kinetic response of thermosetting adhesive systems to heat

Temperature effects on internal mat characteristics during testing
In order to resolve the role of the adhesive in affecting the shear strength of compressed
fiber samples, a number of fiber samples were compressed in the absence of adhesive, and the
results compared with corresponding samples pressed with adhesive. Clearly, the interplay of
mechanisms which influence the structure and properties of compressed fiber networks is highly
complex; it is beyond the scope of the present discussion and will be the subject of future
publications. Such mechanisms are, however, assuredly influenced by fiber type and
juxtaposition, transient moisture and temperature conditions, and the magnitude and duration of
applied compressive stress.
Figure 8 shows representative shear resistance values of non-resinated miniature fiber
discs. Pressing temperature appears to affect measured values. This is no doubt attributable to the
interplay of mechanisms listed above. Shear resistance does appear to decrease with increasing
pressing temperature, while almost no influence can be detected with increasing pressing time.
Under pressing conditions of low temperature and high specimen density, a decreasing trend of
shear resistance is, however, evident; this might be attributable to thermal softening of cell wall
material.
Shear Strength [N/mm²]
1,2
0,8
0,4
0,0
125°C; 600kg/m³
125°C; 500kg/m³
100°C; 400kg/m³
125°C; 400kg/m³
150°C; 400kg/m³
0 20 40 60
Pressing Time [s]
80 100 120
Figure 8. Shear Strength of non-resinated miniature fiber discs pressed at different
temperatures and densities.
Temperature Effects On Shear Strength Development Of Resinated Samples
The shear strength development of resinated miniature fiber discs pressed at 100°C,
125°C and 150°C are presented in Figure 9. These initial results show a strong correlation
between measured shear strength and pressing time (hollow symbols on Fig. 9). Solid symbols in
Fig. 9 are data generated by offsetting the non-resinated shear strength values from the
corresponding resinated values. As one may expect, inferred adhesive shear strength values
increase with increasing pressing temperature and pressing time.