Figure 2: Pictorial and formula for using FTIR-ATR. Diagram Source: Attenuated Total Reflectance, Wikipedia, online 12 July 2020,
https://en.wikipedia.org/wiki/Attenuated_total_reflectance (Accessed: 28 October 2020).
June 2021 SPRAY 25
Analytical & Physical Comparisons
Both analytical measurements and physical property tests were
used to ensure that the results of the analytical represented the
physical and vice-versa. The analytical tests consisted of Fourier
Transform Infrared-Attenuated Total Reflectance mode (FTIRATR)
and Intrinsic Viscosity (IV). Using FTIR-ATR (see Figure
2), the analytical test focused on the carboxyl acid end group,
to determine if the molecular weight (Mw) was decreasing. The
test essentially tracked the products of UV degradation of PET.
Major products of UV degradation are peresters and aromatic
carboxylic acids. The wavelength numbers referring to these two
are 1773 and 1690 cm-1.
An increase at 1690 cm-1 indicates more aromatic carboxylic
acids content and higher level of degradation. Another indica-
Figure 3: Fit Group Oneway analysis of the three exposure profiles at the (left) 1715 Peak Height Ratio and (right) 1690 Peak Height Ratio.