2.2. Samples preparation
The PET was dissolved in a MW cavity (Whirlpool MWD308/SL)
operated at four on/off switch regimes equal in percentage to: 25,
50, 75 and 100%. The power of the cavity was 700W. The
dissolution temperature was established depending on the
thermal prehistory. For example, the first series of specimens
was dissolved at temperatures not exceeding 393 K, while the
second one was dissolved at nearly 433K. This means that PET in
the first series was amorphous, while in the second case it was
semi-crystalline. However, the cloud point temperatures of both
series were found nearly equal and dependent on DGEBA–PET
composition only. 25 g glass vials were used to dissolve 10 g of PET–
epoxy mixtures. Specimens with 0, 2, 3 and 4 phr PET content with
respect to DGEBA were prepared. DDS in stoichiometric amount
was added prior to curing. It is noteworthy that DDS acted as a cosolvent:
all DGEBA with PET compositions became transparent at
room temperature after the addition of DDS, while they were not
without DDS. The same MW cavity was used to cure the specimens.
The MW curing was performed in the following manner: 1 g of the
epoxy–PET mixtures was poured onto 10 g faience tiles (75mm
75 mm and 5 mm thick) and covered with 10mm Teflon foil. Four
faience tiles were placed symmetrically onto the rotating glass
plate of the cavity. All drops of the epoxy–PET mixtures became
nearly 0.8 mm coatings after MW heating for 2 min. The switch on
regime was 25%.
The cured DGEBA–PET specimens that remained transparent
after MW heating were polished finely and used to analyze their
structure applying scanning electron microscopy, SEM, and atomic
force microscopy, AFM.