Discussion
Discoloration and loss of mechanical strength of plastic chairs exposed to sunlight for several days is due to
Answer: C
The damage is due to photo-degradation.
Ultraviolet radiation in sunlight carries enough energy to break chemical bonds in polymer chains, or to excite chromophores and impurities that then generate free radicals. Chain scission and the new chromophoric groups that form cause yellowing or fading, surface chalking and embrittlement, so the chairs discolour and lose strength.
Oxidation usually accompanies the process (photo-oxidation), but the trigger is light, which is what the situation describes. Thermal degradation needs much higher temperatures than outdoor sunlight gives, and 'hydrophilic degradation' is not a recognised degradation mechanism for such plastics.
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