Why do most plastics turn white when you bend them?

When pl ast ics are exposed to sunlight , they can under go a process called photo ox id ation , which causes them to become yellow or brown . However , some types of pl ast ics , such as poly eth yl ene , can become white when they are exposed to ul tr av iolet ( UV ) radiation . This is because the UV radiation can cause the poly eth yl ene mole cules to break down and form new comp ounds that are white in color . It ' s important to note that this process can take a long time , and it ' s not common for pl ast ics to turn white due to UV radiation alone . </s>