Weathering irradiance testing

Figure 18.4 Effect on color of Weather-Ometer testing with ( wet ) and without ( dry ) water spray for Spectar copolymer sheeting [7a]. From Fagerburg, D. R. and Donelson, M. E., Effect of water spray and irradiance level on changes in copolyester sheeting with xenon arc exposure, ANTEC 98 Conference Proceedings, Paper 808, Atlanta, GA, April 30,1998, and reproduced with permission of the Society of Plastics Engineers...

In artificial irradiation tests, for PP plates of varied stabiliser content, spectral sensitivity as weU as temperature dependence of irradiation-caused crack formation was quantified. For that purpose, samples were exposed both to artificial weathering tests at various constant temperatures and to spectrally resolved irradiation. The temperature dependence could be modelled by an Arrhenius fit. For fitting the spectral sensitivity, a plateau function was chosen. Subsequently, the stabiliser content was parameterised and extrapolated. 

The above-mentioned codes contain requirements for accelerated durabiUty tests. In addition, interlayer manufacturers and laminators expose test samples for several years under extreme weather conditions, eg, the Florida coast and Arizona desert. The laminated products weather extremely well, with no change in the plastic interlayer. Occasionally, clouding is noted around the edges when exposed to high humidity for long periods, but this is reversible. Colored areas of PVB laminates may fade while subjected to extensive uv/solar irradiation, which could cause an appearance issue. This has not, however, been shown to alter the laminate s other performance properties. 

The general requirements for accelerated weathering apparatus are given in ISO 4892-1 [29], whilst ISO 4892 Parts 2-4 [26-28] deal more specifically with xenon arcs, fluorescent tubes and carbon arcs respectively. ISO 4892 refers to ISO 9370 [30] (Instrumental determination of radiant exposure in weathering tests), and CIE publication 85 (Solar spectral irradiance) [31]. 

In an attempt to accelerate testing, higher irradiances were employed in the Weather-Ometer . Reciprocity is a necessary condition for this acceleration to be... 

Light Exposures. Silk fabric samples, 0.25 m x 0.17 m, were mounted in Atlas Electric Devices aluminum sample holders according to AATCC Test Method 16E-1982 (7). An Atlas Ci-35 Weather-Ometer xenon-arc was used on continuous light cycle. Exposures were conducted at an irradiance of 0.35 W/m2 measured at 340 nm and the irradiance was monitored and controlled automatically. Borosilicate inner and outer filters were used to simulate the solar spectrum. The relative humidity was maintained at 65% and the black panel temperature was 50°C. The actual fabric temperature during the irradiation was measured, using small thermocouples threaded into the fabric, and was found to be 35 C. Control samples for these tests were kept in the dark at 35°C and 65% RH for the same time period as the illuminated samples. 

Degradable Low-Density Polyethylene (LDPE) Films. Typical xenon arc embrittlement times for unstabilized low-density polyethylene are l600-2UOO hrs. The controls chosen for this research are listed in Table II the thin LDPE garment bag embrittled in 1820 hr and the EcoPlastics LDPE control became brittle after 2075 hr xenon irradiation. The thin garment bag was not brittle, as determined by a fold test, after 18 months outdoor exposure. The Dupont "Sclair" LDPE control listed in Table II was unusual since it had short embrittlement times of 1175 hr in the Weather-Ometer and 6.5 months outdoors. This film was used as a yardstick to measure the Degradable LDPE films since a Degradable Plastic should not last more than 6 months, perhaps less, outdoors and 1200 hr in the xenon arc Weather-Ometer. 

L. Woo, S.Y. Ding, A Khare, and M.T.K. Ling. Failure progression and mechanisms of irradiated polypropylenes and other medical polymers. In G. Wypych (Ed.), Weathering of Plastics. Testing to Mirror Real Life Performance, Plastic Design Library, 1999. 

Experience has show n that not only the black panel temperature but also the temperature in the test cabinet can affect the test results. This may at first be rather surprising, but it becomes understandable when we observe more closely the effects of the addition and removal of heat on a sample in a weathering device. The surface temperature of an irradiated sample depends on the one hand on the properties of the sample itself (material, type of surface) and on the other, on the conditions of exposure. Here we will take the sample and how it is held in the sample holder as given and direct our attention exclusively... 

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