Scratched Surfaces: Chemistry & Health Impacts

[kenny1999]

When something in our daily life used for years we could often find its surface scratched slightly, even if we use it very carefully and don't make scratches intentionally. I'd like to know, from chemistry or molecular point of view, did it lose any atoms or particles away from the scratched part?

For food container made of PP or glass, their surface could get scratched as well, is it bad to our health as those particles could go to our food easily?

 

[mfb]

It will have lost some atoms. Not necessarily as many as the depth of the scratch suggests - many of the atoms will have moved to the side of the scratch. The amounts are tiny and shouldn't be an issue with household materials.

Materials can lose atoms from the surface even when there is no scratch.

 

[Rive]

For food container made of PP...

In case of plastic containers the main problem with scratches is that it makes cleaning difficult and the remaining foreign material can breed many bacteria. So it does not come from the material of the container, but foreign material.
It is the same for poorly made metalware: poorly connected plates, concave edges, grooves can retain food remains.
Glass is a bit better since it is less sensitive fro aggressive cleaning (chemicals) and usually has less sharp edges/grooves due the way they are formed/made.

 

[kenny1999]

Materials can lose atoms from the surface even when there is no scratch.

Is it because of weaker molecular force surrounding the atoms on the surface?

 

[kenny1999]

In case of plastic containers the main problem with scratches is that it makes cleaning difficult and the remaining foreign material can breed many bacteria. So it does not come from the material of the container, but foreign material.
It is the same for poorly made metalware: poorly connected plates, concave edges, grooves can retain food remains.
Glass is a bit better since it is less sensitive fro aggressive cleaning (chemicals) and usually has less sharp edges/grooves due the way they are formed/made.

Isn't plastic (for example PP) as inert as glass? We know that plastic is very inert...

 

[mfb]

Is it because of weaker molecular force surrounding the atoms on the surface?

Well, atoms from the interior can't escape without becoming atoms at the surface first. But yes, things at the surface tend to be bound weaker.

Isn't plastic (for example PP) as inert as glass? We know that plastic is very inert...

Plastic often allows the motion of smaller molecules through it, they escape over time (outgassing).

 

[Rive]

Isn't plastic (for example PP) as inert as glass? We know that plastic is very inert...

As far as I know it is indeed very inert (at least some of them), but not as inert as glass: nor it is that hard against scratches.

As I recall there was a problem with multi-use plastic bottles that after a few uses (5-7) most of them had surface problems: partially on the outer surface, but also due the chemicals required for the industrial level cleaning - while with glass bottles it was 50+ reuse (and the limit was because by that time some customer had broken them).

 

[kenny1999]

Well, atoms from the interior can't escape without becoming atoms at the surface first. But yes, things at the surface tend to be bound weaker.Plastic often allows the motion of smaller molecules through it, they escape over time (outgassing).

Hi, Does PP (Polyprop... forget how to spell) outgrass as well? Do the chemicals released contaminate food and cause health issues when used as food container?

 

[mfb]

If you use it as intended it doesn't cause health issues, otherwise they wouldn't be allowed to sell it.

 

[Bystander]

Check mold growth on the corrugated flexible straws used in hospitals; about one week between unwrapping and visible mold, i.e., black.

 

[BillTre]

I used to run a fish facility for a large research group.
We used a lot of plastics in what we did and had to sort through a variety of problems they were involved in.
We can up with an easy (if you are a fish facility) and extremely sensitive bio-assay for plastics that would cause us problems. We found that about 1/3 of the plastic/rubbery materials we tested were pretty bad in our test
(Test: using genetically indistinguishable freshly laid fish embryos, separate into control vs. sample populations, in 100 mls of fish water, add sample material to one and do daily checks on embryo health/development/viability for next 5 days).
If you use products labeled as food grade, or better medical grade, you should be fine.
But these are not going to be the cheapest choices.

For any kind of plastic (such as polypropylene), there will be different sources, producing different quality product, that is used in different kinds of products.
Good quality PP is common in biology labs because it is strong, solvent resistant, and can be autoclaved (sterilization technique). Useful features.

Some lots (production runs) of plastic will have more or less amounts of unreacted plastic precursor molecules. These could diffuse out later.
Some plastics will have intentional additives (for UV resistance, color, fungal resistance, slipperiness, ??) than could diffuse out later.
Some plastics can be treated to remove some contaminants. I used to work for a company that made animal containers for researchers. After melting the plastic they were going to use to plastic injection containers, they would draw a vacuum on the liquid plastic to remove volatile compounds, and then do it again.

To some extent, probably all kinds of plastics will be able to absorb some water and gasses.
There are special "breather" bags for transporting fish, made of plastic that can pass enough CO₂ and O₂ to be able to keep the packaged fish alive for days,. Air can be excluded from the bag, making a smaller package to send.
Plastics that absorb more water, seem to be more susceptible to growth of fungi and stuff like that.

 

[kenny1999]

I 'd like to get to know some more concepts about plastic

1. When I get a plastic container that is smelly, is it the same as what we say "outgassing"?

2. When a plastic outgasses (how to spell?), is it in vapor form?

3. When a plastic container is found smelly, does it mean it's of poor quality?

 

[BillTre]

I 'd like to get to know some more concepts about plastic

1. When I get a plastic container that is smelly, is it the same as what we say "outgassing"?

2. When a plastic outgasses (how to spell?), is it in vapor form?

3. When a plastic container is found smelly, does it mean it's of poor quality?

1. Probably, in most cases. Could be a release agent on the surface though.

2. Probably. Or you would not be able to smell it.

3. Not necessarily.
Some plastics might be intended to have certain smelly additives for some purpose, like fungal resistance.
That doesn't make them low quality.

 

[kenny1999]

Hi all again.

I'd like to know. I've been hearing that scratched (even slightly) on Stainless steel cookware would release kinds of harmful chemicals that would be bad for health. I've asked this
questions on Yahoo and other forums. Some said Yes and some said No. What's the truth?

 

[jedishrfu]

@kenny1999 there's no way for us to answer this question where you will find the truth you seek.

The best you can do is to go to your doctor and ask him or her this question. They will be able to answer it
Or direct to a credible source that can answer it.

Truthfully, I’ve never heard of this particular issue. However, I did find an article that said scratched stainless steel pots can release trace amounts of nickel and chromium into your food but that these amounts are so small as to not pose any risk to health. Bottom line did use a Brillo pad to clean and scratch your pots for peace of mind.

Nothing more to add to this thread. Closing it now.

Thank you all for contributing here.

Jedi