The DSC technique was employed, in analysis of ethanolysis
products of PET, in order to evaluate the best reaction time, since
it is possible to observe from melting temperatures the obtaining
of monomers or oligomers of different molecular weight. Fig. 4
presents the DSC curves for obtained products after depolymerization
of PET by ethanolysis reaction. Curve A is referent to the
product obtained after 30 min of reaction, in which the signal that
appears over 150 ◦C indicates the presence of oligomers of different
molecular weights. The melting temperature is function of lamellar
thickness, which presents the trend to be larger with increasing the
molecular weight as well as the existence of oligomers with different
sizes. In curve B it is possible to observe signals in the range of
100 and 180 ◦C suggesting the presence of oligomers of low molecular
weights arising from the incomplete depolymerization process
of PET for 60 min of reaction. However, the products obtained in the
limit of PET depolymerization by supercritical ethanol are diethyl
tereftalate (DET) and ethylene glycol, as presented in Fig. 5. Curve C
proves the obtaining of pure DET for 120 min of reaction. The peak
at 43 ◦C was associated to the melting of DET, which presented high
purity based on its single sharp peak. The yield of DET for 120 min
of reaction was 80%. Therefore, the following data are referent to
the product obtained from 120 min of ethanolysis of PET.
The diethyl terephthalate, like all esters, has two strong characteristic
bands in IR spectroscopy, one due to the C O stretching
vibration and the other one due to the C O stretching vibration.
Fig. 6 shows the FTIR spectrum of DET. The band that appears at
1727 cm−1 was related to the C O stretching vibration. The C O C
presented two bands at 1130 cm−1 and at 1270 cm−1 attributed
to symmetrical and asymmetrical C O C stretching, respectively.