Another interesting observation is the influence of
catalyst addition on the reaction enthalpy presented in
Figure 3. The curing reactions of UF resins are typically
exothermic, so it can be assumed that the reaction enthalpy,
ΔH, will be proportional to the degree of conversion,
α, during the curing process. The increase of
ΔH with the increase of catalyst content was noticed in
the previous research on UF adhesive cure and was explained
by the catalyst effect on decreasing of pH value
resulting in the increased adhesive reactivity [17]. Our
results showed similar behavior for UF2 adhesive, but
only at the lower levels of catalyst addition, up to 1%.
Contrary, UF1 adhesive, having higher F/U molar ratio,has shown no significant change in ΔH in regard to catalyst
addition.