hot water submerged bags with esters inside

[stabmaster]

I am trying out all different sorts of bags to encapsulate a wax (ester) "pentaerythritol adipate stearate" which melts at around 135F. The bags are to store heat in the phase change region and over a temperature range of between 100F and perhaps as high as 190F. I have been having problems with different material compatabilties. A slight elasticity is preferred as there may be a volumetric expansion of 10%. Even when the bags are evacuated of gas, oxygen is entrained within the molecular matrices and will eventually escape, so there is potentially a volumetric expansion associated with that (boyle's law). The bags are underfilled so that even with the expansion there should not be enough pressure to cause a break;

however, the temperature may be a problem.
The requirements of the bag are that it must be relatively impermiable to water and air on the outside, and submersible in hot water which may fluctuate from 100 to 190F daily. Perhaps 20,000 cycles of expansion/contraction. The elasticity required is not known but the volumetric expansion of the entire bag must allow for a 10% change. The inside of the bag must be compatible with the same temperature fluctuations and it must be compatible with esters. Also the bag may contain copper wool. There is puncture resistance to consider.

Fluoropolymer film seems like an obvious homogenous choice. It seems too easy, but anything that is layered with aluminum (Mylar, etc.) either delaminates upon cycling volume or else the seal breaks at the temperatures in consideration.

Any help is appreciated!
Is there any advice?

 

[Demon3]

Esters are non polar and water very polar so it will be hard to choose a polymer that is compatible (doesn't swell) in either one. For example nylon will resist the ester but is softened a lot by water and will allow water to pass through. Something non polar like PE will not adsorb water but may swell and soften with the hot ester.

Your choice of fluoropolymer is a good one, that is so low polarity (solubility parameter) that it will not be affected by water or the ester. Silicones may well work as well.

The other option is multilayer films as you suggested. In drug packaging multilayer films are used for their special properties, up to 7 layers in some cases. Aluminium is one option as a barrier layer but very thing silica (SiOx) layers are common as well. It won't delaminate if it's made properly with the right layers and tie layers.


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

 

[stabmaster]

Thank you! I've found that PTFE fluorocarbons of any sort will cost about 2 to 4x the cost of what they are to contain; therefore, the price is beyond our reach.

In multilayer films, I have a dozen spec sheets but none which contain facts that I am interested in. I think that the temperature considerations are the most important, as I've tested the multilayer films with polyethylene on the inside and they tend to creep open at 190F. I can't seem to find any HDPE or HDPE/Aluminum/BOPET. I assume this combination is not easy or reasonable to produce, or else there is something better.

Is there any multilayer film available that has something that will work like this?

Thanks for the tip Demon3- I am looking into silicone right now.

 

[unclesyd]

I don't have my data any more but you might want to look at Nylon 12 the old oven roaster bags. They will take the temperature and have a much lower water adsorption than Nylon 66 or Nylon 6. Good to 400F.

http://www.alcoa.com/reynoldskitchens/en/product.asp?cat_id=1337&prod_id=1790

Here is the new Polyester bag that is good to around 400F.

http://www.glad.com.au/gladProducts/foodDetails.asp?pId=6

 

[patprimmer]

Polyester will hydrolyse fairly quickly at 190 F, so care would need to be taken to compare degradation of the PET vs the time of exposure during the life of the bag.

Nylon 6 or 6/6.6 copolymer are common in multilayer films for food packaging. While they do soften due to moisture absorption, they still retain useful properties. Nylons that have moisture conditioned are used in a huge number of load bearing applications.

Nylons will also hydrolyse, but at a much slower rate than polyester. It will also be more ductile.

The real problem is the inside layer. Any PE, even HDPE will be pretty useless re load bearing at 190 deg F. Polypropylene will do better.

We are currently doing work on nylon that is good water barrier, but it is not fully developed yet.

Someone might do a film grade nylon 12 with nanoclay filler. That will ruin mechanical properties, but substantially improve barrier, so a multi layer nylon 12 might work, say standard grade outside surface 15 microns, nano filled say 60 microns and weldable layer say 20 microns. The weldable layer might be plasticised nylon 12, or nylon 12 with tie layer or compatibiliser type additives.

To develop a custom multilayer structure, you would need considerable volume of usage as equipment to do this is difficult to start and has high production rates.





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.

 

[IRstuff]

Have you considered what they use to encase sodium acetate glove warmers? It's a phase change material that requires boiling to reactivate. It looks like a polyethylene bag. Seems rugged enough.

TTFN

FAQ731-376

 

[unclesyd]

http://www.chemtec.org/books/pdl/pdl1.html

 

[Demon3]

I did a search for phase change materials and found this:

http://www.micronal.de/portal/basf/ien/dt.jsp?setCursor=1_290798

They are beads with a microencapsulated wax that does what you want. Because the wax is already encapsulated in a polymer shell you can probably get away with a bag that doesn't need to be elastic or have great barrier properties. No idea on cost but may be not too much as itÄs used in building materials like plaster.


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

 

[IRstuff]

Various hand warmers:

http://www.nahpco.com/small_colorful.htm

http://www.hot-pad.com/products.php?gclid=CPOqvc-O3IsCFQKSQAodSA_ZXw

http://www.bodyheaters.com/store/reusable-heat-packs-c-24.html

TTFN

FAQ731-376

 

[stabmaster]

Well I went with Teflon. The hand warmers tend to be salts rather than esters or other polymers.

polymers cost around $1.00 per pound. they tend to hold their phase change enthalpy properties over 10000 cycles, whereas the performance of salts deteriorate a great deal over 3 or 4 cycles.

Until i can find an alternate material, I'll have to go with teflon.

 

[Pud]

Would this do what you want?

You have to request a data sheet, but as it's a PA/PP alloy it is supposed to have the benefits of each...

http://www.arkema-inc.com/index.cfm?pag=104

I note there are film/flexible grades.

Cheers

Harry

 

[unclesyd]

Your use of Teflon reminded me of Tedlar a product we used as substitute for Teflon in
a very severe environmental application. It is made into all types of bags, mainly for sample bags.
In our application we saved a ton of money.

http://www.dupont.com/tedlar/products/pvffilms.html

 

[Demon3]

Just a note to be careful as the tradename Teflon covers 3-4 different fluoropolymers so be sure what you're getting.


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