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

Experimental 86
2.6.1 Vessel Material
The first parameter under investigation has been the material of the vessel
containing the reacting mixture.
The main requirement that the material must satisfy is the transparency to
microwave. In fact these materials do not get warm directly, when radiated, and
instead allow the absorption by the sample of the maximum quantity of the available
energy.
Materials reflecting the radiations, as metals, must be absolutely avoided.
Moreover the vessel material must be inert to polymerization reactions and
sufficiently resistant to high temperatures.
The first qualitative tests have been performed using transparent commercial
glasses of polystyrene (PS), a thermoplastic polymer with a T g ≈ 100 ◦ Canda
T m ≈ 270 ◦ C. However in some cases during the curing process temperatures
higher than 160 ◦ C have been reached. Therefore the PS vessel has undergone the
glass transition, with consequent mechanical stability loss and following softening.
For this reason vessels of PP have been chosen, because polypropylene is a
thermoplastic polymer, microwave transparent, with a good thermal resistance 24 ,
and it preserves its mechanical properties up to the melting point at a temperature
of about 180 ◦ C. However the best material for carrying out microwave experiments
is polytetrafluoroethylene, because it microwave transparent, very non reactive, it
has an elevated mechanical stability and excellent antiadhesive properties, but it
is very expensive. In Table 2.7 a summary of the properties of some materials,
when used as vessels for microwave experiments, is reported.
Therefore the experiments for the kinetic analysis have been performed with
PP cylindrical vessels of the size reported in Table 2.8. The vessels, placed on a
glass pedestal of 2 cm of height, has been cut at about 4-5 cm of height for enabling
24 T g ≈−17 ◦ C.
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