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Conversion—temperature—property relationships in thermosetting systems: Property hysteresis due to microcracking of an epoxy/amine thermoset—glass fiber composite
Author(s) -
Vallely Amy S.,
Gillham John K.
Publication year - 1997
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/(sici)1097-4628(19970404)64:1<39::aid-app4>3.0.co;2-s
Subject(s) - thermosetting polymer , materials science , composite material , isothermal process , epoxy , composite number , torsion pendulum clock , hysteresis , glass fiber , glass transition , fiber , thermodynamics , polymer , physics , quantum mechanics
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 g 0 = 0°C to T g∞ = 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. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 39–53, 1997