UF adhesive samples were diluted to the concentration
of 50%. Addition of NH4Cl was 0.2 mass%, for all
DSC measurements intended for evaluation of the activation
energy for both UF adhesives. The curing reactions
of the UF adhesives were monitored using differential
scanning calorimeter (DSC Q20 TA Instruments,
USA). Small amounts of the test samples (approx. 4 to 5
mg) were placed in hermetically sealed aluminum pans.
All scans were run in dynamical regime with different
heating rates (5, 10, 15 and 20 °C/min) in the temperature
range from 40 to 200 °C. Before the test run, the
temperature of the heating block was equilibrated at
40 °C. The purge gas was nitrogen. Additionally, the
catalyst influence on the adhesives curing was obtained
with the following content of NH4Cl: 0.2; 0.6; 1.0; 1.5
and 2.0% and at the heating rate of 10 °C/min. The DSC
curves were monitored in real time, showing the generated
heat as a function of temperature. The instrument
software was set to show the exothermal peaks
in the upwards direction. The area under the exothermal
curve, presenting the reaction enthalpy, and the
peak temperature were determined using TA Universal
Analysis software procedure.