Weather resistance tests

One of the first attempts to produce polyurethane was from the reaction of an intermediate polyol of 1,3- and l,4-bis(hydroxyhexa uoroisopropyl)benzene m- and -12F-diols) by reaction with epichlorohydrin. This polyol was subsequentiy allowed to react with a commercial triisocyanate, resulting in a tough, cross-linked polyurethane (129,135,139). ASTM and military specification tests on these polyurethanes for weather resistance, corrosion prevention, bUster resistance, and ease of cleaning showed them to compare quite favorably with standard resin formulations. 

Fire and Wind Hazards. Weather resistance of roof covetings is not necessarily correlated to fire and wiad resistance. Underwriters Laboratory and the Factory Mutual System test and rate fire and wiad hazard resistance, and some durabiUty tests. Organic felt or fiber glass mat base shingles are commonly manufactured to meet minimum UL requirements, which, ia addition to minimum mass, require wiad and fire resistance properties. 

Very light and weather resistant systems require very long outdoor exposure times. In order to accelerate the testing of pigmented systems, test methods have been developed which simulate outdoor conditions. The evaluation of such a test is not only conveniently accelerated, but the resulting data are easy to reproduce and independent of location, climate, date, and time. 

This test (ASTM D529) evaluates the relative weather resistance of asphalt used for protective-coating applications, especially for roofing. No direct measure of outdoor life or service can be obtained from this test. Methods for preparing test panels (ASTM D1669) and failure-endpoint testing (ASTM D1670) are available. 

None of the chemical methods (e.g., mandelic acid or methanol test) gives a perfect indication of weather resistance. Most of them only measure partial qualities of the photochemical reactivity [1.58]. 

Accelerated Tests. Weather resistance in an accelerated test is defined as the resistance of plastics towards changes caused by simulated open-air weathering (simulation of global radiation by means of filtered xenon arc radiation and periodic rain). After the weathering (measured by the product of intensity and duration), defined properties of the test sample are compared with those of an identical unweathered sample. Properties should be considered which are of practical importance, such as color or surface properties. For standards, see Table 1 ( Weathering in apparatus ). Apparatus test chamber, rain and air humidification equipment, air flow equipment, radiation measuring equipment. 

Due to high application levels of plasticizers, their behavior with respect to environmental influences (weathering resistance) and impact on the polymer matrix (effect on optical properties or plastics lifetime) have to be tested. 

Fade and weather resistance can also be evaluated using laboratory test chambers, fadometers, and weatherometers, designed to simulate a variety of actual environments in an accelerated fashion. The types of tests are classified according to the nature of the light source ... 

Fig. 1 compares the performance of PVDF resin-based coating systems with competitive coatings for their weather resistance. Panels coated with Kynar 500 and other coating systems were exposed on a South Florida test fence for 10-17 yr. The top of the panels was unexposed while the lower part was exposed to sunlight for 10-17 yr. It was concluded that Kynar 500 PVDF offers superior color retention, greater gloss retention, and better resistance to chalking than other systems tested. 

Permanence Tests. Corrosion resistance, weather resistance, oil resistance, resistance to chemical agents, heat and light degradation, aging. 

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