"loop" is one of the most overused knotting terms, and so results in continual
confusion, ambiguity; I take the problem here to be joining ends of slick thin tiny
tape to make a circle of the stuff (to what end, though? --could make it easier
to use in the mouth (which could lead to making it more likely to be used!)).
Well, thank you for an exercise in most frustrating material!!
Is this going to get us to give up flossing?
In any case, the most obvious solution to my mind to bend to ends of this slick,
tiny tape together is the Blood bend/knot--both for security AND easy tying!
(Did I say "easy"?
)
Well, if you have some tweezers, you can bring each line around on opposite sides
of the tweezer end (or some other device that can pull ends with), and make
relatively easy wraps of the ends around the opposing SPart and then bring both
ends together to be tweezed-nipped and thus pulled through the center point,
and then draw up the knot carefully (perhaps maintaining grip on the ends until
the knot body tightens enough to hold them).
And maybe the Fisherman's would work were one to finish it with the extension
of tucking the ends back down between the two lines at the center before
pulling the Overhand components tight against each other. (worked for me)
Perhaps some of the knots you found wanting might also work if you take care
to hold the ends while tightening--which can be hard to do in this material.
*knudeNoggin*