Would this work for yoyo string ???
There used to be Kevlar string that was made for a flamable yoyo, can’t remember any of the details but I know the string had to be Kevlar so the yoyo wouldn’t ignite the string. As far as your question goes I don’t know the answer I assume it would work, not sure how well, but you know what they say about assumptions.
Its needlessly expensive. General Yo makes kevlas string twists made of 50/50 Kevlar Poly I believe for 1 dollar each.
But, how long of a string do you need to make a yoyo string?
7.5 x 4 x 2 feet? 60 feet per string? I don’t know.
You can easily use around twenty-five yards of thread in a single string. It makes more sense to use a nylon and polyester blend string than a Kevlar and polyester blend. Nylon is cheaper, has most of the properties of Kevlar, is cheaper, has a similar chemical structure, and is cheaper.
#82 string twists the kevlar string, general yo just distributes it.
Okay?
precision of language is very important 
(anyone get the reference?)
+1 for Nylon > Kevlar for yoyo string
Google for 10 minutes and know why.