UV degradation in plastic aerosols
Figure 3: Intrinsic Viscosity values of outdoor weather exposure vs. unexposed (control) each month for duration of study.
tion of degradation is a decreasing peak height at 1715 cm-1,
which refers to a smaller amount of polymer PET. If degradation
has occurred, then plotting these two peak heights as a function
of time should correlate—whereas the value at 1715 cm-1 should
decrease with time, the value at 1690 cm-1 should increase with
time. The Fit-Plot analysis indicates that of the three sunlight exposure
variables over time, no significant difference was observed
(see Figure 2). This result indicated that the indoor sunlight
conditions accurately correlated with the outdoor exposure and
could be used as a reliable substitute. When comparing only the
two artificial chamber values in a time-scale equivalence line plot,
a slight degradation was observed in the FTIR-ATR data analysis.
Intrinsic Viscosity was also measured (see Figure 3). Again,
analytically, the measures indicated a slight degradation over the
12-month sunlight exposure samples. The generally accepted
industry guideline for interpreting degradation using Intrinsic
Viscosity results is to stay within 5% of the baseline (control)
value. Values that exceed 5% could indicate a potential physical
performance loss due to excessive degradation. In this case, the
control is 0.77dL/g, so an allowable drop would be to 0.73dL/g.
The minimum value measured was 0.723dL/g. However, a physical
test should be done to correlate any impact on the container
with the analytical degradation from either the FTIR-ATR or IV.
Physical properties such as tensile and burst strength were
measured. Evaluation of the data showed that all analytical tests
had common data points at given points in time. Using that for
comparison of the tensile measures (modulus, stress and strain)
showed that modulus and stress were not significantly different.
Strain at break comparison did show the outdoor samples had
a measured decrease, however, due to the tensile bar cutting
process, there were micro-fissures on the cut edge of the samples
and the Strain at Break would therefore have an inherent condition
that would lead to lower accuracy (see Figure 4). If the strain
was a significant factor, it would show up as an increase in the
modulus and peak stress decreasing, neither of which are significantly
different in their respective data sets. Moreover, the burst
strength values would decrease.
Burst strength testing was conducted on continuously exposed
outdoor samples that were pulled in monthly intervals. The burst
values fluctuated between 1–2 Bar over the 12 months. However,
the minimum burst values were always above the minimum
regulatory entity requirements. Even though analytical properties
by FTIR-ATR and IV, and physical property of Strain at Peak,
indicated some degradation, there was no negative impact to the
other tensile properties and the burst strength values did not indicate
a significant decrease over time. The burst strength values
obtained on the aged containers did not decrease over one year,
which indicated that the degradation observed in the analytical
test results was not significant.
Correlation of Outdoor vs. Simulated
It is industry knowledge that UV light causes virtually all polymers
to degrade at some level, thus slight material modifications
can impact the degradation. In order to validate a methodology
providing a consistent and repeatable result in a simulated
(artificial light) lab environment, correlation was achieved across
UV exposure methodologies (Outdoor Exposure vs. Simulated
Xenon-Arc Dosage), as per aforementioned section.
Analytical & Physical Comparisons
Using the collected data, the Total Ultraviolet Radiation (TUVR)
as measured by total radiation dosage—over the one-year timeframe—
was broken down to a daily and subsequently hourly
radiation dosage. The value was then used as an input into the
equation using the “PARG Profile” to create a simulated exposure
timeframe. The profile and dosage time allow for repeatability
when comparing materials and product formula changes by an
interested party.
26 Spray June 2021