Exposure duration, polymer weathering

In devices in which wetting is hy immersion, the sample is immersed in water while the surface is exposed to light. Since water absorption hy polymers from a humid atmosphere or hy direct wetness is a diffusion-controlled process, the frequency and duration of the exposure to moisture is often a critical parameter. Weathering processes can he accelerated by more frequent swelling and contraction than occius in practice. The length of the required wet period depends on the water diffusion coefficient and water absorption capacity of the material as well as on its thickness. Rain, humidity periods, or both ranging up to hours may be required for some pol5uneric types. 

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