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Time-Temperature-Transformation (TTT) Diagrams of High T(g) Epoxy Systems: Competition between Cure and Thermal Degradation,
PRINCETON UNIV NJ DEPT OF CHEMICAL ENGINEERING
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The cure behavior and thermal degradation of high T sub g epoxy systems have been investigated by comparing their isothermal time-temperature- transformation TTT diagrams. The formulations were prepared from di- and trifunctional epoxy resins, and their mixtures, with stoichiometric amounts of a tetrafunctional aromatic diamine. The maximum glass transition temperatures T sub g infinity were 229 C and greater than 324 C for the fully cured di- and trifunctional epoxy materials, respectively. Increasing functionality of the reactants decreases the times to gelation and to vitrification, and increases the difference between T sub g after prolonged isothermal cure and the temperature of cure. At high temperatures, there is competition between cure and thermal degradation. The latter was characterized by two main processes which involved devitrification decrease of modulus and T sub g and revitrification char formation. The experimentally inaccessible T sug g infinity 352 C for the trifunctional epoxy material was obtained by extrapolation from the values of T sub g infinity of the less highly crosslinked systems using a relationship between the glass transition temperature, crosslink density, and chemical structure. Originator-supplied keywords include Epoxy resins, Glass transition temperature, Cure, Degradation, Gelation, Vitrification, Devitrification, and Torsional braid analysis.
APPROVED FOR PUBLIC RELEASE