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Strength of Plastic Bottles
Name: Marcus
Status: Student
Grade: 4-5
Location: FL
Country: United States
Date: Fall 2009
Question:
I am doing a science investigation about the strength of
plastic water bottles. I have noticed that some water bottles are
thinner and do not seem to be as strong as they used to be. Are
there any advantages for water bottles to be made stronger (or
weaker)?
Replies:
Well, the obvious advantage to making them weaker is that manufacturers
can use less material, which makes them less expensive.It also would make
them slightly lighter, which reduces transportation costs.
Richard Barrans
Department of Physics and Astronomy
University of Wyoming
There are many factors that go into the design of a bottle (water or
otherwise). Some of the issues are:
The wall thickness is important, as you have already discovered. But there
are other factors.
What environment is the bottle going to be exposed? If it softens at
elevated temperatures, that may eliminate a particular bottle.
What is the internal pressure to which the bottle will be exposed?
Carbonated sodas that may be used in the bottle, even if that was not the
intended use, has to be taken into account.
Your observation that thin-walled bottles are weaker than
thicker-walled bottles, is exactly what is to be expected.
On the other side, the thinner the bottle walls, the less material
is used to construct the bottle. That makes it less expensive to
manufacture. This is more complicated than just the cost of material. Those
bottles have to be transported. So the "net" weight versus the "gross"
weight is important.
The greater the "net" weight, the more product that is shipped compared to a
high "gross" weight".
Even more subtle, if you deliver a water bottle that holds 1 gallon
(8.3 pounds), no one who is going on a hike is going to want to carry that
extra baggage. Also if you are going to be exposed to below freezing
temperatures, the bottle may fracture and the water (ice) is lost.
So there are many factors that come into considering the
construction of a beverage bottle.
Vince Calder
Hi Marcus,
A water bottle must be strong enough to hold water and not break --
even when handled roughly or dropped. Companies work hard to determine
what is "strong enough", and have many tests and requirements.
If the water bottle is "strong enough", then the next goal is to make
it lighter. The material it is made out of is expensive, and companies
try to make the bottles lighter (use less material) to save money.
Using less material also means less energy used and less trash
created, which is good for the environment.
Hope this helps,
Burr Zimmerman
Hi Marcus,
Actually, the plastic used for all disposable water bottles is the
same, namely food-grade (very pure) polyester terephthalate. The
differences you are seeing are only because some bottles are thicker
than others. The reason for the thinner bottles is simply to use less
plastic, so there is less material waste if the bottle is thrown away,
and to make the bottle cheaper to make. The thinner bottles are
weaker, simply because they are thinner to save plastic, not because
the plastic is any different. They are weaker, but still strong enough
to do the job they are intended to do.
Regards,
Bob Wilson
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