Conversion—temperature—property relationships in thermosetting systems: Property hysteresis due to microcracking of an epoxy/amine thermoset—glass fiber composite
✍ Scribed by Amy S. Vallely; John K. Gillham
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 400 KB
- Volume
- 64
- Category
- Article
- ISSN
- 0021-8995
No coin nor oath required. For personal study only.
✦ Synopsis
A single specimen of an epoxy/amine thermoset-glass fiber composite was examined, using a freely oscillating torsion pendulum operating at Ç 1 Hz, for different conversions (as measured by T g ) from T g 0 Å 0ЊC to T gϱ Å 184ЊC during cooling and heating temperature scans. T g was increased for successive pairs of scans by heating to higher and higher temperatures. The data were used in two ways: (i) vs. temperature for a fixed conversion to obtain transitions, modulus, and mechanical loss data, and (ii) by crossplotting to obtain isothermal values of the mechanical parameters vs. conversion (T g ). Hysteresis between cooling and subsequent heating data was observed in temperature scans of essentially ungelled material ( T g õ 70ЊC) and was attributed to spontaneous microcracking. Hysteresis was analyzed in terms of the following three parameters: T crack , the temperature corresponding to the onset of microcracking on cooling; T heal , the temperature at which the specimen heals on subsequent heating; and the difference between isothermal cooling and heating data vs. conversion. Results were incorporated into a more general conversion-temperature-property diagram which serves as a framework for relating transitions (relaxations) to macroscopic behavior.