Page 634 - Handbook of Thermal Analysis of Construction Materials

Section 3.0 - Applications 601

describe the development of the mechanical properties of the material over
several decades of time. The results of the study also demonstrated the
power of the various thermoanalytical tools for increasing understand-
ing of industrial polymers and controlling compositional variability in
applications.
Another example of the applications of thermoanalytical techniques
for adhesives characterization, in general, is the work done by Ludbrook and
Whitwood. [37] They have used DSC and DMA in conjunction with lap shear
strength testing to relate the degree of cure of several toughened epoxy
adhesives to the build-up of mechanical strength. DMA was also used to
measure the T of adhesives and its changes with curing.
g
It was concluded that DSC and DMA permit understanding of and
defining the properties of curable adhesive formulations by relating me-
chanical performance to the extent of cure. This allows the isolation of the
changes of mechanical properties that result from incomplete cure from
those due to other factors such as aging. Since it may be necessary to screen
many potential formulations to achieve the desired mechanical properties
and cure characteristics during adhesive development, DMA is a very useful
tool for broad characterization of the mechanical properties as a function of
temperature. Finally, they concluded that alternative mechanical test meth-
ods, such as lap shear strength, only gives a pass/fail criterion whereas DMA
enables the influence of compositional changes to be correlated with the T
g
and allows the influence of such changes to be studied as part of an overall
experiment design.
Allsop, et al., [38] found that DMTA and modulated DSC (MDSC)
could be used to identify useful secondary components for adhesive
formulations. Thermal analysis techniques have been successfully applied
by the Naval Aviation Depot, North Island, in the evaluation and repair of
advance composite components. [39] Differential scanning calorimetry (DSC)
has been used to detect a residual exotherm in undercured FM300 film
adhesive and the amount of residual exotherm has been correlated to a
reduction in the lap shear strength of the adhesive. A similar correlation has
been obtained between lap shear strength and the reduction in the glass
transition temperature (T ) as measured by DMA. A reduction in the T of
g
g
thermally exposed AS4/3501-6 laminates has been detected using TMA.
The authors correlated the T to the reduction in the mechanical properties
g
of the material.
Eastman [40] published a paper on “The Anatomy of Hot Melt
Adhesives by Thermal Analyses.” By using DSC, TMA, and TG, the author
attempted to show relationships between measurable thermal properties