In some cases, plastic doesn't either. It will "dry" out and either crack or begin to flake off. I've had plastic gasoline containers where the plastic rings that you tighten down to prevent leakage, simply crack down the sides when trying to unscrew them to get to the fuel, especially in winter time.
This is not to say all plastic is this way, some plastics that are more flexible, like on the gas containers themselves, can last for years. But the cap rings are made of hard plastic.
This is not to say all plastic is this way, some plastics that are more flexible, like on the gas containers themselves, can last for years. But the cap rings are made of hard plastic.