More and more, laundry detergent is coming in “pods” – single doses enclosed in a plastic(?) skin. They are undoubtedly convenient. No need to measure, just drop one in the washer with your laundry and press start.
But here’s the question – to what extent does the plastic coating dissolve? Does it go all the way to component molecules? Or does it become a kajillion microplastics which are now infesting my laundry? THAT does not seem to be worth the convenience.
I don’t use the pods myself but I thought they were like pills or medicine capusles and dissolved in a similar way.
Some times the pod does not even completely disintegrate, and there’s a blob of goop left in the laundry. The soluble film is commonly some compound like Polyvinyl Alcohol (PVA) that is nominally biodegradable though we know that alone is no guarantee of how thoroughly or quickly it degrades.
The coating is usually polyvinyl alcohol. It does supposedly dissolve completely, so doesn’t produce microplastics, although there is controversy about whether the dissolved PVA is completely safe. However, the risk is to the environmental ecosystem, not to the individual wearer of the washed clothing.
The interesting thing about polyvinyl alcohol is that, unlike most polymers, the individual “mer” doesn’t exist. Polyethylene is made by conjoining lots of ethylene molecules, but you don’t make PVA by linking “vinyl alcohol” molecules – the only exist in polymerized form. (When you do that classroom experiment of making “slime” from PVA and borax, you’re not polymerizing the alcohol, you’re just cross-linking existing polymer chains. Likewise if you make Slime from polyvinyl acetate – dilute Elmer’s Glue-All with borax for the cross-linking)
PVA films thus ought to break down to components smaller than an alcohol, which is pretty small, and couldn’t rightly be called a “microplastic”.
Of course, nothing in this world works perfectly. I haven’t read the cautionary articles cited above yet.
Not to pick a nit, but FYI, the word you seek is monomer.
This is all interesting. I’ve never heard of polyvinyl alcohol and never did that classroom experiment.
But I take it that microplastics are not a concern in this case. Thanks for the replies.
You probably have, but just don’t realize it. Pretty much every white glue (Elmer’s, Aleene’s, Mono Multi) or yellow wood glue (Titebond, Elmer’s Wood Glue, Gorilla Wood Glue) are at their hearts, polyvinyl acetate (PVA) glues.
Anyway, a few articles note that PVA is typically fully soluble in water, and the bugs in use at wastewater treatment plants happily eat it.
OK, which is it then-
polyvinyl alcohol [CH2CH(OH)]n
or
polyvinyl acetate (C4H6O2)n ?
While both may be referred to as PVA, they aren’t the same!
In the context of adhesives, polyvinyl acetate glues apparently are sometimes made with polyvinyl alcohol:
It is used in papermaking, textile warp sizing, as a thickener and emulsion stabilizer in polyvinyl acetate (PVAc) adhesive formulations…
But it’s true that the actual adhesive isn’t polyvinyl alcohol.
I think I got my PVAs mixed up.
Polyvinyl alcohol is the stuff sold by chemistry stores for “slime” projects. You cabn cross-link the PVA chains with borax. It’s clear, but is often tinted green for better resemblance to “slime”, in which case it’s clear green, looking like line jello. (When I did this experiment with kids years ago, I wore a button that read “don’t eat the experiment”. You actually can eat it without harm, but I don’t recommend it.) This is probably the stuff laundry pods are made out of, with enough cross-linking that it has a little more body.
Polyvinyl acetate is the stuff sed in glues, and it’s sort of translucent white. You can use it for “slime” experiments, too, but it won’t be a nice transparent material. It’s a lot easier to get hold of than polyvinyl alcohol, though.I don’t think this is used for laundry pods.
Incidentally, there are plenty of other water-soluble polymers you can use for applications like this. Some of them are great at absorbing water and holding it in a “jelled” form. They use it in diapers and sanitary pads and the like. Polyoxyethylene (AKA Polyethylene Glycol) is one of these. Interestingly, Polyoxymethylene isn’t water-soluble at all. It’s polymerized formaldehyde, and used to be the basis for Air-Wick. short chains of the polymerized formaldehyde would spontaneously depolymerize and evaporate, releasing perfumes embedded in the suff. The problem is that formaldehyde is a group 1 carcinogen, so that don’t make room deodorizers from it anymore. But they learned that if they made the polymer chains longer and stabilized the ends you got a tough, water-proof plastic that was easy to machine. And make K’nex blocks out of.
I specifically recall my high school chem teacher warning us to not eat the result of an ester reaction. Half the class got peppermint, half banana. This wise man went on to correctly predict many of us would nevertheless eat some of the experiment.
I don’t use laundry pods, but I do use pods in the dishwasher. You don’t eat your laundry, so I’d think the dishwasher pods would be of greater concern, but I find that the pods always dissolve completely and the product (Quantum Ultimate) cleans really well, so I don’t worry about it. Not a scientific answer, but I never considered it a problem or a risk.
Doesn’t this really depend on the degradation conditions, like in @markn_1’s cite? PVA may be readily biodegradable under ideal lab conditions, but the real world is rarely that way:
But in recent years some researchers have questioned the assumptions in these tests. For example, Charles Rolsky and Varun Kelkar of Arizona State University presented on the topic at the American Chemical Society Spring 2021 meeting and will speak again at ACS Fall 2022 in Chicago (Int. J. Environ. Res. Public Health 2021, DOI: 10.3390/ijerph18116027).
Rolsky and Kelkar, as well as other critics, point out that although the microbes in most septic systems and municipal wastewater treatment plants can metabolize dissolved PVA, water usually flows through such systems in a matter of hours, not weeks. They say that aging sewage pipes and other infrastructure problems in many areas mean a shocking amount of wastewater goes into natural waterways untreated. The prevalence of PVA-eating microbes in rivers, lakes, and oceans is less well characterized than it is in wastewater plants, they add.
Ramani Narayan, who studies bioplastics and polymer biodegradation at Michigan State University, says much of the discrepancy and confusion has to do with how well established and acclimated the PVA-eating microbes are in the test environment. For instance, when Narayan and his students used sewage sludge microbes accustomed to munching PVA, over 88% of the polymer’s carbon converted to CO2 within 70 days. In contrast, nonacclimated sludge broke down only about 30% of pod-grade PVA.
So it’s probably highly variable from area to area, and you probably have to sample many wastewater plants & exit points around the world, at different times of the day & year, to properly understand how much of this stuff is ending up intact into the oceans. It’s like eutrophication… that it can be managed well and mitigated doesn’t mean that it will be.
One study suggests up to 75% of the pod residue enters waterways without sufficient treatment, but its methodology isn’t perfect, depending on surveys & models rather than actual field samples. Not sure if anyone has actually attempted a large-scale sampling of this stuff in the wild.
That said, though, there are many sources of known, verified, all but guaranteed non-biodegradable microplastics pollution that we just shrug at and use regardless. How many people wear synthetic plastic clothing without even knowing it? Every time you wash or dry them, microplastics run into the oceans.
Pods seem like a very distant, much lesser, evil…
I’m not really even sure how harmful microplastics (of any sort) are to begin with. There’s still a lot of uncertainty around them, at least the last time I checked (a few years ago). Has there been substantial evidence of harm since then?