This topic is completely outside of my area of expertise. I bet I'm going to be starting many a post with this sentence on this blog, so it seems like something appropriate to start this blog with. But yes, carbon fibers. The picture that first popped into my head was a string of something made out of stretchy carbon, like a polyethylene bag, but spun into some sort of fibers to make a sweater. The first sentence of the review mentions that these are things that are 92% at least made of carbon and later it's mentioned that they can be incorporated into textiles, so I was on the right track, if not completely wrong in the end anyways.
I made a point of not checking the Wikipedia entry on 'carbon fibers' until after finishing the review. But maybe I should have since it complements the article very well, especially in terms of polyacrylonitrile (PAN) that is used for making most of carbon fibers today.
So carbon fibers. Basically you take an ordered material, such as PAN, or some sort of tar pitch that is sort of polymeric, or even cellulose, and as I learned at the end even polyethylene. Now you have to spin this material into fibers with a big spooling machine, and the way this is done, with solvents, with additives, or without all that, and depending on the shape of the vessel and the speed of the spinning, will give you fibers that hopefully won't fuze together at the end. Afterwards this material is heated until heteroatoms are lost and you're mostly left with carbon. Then the temperature is increased to as much as a couple thousand degrees Celsius in order to turn the stuff into a material that is mostly graphite, but is sort of bent and has some hole features. That turns out to be key in fibers having these high tensile strengths. They end up being used in composite materials with plastics and make them much, much stronger.
The review is very detailed and goes into the steps that are needed to turn PAN into a cyclyzed and dehydrogenated polymer that is ready for carbonizing… but then you have to oxidize it or the carbonization process won't take place properly. The oxygen leaves with some hydrogens and also helps HCN to leave (getting rid of that pesky nitrogen part and getting the carbon content high). Sounds like an enormous industrial undertaking, and it was, as you start realizing as you go through this 30 page review. PAN precursors very were successful, but people are always interested in using renewable sources (such as pitch from coal… okay maybe not that section) such as cellulose. It turns out that cellulose needs to be spun very orderly before carbonizing to have a chance and it still doesn't compete so well with PAN (has anyone tried chitosan?). Lignin sounded like a better plan to me by the time I got to that section, since lignin has less heteroatoms to start with and seems to me to be better set up for carbonization than cellulose which really loses a lot of weight as CO due to the high oxygen content. However, lignin gave really bad results and was a big disappointment in terms of the section as well. It sounded like reminiscing by the primary PI with no pictures and anecdotes with paragraphs that took up half a page or more. This section almost killed me with its writing style and practical failures. That is, until I made it past it and got to the PE section where the results seem to be a bit better. Plus PE allows to make carbon fibers with weird shapes…
One thing I forgot to mention is that obviously carbonizing this stuff in an oxygen atmosphere is not done too often since your carbon will burn and fly away as carbon monoxide or dioxide, and the atmosphere affects the graphitization of the fibers. The last section is actually pretty fun and it talks about the structure of the final stuff with some pretty hypothetical schematics of what they look like. Plus, I realized that Raman spectroscopy is a good way to determine the level of carbonization and that it's possible to take an X-Ray of a carbon fiber… but solid state NMR with magic angle spinning still sounds (and looks from the date in the review) more reasonable. I don't have any wish to make my summary of this 30 page review to get to record proportions, especially since this is my very first post. So… in the end, if you don't know much about carbon fibers, you're probably better off with reading Wikipedia. You will definitely learn more from reading the review and it will definitely be more memorable. But, you know… 32 pages. They really went overboard in some places, and especially in that lignin section. Still, I bet it's a useful summary for the many excellent scientists in industry, and some in academia I guess, who are working in this very important area that I am ashamed to say I was ignorant of before.
I do not check the biographies of the authors before finishing the review. That way lies madness, and by madness I mean time-wastage. Afterwards, I checked and it's a PI with two students, and two people who work at a specialty institute for carbon fibers. They are Germans, which sounds about right as this is one of those countries (along with the States and Japan like I learned from the review) that are capable of funding these huge research efforts into these products that have very clear industrial applications but require a lot of development.