Evolution of properties with increasing cure of a thermosetting epoxy/aromatic amine system: Physical ageing

✍ Scribed by Jong Keun Lee; John K. Gillham

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 214 KB
• Volume: 90
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/app.12915

✦ Synopsis

Abstract

Isothermal physical ageing below the glass‐transition temperature (T~g~) of a high‐T~g~ thermosetting difunctional epoxy/tetrafunctional aromatic amine system was investigated at different ageing temperatures (T~a~) and chemical conversions (monitored by the T~g~) using the torsional braid analysis freely oscillating torsion pendulum technique. In the absence of chemical reaction during an isothermal ageing process, the rate of isothermal physical ageing passes through a minimum with increasing conversion. The minimum is related to the minimum in mechanical loss between the secondary relaxation in the glassy state (T~β~) and the glass‐transition relaxation (T~g~) (the temperatures of both of which increase with increasing conversion). If isothermal ageing rates for all conversions (beyond gelation) would have been measured directly from temperatures below T~β~ to above T~g~, it is concluded that two maxima in isothermal ageing rate would have been observed corresponding to the two relaxation processes. There exists a superposition in isothermal ageing rate versus T~g~ − T~a~ [by shifting horizontally (and vertically)], which implies that the ageing rate is independent of the details of the changing chemical structure attributed to cure. Controlling mechanisms during physical ageing are segmental mobility associated with the T~g~ region and more localized motion associated with the glassy‐state relaxation T~β~. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2665–2675, 2003