Understanding Plastics for Humans, Installment 2: What Are Polymers?

Buoy reusable food container – 32oz / 0.95L Lid

In installment one, here, we looked at how the processes of life and the characteristics of geology work together to produce petroleum, pictured below.

Petroleum / Oil

To make chemicals, refineries break that big petroleum molecule down to more manageable building blocks. Two of the most important building blocks for plastics are Ethane and Propane. Ethane has two carbons and the rest of the slots on the carbons are taken up by hydrogens. Propane is the same but has three carbons.

Ethane and Propane

To make Polyethylene, either high density, the one Buoy uses, or low density, the kind they use to make bike bottles, you crack ethane into ethylene. Ethane has three hydrogens per carbon and only a single bond in between the carbons and Ethylene has only two hydrogens per carbon and a double bond between the carbons.

Ethane to Ethylene to PolyEthylene

When reacted in the presence of a polymerizing catalyst, one of those double bonds on the ethylene swings over and grabs a carbon from another ethylene, which gives its spare double bond to another ethylene and on and on and that’s what a polymer is. The difference between high density polyethylene and low density polyethylene is that they put branches into the LDPE so that it can’t lay against the next molecule like a railroad tie but forces all kinds of space between the strands. This makes it flexible without additives, and that “without additives” part is important later.

#3 plastic is Polyvinyl Chloride. The polymer is made from Vinyl Chloride, which you can see looks just like polyethylene except that one of the Hydrogens is a Chlorine.

Vinyl Chloride becomes PolyVinyl Chloride (PVC)

Organic systems have no way of taking that Chlorine off, so PVC is super-durable and used in many harsh environments. The source chemical, which is a gas, Vinyl Chloride, is what spilled in that Ohio train wreck in 2022. Persistent exposure to Vinyl Chloride, as among some workers and those folks near the train wreck if the cleanup isn’t good, is liver cancer because the liver metabolizes Vinyl Chloride and if it has to work too hard to get rid of it, the liver breaks. PVC is used to make records, pipes for pools and water, sexy pants if you use an additive that makes it soft. And remember that last one because it comes up later.

Polypropylene is the three-carbon version of Polyethylene.

Propane is cracked to get Propylene.

You crack Propane to make Propylene, which has a double bond between two of the carbons. You start stringing those together and you get a straight, long-chain polymer, just like Polyethylene, just there’s this group sticking off every two carbons, so it’s typically not as hard as Polyethylene because it can’t lay together as densely.

PET or Polyester (#1 plastic) is made by forming a polymer with Ethylene Glycol, which is antifreeze, and Terephthalic Acid.

Ethylene Glycol plus Terephthalic Acid makes Polyester (PET)

The result is a very strong chain that is used in clothes mainly but also most disposable water bottles, the lining of Tetra Pak containers and many other applications.

Finally, there’s number 6, Polystyrene, which is a polymer made of chaining together styrene. This is what foam, like egg containers, are made from.

Styrene chained together to make PolyStyrene

But what about #7. The number 7 is the most discouraging part of the lie about recycling that we’ve been sold: #7 just means “other” which means that it can be any of the hundreds of plastics that are not 1 through 6, which means it can’t really be recycled, unless you’re making a park bench or a plastic brick, but even then… As for the practical recycling of the other numbers: In the US, only 1 and 2 are regularly recycled from curbside collection bins. That’s PET and HDPE, the latter being the one Buoy uses. Number 5, Polypropylene could be recycled and is recycled in Europe but not frequently in the US. PolyVinyl Chloride is not recycled and neither is PolyStyrene, so fair to ask why they have that little recycling symbol around them at all and that would be the con game that was played on us by those who benefit from us unconsciously consuming disposable plastics.

© Buoy, 2023

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