Light accelerated weathering

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. 

Accelerated weathering is based on using an artificial light source in a cabinet in which the humidity, water spray and temperature can also be controlled. The core feature of an... 

Further uncertainty arises from the environmental exposure. For accelerated tests, repeatability can be estimated from exposure of replicate test pieces and minimised by control of the exposure conditions. Particular points to consider are spatial variation in temperature as well as mean temperature and air flow in ovens. In accelerated weathering apparatus, spatial variation and variation with time of light sources can be very significant. 

Accelerated weathering tests are performed in special test chambers all of which are similar in that a coated specimen is exposed in a controlled environment containing a high intensity ultraviolet light source and a facility for spraying water onto the test surfaces. 

Resistance to light and weather generally depends on the chemical composition, structure, defects, particle shape and size, and concentration of the pigment [1.53], However, these properties also depend on the medium in which the pigment is used. Testing is carried out by open-air weathering, accelerated weathering, and chemical test methods. 

Accelerated weathering is carried out in special weathering devices (e.g., Weath-erometer, Xenotest) which simulate exposure to sunlight and periods of rain. The spectral composition of the light used (Fig. 12) should match the global radiation ... 

Southern pine with a dual treatment of chemical modification with butylene oxide or butyl isocyanate followed by lumen-fill treatment with methyl methacrylate, or southern pine impregnated with methyl methacrylate and polymerized in situ, resulted in modified woods that were resistant to accelerated weathering and to ultraviolet light alone. Physical, chemical, and microscopic changes occurring as a result of ultraviolet light irradiation are described. 

Accelerated Weathering. The radial faces of all test specimens were exposed to a 6500-W xenon arc light source (which... 

Table II.—Rate of accelerated weathering and overall weight loss of southern pine sapwood after 1,800 hr light exposure...

Figure 1. Erosion of Southern pine summerwood in UV-light/water-spray accelerated weathering chamber. Key O, control +, MMA Bulso X, BuO A, Bui so + MMA , BuO +...

Figure 5. SEM photomicrographs of radial Southern pine surfaces showing effects of 1800 h of UV light in an accelerated weathering chamber. Key upper, unmodified wood before exposure (5OX) center, unmodified wood after exposure (100X) lower, BuO-modified wood after exposure (100X) ...

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