I made these Christmas tree ornaments from used k-cups. An easy craft to make with your family. Acrylic paint and plastic don’t work well together. Whenever I have a difficult to paint object, I go to my usual method, using watered down school glue and used one layer of a cheap napkin to cover the item. Let dry and decorate any way you wish.It does take time for the napkin and glue to dry before you can paint it. You could use good markers instead.