Making Carbon Fiber

Carbon fiber...the wonder polymer...stronger than steel, and much lighter...but how does one make it? It's made something like this: We start off with another polymer, one called polyacrylonitrile. We take this polymer, and heat it up. We're not sure just exactly what happens when we do this, but we do know that the end result is carbon fiber. We think the reaction happens something like this: when we heat the polyacrylonitrile, the heat causes the cyano repeat units to form cycles!

Then you know what we do? We heat it again! This time we turn the heat up higher, and our carbon atoms kick off their hydrogens, and the rings become aromatic. This polymer is a series of fused pyridine rings.

Then...guess what?...we heat it...AGAIN! Slow roasting the polymer some more at around 400-600 oC causes adjacent chains to join together like this:

This expels hydrogen gas, and gives us a ribbon-like fused ring polymer. But don't think we're done yet! Next we crank up the heat, anywhere from 600 all the way up to 1300 oC. When this happens, our newly formed ribbons will themselves join together to form even wider ribbons like this:

When this happens, we expel nitrogen gas. As you can see on the polymer we get, it has nitrogen atoms along its edges, and these new wide ribbons can then merge to form even wider ribbons. As this happens, more and more nitrogen is expelled. When we're through, the ribbons are really wide, and most of the nitrogen is gone, leaving us with ribbons that are almost pure carbon in the graphite form. That's why we call these things carbon fibers.

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