'Nylon' or polyamide plastics is injection moulded in a brittle, dry state.
It must absorb moisture to gain or regain it's impact resistant properties.
Just time in the atmosphere will suffice, or you can speed things along by soaking in cold or warm water. Boiling is not advisable, although I have often seen it recommended.
I prepacked my props, directly off the moulding machine, in a poly. bag liner within the storage carton. I splashed a cupful of water into each liner before closing, found it was absorbed when it came to packaging for shipping and that the propellers were just fine.
Peter