The correlation coefficients of linear regression
were very high, from 0.990 to 0.999. As, both OFW and
KAS models show that the activation energy, Ea, de-pends on the degree of curing reaction, α, it was interesting
to notice a different behavior of kinetic models
between the adhesive systems used in this research.
At the beginning of UF1 adhesive cure, the increase
of reaction degree (crosslinking) up to 30% resulted
in the increase of Ea. With the progression of
curing reaction from 30 to 70% Ea remained at constant
values, but increased again toward the end of curing
reaction (Figure 7). This suggests that at the final
stage of curing process of UF1 adhesive, the activation
energy increases due to the diffusion-controlled reaction,
rather than to follow the kinetic factor [13,16]. UF1
adhesive has slightly higher F/U mole ratio, but the DSC
data clearly show its higher reactivity in regard to UF2
adhesive. This might influence the more intensive increase
in molecular weight of UF1 adhesive during
cure, which also might hinder the required mobility of
the molecules with high degree of polymerization at
the later stages of resin cure and thus increasing the
activation energy.