Since most of the rotational energy and weight of the yoyo/axle is felt by the string loop around the axle, I would assume that the highest friction is concentrated on the “bottom” part of the string loop. This friction goes into a very small part of the string, causing it to heat up much faster than the rest of the string. Friction between the string and the side walls will be much less than the loop and axle, plus, it is distributed over a much larger area of string, causing less string heating than at the axle. So, based on physics, I would assume the string fails near the loop.
But, if the inner walls of the yoyo are not smooth, compared to the axle surface, you could get some serious friction and wear on the string that way, and all bets are off.
I would hope so. I’ve been playing with some steel axle plastic yoyos (Duncan Imperials and Butterflys) and cheap poly strings for a while and have yet to have a problem, but, I don’t play one of those yoyos for hours on end. Also, I have found the star response of these plastics does respond better to 50-50 cotton/poly string than 100% poly. Personally, I don’t have any wood yoyos to try things out on, so your mileage may vary with wood…
Polyester is a form of plastic. Poly strings are polyester thread. The thread is very thin. So you put thin threads made from plastic, and add a wooden axle creating friction on those very thin threads it causes them to melt, or at least heat up and wear out quickly.
Wood while we can get it to feel smooth, is never truly 100% smooth, so there will always be some friction, which is why 100% poly string doesn’t work with wooden fixed axles.
Mainly axle friction, BUT this is really only an issue if you are throwing hard to do longer sleeper-based tricks, as opposed to more modern stall-based fixed axle play. Tricks like Cold Fusion or Kamikaze will wear strings quickly if the axle is even a little rough, and the problem is exacerbated slightly by poly in my experience (like jhb said - you’ll observe it as premature wear, not actual melting, which would be too miniscule to observe). If you are doing a lot of Flips, Varials, Moons, etc, I don’t think you’ll notice any real difference in string wear - it might even lean toward poly a little bit.
I would play what FEELS right, and don’t worry about the wear unless you’re playing extremely thin string.
Honestly, I just really prefer how wood and cotton feel together.
What is more important to you: performance or color options?
I ask; because if you seek maximum performance potential and string longevity; than why would you even be concerned about a 'lack of string color choices in cotton string?
And since you have become aware of the potential and or inevitable shortcomings of using poly string; why can’t you just use whatever poly color string you want and just change it often(before it breaks)?
… performance trumps color choices… all day long🤓
I happen to like poly strings with my fixed axle yoyos. But then again; I don’t hesitate to change strings in a heartbeat if I see or feel something ‘funny’ during play.
… Fixed axle 2A; I always use either 50/50 or cotton. Never full poly.
You want to see a yoyo go flying? Crank up some 2A on No-Jives with poly string.