Canadian Plastics

The Sweet Smell of PU

I once had a great idea. The plan was to develop a new way of manufacturing automotive suspension bushings and anti-vibration mounts with variable elasticity to allow the mount to be custom-tuned to t...

June 1, 2003   By Jim Anderton, technical editor



I once had a great idea. The plan was to develop a new way of manufacturing automotive suspension bushings and anti-vibration mounts with variable elasticity to allow the mount to be custom-tuned to the resonant frequency of the machine to which it was mounted. Like many in the same situation, I turned to a two-part polyurethane casting resin, which I hand poured into molds.

At the time, I had no idea how sophisticated that sticky goo was, but later in university I learned two interesting things about PU. One was the complexity of the chemistry, in which an isocyanate reacts with a kind of “super alcohol” called a polyol. Most people don’t see very many isocyanates lying around the kitchen, but polyols are everywhere, mainly as the glycol that forms the basis of automotive antifreeze. Isocyanates contain, you guessed it, cyanide. Actually, they’re a brew of cyano compounds, and when venting the fumes from the setting process you really need to think about keeping them away from people. My single car garage didn’t have the Good Housekeeping Seal of Approval. Consequently, my sinuses got a real workout.

Polyurethanes can be tricky to master and they’re also a lot older than many people realize. They were first developed in 1937 by a team led by Otto Bayer at the Leverkusen labs of industrial giant I.G. Farbenindustrie, and by 1952 the firm announced the development of thermoplastic linear polyurethanes (TPUs), opening the door to injection molding and the rapid expansion of new applications. The prolific Bayer was involved in that discovery, too, and by the early ’60s Bayer-Mobay (later Miles Inc.) and BFGoodrich had extrusion and injection grades under the trade names Texin and Estane.

What the incredibly varied chemistry of PU gives you is the ability to mold parts with a wide range of elasticity, from rubber ball soft to rock hard. Applications include insulating foams, automotive and industrial seating, forklift tires, seals and gaskets, coatings, adhesives, ski boots, as well as the application I pay the most street level attention to, spandex. Useful stuff.

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If you’re planning to mess around with polyurethane casting resins in your garage, however, take it from me: read the Material Safety Data Sheet, open the door and definitely wear gloves. Bring your wallet, because at something like fifty or sixty bucks per litre of mixed compound, casting isn’t the way to a mass-production fortune. And my brilliant idea for polyurethane bushings? As yet, I can’t afford a 100-ton press and multi-cavity mold, but when I win the 6/49 lottery….


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