Question

4.  Why does plastic not rust like iron?

Answer 1

Iron and steel rust when they come into contact with water and oxygen. They rust faster in salty water or acid rain. Now what about Plastic. ... Polymers often are made of carbon and hydrogen and sometimes oxygen, nitrogen, sulfur, chlorine, fluorine, phosphorous, or silicon.

Answer 2

it can't rust simply because it doesn't contain any iron or any of it's alloys. In fact, not even all metals rust. Certain metals like brass, aluminum, silver, copper and plenty of others will corrode, but they don't rust because they don't contain iron. You can learn a lot more information about how corrosion and rust work in this article"the science behind corrosion " A great article that should help you understand how rusting works.
Hope it helped!