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: 57
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Although vitrification is a thermal transition from a rubber to a glass and does
appear in DSC measurements,632 the determination of the point and quantification of
the shift in baseline heat flow or Cp usually occurs around the end of the curing (since it
is a decrease in the reaction rate) and as such is usually masked by the curing reaction
exotherm. This is one of the clearest applications of TMDSC, since the curing exotherm
appears in the loss Cp and the vitrification appears in the storage Cp.633-64' A series of
isothermal TMDSC plots identifying the vitrification point are shown in Figure 2.31.642
DMA has been used extensively to investigate the vitrification point, and
continues to be the most common method. The first epoxy TTF diagram, proposed by
Gillham and Enns,643 was constructed primarily from torsional braid analysis (TBA),644 a
specialized torsional DMA measurement. Gillham defines the vitrification in TBA and
3.5-
3.2-
0 3.0-
2.8-
-1 1 60 0C
, . _,1 8 0 C
2.4-
CD
I I
2.1 I
U 50 100 150 200 250 29.9
Time (min)
Figure 2.31: TMDSC isotherms showing vitrification as half height drop in storage Cp.57
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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/m1/73/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .