Plastic can be used as an additive in epoxy, but there are a few things to keep in mind. First, the plastic should be in small pieces so that it mixes evenly with the epoxy. Second, the plastic should be compatible with the epoxy you're using; otherwise, it could cause the epoxy to not cure properly. Third, too much plastic can make the epoxy brittle, so it's important to use just enough to get the desired effect.