| MadSci Network: Chemistry |
Do containers for heating things, eg: kettles, made of polypropylene or
stainless steel release components of these materials into the heated
substance, eg. boiling water?
The quick answer to this question should be no. However, since some
manufacturers make products differently, it is difficult to make a general
statement. Containers are made differently in terms of costs and
materials. This combination sometimes makes for products that
under-perform. Now if all things were equal, nothing should be released
into boiling water. Let's take a closer look at the two materials you
suggested.
Stainless steel is an alloy steel that resists corrosion. An alloy may be
defined as a substance that has metallic properties and is composed of 2 or
more chemical elements. Many alloys consist predominantly of one metal
("base metal") with minor additions of other elements. Based on this, the
chances of "something" being released are very slim. However, there could
be a coating on the steel that could break down from wear and be released
into the boiling water.
Polypropylene is a hydrocarbon polymer made typically from a free radical
process using catalysts. The polymer could have also have additives to
change the properties. Based on the diffusion of these "impurities"
through the polymer, which should be low, but keep in mind that diffusion
increases with increasing temperature, there is a chance that "something"
could leave the container. However, the chances of this occurring are low.
This is a generic answer since it will depend on the manufacturing process.
The polymeric material has a better chance, albeit slim, of releasing
"something" into the heated substance than does steel. If the material is
from a trusted manufacturer, this is not something I would concern myself
with too much.
Hope this helps.
Dan Berger adds:
Almost anything made of plastic contains plasticizers, usually esters, which
make the plastic more flexible. Something designed to hold boiling water
should not leach plasticizer into the water, but beware of putting hot
liquids into, say, plastic squeeze bottles!
As for stainless steel and other metals, if you boiled the water long
enough you'd get some reactions with the metal container; mostly the
release of metal ions into the water (for example, cooking spaghetti sauce,
which contains tomatoes -- acidic -- in cast-iron pots results in high-iron
spaghetti sauce). But iron is good for you, and so are most other metals
you would find in cookware. (In the olden days, when people cooked in pewter
and even in lead-lined vessels, there was a serious problem with lead
contamination in food. Some people think this contributed to the fall of
Rome; see Reay Tannahill, "Food in History."
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