FDA approved plastic for use in -40C, -40F, with impact toughness

[Erica1]

Hello.
I am investigating what material to use in a part used in a freezer at -40C.
The material now used is an unfilled copolymer POM.
What has happened is that it does not have enough impact toughness and chips falls of if the part is "mistreated".
So I wish to improve the impact toughness.
I don't know the necessary yield strength but the same as unfilled POM is enough.
The part is injection molded and it would be good to be able to use the current mould.
I'm thinking of finding a POM with some kind of additive mainly because I don't have enough knowledge to know what else to look at.
Do you guys have any tips for material for me to look into?
Thanks.

 

[patprimmer]

Impact modified POM or Polyester elastomer like Hytrel or Arnitel.

DSM or DuPont should be able to help.

Polycarbonate may also be suitable depending on actual properties required.

Regards

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[Erica1]

Thank you for your tips.
I think the polycarbonate seams very interesting.
I read that it does have poor resistance to chemicals but do it withstand washing detergents? Is there something else strange with this material? And thanks for the tips to contact DuPont I will do that but first try to get a little background to have things to talk about.

 

[patprimmer]

It depends on type of detergent, time and temperature.

Polycarbonate like all materials has a full range of unique properties.

We always need to consider compromises for acceptable balance when matching materials to applications, and that is impossible to consider with piecemeal and incomplete information.

Regards

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[Pud]

LLDPE is good for -70 Deg C whilst retaining impact strength.

The lower the MW the better...

Although as Pat mentioned, an impact modified POM would be much easier change and be much better.

Cheers,


Harry

 

[Demon3]

What kind of freezer is it? Domestic freezers work at -18C. The reason I ask is that at -18C you will still get good impact resistance from cheaper polymers like ABS and HIPS. At -40C it won't be quite so good because the Tg of the polybutadiene rubber in those polymers is around -60C. I would suggest you try ABS. Decent chemical resistance and good impact resistance. Plus it's cheap.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[Erica1]

The freezer is an big industrial freezer for small things like peas.

 

[Erica1]

Ps. Can I edit a post like the one above for errors in the spelling and to add that the price is not very important.?

 

[patprimmer]

This forum is in the stone age.

Once you write it, it's carved in stone ;-)


That is unless you are rude or well outside the forum rules, then they seem to get deleted entirely.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[JXLADAY]

Eric

some PC grades have good impact property at -40C, but as you said, it's chemical resistance is poor, And for detergant and cleaners, Mild soap solutions are generally compatible, Stronge akaline materials should be aviod.

Regards

 

[Erica1]

I am thinking of changing the material to Delrin instead of Hostaform because it has 11kJ/m2 compared to 6kJ/m2 in impact strength at -30C. But I read that homopolymer has more breaking down in alkali which is used in the cleaning but is this an issue at this relatively low temperatures?

 

[Demon3]

An often overlooked point is that while PC has great impact resistance, that's only true for thin parts. The impact resistance is way lower for thicker parts.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[btrueblood]

Erica,

Homopolymer breaking down in alkali won't be an issue if you can control the temperature.

That said, we saw degradation of acetal polymers at temperatures above about 140-160 F in an alkaline (NaOH and NaOCl) clean-in-place application, and had to move to fluoropolymers because we couldn't guarantee that users would not mix the powdered cleaning solution with hot (190-210 F) water.

So that if is a very big IF.

 

[patprimmer]

Off the top of my head, Acetal is very resistant to almost all chemicals except acids at room temperature or lower. Plain distilled water will degrade it slowly starting at about 60 deg C and accelerating a lot at about 80 deg C.

It is really susceptible to acids at any temp and quite susceptible to hydrolysis at elevated temps.

Co-polymer is down a bit on physical properties, but is a bit better to chemicals.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Erica1]

Thanks for the latest answers they have gide me alot of good information.