Conversion?temperature?property relationships in thermosetting systems: Property hysteresis due to microcracking of an epoxy/amine thermoset?glass fiber composite

Autor: John K. Gillham, Amy S. Vallely
Rok vydání: 1997
Předmět:
Zdroj: Journal of Applied Polymer Science. 64:39-53
ISSN: 1097-4628
0021-8995
DOI: 10.1002/(sici)1097-4628(19970404)64:1<39::aid-app4>3.0.co;2-s
Popis: A single specimen of an epoxy/amine thermoset-glass fiber composite was examined, using a freely oscillating torsion pendulum operating at ∼ 1 Hz, for different conversions (as measured by T g ) from T g0 = 0°C to T gx = 184°C 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 < 70°C) 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.
Databáze: OpenAIRE
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