Polypropylene handle cleaning

[R.D.Hatch]

I have accumulated some Dexter Russell kitchen knives with the white polypropylene handles. Some of them have yellowed or discolored over time and regular hand washing does not clean them up.
Anyone have experience in restoring the white to these type of handles.
Thank you in advance.

 

[SkrufKnifer]

Soak in bleach water.