the resin systems. In addition, static mechanical tests and density measurements were integrated with the thermal characterizatio n methods to correlate resin properties with process time. Flexural th ree-point bending experiments showed that the resins tended to have hi gher yield stress and toughness values at extended cure times. The imp roved mechanical properties could be attributed to the full developmen t of the epoxy molecular structure, in the form of cross-linked networ ks and molecular rearrangement. These results suggest that extended cu re times or high temperature post-curing may be required to obtain the resin's ultimate mechanical properties for high performance composite s.