No direct experience with using it as a handle material, how ever I know that the Black palm that I have seen was used for making archery equipment IE. Bows/arrows. The Palm is so hard that it was even used for arrow points. I tried to use black palm here in Calif. for bows but our climate is to dry and the palm became too dried out and brittle for my porpoise.
So I can only suggest you let it stabilize to your climate before working to shape them seal it well.
Hope this is of some help, and I hope you put some pictures up when you have finished your knife.