“It’s made of plastic” is a common put-down. Marketers selling\nhigher-end bits made of plastic (like gun parts) try to evade the\nstigma by calling it “polymer”, but that’s just a stupid\neuphemism: every plastic is a polymer, though not every polymer\nis a plastic. The word “polymer” says nothing to indicate that\nthis might be a superior sort of plastic. Yet there are superior\nsorts; plastics vary widely in their characters. Some analogies\nbetween plastic and human characters:
\nPolyethylene, polypropylene: Snow White (simple, pure, weak).\nThese are the cheapest and most common plastics, and are made of\njust hydrogen and carbon atoms. Ethylene (two carbons and four\nhydrogens) is polymerized to make polyethylene, and the quantity\nof ethylene made each year is measured in cubic miles. They can\nof course have pigments added to them to give them color, but are\ncommonly used in uncolored, nearly-pure form. Chemically they\nare unreactive, which makes them good for containers of all\nsorts; they are even used for chemistry beakers. That same\nunreactivity makes them very hard to glue, and means they don’t\ndeteriorate with time. Leave them out in sunlight, though, and\nthe UV quickly weakens them to where they crack easily.
\nNylon: Arnold Schwartzenegger (strongman). Plastic nuts and\nbolts, which need to be strong, are usually nylon, as is\nmonofilament fishing line and womens’ hosiery (delicate, but\nstill strong for its weight). Nylon adds nitrogen to the list of\natoms it contains; it’s chemically known as a “polyamide”, a\nclass which also includes proteins.
\nNylon with 30% glass fiber reinforcement: Arnold Schwartzenegger\non steroids. It’s as strong as cast aluminum (though extruded\naluminum can be much stronger). When guns are made of plastic,\nthis is usually the plastic they use; likewise for the plastic\nhousings of electric drills and other power tools.
\nPolycarbonate: Achilles (warrior with a fatal weakness).\nPolycarbonate is what they make bulletproof windows from, and\nsafety glasses, and the transparent fronts of car headlights. Its\nweakness is chemical attack: a splash of acetone, and it\ninstantly “crazes”, a network of fine cracks appearing across its\nsurface as built-in stresses are relieved. (If the part has any\nbuilt-in stresses, that is; molded parts probably do, but flat\nsheets might not.) Polycarbonate is often protected by a surface\ncoat to block chemical attacks. It’s the main plastic that gives\noff the notorious bisphenol A (BPA), which is probably not so bad\nas it’s reputed to be. But it still doesn’t make sense for food\ncontainers to be made from polycarbonate, since they don’t need\nto be bulletproof and polycarbonate is pricey.
\nPolyvinyl chloride (PVC): Dr. Jekyll and Mr. Hyde (a character\nwho varies wildly depending on which drugs he takes, with more\nthan a bit of evil in him). PVC is normally rigid, and is used\nin that form for house siding and sewage pipes, but can be pumped\nfull of plasticizer to make it flexible; in that state it’s used\nfor inflatable boats, shower curtains, imitation leather, and\neven sex toys. In pure form it’s not a stable chemical; its\nstaying good depends on added “stabilizers”, which themselves can\nbe somewhat evil: they often contain the toxic element lead,\nwhich normally is locked in the plastic but is unleashed when the\nplastic deteriorates or is burned. Burning it also gives off a\nvariety of toxic chlorine-containing substances. The\nplasticizer, if used, evaporates away over years (in cars,\nlanding on the inside of the windshield and producing an annoying\nhaze which has to be wiped away), and eventually the remaining\nplastic gets brittle and cracks. The plasticizer is often a\nphthalate, another notorious class of chemical and also probably\nnot as bad as popular repute would have it, but still not good\nfor you and a pain to clean up. (People commonly regard soft\nplastics in cars as good and hard ones as bad and cheap, but I\ndon’t think they’ve made the connection between having soft\nplastics around and needing to clean off the inside of the\nwindshield, or for that matter having phthalates in the air they\nbreathe when getting into a car on a hot day.)
\nPolyurethane: an android from the movie Blade Runner (strong,\nversatile, dangerous, doomed). Polyurethane can be made either\nhard or flexible, with the flexible varieties used to make\nrubbers and foams, but polyurethanes have a tendency to decide\n“now it’s time to die”, losing almost all of their strength,\nwith foams crumbling or turning to goo and rubber parts cracking.\nThey are made using isocyanates, in a reaction which could be\nthought of as Nazi chemistry since it was in fact invented in\nGermany during that era and since isocyanates are quite toxic.\n(That’s just a resemblance, of course; in reality Nazi ideology\nhad nothing to do with chemistry.) Though toxic (methyl\nisocyanate killed thousands of people in the Bhopal disaster),\nisocyanates are not cyanides (which are even worse), and in\nfinished polyurethane there are only traces of isocyanates left,\nthough they might be the cause of the annoying smell that new\npolyurethane foam often has. But burning polyurethane does\nproduce some hydrogen cyanide, and polyurethane foam burns\nunusually vigorously, unless it’s been treated with flame\nretardants, which thus have been mandated by law in some places\nbut which themselves might be a health issue.
\nBakelite, aka phenol-formaldehyde: well, nobody really comes to\nmind as a corresponding character, but it’s rigid, brittle, and\ncan take a lot of heat. Bakelite was one of the first plastics,\nand is thermosetting: it doesn’t melt but rather has to be formed\nfrom its ingredients (phenol and formaldehyde) into its finished\nshape (requiring a mold, heat, and pressure). With it we’re back\nto things that contain only the safer elements (carbon, hydrogen,\nand in this case oxygen). Phenol and formaldeyhde are each\nnasty, but their nastiness is consumed when they react together.\nBakelite’s brittleness can be mitigated by using appropriate\nfillers, particularly fibrous ones. Its heat resistance is such\nthat, mixed with high-temperature fibers, it is used for heat\nshields for reentry from space (which burn away but do so slowly\nenough that they don’t burn through). It also sees a lot of use\nin things like electrical circuit breakers, where other plastics\nmight melt into a blob and let their metal parts short-circuit.
\nPolystyrene: Joe Sixpack (common, cheap, weak, nasty). It’s not\nheat-resistant, not chemical-resistant (it dissolves in a wide\nvariety of solvents), and is brittle. But it can easily be blown\ninto a foam (styrofoam), which because of the bubbles is a good\ninsulator; being a foam also mitigates its brittleness. When\nheated it de-polymerizes and gives off styrene, which has a\ndistinctive acrid smell. It can be improved into “ABS” by adding\nlarge proportions of acrylonitrile and butadiene into the\npolymerization process; ABS has the same distinctive smell when\nheated but is considerably tougher, making it suitable for a wide\nvariety of consumer products (though it’s still much weaker than\nnylon). Legos are ABS. If there’s a plastic which really\ndeserves the putdown “it’s made of plastic”, it’s ABS: it’s\ncommon enough to be the sort of thing people think of when they\nhear “plastic”, and is generally mediocre. But as human\nanalogies go it’s a step above Joe Sixpack; call it Joe Blow.
\nTeflon: Queen Victoria. “Nobility” in chemistry means a lack of\nreactivity, an immunity to chemical attack; “noble metals” are\nnoble not because they’re expensive, but because they snootily\nlook down their noses at other chemicals and refuse to have\nrelationships with them. In plastics it’s harder to get nobler\nthan teflon (polytetrafluoroethylene; PTFE), which differs from\npolyethylene by having all its hydrogens replaced with fluorines,\nwhich are much more difficult to dislodge. Fluorine chemistry\nbeing a difficult and dangerous sort of chemistry, PTFE doesn’t\ncome cheap. It’s used to coat nonstick pans, where its\nnonreactivity translates into things not sticking to it. As best\nI can tell (though information on this is scarce), even the newer\n“ceramic” nonstick coatings often have an imperceptibly-thin\nlayer of a molecule with a highly-fluorinated tail that resembles\nPTFE; the ceramic gets the publicity but the highly-fluorinated\nchemical does the work of making the coating nonstick… until it\nwears off, which because of the thinness of the layer happens\nmore quickly than it does with the older sort of pan which has a\nvisible layer of PTFE. (Modern nonstick pans are often regarded\nwith suspicion; but the old mainstay in that department, cast\niron, gets its nonstickness by being “seasoned”: coated with a\nlayer of burnt, polymerized oil, no doubt containing many\ncarcinogens.)
\nThose are just some highlights of a complicated subject; I\nhaven’t even mentioned some major plastics, and there are a host\nof minor ones, as well as innumerable subvarieties of the major\nones. (Take polyethylene, normally weak, react it until the\nmolecular chains are long, then stretch it until they are\naligned, and you get an extremely strong fiber, suitable for\nhigh-strength ropes or bulletproof vests: not Snow White but\nWonder Woman.) With such a varied cast of characters, it’s a\npity that they all get lumped together as “plastic” in common\nusage. I suppose it’s somewhat inevitable, since you can’t just\nlook at a piece of plastic and tell what sort it is. But more\npublic awareness of the differences would be nice.
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