CONVERSION-TEMPERATURE-PROPERTY RELATIONSHIPS IN THERMOSETTING SYSTEMS - PROPERTY HYSTERESIS DUE TO MICROCRACKING OF AN EPOXY/AMINE THERMOSET-CLASS FIBER COMPOSITE

摘要

A single specimen of an epoxy/amine thermoset-glass fiber composite was examined, using a freely oscillating torsion pendulum operating at similar to 1 Hz, for different conversions (as measured by T-g) from T-g0 = 0 degrees C to T-g infinity = 184 degrees 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 degrees 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-beal, 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. (C) 1997 John Wiley & Sons, Inc. [References: 10]