An essay comparing commodity and engineering plastics to literary character types—why “polymer” is often marketing spin, and how chemistry shapes toughness, clarity, heat tolerance, and reputation.

The characters of plastics

“It’s made of plastic” is a common put-down. Marketers selling higher-end bits made of plastic (like gun parts) try to evade the stigma by calling it “polymer”, but that’s just a stupid euphemism: every plastic is a polymer, though not every polymer is a plastic. The word “polymer” says nothing to indicate that this might be a superior sort of plastic. Yet there are superior sorts; plastics vary widely in their characters. Some analogies between plastic and human characters:

Polyethylene, polypropylene: Snow White (simple, pure, weak). These are the cheapest and most common plastics, and are made of just hydrogen and carbon atoms. Ethylene (two carbons and four hydrogens) is polymerized to make polyethylene, and the quantity of ethylene made each year is measured in cubic miles. They can of course have pigments added to them to give them color, but are commonly used in uncolored, nearly-pure form. Chemically they are unreactive, which makes them good for containers of all sorts; they are even used for chemistry beakers. That same unreactivity makes them very hard to glue, and means they don’t deteriorate with time. Leave them out in sunlight, though, and the UV quickly weakens them to where they crack easily.

Nylon: Arnold Schwartzenegger (strongman). Plastic nuts and bolts, which need to be strong, are usually nylon, as is monofilament fishing line and womens’ hosiery (delicate, but still strong for its weight). Nylon adds nitrogen to the list of atoms it contains; it’s chemically known as a “polyamide”, a class which also includes proteins.

Nylon with 30% glass fiber reinforcement: Arnold Schwartzenegger on steroids. It’s as strong as cast aluminum (though extruded aluminum can be much stronger). When guns are made of plastic, this is usually the plastic they use; likewise for the plastic housings of electric drills and other power tools.

Polycarbonate: Achilles (warrior with a fatal weakness). Polycarbonate is what they make bulletproof windows from, and safety glasses, and the transparent fronts of car headlights. Its weakness is chemical attack: a splash of acetone, and it instantly “crazes”, a network of fine cracks appearing across its surface as built-in stresses are relieved. (If the part has any built-in stresses, that is; molded parts probably do, but flat sheets might not.) Polycarbonate is often protected by a surface coat to block chemical attacks. It’s the main plastic that gives off the notorious bisphenol A (BPA), which is probably not so bad as it’s reputed to be. But it still doesn’t make sense for food containers to be made from polycarbonate, since they don’t need to be bulletproof and polycarbonate is pricey.

Polyvinyl chloride (PVC): Dr. Jekyll and Mr. Hyde (a character who varies wildly depending on which drugs he takes, with more than a bit of evil in him). PVC is normally rigid, and is used in that form for house siding and sewage pipes, but can be pumped full of plasticizer to make it flexible; in that state it’s used for inflatable boats, shower curtains, imitation leather, and even sex toys. In pure form it’s not a stable chemical; its staying good depends on added “stabilizers”, which themselves can be somewhat evil: they often contain the toxic element lead, which normally is locked in the plastic but is unleashed when the plastic deteriorates or is burned. Burning it also gives off a variety of toxic chlorine-containing substances. The plasticizer, if used, evaporates away over years (in cars, landing on the inside of the windshield and producing an annoying haze which has to be wiped away), and eventually the remaining plastic gets brittle and cracks. The plasticizer is often a phthalate, another notorious class of chemical and also probably not as bad as popular repute would have it, but still not good for you and a pain to clean up. (People commonly regard soft plastics in cars as good and hard ones as bad and cheap, but I don’t think they’ve made the connection between having soft plastics around and needing to clean off the inside of the windshield, or for that matter having phthalates in the air they breathe when getting into a car on a hot day.)

Polyurethane: an android from the movie Blade Runner (strong, versatile, dangerous, doomed). Polyurethane can be made either hard or flexible, with the flexible varieties used to make rubbers and foams, but polyurethanes have a tendency to decide “now it’s time to die”, losing almost all of their strength, with foams crumbling or turning to goo and rubber parts cracking. They are made using isocyanates, in a reaction which could be thought of as Nazi chemistry since it was in fact invented in Germany during that era and since isocyanates are quite toxic. (That’s just a resemblance, of course; in reality Nazi ideology had nothing to do with chemistry.) Though toxic (methyl isocyanate killed thousands of people in the Bhopal disaster), isocyanates are not cyanides (which are even worse), and in finished polyurethane there are only traces of isocyanates left, though they might be the cause of the annoying smell that new polyurethane foam often has. But burning polyurethane does produce some hydrogen cyanide, and polyurethane foam burns unusually vigorously, unless it’s been treated with flame retardants, which thus have been mandated by law in some places but which themselves might be a health issue.

Bakelite, aka phenol-formaldehyde: well, nobody really comes to mind as a corresponding character, but it’s rigid, brittle, and can take a lot of heat. Bakelite was one of the first plastics, and is thermosetting: it doesn’t melt but rather has to be formed from its ingredients (phenol and formaldehyde) into its finished shape (requiring a mold, heat, and pressure). With it we’re back to things that contain only the safer elements (carbon, hydrogen, and in this case oxygen). Phenol and formaldeyhde are each nasty, but their nastiness is consumed when they react together. Bakelite’s brittleness can be mitigated by using appropriate fillers, particularly fibrous ones. Its heat resistance is such that, mixed with high-temperature fibers, it is used for heat shields for reentry from space (which burn away but do so slowly enough that they don’t burn through). It also sees a lot of use in things like electrical circuit breakers, where other plastics might melt into a blob and let their metal parts short-circuit.

Polystyrene: Joe Sixpack (common, cheap, weak, nasty). It’s not heat-resistant, not chemical-resistant (it dissolves in a wide variety of solvents), and is brittle. But it can easily be blown into a foam (styrofoam), which because of the bubbles is a good insulator; being a foam also mitigates its brittleness. When heated it de-polymerizes and gives off styrene, which has a distinctive acrid smell. It can be improved into “ABS” by adding large proportions of acrylonitrile and butadiene into the polymerization process; ABS has the same distinctive smell when heated but is considerably tougher, making it suitable for a wide variety of consumer products (though it’s still much weaker than nylon). Legos are ABS. If there’s a plastic which really deserves the putdown “it’s made of plastic”, it’s ABS: it’s common enough to be the sort of thing people think of when they hear “plastic”, and is generally mediocre. But as human analogies go it’s a step above Joe Sixpack; call it Joe Blow.

Teflon: Queen Victoria. “Nobility” in chemistry means a lack of reactivity, an immunity to chemical attack; “noble metals” are noble not because they’re expensive, but because they snootily look down their noses at other chemicals and refuse to have relationships with them. In plastics it’s harder to get nobler than teflon (polytetrafluoroethylene; PTFE), which differs from polyethylene by having all its hydrogens replaced with fluorines, which are much more difficult to dislodge. Fluorine chemistry being a difficult and dangerous sort of chemistry, PTFE doesn’t come cheap. It’s used to coat nonstick pans, where its nonreactivity translates into things not sticking to it. As best I can tell (though information on this is scarce), even the newer “ceramic” nonstick coatings often have an imperceptibly-thin layer of a molecule with a highly-fluorinated tail that resembles PTFE; the ceramic gets the publicity but the highly-fluorinated chemical does the work of making the coating nonstick… until it wears off, which because of the thinness of the layer happens more quickly than it does with the older sort of pan which has a visible layer of PTFE. (Modern nonstick pans are often regarded with suspicion; but the old mainstay in that department, cast iron, gets its nonstickness by being “seasoned”: coated with a layer of burnt, polymerized oil, no doubt containing many carcinogens.)

Those are just some highlights of a complicated subject; I haven’t even mentioned some major plastics, and there are a host of minor ones, as well as innumerable subvarieties of the major ones. (Take polyethylene, normally weak, react it until the molecular chains are long, then stretch it until they are aligned, and you get an extremely strong fiber, suitable for high-strength ropes or bulletproof vests: not Snow White but Wonder Woman.) With such a varied cast of characters, it’s a pity that they all get lumped together as “plastic” in common usage. I suppose it’s somewhat inevitable, since you can’t just look at a piece of plastic and tell what sort it is. But more public awareness of the differences would be nice.

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