ABS: Al Balding golf clubs to drain pipe
As a boy, my father once gave me an old golf club, an Al Balding signature driver as I recall. The sticker declared, proudly, that the head of that awesome weapon was made of a wonder material called ...
March 1, 2003 by Jim Anderton,technical editor
As a boy, my father once gave me an old golf club, an Al Balding signature driver as I recall. The sticker declared, proudly, that the head of that awesome weapon was made of a wonder material called “Cycolac”. Today, that’s one of GE’s trademarks for a material we know as ABS. It’s a good thing that the term rolls off the tongue easily, because its real name, Acrylonitrile-Butadiene-Styrene, is not only awkward, but suggests that this combination of three polymers, (a terpolymer) is complex, difficult to make and expensive. The first two are true, and the fact that the stuff is cheap enough to make commodity drainpipe is remarkable when you take a deeper look at what ABS is, and how it’s made.
ABS wasn’t invented, or discovered with drama like nylon or Teflon. This resin came about the old fashioned, unromantic way, by grinding it out in the lab. Who invented ABS? It depends how you look at it. In 1946, the Naugatuck Chemical Company introduced a mechanical blend of styrene-acrylonitrile copolymer and nitrile rubber, called ABS Type A. ABS as we know it today really developed in 1950 in the labs of U.S. Rubber, Standard Oil and B.F. Goodrich, by grafting butadiene rubber onto a styrene and acrylonitrile backbone. There was simultaneous development by Rohm & Haas and Borg Warner, with Union Carbide, Monsanto and others developing new methods of polymerizing ABS into the mid-sixties. Development is still going on at many firms, including BASF and GE.
The actual polymerization process is fabulously complex, and barely understandable to non “lab rats” but its useful properties, namely that the stuff is tough, cheap, easy to process by a variety of methods and can be colored, come from the synergy of the three main components. It’s a huge oversimplification, but one way to think about it is that acrylonitrile gives temperature and chemical resistance, butadiene offers toughness, and styrene makes it cheap and easy to process. The relative proportions of the three components vary by grade (and added modifiers), so there’s not really any one “ABS” resin. A typical ratio could be 20-30% acrylonitrile, 20-30% butadiene and 40-60% styrene. Commercial ABS resins have added chemistry to beef up the two primary weaknesses of “pure” ABS: poor heat resistance and weatherability.
What makes it so tough? The toughness of ABS is, for my money at least, its most interesting property. If you pull back from the atomic level and look at the whole polymer chain, ABS doesn’t have a simple “bowl of spaghetti” conformation, but instead looks like the branches of a tree, with small sub-branches running away from each length. And that’s what makes ABS tough, because the branches don’t have the same composition as the main line; they’re butadiene rich. Another term for butadiene is “synthetic rubber”, so in effect, ABS has “domains” rich in flexible rubber surrounded by more rigid styrene-acrylonitrile regions. The softer rubbery regions relieve local stresses under impact, preventing, for a while at least, the microscopic crack formation that leads to what engineers call the “critical Griffith crack length”. That’s the crack that breaks ships in two and causes airplanes to fall out of the sky, but that’s also another story. Does all this chemistry work? Judging by what I put that old Al Balding driver through, I’d say, “Absolutely!”