Is HDPE good for (-40C) applications?

[ShiranS]

Is HDPE good for Deep Freezer Applications (-40C)? HDPE has a very low Tg and most datatsheets list brittleness temperature as -75C for HDPE. Therefore shouldn't hdpe be better for Deep Freezer applications? Such as a crate. However what ive seen is that suppliers list PPCO in their data sheets for Deep Freezer applications and HDPE for low temperature applications. I would really appreciate some help with why HDPE if at all doesn't perform well at -40C.

I just started working for a plastics molding company and they've historically had trouble with HDPE (0.964 density) in the (-40C) environment. I saw recently they had used LLDPE + HDPE blend for a crate and it had critically failed. At room temperature LLDPE + HDPE is a horrible blend but I don't have testing data for (-40C) to say that's why the crates failed at (-40C). I'm in the process of building a cooling bath to test it but before I do that, would anyone be able to advise me if HDPE can perform well at low temperatures? Should I look to add an impact modifier? Or a HDPE with density of 0.95? Or a LDPE/HDPE Blend? Or could it be a processing related issue? Any advise would be most appreciated. Thank you

 

[Demon3]

The only way to tell if the impact resistance is good enough is to cool and drop the part. If it's not good enough then you could add a few percent of SBS such as Styroflex 3G66 or Kraton. That would help as it contains butadiene rubber impact modifier that has a low Tg and is effective at -40C.

Dr. Chris DeArmitt

Plastics consultant to the Fortune 500:

http://www.phantomplastics.com

Webinars on plastics, fillers & impact modification:

http://www.plastictraining.com

 

[ShiranS]

Thank you Dr.DeArmitt for your reply.

I wrote to Kraton Polymers earlier today to see if they have an additive that can help me. By you confirming my thought process it slightly puts my mind at ease.

I'm testing a HDPE crate tomorrow at (-40C) to see if it fails and how it fails. Will report back here my results so that everyone can learn something from this.

 

[Demon3]

I remember when I worked at Electrolux/Frigidaire we tested all kinds of PP for a freezer drawer and one of the copolymers was best. I think it was a block copolymer rather than random but it was a long time ago. Check

http://www.matweb.com

where you can scan PE and PP grades by low temperature impact resistance. Go for a heterophasic PP as that's what they use for car bumpers that need very good low temperature impact resistance.

Dr. Chris DeArmitt

Plastics consultant to the Fortune 500:

http://www.phantomplastics.com

Webinars on plastics, fillers & impact modification:

http://www.plastictraining.com

 

[IRstuff]

Crates and box shapes are tricky. Hitting the floor on a corner might do bad things, even at room temperature.

TTFN
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[ShiranS]

Thank you again for the help and advise.

I tested the crate after cooling to (-40C). The HDPE crate did not fail as badly as I thought it would. But out of three crates one cracked slightly on the sidewall.

The PPCO-Block crate I tested did not break at all. However it had stress whitening marks which some customers don't like.

I was able to make a (-40C) cooling bath using Dry Ice last week. I tested the impact stregnth of the various materials and compositions and it showed that the PPCO material had the best impact strength at (-40C). However it had a large drop in impact strenght from room temperature. HDPE on the other hand had only a slight drop in impact strength from rooom temperature to (-40C). Which makes me beleive if I can secure a better grade of HDPE, my problem will be solved.

Kraton polymers also recomended one grade to use in both HDPE and PPCO crates. I'm hoping to test this next.