There are two ways to approach the use of VC-3 when discussing plastic compatibility. If you apply VC-3 directly to a plastic fastener, there is a limited selection of substrates which are compatible. Please review the table here as a start, and be sure to test first.  The second way to use VC-3 is when you are installing a metal fastener into plastic. Because VC-3 must be dried first, all the solvent will have evaporated and you should be left with an inert plastic threadlocker.  You can then install that fastener into practically any type of plastic assembly.