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IMPACT TESTS OF ULTRAVIOLET LIGHT-EXPOSED PVC PLATES
The UV exposure of PVC samples was carried out at the Department of Materials Science
and Engineering, The University of Alabama at Birmingham (UAB).
There are artificial and natural sources of the ultraviolet radiation. Artificial sources include
sunlamps, mercury vapor lamps etc. The sun is a natural source of ultraviolet radiation. UV
radiation consists of three main components, namely UV-A, UV-B, and UV-C.
UV-A radiation (320400 nm) is only slightly affected by ozone levels, so the earth's surface
receives a large amount of this radiation. The physical units are Joules per square meter, Watts
per square meter, or microwatts per square centimeter. UV-B radiation (280320 nm) is strongly
absorbed by ozone levels in the stratosphere, so only a small amount reaches the earth's surface;
with the thinning of the stratospheric ozone, more UV-B can reach the earth's surface, becoming
an environmental problem. UV-C radiation (100280 nm) is destructive and causes the most
damage to the biosphere, but it is completely absorbed by ozone and oxygen molecules in the
upper atmosphere, so this is of little importance.
In this study we investigated UV-A radiation. A South New England Company
Photochemical Reaction Vessel RPR-100 equipped with 16 lamps of 350-nm wavelength
circumferentially arranged was used to expose the samples to UV radiation. The UV intensity of
the lamps was approximately 92009500 microwatts per square centimeter at the center of the
specimen chamber, which is about five times the intensity encountered on a clear sunny day in a
place like Arizona. The intensity of the UV radiation in outdoor conditions is approximately
15002000 microwatts per square centimeter. These are only approximate guidelines, as the
cloud conditions, air quality, pollution, etc. influence the actual values of radiation to a large
extent.
A set of 30 samples was sent by CRREL. The approximate dimensions of the samples were 4
4 in. Of these, ten samples were saved as control, ten samples were subjected to 20 hours
of exposure, and remaining ten for 200 hours. The UV test chamber had a 9- 12-in. space for
holding the samples.
The testing involved exposing 10 samples for each time span. Two samples, connected using
eyehooks, were hung from the top of the UV chamber using a nickel wire. Five sets of these
samples were hung together in the chamber. These samples were further rotated to various
positions to get the same amount of exposure for each sample. The layout of the samples in the
chamber is shown in Figure 15.
The rotation scheme for the 200-hour test was such that each set of samples was placed at
positions 1, 2, 3, 4, and 5 for 40 hours. Further, the face of each sample was rotated 180o after 20
hours of exposure at a particular position. For the 20-hour exposure time, positions 1 and 5 were
assumed to be equivalent and so were positions 2 and 4. Hence the rotation scheme involved
exchanging samples at position 1 with 2 and positions 4 with 5 after 10 hours. The sample at
position 3 wasn't moved throughout the exposure duration. Figure 16 shows the inside of the UV
test chamber with a single representative PVC specimen hung using nickel wire.
Figures 1719 show the difference in discoloration due to degradation for the PVC control,
PVC 20-hour UV exposed, and PVC 200-hour UV exposed specimens.
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