If plastic was made in 1907 how do they know it may take up to 1000 years to decompose?
In: Chemistry
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.
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.
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 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.
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?
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.
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.
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”.
Like pouring a cup of water in the sink. You don’t have to pour the entire cup to estimate when it’s going to run out.
PhD in plastics engineering here. There’s a technique known as time-temperature superposition, which allows us to predict how long it will take to degrade plastics by subjecting the plastics to high temperatures (keeping most details out of it) and seeing how long it takes to degrade at this high temperature. Then we use this information to compute how long it will take the plastic to decompose at ambient (room) temperatures. This method gives a very precise number much more accurate that a qualitative 1000s of years. The most stable plastics would probably survive for 100s of years, not 1000s.
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