Stone Age, Iron Age, Polymer Age There was a time when everything from arrowheads to armchairs was made from stones. Other features of those good old days were air-conditioned caves and charbroiled saber-toothed tiger steaks (if you caught him instead of the other way around). Fortunately, this age ended when someone discovered how to reduce iron oxide to metallic iron using coke (carbon) as the reducing agent. That all hapnened several thousand vears ago, so the caveperson chemist who got the patent righis to t h i iron age wasn't educated a t MIT or the Universitv of Chicago. But this chemical discovery profoundly changed the way people lived. It led to all sorts of new products like swords and plowshares and the inner-spring mattress. Can you imagine how those stoneagers would have reacted the first time they put on a snit of armor, or went up the Eiffel Tower, or took the train to Chattanooga? Well, brace yourself, because chemists are a t it again! This time, we're about to enter the Polymer Age. You may think we're already there, with ycur polyester shirt, polyethylene milk bottle, and polyvinylchloride suitcase. We walk on polypropylene carpets, sit on polystyrene furniture, ride on polyisoprene tires, and feed our personal computers a steady diet of polyvinylacetate floppy disks. In just the last 40 years, the volume of polymers produced in the United States has grown 100-fold and, since 1980,actually exceeds the volume of iron we produce. But the best is yet to come. The structural materials with which we have been building hridges since even before the one to Brooklyn, and automobiles since the Model T, would seem to he the last stronghold of the iron age (pun intended). Would anyone dare to suggest that polymers could compete on this sacred ground? Well, no one perhaps except chemists. Right now, there's talk of an all-plastic automobile, and you're already flying in commercial airliners with substantial structural elements
made of composite polymers. One of these, poly(para-phenvlene terephthalamide), has a tensile strength slightly hight this polymkr really scores is kr than that of steel. ~ uwhere in applications where the strength-to-weight ratio matters a lot, as it does in airplanes. Even with its cumbersome name, this polymer has a strength-to-weight ratio six-fold higher than steel! T o appreciate this advantage, you should know that a 1-pound reduction in the structural weight of an airnlane reduces its take-off weieht hv 10 nonnds (countina the fuel to lift the pound and t h i fuei to lift the extra fuelL No wonder this oolvmer. . . under the trade name Kevlae, is used to build tail sections for the biggest airliners. Oh, and bullet-proof vests, too. So what about this all-plastic automobile? Of course, weight reduction is the name of the game in trying to build fuei:efficient cars. Already there are Hutomobile driveshafts made of polymers strengthened with stiff fibers, and similar compositesare used f& leaf springs (oops, there goes the inner-spring mattress!). Right now, U S . cars contain about 500 pounds of plastics if you count, as well, the rubber and paint and sealants and lubricants and upholstery. But what about the engine and the electrical system? What will we do about these in this allegedly all-polymer car? Gee. I'm glad vou asked.. . .
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These short vigenenes are taken from "Opportunities in Chemistry", Copyright 1985 by the National Academy of Sciences and reproduced with its permission. This comprehensive report on future directions and goals for chemical research contains much information both on chemistry and manpower and education that is of use to the teacher; these vignenes are being reproduced because of their obvious wide utility in the classroom. me full report can be purchased for $28.50 clothbound and 518.50 paperbound from: National Academy Press. 2101 Constitution Avenue. NW, Washington. DC 20418. A quantity discount of 15% for 5-24 copiesand 25% for 25-499 copies is available; all orders must be prepaid.
Volume 63
Number 9
September I986
743
