Characterization of Cure Kinetics and Physical Properties of a High Performance, Glass Fiber-Reinforced Epoxy Prepreg and a Novel Fluorine-Modified, Amine-Cured Commercial Epoxy. Page: 24
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Both types of DSC instruments generate plots of heat flow as a function of the
programmed temperature. However, due to the difference in measurement techniques,
the heat flow ordinate value is calculated differently. Since the heat-flux DSC measures
the temperature difference between the sample and reference cells, calculation of the
heat flow requires an accurate temperature and sample dependent thermal resistance
value of the system as a proportionality factor.72'73 The power-compensation DSC also
requires a thermal resistance value; however, that value represents the heating
elements, not the entire system, and is constant74 over a wide operating temperature
range.7s-77 The power-compensation DSC maintains the programmed temperature
ramp in both sample and reference, ensuring greater temperature control in the
sample.78-80 This is important in temperature sensitive reactions, including thermoset
curing. The sensitivity and limits of detection,81,'82 as well as the linearity of the
signals83'84 of both types of DSC have been evaluated. Schawe and Hihne have
thoroughly described the linearity,85s signal86 and influence of materials properties87'88 of
power-compensation DSC measurements. The influence of changes of heat capacity of
a sample during a measurement has been established89 and evaluation techniques90
have been proposed to account for it. To determine the extent of a curing reaction or
the degree of cure, u, the change in enthalpy is compared to the total change in
enthalpy of the complete reaction, as represented by Equation 2.1 and illustrated in
Figure 2.3. This technique is common in research.91-"
a = AH/AHtotal (2.1)24
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Bilyeu, Bryan. Characterization of Cure Kinetics and Physical Properties of a High Performance, Glass Fiber-Reinforced Epoxy Prepreg and a Novel Fluorine-Modified, Amine-Cured Commercial Epoxy., dissertation, December 2003; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc4437/m1/40/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .