If plastic was made in 1907 how do they know it may take up to 1000 years to decompose?

In: Chemistry

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Simple math.

If it takes 500 years to decompose 50% of a plastic sample, then it takes 1000 years to fully decompose.

If it takes 10 years to decompose 1% of a plastic sample, then it takes 1000 years to fully decompose.

Edit: As many of you have pointed out, yes, the relationship might not exactly be linear. I just gave an example to how we can find the time to decompose without actually waiting that long. It could be exponential, or any other model that can be solved by math. This was just an example so it would be easy for anyone to understand.

Let’s say you see a piece of wood. And a bunch of termites are chewing away at it. Each day, you can measure how much material is being eaten by the termites. You also have information on other, smaller pieces of wood that have been COMPLETELY eaten by termites so you know HOW the termites eat wood (do they eat the same amount each day? Maybe they eat a little bit at first, eat a lot later, and then slow down, or maybe they eat a small amount initially, but gradually eat more, and more each day, etc.).

Using this information, you can mathematically predict when that piece of wood is going to get completely eaten.

It’s the same thing with plastic, except instead of that piece of wood, it’s plastic, instead of termites, it’s the summation of all the natural processes that break down plastic.

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It has been explained below – but it just made me think of an even more absurd example: we have experimental evidence, that the half-life of proton (which is, simply speaking, the typical time it takes for a proton to decay) is at least 1.67×10^34 years, even though that’s 24 orders of magnitude longer than the existence of the Universe, so it’s … pretty damn sure nobody has watched a proton that long! It’s simply because there is a *lot* of protons to watch and particle decay happen randomly, so even if the average time is unfathomably long, if you watch enough protons, one would be almost guaranteed to decay in an accessible time frame if their half-life were “short” enough. (We still do not know whether they decay at all, this is just as close as we come experimental get to saying that they don’t as we can.)

There are different types of plastic, and they all break down eventually. I’d believe the thousand years is a generalization, isn’t it?

I read a comment about a plastic engineer that said that plastic doesn’t take up to 1000 years to decompose. May have been bullshit.

He said something like the stabilizers that help the plastic not break down don’t take up that much to decompose.

You know how when you are downloading/copying/transferring files on your computer, it says how long it’ll take, even though it isn’t completed yet. Calculation is based on how much competed over a short period of time, much like plastic decomposition can be observed in a few years, to determine how long before it’s mostly broken down.

I can explain this like you’re actually five.

You have five pieces of candy, and every minute you eat one. So how long will it take to eat all of them? That’s right, 5 minutes total.

We can do the same for this math problem, we measure how long it took to eat one candy to estimate how long it takes to eat the others without even having to eat them.

There’s a lot of patronizing answers on here but it’s a fair question.

Basically, you assume that a certain plastic decomposes by a physical and chemical process which we understand and can quantify in a mathematical model.

Then you do some algebra using the equations that describe that model and, voila, you have your answer.

Of course this assumes there are no other processes that affect decomposition that aren’t captured in the initial model.

You don’t need to time me over the course of a 100 mile drive to tell if I’m going 100 miles an hour. You can simply measure how long it takes me to go one mile and multiply that by 100.

IRL the vehicle measures how fast the wheels are rotating. Knowing the circumpherence of the wheel allows the vehicle to compute how far you would go at a given speed in an hour. It doesn’t take an hour to calculate that.

Same thing with plastic. You can measure how much it decomposes in one year, and determine how many more years (approximately) it would take to break down all the way.

We did experiments. Put it under really intense heat and ultra-violet lamps, packed it into material with enzymes and microbes, etc. We took lots of measurements at how fast the material breaks down, and projected it outward. Plastic doesn’t last 1000 years and then one day falls apart, it is affected by the environment and steadily breaks down, in a predictable fashion.

Imagine you only had the first half of a video of an ice cube melting. Can you extrapolate what happens in the second half of the video, and how long it will take?

Well it doesn’t.

There is not material called “THE PLASTIC”, just like how there is no such thing as “THE METAL”.

There are gazillion kinds of plastics, some of them are very resistant to the elements, some of them decompose when hit by a stiff breeze.

The “plastics take 1000 years to decompose” is a very nice and illustrative argument against littering. Without much insight on whats going to happen to said stuff.

As that depends on what kind of plastic we are talking about, how thick the thing you want to see disappear, where do you leave it (buried in earth, most plastics can last extreme long)… etc.

And ofc, there are unknown factors, like “will anyone create GMO organisms with the enzimes to eat the stuff”.

The conceptual study design to determine something like this is modified and used in many other endeavors on weathering predictions. Engineers want to know how long steel might take to corrode in different environments, so they might design purposefully stressful conditions and add a piece of steel to it. The conditions might not reflect actual ambient conditions but by doing this they make room for a margin of safety in their predictions (i.e., if high humidity, salty air, and high temperatures corrode steel X fast, it’s safe to set a floor on how soon we ought to expect corrosion in less harsh conditions). This is also a common practice in running stability test son pharmaceutical or food products – accelerating degrading conditions to estimate the expected shelf life of consumer-goods. In the case of plastic, it’s possible to design chambers or experiments where a piece of plastic decomposes in only, say, 2 years and design a model which might predict how that plastic would decomopose under less harsh (“ambient”) conditions.

The same way you can figure out how long it will take to fill a 5 gallon bucket by figuring out how long it takes to fill a 1 gallon bucket. The rate doesn’t change, just the time.

If it takes 1 minute to fill 1 gallon, then it’s going to take 5 minutes to fill 5 gallons.

Maybe by then it will turn back to oil! So we really dont have an oil shortage! We just have to wait 1000 years lol.

You don’t need to observe the full lifecycle of a material or molecule or atom to understand how it works. In this case, you can say that a plastic bag in the forest decomposes or breaks down X% over a one year period, so using that math and knowledge you know that it will take Y years to break down completely.