amorphous or semi-crystalline polymers for creep resistance? 1

[loughnane]

I have multiple resources telling me how good Nylon and Acetal are for creep-resistance, but then a few other resources telling me that amorphous polymers are generally better for creep-resistance.

I suppose that conflict could be explained away by the word 'generally', but it seems tough to find comprehensive data (experimental creep data for common polymers would be a great comparison, but is ridiculously hard to find).

Anyone have intimate knowledge this or can point me to a really good resource?



Chris Loughnane - Product Design

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[patprimmer]

I have good creep data on nylons and acetal. I have not seen much on amorphous materials.

Generally a manufacture not releasing data indicates the data does not show the product in a favorable light.

Also a change in environment will change the relative creep performance of the polymers in question. For example, test nylon 6.6 vs acetal at room temperature and the acetal easily wins, but test them both at 120 deg C and the nylon will almost certainly win.

Also testing at equal deflection vs testing at equal load will very likely alter rankings.

Also testing along and across the flow might make more difference to a semi crystalline with a very linear chain than it does to an amorphous polymer.

Also reinforcements can make a huge difference and can improve some polymers a lot more than others. Nylons respond exceptionally well to reinforcements.

Also semi crystalline polymer performance is very dependent on cooling rate (time for crystals to form) during and after moulding whereas amorphous polymers are much less sensitive in this area re this property.

This might help explain the inconsistencies in the data you have.

Regards
Pat
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[klank]

Hi.

I have the best experience with amorphus materials for parts who are not allowed to creep so much. Fx for parts to use in the medico industry.
Also amorphus materials seems to creep equally in X, Y and Z (if there is not added GF or so) and if gated properly, which not always is the case for Semi crystalline materials.

A nice material for this purpse could be ABS, which e.g. is used for LEGO blocks, where the creep-tolerances are extremely high!!!

I have added a paper with some average values for some different plastics i use in the engineering of injection molds.

p.s. sorry for my bad english.



jeg har den bedste erfaring med A for emner der ikke må svinde for meget.
Desuden har A også en større tendens til at svinde i alle retninger end SC.

 

[btrueblood]

klank,

Shrinkage is not the same as creep.

 

[klank]

Sorry. my bad, then.

 

[loughnane]

Many thanks Pat

Chris Loughnane - Product Design

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[patprimmer]

klank

According to my very bilingual secretary when I worked as a Market Development Engineer for Bayer, the literal translation for creep resistance from German to English came out something like crab walking or crab/sideways crawling resistance.



Regards
Pat
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[Demon3]

Crystals act as extra entanglements which means you can expect semi-crystalline polymers to have better creep resistance all else being equal. So, I would expect semi-crystalline polystyrene (Xarec,

http://www.xarecsps.com/)

to have better creep resistance than normal amorphous polystyrene.

Adding fillers to semi-crystalline polymers increases HDT and Vicat dramatically (up to near Tm) whereas they are much less effective in amorphous polymers increasing HDT to near Tg. This also is an indication that the former are more creep resistant especially when filled.

Chris DeArmitt PhD FRSC CChem