Tuesday, May 07, 2013

"Downcycling" of Plastics - It's Time to End the Destructive Namecalling

It’s time that we laid to rest the notion that recycled plastics are “downcycled”.

Downcycling is a recently popularized word use to describe recycling (more accurately, reprocessing) of a material where the new product is “less valuable” than the products from which it is formed. Plastics are often accused of being downcycled. The most commonly given example is that of plastic bags being turned into park benches, but other examples exist too such as water and soda bottles being turned into fleece clothing.

There are 2 problems with this definition. The first is that it places value judgments on products forcing one to decide what is more desirable as a product. Is a park bench really any less desirable than a pallet of plastic bags? Not everyone will agree on these decisions. Considering that in many cases, a single-use disposable plastic is being turned into a durable good, I would think that anti-consumerism sentiment would favor these products, but that doesn't seem to be the case.

There is something a of a factual basis for disliking reprocessing since it is well known that plastics are degraded every time that they are processed [*] – the molecular weight decreases because of the extra thermomechanical cycle. The logic then is that this degradation inherently devalues whatever the plastic is recycled into. If those single-use water bottles become t-shirts, it’s downcycling. If those single-use plastic bags become wood/plastic composite decking, it’s downcycling. If a disposable plastic of any sort ends up in a non-disposable plastic, it’s downcycling.

The problem with this argument is that ALL recycling of all materials (plastic or otherwise) must therefore be considered downcycling. Plastics we’ve already discussed, and most people are not too surprised to learn that paper (which is also based on organic macromolecular molecules) is degraded as it is recycled. Just like the polymer chains degrading plastic, the fibers in paper degrade and so office paper becomes newspaper becomes cardboard becomes tissue paper. But certainly no one suggests that we stop recycling paper because it is degraded. So why is that accusation made against just against plastics?

Metals are commonly thought to be above downcycling. It is widely claimed that aluminum cans become new aluminum cans, but it is a little more complicated than that. The cans contain about 4% organic materials from the label that must be removed and made up for with virgin aluminum. In the melting process, various salts form that need to be removed and made up for with new aluminum. (Take a look at the complicated flow diagram on page 3 of this article and don't tell me recycling cans just means remelting and reforming them). In other words, new cans cannot be made from just recycled cans. It is not a closed loop. The recycled aluminum need to be tinkered with. The same is true with steel. There are endless grades of steel that become mixed together in a recycle stream, and while the final product is steel of some sort, it also needs to be monkeyed with to be usable. So just like recycled paper, the reprocessed metals are not as good as the original material, but no one suggests that we stop recycling them. So why is bias against recycling plastics?

But let’s turn back to our initial example of plastic bags and milkjugs being turned into park benches and how the park benches are just not “valuable”. The strongest argument against these products being less valuable is that many polylumber and wood plastic composites (WPC) are in fact made from virgin resins and not recycled resins. Trex is able to make their WPC from recycled plastic, but others are not. So is a park bench made from recycled plastic less valuable than one made from virgin resin? If you can’t tell the difference, then there isn’t one and this whole distinction of valuable/less valuable goes away. As does the term downcycling.

The same goes for clothing made from PET. While some clothing is made from recycled PET bottles, most PET based clothing is made from virgin resin. How can anyone state that one garment is less valuable than the other?

Does it really make more sense to make durable goods from virgin resins? To drill another oil well for the petroleum needed to make the virgin resin? Should we just landfill all the plastics instead? (or burn them to create electricity such as is done with the garbage here in the Twin Cities)? If not, then it is time to recognize that recycling plastics is a disposal option that should be pursued further. Recycling rates for all materials, not just plastic are unacceptably low, but poo-pooing the recycling of plastics as "downcycling" will do nothing to increase them. The term should be dropped from all usage as it is of no value at all.

[*] There are processing aids that can be used for many plastics to negate or in fact overcome these issues entirely.


Chemjobber said...

Very education -- thanks for writing this, John.

Chemjobber said...

Uh, that's "educational."

Bend said...

Thanks for the post. I would like to ask you to clear something up for a co-worker and me on a tangential topic. As I was reading your discussion of the degradation of cellulose fibers and polymer chains, along with your discussion of waste materials in metals during recycling processes I noticed that a discussion of glass was conspicuously absent. I would think that if properly washed and sorted, glass would be perfectly recycled with little to no loss.
But when I was thinking of glass I thought that like the thermoplastics and cellulose already discussed, glass is a polymer, albeit a covalently adaptable network polymer. I mentioned this to another polymer chemist (a better one than am I) and he said that glass is not a polymer because it’s not organic. I said that PDMS didn’t have an organic backbone and he said that the methyl groups, however, are. So I asked about various polyphosphazines and polysulfur at which point he stopped me and said that we had to draw the line somewhere or just about any solid or liquid could be considered either a polymer or a supramolecule. “Should diamond be considered a polymer?” he asked. I answered then, and answer now affirmatively. How do you see this? Are glass and diamond polymers?

Jasper said...

can the benches etc be recycled? if the process of recycling plastic inevitably degrades the material until it can't be recycled again, would it be an accurate interpretation that recycled plastics lose value, as compared to some other materials that might remain viable indefinitely with some tinkering?