Welcome to AAPK!!!
It looks very much like an Imperial knife, and the shell-handled design means that it is from the 1930's or newer.
While these have pretty much no collector value in that condition, I know that it should and does have tremendous sentimental value! And it looks like your great great grandfather treasured it and used that knife regularly.
As to the advice on Celluloid, normally it is unstable and apt to damage old knives, but the thin celluloid wrap on these old Imperial knives is as stable as celluloid can be. I have not heard of any outgassing.
That said, if it were mine I would take care of it, maybe put it in my pocket on an occasional Sunday (just for the nostalgic feel of it), and would be prepared to pass it along to my children someday.
Thank you for sharing!!!
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