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  • Writer's pictureNed Patton

What can you Make out of the Strings?

I thought with this post I would provide a few examples of things that can be made using the different strings (fibers) that are available in the String and Glue (Composites) business. So, first, and introduction to the pics in this post. To the left three is a wheel for a Ford Shelby GT. To the right is a graphite bike frame, and below that a bed liner from a GMC pickup.

The wheel is carbon/epoxy as is the bike frame, but the pickup bed liner is made from thermoplastic bulk or sheet molding compound which is probably Polypropylene or PES with chopped graphite fiber reinforcement.

There is a pic to the left of a futuristic looking structure that is an artist’s concept for what a fiberglass building might look like.

And finally there is a pic below of a Spectra tow line being used by a tug boat pulling a rather large ship.

These are just a few examples of things that are made out of composites and samples of some of the more common and more important strings (fibers) that are used in the industry. Of course, by far the highest tonnage use of fiber in composites is glass fiber, and most of that fiber is E-Glass. This fiber is so named because of its electrical resistance – hence E-Glass or Electrical Glass. E-Glass is an alumino-boro-silicate glass that has less than 1% by weight of alkali oxides. Glass is primarily silicon dioxide or silica, with the addition of a little of this and a little of that to make the glass more workable, or stronger, or stiffer, or more chemically resistant, etc. These additions also reduce the temperature at which the glass softens and can be worked into shapes or drawn into long continuous fibers. And of course, once you have long continuous fibers you can use those fibers together to make a composite material. Most recreational boat hulls have been made with fiberglass cloth (called woven roving) and either polyester or in more modern times vinyl ester resins. Higher performance boats have used a little Kevlar and even epoxy resins with E-Glass reinforcement to make the hulls.

Carbon fiber is the second most common fiber used in composites behind E-Glass. And there are two types or structures of carbon fiber, a “Turbostratic” structure and a “Graphitic” structure. The figure below shows what I mean.

The Turbostratic fibers are mostly made from the PAN (PolyAcryloNitrile) fiber that I talked about in the original post about strings. PAN based carbon fiber is the most common and highest tonnage use carbon fiber, and the largest manufacturer of PAN based carbon fiber is Toray Industries. Pitch based carbon fiber is the Graphitic structure fiber, and it has a higher elastic modulus than PAN based carbon fiber, but it is more brittle than the PAN based Turbostratic fiber. Just looking at the pic above and thinking about how the 6-carbon Benzene rings are connected together allows you to understand the differences in these two fiber types. The Benzene ring is a very stiff structure since those carbon-carbon bonds are very stiff. And since the Benzene ring is flat, when you hook a bunch of them together in a layered structure, you get graphite – hence the name “Graphitic” for the structure that you see. A single layer of graphite is called graphene, and it could be the strongest two dimensional material ever derived once we understand how to make it.

Kevlar is in the class of fibers called “Aramid” or aromatic polyamide fiber. The “aromatic” comes from the Benzene ring that is part of the chemical structure of Kevlar fiber. It is in the class of aramid fibers with Nomex and Technora, and was originally developed by Stephanie Kwolek at DuPont in 1965. She was working with nylon fiber, trying to make a stronger fiber and came up with a witches brew of organic chemicals found that she had made what is called a “liquid crystal” polymer. When she convinced her technician to draw a fiber out of the solution of cloudy liquid crystals she ended up with a fiber that was stronger than nylon could ever be. The original fiber was Nomex, but with a few tweaks to her recipe, she finally made the first Kevlar fiber. And the rest is history, since Kevlar has become the fiber of choice for a number of applications.

Finally, the marine tow rope is made of Spectra which is an ultra-high molecular weight polyethylene fiber. Yes, I said polyethylene, that same stuff you buy at Home Depot to lay down on the floor when you paint your bedroom walls. When you make a fiber out of an ultra-high molecular weight – read as VERY long chain – polymer, it is stronger than steel and floats on the water. It is also completely impervious to most chemicals since it is polyethylene, and it doesn’t degrade rapidly from UV exposure like some of the aramid fibers do. So, Spectra has taken over the high performance yachting world, and there are a number of racing sailboats that have Spectra sails and Spectra rigging.

I could of course talk about this nearly endlessly, but it’s time to move on to another subject with next post. Stay tuned. I've got lots more to talk about.


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