Kinetic Analysis and Characterization of Epoxy Resins ... - FedOA

Results and Discussion 145
ditions.
The best operating conditions for the microwave curing process have been
determined studying the influence above all of three parameters:
1. power ;
2. radiation time;
3. mass of the sample.
The power and time of radiation influence the quantity and the rate of energy
transfer between the oven and the sample. While the mass of the sample influences
the energy development during the polymerization. In fact initially the temperature
raises exclusively for dielectric heating, but as soon as the temperature
overcomes a critical value, corresponding to the activation of curing process, the
thermal profile is controlled, above all, by the heat generated by the exothermicity
of the reaction itself.
This heat is proportional to the mass of the sample and
depends in a complicated way on the energy flux received from the oven, through
microwave radiation, and on the energy exchange with the outer environment.
Only an accurate selection of these three factors ensures a complete conversion of
the sample, avoiding thermal degradation phenomena.
The values of microwave cycle parameters and reactants quantity corresponding
to the achievement of this condition have been determined after several experiments
and they are listed in Tables 3.23 and 3.24.
In Figure 3.37 the DSC dynamic scan between 0 up to 220 ◦ C with heating rate
of 10 ◦ C/min on a fragment of epoxy resin microwave cured as reported above is
illustrated.
No residual enthalpy is present, therefore a complete conversion has been reached.
Furthermore the light yellow colour of the resulted slab indicates the absence
of thermal degradation phenomena. So with the parameters reported in Tables
145