How much is in the cup?


One of my favorite proverbs goes: The optimist says the cup is half full, the pessimist says half empty, but the engineer asks, "How much is in the cup?"

I just read about a recent confirmation that "liquid styrene" may be a carcinogen. Not surprised, but not worried either.  What worries me more is that people will add "poly-" to this material and see this news as reinforcement of their fear and loathing of polystyrene, especially foam polystyrene food/beverage packaging.

Coffee cup
Image courtesy Apple's Eyes Studio/
freedigitalphotos.net.

Styrene is the monomer for polystyrene, of course, and as such is a building block for this plastic, just as vinyl chloride is a building block for PVC, and BPA and phosgene are building blocks for polycarbonate. There should be no monomer left when polystyrene is made, likewise for PVC and PC. But people still confuse building blocks with additives, and think that the plastics have these offensive materials "in them" as ingredients.

And this is where the engineer comes in. Numbers matter. They also did to Paracelsus, the Renaissance physician who is known for saying "The dose makes the poison." Substances have to get onto or into the body in significant amounts to be harmful. It is prudent and efficient manufacturing to get as much monomer as possible converted to polymer, especially in the case of styrene which would add an undesirable aroma to any package if it were still there in a high enough concentration. 

Do EPS containers have any styrene "in them?" In theory, yes, as we can never get the last molecule to react. Is this residual enough to matter? That, indeed, is the question, not whether there is any styrene in it. The answers must come from toxicologists and similar scientists, not from the plastophobic public nor the politicians who want to give them what they say they want.

We've been there before. In the 1970s it was discovered that vinyl chloride was a carcinogen, and PVC makers scrambled to purify their processes so that minimal monomer remained. They did so to the satisfaction of the authorities, and the issue subsided and has remained there ever since. The worries about PVC today center on the red-herring dioxin issue, as well as phthalate plasticizers and some heavy-metal stabilizers and pigments, for which there are plenty of alternatives.

Lesson to PS and PC makers: set some standards for residual monomer and stick to them. And tell the plastophobes that these substances are NOT ingredients and we are keeping their levels well below danger points. There is plenty of precedent; the danger of taking too much Tylenol, for example, is well known.

But what troubles me the most is how ready people are to believe those who twist or even ignore science to attack plastics. Where does this fear come from? I have been proposing that we study the roots of the public antiplastic mindset for a long time, but no-one comes forth to do it. I'll say it again here; until we learn the causes of this behavior, we won't be able to properly deal with it.

Allan Griff is a Plastics Engineer who does public and private training seminars as well as general consulting and webinars in his specialized areas of extrusion and the environment. He lives in California and can be reached at [email protected], website www.griffex.com 

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