why spinning makes fibers hold
Here's something that I just realized yesterday
... and it's certainly in the known category. So, why didn't I know it already?
My question (posed to myself) was ... why do plant fibers hold together in string or thread when they are only short pieces of fiber as from a cotton tuft? Are they "glued" together somehow? Why don't they just pull apart? Where is the extra force that comes into play to make the fibers resistant to a simple pulling action?
Well, it's entirely due to the spinning of the fibers, I discovered. I'm so sure of this, I'm not even going to bother looking it up on the web.
What happens when the fibers are "spun" is that they are transformed into a helix instead of a straight run of fiber. As a straight fiber touching along the length of another fiber, there is "some" amount of friction between the two fibers. But if you spin them together, they wind up like a spring one about the other ... and in the process, they become shorter since the formerly straight line is now taking the form of a helix ... get it so far?
For best results, the spinning should have one element wound and another as a "base" unwound thread, i.e. two threads put together with one as a helix and one straight. That way, when you hang something from the string it won't unwind as gravity pulls on the suspended object because ... though one element would unwind ... the other would then wind up in the other direction. As it happens, this is probably not the case in most threads because I remember once suspending something from a single thread and watched as it "unwound" itself via gravity. This upset my little experiment until I realized what was happening and doubled the thread so as to cancel out the unwind. Get it?
Back to the Helix
Now, when you pull on the wound thread, that helix tries to straighten out and thereby squeezes the threads inside the helix. So, the pressure holding fibers together goes way up and consequently, the normal friction between them goes way up ... and ... voila! the fibers are "bound" to one another mechanically. The tighter you pull, the greater the squeezing pressure, the greater the friction ... the strength increases to the limit of a hypothetical solid thread of that diameter attained when the thread finally (and inevitably) breaks.
There is no glue or hooks are anything new in the tread ... just the simple mechanics of a "helical bind". Now, why didn't I know that before? It's because I'm ignorant ... in some things ... but not stupid ;o)