Accelerated Outdoor Weathering

ASTM D 4364 Practice for Performing Outdoor Accelerated Weathering Tests of Plastics Using Concentrated Sunlight ... 

The Sedona paper described a simple experiment exposing polystyrene standard reference materials (SRMs) to outdoor accelerated weathering conditions under concentrated solar irradiances at four different levels out to the same level of radiant energy. The exposure temperatures were held constant across different irradiance intensities via linked exposure devices. The data from the Sedona paper showed significant deviations from strict reciprocity predictions for the polystyrene SRMs in the experiment as shown in Fig. 11.2. The data indicated that the assumption of strict reciprocity was not a valid assumption for the data shown. 

Azuma, Y., Takeda, H., Watanabe, S., et al. Outdoor accelerated weathering tests for polypropylene and polypropylene/talc composites. Polym. Degrad. Stab. 94, 2267-2274 (2009)... 

Published by the Plastics Design Library, PDLCOM is an exhaustive reference source of how exposure environments influence the physical characteristics of plastics. Data include resistance to thousands of chemicals, weathering and UV exposure (i.e. color change after accelerated weathering or outdoor exposure) sterilization (radiation, ethylene oxide, steam, etc.) thermal air and water aging environmental stress cracking and much more. 

Figure 18.6 Effect of outdoor exposure, Miami, FL, on the color of selected materials [2], From Weathering of polyester and copolymer sheeting, presentation given by D. R. Fagerburg at the Atlas School for Natural and Accelerated Weathering (ASNAW) course, Miami, FL, May 1999, and reproduced with permission of Atlas Electric Devices Company...

In all the paint systems tested in the atmosphere, the presence of the chloride contaminant at its highest concentration, causes the appearance of small blisters. Such blisters may in time burst due to the oxide built-up inside them, as was seen in the case in the CR system ("Table III.") In the P system ("Table III."), the blistering seen with the third level of chlorides continues after two years outdoor exposure, without rust coming through the coating. This same effect is also seen in salt fog test panels, but it does not appear in those test specimens subjected to accelerated weathering tests. 

Extensive information on the durability of polymers based on outdoor and accelerated weathering tests is available from work carried out at NREL and other... 

In this work, the expression "long term" requires defining. For photo-oxldatlon It refers to natural outdoor exposure up to 38 year duration and artificial accelerated weathering up to two years. In the case of thermal oxidation samples have been maintained at constant temperature for up to seven years. 

In 1950 Wallder, et al.O.) established that 100 hours accelerated weathering was equivalent to one year of natural outdoor exposure for LDPE containing 1% or more of a well dispersed carbon black. Longer exposures outdoors have shown,(2) however, that the relationship Is not linear due to a complex relationship between the photo-lnltlated and thermal d radatlon processes that occur under two different sets of conditions. 

Low-Density Polyethylene. The data from outdoor weathering are summarized In Figure 1. The low-temperature brittleness (LTB) measurements show that a well-dispersed carbon black of > 1% concentration and < 35 millimicrons (mu) particle size Is necessary for maximum resistance to photo-oxldatlon. The results from elongation measurements agree with those found for LTB, as would be expected, since both measurements reflect the notch sensitivity of polyethylene to micro cracks caused by photo-oxldatlon. Accelerated weathering studies on these compounds have been reported previously (2) and Indicate the same ranking as found in outdoor exposure. 

Only the 12 row shows natural, outdoors weathering (35,000h) all other figures are related to accelerated weathering, in Q-Sun 3000 (0.35 W/m at 340 nm, 102 18 cycle, 63°C black panel temperature). The data are arranged in the order of decreasing of the yellow component (b) compared to the initial value. 

Typical questions addressed by folks considering accelerated weathering data obtained in a weathering box are— what really means 1000 hrs or whatever— in the weathering box with respect to the real world To what time period outdoors is corresponds What is an equivalency coefficient—or whatever— between the weathering box and outdoors conditions ... 

Let us introduce one more term, the acceleration factor. The acceleration factor—in this context—is the ratio of time for the same extent of fading outdoors to that in the accelerated weathering box. For example, an accelerated factor of 10 means that a one-month accelerated weathering test corresponds to 10 months... 

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