For polyethylene, the area of the peaks at 1780 and 1700
cm-1 was used for the oxidized components (carbonyl
forming bands) and the area of the peak at 1465 cm-1
was used to represent the natural component of PE. For
polypropylene, the same area of 1780 and 1700 cm-1 was
used for the oxidized components, whereas the area belonging
to the peak at 2720 cm-1 was used to represent
the natural component of PP.
Res ults
The carbonyl index is a useful and broadly used measure
to quantify the degree of degradation of polymers.
Yet, it is not an absolute measure of degradation and it
can, therefore, not be directly translated to the loss of
mechanical properties of the given polymer. Hence, we
compared the data of our measurements with studies in
which degradation was induced under controlled laboratory
conditions and in which the carbonyl index was defined
in the same way as in our study.
Figure 9.6 and Figure 9.7 show the obtained FTIR spectra
for PE and PP, respectively, showing the formation of the
carbonyl groups at 1720 cm-1, which is characteristic for
the oxidation of the material. Table 9.6 shows the calculated
values of the carbonyl index (CI) for the studied PE
and PP samples. Higher values of CI indicate stronger oxidation.
Note that CI values of PE and PP cannot directly
be compared to each other, because the basis of calculating
the CI value is different for both polymers (i.e. the
area belonging to the peak that represents the natural
component of PE and PP are different).