Plastics, Then and Now

I recently heard a song from the very late 1970s in which plastic was used as a synonym for “phony”. This made me remember how in my early youth, plastic was generally (though not exclusively) used as a cheap replacement for better quality materials. While at the time of this writing (2020) it is possible to find cheap things made of plastic, it is by no means the case that plastic is merely a cheap alternative. Often, these days, plastics are a superior alternative. PeX pipes are better and longer-lasting than copper pipes. Plastic pipes are strongly preferred to metal pipes for gas lines buried beneath the ground. I’ve got more than a few glass-reinforced nylon gardening tools and prefer them to metal ones. What is commonly called “carbon fiber” is commonly an epoxy plastic reinforced with carbon fibers, and it may be the pre-eminent high-tech material of our day.

It’s interesting to trace the factors which went into plastics becoming frequently superior materials, because it wasn’t just one thing. The introduction of new plastics, such as more advanced epoxies, clear polycarbonates (possibly better know as Lexan), and PeX had a significant impact. They enabled all sorts of new uses for plastics that hadn’t been possible before, and in some cases enabled new sorts of things. Bulletproof glass, for example, is frequently made as a laminate of glass and polycarbonate, the glass giving hardness and the plastic shatter-resistance. That’s very hard to do, in an optically clear way, without plastics.

Another advance in plastics was the development of economical composite plastics. The most famous composite is, of course, fiberglass, though not far behind it is carbon fiber. Another great one that’s been in common use for 10-20 years now is glass-reinforced nylon. Almost as strong as low-grade steel, it is far more rigid and doesn’t rust—it’s great for gardening tools. More generally, composite materials have made for all sorts of things both strong and light. Ladders, camera tripods, bicycles, shovels—anything where one wants weight and strength, it is usually the case that the cheap one uses metal and the good one uses composite plastics. (To be fair, there are some very advanced aluminum alloys, these days, though.)

Another improvement to plastics was simple experience with the making of things out of plastic. The making of things out of plastic is as much an art as a science. The exact temperatures used in injection-molding plastics has an enormous impact on the quality of the resulting part. In the 1970s and 1980s, widespread injection molding of plastics was near its infancy. Worse, since all it was fit for was making the cheapest stuff possible, there was not much money or incentive to make the stuff better. Eventually, however, people learned how to do it. How to design stuff made of injection-molded plastics was another area of improvement, with the right thicknesses, reinforcements, etc. being learned through experience as well.

To my mind the most interesting advancement in plastics, however, has been learning how to make them in ways that go beyond the chemical formula. A good example of this is how polyester went from being an awful but cheap replacement for silk in the 1970s that felt akin to wearing a garbage bag to a vastly superior fabric for athletic clothes. These days, if you’re going to do something that will make you sweat, you will be far more comfortable in a wicking fabric, which are mostly made of polyester. The trick is that when making the polyester strands, instead of making them thick, so that one is almost making the cloth out of fishing line, one makes the plastic strands incredibly thin. These are then spun together much like natural fibers, and produce a fabric which is light weight, breathes well, and tends to pull moisture away from the body and allow it to evaporate on the surface. On the flip side, making polyester in very thick sheets has created its use for things like unbreakable drinking glasses. Admittedly more prone to scratching than glass is, they never shatter when you drop them and they are much better insulators, helping to keep the drink at whatever temperature it started at.

Probably the best example, however, is Ultra High Molecular Weight Polyethylene, sometimes sold under the brands Dyneema or Spectra. As a super-quick background, if you don’t know it, plastics are polymers, which means that they are a chain of simpler molecules known as monomers. These monomers are frequently liquids. The way plastics are synthesized is from a monomer stock, with a chemical reaction catalyzed by a catalyst that combines the monomers into chains, which form solids. Polyethylene comes in varieties, based on how many monomers are in the (typical) polymer chain. Low density polyethylene has a few hundred, and they tend to be in branched chains that don’t stick together well. This is the sort of plastic one finds commonly in grocery store bags. High density polyethylene has (typically) 700-1800 monomers in a polymer molecule, and arranged in much straighter lines, which stick together better. This is the plastic one finds in things like soda bottles. Ultra high molecular weight polyethylene has anywhere from 100,000 to 250,000 monomers in a polymer molecule. It has greater tensile strength than steel (by weight), similar abrasion resistance, similar friction to Teflon, and is highly chemically resistant to corrosion from acids and alkalies. It’s truly amazing stuff. And what’s really interesting is that (one of the more common forms) is made with a metal spinneret, in a matter not entirely unlike the way a spider spins its silk from its spinnerets.

In the early and mid 1900s, chemistry got most of the glory when it came to advances in technology, bringing us wonderful new materials. In the later half of that century, it turned out that chemical formulae were only a small part of the story. How you put things together is at least as important as what you put together. It’s an interesting lesson, not in the least because metals were often seen as so superior to biological materials, but it turns out that our best materials are often made by imitating biological materials.

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