Polystyrenes will break down when exposed to which factor?

• A. Water
• B. Ultra-Violet Rays
• C. Ozone
• D. Heat only

Answer: (B)

Polystyrene degrades primarily through photodegradation from ultraviolet light. UV photons carry enough energy to break bonds in the polymer, especially in the aromatic rings of the styrene units, creating reactive radicals. Once these radicals form, they react with oxygen in the air, producing peroxy radicals and initiating a chain of oxidative reactions that break the polymer chains (chain scission) and form carbonyl compounds. This leads to embrittlement, cracking, chalking, and yellowing—clear signs of breakdown when the material is exposed to sunlight.

Water doesn’t readily hydrolyze or attack the stable C–C backbone of polystyrene under normal conditions, so mere exposure to water doesn’t cause the same degradation. Ozone can crack certain unsaturated or highly reactive polymers (like natural rubber), but polystyrene’s structure is relatively resistant to ozone attack. Heat can cause degradation, but it generally requires higher temperatures to do so and isn’t as effective on typical outdoor, ambient-condition exposure as UV light is. So ultraviolet rays are the most effective and common factor that causes polystyrene to break down.