How to identify

This is off-topic, but since you folks are so knowledeable... I recently bought a surplus roll of fiber said to be kevlar. It is yellow as expected, and also quite stiff (doesn't stretch). I put some of it close to a flame and it didn't melt and wouldn't catch fire, but it would char. I am wondering if there is a simple yet foolproof way to identify the fiber as kevlar. Any other ideas/opinions?

Reply to
Tidris
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You'll need to research it, but Kevlar should have a specific density, it will float in some liquids and not in others.

The best way is to verify it through the manufacturer.

Real chemical ID of plastic might require burning a sample and running the byproducts through a gas chromatograph - very expensive for you and me.

You could also do some testing like tensile strength which would give you a very good idea, but the equipment is very expensive - you'd have to send it to a lab.

Reply to
Lefty

I understand that a normal scissors won't cut Kevlar. It takes a special shear edge IIRC.

Have you looked at the whole roll - or lots of it - is there a marking every 20 feet ? or 10 meters ? or whatnot ?

Is there an edge that seems to be patterned - e.g. inside of there is a name.

Just some ideas.

Martin

Reply to
Eastburn

Try to cut it with scissors, it should slip out of the way, or fluff up. Then try to break it in tension by pulling. It should be unbelievably strong for it's size.

Barry Lennox

Reply to
Barry Lennox

It certainy sounds like you have some kevlar. There are some other very strong fibers that do not stretch, but as far as I know they will all burn. ( Except Nomex which is not yellow ). So I believe you have some kevlar. I have some I picked up at Boeing Surplus. It is labeled as Kevlar inside the tube it is on. One more thing you might try is dying a bit of it. It does not seem to accept any dyes. Incidently Kevlar degrades under ultraviolet light.

What are you going to use it for? And why is it important that it is actually kevlar, assuming it is strong enough, etc. for your uses.

Dan

Reply to
Dan Caster

The roll has several miles of string in it, so obviously I haven't looked at much of it yet. However I haven't seen any markings yet. The string isn't a rope but a bunch of very fine unbrided untwisted parallel fibers loosely held together into a string somehow. The string is thin, I would guess under 1/32 inch diameter if I twist the fibers together with my fingers.

I will be trying to use it in fiber reinforced plastic applications with epoxy resin.

Reply to
Tidris

Thanks for all the ideas. I have concluded the string is most likely kevlar.

Reply to
Tidris

I will try to use it as replacement for fiberglass in some fiber reinforced plastic hobby projects of mine. It doesn't have to be kevlar, of course. I wouldn't mind if it was zylon or carbon fiber instead. However I can easily rule out carbon fiber based on the color and lack of brittleness. I think zylon is yellowish/orangish, so it could be confused with kevlar. I guess the most critical thing will be for the fiber to be compatible with the epoxy resin I will use...

Reply to
Tidris

Research to see if it is a thermoplast. You can melt thermoplasts, but not other kinds of plastic. If it does not melt, then it is not a thermoplast.

This should narrow things down a little.

You might also look at solvent compatability / incompatability.

Certain plastics will dissolve readily in common solvents, and others will not. This will narrow things down much further.

Reply to
Lefty

I had never heard of Zylon, but I did a search and found the MDS. Apparently it softens and can be injection molded, and will burn. So I think you have kevlar. As far as I know kevlar is compatible with all epoxy resins.

Dan

Reply to
Dan Caster

The zylon I have read about is suppossed to be like kevlar but with twice the tensile strength and a higher working temperature. However it is more sensitive to light than kevlar.

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Reply to
Tidris

I found an American company using the same name for a different plastic. I suspect either Kevlar or the somewhat similar Zylon are compatable with epoxy adhesives. Epoxy does not stick to the high strength fiber Spectra.

Dan

Reply to
Dan Caster

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