Is it safe to microwave plastic? (yeah it is a relevant question)

Sooo i wanna try making keychains by drawing on plastic and then microwaving it, but im worried that maybe microplastics can get on inner walls of the microwave and then on food. i don't wanna poison my entire family i could use oven, but its too much of a hassle because its not electric which means that i literally have to light a match or a use a lighter to make it work. i think i don't need to explain why thats a bad idea