Cause of Plastic Container Deformation in Microwave Oven

In summary: Tupperware does make a bowl with a lid that has a vent in it and will release pressure without splattering all over the place. It's true you should never nuke any plastic bowl without the words "microwave safe"...or at least a warning on the side. Tupperware does make a bowl with a lid that has a vent in it and will release pressure without splattering all over the place.
  • #1
v0id
45
0
Greetings,

Earlier this afternoon I managed to ruin a perfectly good plastic container in a microwave oven by unwittingly deforming it. I curious as to why it happened.
All I did was warm it (and the chilli inside it) for about a minute with the lid firmly secure. I've been told this was a stupid move and to never attempt warming things with the lid in place ever again. But I'm not convinced. Upon removing it, I noticed that it had imploded. Depressurization doesn't make sense in this case, unless my knowledge of EM interactions is laughably bad. A lot of Googling turned up molecular deformation of the plastic itself as a possibility (but none of the aforementioned lid warning), but why would the plastic deform in the shape of a cavity and not with the lid removed?
 
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  • #2
A lot of containers are thermoplastic, they are formed by heating the plastic and injecting into a mold.

Water gets heated by microwaves and a high pressure steam will form in a closed container.
For example, don't put uncracked eggs in the microwave.
They will explode.

The steam is hot enough to make the plastic soften.
Some escapes the container, if it dosn't blow the lid off and make a mess in the first place. When the microwave shuts down the steam cools quickly creating a vacuum.
Then the container cools below its forming temp giving the imploded shape.

With lid off the hot gas quickly leaves the container so that it doesn't get a chance to heat the plastic.
 
  • #3
NoTime said:
A lot of containers are thermoplastic, they are formed by heating the plastic and injecting into a mold.

Water gets heated by microwaves and a high pressure steam will form in a closed container.
For example, don't put uncracked eggs in the microwave.
They will explode.

The steam is hot enough to make the plastic soften.
Some escapes the container, if it dosn't blow the lid off and make a mess in the first place. When the microwave shuts down the steam cools quickly creating a vacuum.
Then the container cools below its forming temp giving the imploded shape.

With lid off the hot gas quickly leaves the container so that it doesn't get a chance to heat the plastic.

Smart guy ^ ^ ^
 
  • #4
NoTime said:
A lot of containers are thermoplastic, they are formed by heating the plastic and injecting into a mold.

Water gets heated by microwaves and a high pressure steam will form in a closed container.
For example, don't put uncracked eggs in the microwave.
They will explode.

The steam is hot enough to make the plastic soften.
Some escapes the container, if it dosn't blow the lid off and make a mess in the first place. When the microwave shuts down the steam cools quickly creating a vacuum.
Then the container cools below its forming temp giving the imploded shape.

With lid off the hot gas quickly leaves the container so that it doesn't get a chance to heat the plastic.

Thanks a lot, that makes perfect sense.
 
  • #5
NoTime said:
A lot of containers are thermoplastic, they are formed by heating the plastic and injecting into a mold.

Water gets heated by microwaves and a high pressure steam will form in a closed container.
For example, don't put uncracked eggs in the microwave.
They will explode.

The steam is hot enough to make the plastic soften.
Some escapes the container, if it dosn't blow the lid off and make a mess in the first place. When the microwave shuts down the steam cools quickly creating a vacuum.
Then the container cools below its forming temp giving the imploded shape.

With lid off the hot gas quickly leaves the container so that it doesn't get a chance to heat the plastic.

That was a very practical response, you must be an engineer. :wink:
 
  • #6
Or a Chef! ;)
 
  • #7
I manage to do a little of both.
Thanks for the kind words :smile:
 
  • #8
Some plastic containers (like styrofoam that to go food is often served in) will just start to melt due to the heat.

In the cases where a closed lid makes a difference, the other factor is that a lot of heat will be trapped inside the container, causing it to soften quite a bit.

If the container is micro-wave compatable, then a nearly closed lid might seal up and become concave as the air/steam inside cools, but not the rest of the container which is stiffer than the lid. With a fully closed lid, the lid will be popped loose (hopefully), or the container will expand.
 
  • #9
There are microwaveable plastic containers, if heating with a lid on is important (as it si in the case of chilli). TupperwareTM makes a bowl with a lid that has a vent in it and will release pressure without splattering all over the place. That one's called an "Oval Cooker", but there are many kinds of microwavable plastic bowls.

It's true you should never nuke any plastic bowl without the words "microwave safe" associated with it. This time you just got deformed plasticware; next time it might explode in there. And you probably ended up eating some plastic with that chilli.
 
  • #10
Personally, I am worried about chemically altering the plastic and having chemicals leach into the food.
 
  • #11
DaveC426913 said:
Personally, I am worried about chemically altering the plastic and having chemicals leach into the food.

Why? What is leaching? It is thermoplastic deformation.


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  • #12
Why? What is leaching? It is thermoplastic deformation.
Could be a surface treatment or other compound mixed in with the plastic that vents if heated.
 
  • #13
Eh, its so minute its not going to kill you. :tongue2:
 
Last edited:

What causes plastic containers to deform in a microwave oven?

The main cause of plastic container deformation in a microwave oven is the heat generated by the microwaves. Plastic containers are not designed to withstand high temperatures and can melt or warp when exposed to the intense heat produced by the microwave.

Can any type of plastic container be used in a microwave oven?

No, not all plastic containers are microwave safe. It is important to check the label or packaging of the container to see if it is labeled as microwave safe. Only containers that are specifically designed for microwave use should be used in a microwave oven.

What types of plastic are safe to use in a microwave oven?

Plastic containers that are labeled as microwave safe are usually made from polypropylene (PP), high-density polyethylene (HDPE), or low-density polyethylene (LDPE). These plastics are more heat resistant and are less likely to deform or release harmful chemicals when heated in a microwave.

Can microwaving food in plastic containers be harmful to our health?

There is no clear evidence that microwaving food in plastic containers is harmful to our health. However, some studies have shown that certain chemicals in plastic, such as bisphenol A (BPA), can leach into food when heated in a microwave. It is recommended to use microwave safe containers and to avoid heating food in plastic for extended periods of time.

How can I prevent plastic container deformation in a microwave oven?

To prevent plastic container deformation in a microwave oven, it is important to use containers that are labeled as microwave safe. Additionally, you should avoid heating food in plastic for extended periods of time and do not use plastic containers that are damaged or cracked. It is also recommended to use glass or ceramic containers for microwaving food instead of plastic.

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