When you add some material like masterbatch to polymer for improve properties the important and effective factor is the interactions between these two material. So number of interactions directly depends on the surface area of materials. Nanomaterials have much greater surface area than bulk materials. Hence when you use nanomaterial for improving the polymers properties the mechanism of interactions may be the same but you need lower concentration of nanomaterials for improvement of polymers.

https://www.sciencedirect.com/topics/engineering/fatigue-failure