Nylon VS PP, which material is better for bristle of auto cutter?

There are two commen plastic materials for bristle block which is used on auto cutter. One is nylon ( Polyamide 6, PA6 ), and the other one is PP (Polypropylene ). Both of them are wildely used on plastic products. But due their different chemical character, you may choose the material for bristle based on different envirement .