[Nhcoll-l] FW: Potential problem with older PE jar lid liners

Tue Jul 31 16:41:15 EDT 2012

That looks great, thanks Scott.

Will you post it directly to Nhcoll-l?

They are at nhcoll-l at mailman.yale.edu

I don’t think you need to be a member to send things in.

Rob

p.s. I am glad CCI chose to gracefully let retirement-ready people go.  The CMN has been much more draconian in its approach.

p.p.s. When I mentioned having equipment available on a rental basis for some consulting work I was thinking you might be able to arrange a by the day rate for using some equipment at CCI.  Whatever the cost of that would be you would simply pass on to the client.  If you want and when you are ready we could get together for lunch and chat about possibilities.

Rob

From: Scott.Williams at pch.gc.ca [mailto:Scott.Williams at pch.gc.ca] 
Sent: July-31-12 7:11 PM
To: rw at protectheritage.com
Subject: RE: FW: [Nhcoll-l] Potential problem with older PE jar lid liners

Rob:

See below for a paragraph I added to address the batch/brand issue.  OK?

Notice of lay-off initially upset me, mainly because I was surprised and it was abrupt.  It seemed to me that there could have been some discussion with affected staff ahead of time, but I guess that was not possible due to management/union agreements.  I had planned to work a few more years until my youngest was away at university or otherwise left the house.  I felt that I could not do much different while kids were still at home and I still enjoyed the work.  But things have been changing here at CCI in ways that I do not like, so I have been having less fun.  This started me thinking more about retirement, but not in any concrete way.  Within a day or two of the announcement (April 12) I started to think that maybe this was not so bad and that a decision about which I had be procrastinating had been made for me.  Since finding out the details and developing a work plan for the remainder of my time at CCI I have become very OK with the decision.  I have been with the gov't for 41 year, 42 next Aug, so my pension is unaffected.  In fact, severance for laid-off is better: lay-off 42 or 43 weeks pay, retirement 30, so this is good.  So considering the increased severance and the 16 month surplus period, the financial consequences are not unbearable.  

At this time I have no plans to do post-retirement consulting, but then I never really gave this much thought.  I am most interested in analysis, and this will be difficult without equipment.  I suppose if there are projects like this one were knowledge not equipment is necessary then I might be interested.  I'd have to give it lots of thought.  I just spent a month at our house in NFLD practising the retired life, reading Tarzan and Conan pulp fiction, and quite enjoyed it.  I not have even started on my Ryder Haggard collection yet, so maybe that's what I want to do.  Time will tell.

Scott

Inactive hide details for "Robert Waller" ---2012-07-31 12:21:33 PM---Hi Scott, Thanks for putting this together so quickly."Robert Waller" ---2012-07-31 12:21:33 PM---Hi Scott, Thanks for putting this together so quickly.

From: "Robert Waller" <rw at protectheritage.com>
To: <Scott.Williams at pch.gc.ca>
Date: 2012-07-31 12:21 PM
Subject: RE: FW: [Nhcoll-l] Potential problem with older PE jar lid liners

  _____  

Hi Scott,
Thanks for putting this together so quickly.

No matter how old I get I still keep discovering things I cannot believe. 

1)      We (natural sciences conservation) did not consult with you before installing PE foam gaskets for ethanol water solutions. I suspect by now millions have been installed.  Good grief.
2)      CCI would surplus you.  Are they nuts??!!!????  When was this announced?  Are you OK with this?  You must be fairly close to retirement anyway.  Are you going to do any freelance consulting work after retirement?  I can imagine you could do very well especially if you can arrange some equipment access in a rental arrangement.

I think your draft email looks good for distributing.  I think there will need to be a lot of discussion around this topic before anything gets settled.  Having some good thoughts about basic material properties put out near the start can only help us.

Still, I am surprised this was not observed before given how many of these liners are in use.  Could you mention if lot to lot variation in the PE foam supply might be an important consideration?

Perhaps working on a design team to come up with a good replacement might be a nice post-retirement project for you.  I suspect we could get something funded for that through a US museum.  It could take a couple of years to get that in place though.

Please keep in touch about this and other things.  We (the field) are not ready to let you go yet!
Rob

From: Scott.Williams at pch.gc.ca [mailto:Scott.Williams at pch.gc.ca] 
Sent: July-31-12 5:40 PM
To: rw at protectheritage.com
Subject: Re: FW: [Nhcoll-l] Potential problem with older PE jar lid liners

Rob:

I drafted the following reply.  As I say, I have not done any investigation, so I am naive on design issues. I pass this by you for comments so that I do not make or imply any insulting assumptions.  Should I send it as is?

In case you do not know, I was laid off in the last round of CCI cuts (along with Greg Young and George Prytulak).  The way it works is you get what amounts to up to 16 months to find another job before you are terminated.  Termination occurs earlier if you refuse a reasonable job offer.  If I do not get or refuse an offer, the first day of my retirement will be in Aug 2013.  Until that time I will be working "normally" at CCI, primarily winding up existing projects, but not starting anything new.  

Scott

I preface these comments with the caveat that I have not investigated the problems associated with the design of leak free bottle caps.  These comments are related to the materials mentioned in the query, not the bottle or cap design. 

The query refers to polyethylene foam.  There are a great many different grades of polyethylene plastic, and polyethylene foam products, available from many different manufacturers.  Also, it is possible that a specific product, or a specific batch of a product may show problems, not shown by others.  Therefore, the following comments must be of a general nature.

Closed cell uncrosslinked or crosslinked polyethylene foams such as Ethafoam and Volara and closed cell foams made of other plastics rely for their compressive strength on the air or other gas filled bubbles or cells in the foam. As the foam is compressed, such as when an object is placed on a foam pad or a foam gasket is squeezed when a bottle cap is tightened, the bubbles deform and the plastic in the cell walls stretches.  The ease of deformation and stretching of the plastic determines the compressive strength.  The long term stability of compressive properties of the foam depends on the long term stability of chemical and physical properties of the plastic, such as elasticity and gas permeability.  In the case of polyethylene, oxidation decreases elasticity and increases brittleness and susceptibility to fracture.  Compression of oxidized polyethylene foam is more likely to cause fracture of embrittled cell walls than compression of more flexible unoxidized polyethylene foam.  Fracture leads to loss of gas and collapse of the foam structure.  In the case of a gasket like a bottle cap liner, this means loss of contact with the joint walls and leakage.

When a foam is compressed the pressure of the gas inside the cells increases.  Since permeability through a plastic membrane is proportional to the pressure difference across that membrane, the rate of permeation of the gas from the cell increases.  Since the pressure in the closed volume of the cell is proportion to the amount of gas in the cell the pressure in the cell decreases as the gas leaves.  In the case of a gasket like a bottle cap liner, this means that the pressure of the foam liner against the joint walls decreases and leakage may occur.  Ultimately all the gas could be squeezed out until all cells have collapsed and the foam liner is no longer a foam but just a pile of sheets of polyethylene film from the cell walls.  Furniture stored on foam shelf liners often shows completely collapsed foam under the feet.  The phenomenon is called compression set.

Polyethylene, like all plastics, contains additives to improve or stabilize long term behaviour.  Polyethylene without antioxidant stabilizers will oxidize quickly in the atmosphere.  Additives can be extracted from polyethylene with organic solvents.  Ethanol is commonly used for this purpose in the analytical laboratory.  It is likely that ethanol in the alcohol collections will extract the additives from the polyethylene liners, leaving the polyethylene foam susceptible to oxidation, which invariably results in embrittlement and fracture.  If oxidizing conditions exist inside the vials of the alcohol collection, then oxidation of the polyethylene foam line is likely with subsequent failure as described. Do oxidizing conditions exist in the vials?

Ethanol is known to be an environmental stress cracking agent.  Bottle cap liners are physically stressed in the zone of compression at the joint between cap and vial rim and therefore may be even more susceptible to environmental stress cracking.  This may show up as cracks located at the transition zone between uncompressed foam exposed to ethanol in the vial and the compressed foam between the vial rim and the cap which is not directly exposed to the ethanol.

Because the plastic matrix in a foam makes up such a small fraction of the volume of the foam compared to a solid piece of plastic of the same thickness (maybe less than 5% of the volume), a small amount of change in physical properties such as brittleness, of the plastic in a foam can have very much greater effect on the foam product than on the solid product.  A small increase in brittleness, sufficient to cause fracture of thin cell walls with loss of gas, and fracture pillars between cells, might lead to collapse of the foam structure but would be unnoticeable in a solid.  

Open cell foam is very different from closed cell foam. There are no discrete gas filled bubbles or cells completely enclosed by plastic. The membrane or window between adjacent cells is open or missing, and only the pillars where three or more cells meet remains. Gas is free to move from cell to cell throughout the entire volume of the foam. Uncompressed open cell foam is not a gas barrier.  Completely compressed open cell foam where the entire gas volume is compressed to nothing may be a gas barrier.  Compressive strength does not depend on compression of gas in cells, but only on the elastic properties of the plastic that constitutes the pillars of the foam.  In this sense an open cell foam is something between a closed cell foam and a solid.  Compressible and elastic open cell foams are made with compressible and elastic plastics.  Polyethylene is not such a plastic.  

Based on the arguments above, use of any type of closed cell foam as a gasket may be inappropriate and open cell foam is probably not be better.  Gaskets made from solid elastic plastics that are impermeable to ethanol may be better choices.  Another alternative may be to avoid gaskets and seek a cap design that has a structure that makes a leak free seal, such as, for example, a V-shaped groove into which a V-shape protrusion inserts.  I do not know if such caps are available.  Perhaps chemical supply houses which sell organic solvents in bottles and sample bottles for liquid specimens or beverage companies that sell pressurized carbonated beverages have developed solutions that may be adaptable, keeping in mind that beverage applications are for relatively short shelf life.

"Robert Waller" ---2012-07-31 04:33:36 AM---Hi Scott, I don't know if you would have seen this or not.  This could be a huge

From: "Robert Waller" < <mailto:rw at protectheritage.com> rw at protectheritage.com>
To: < <mailto:scott.williams at pch.gc.ca> scott.williams at pch.gc.ca>
Cc: < <mailto:callomon at ansp.org> callomon at ansp.org>
Date: 2012-07-31 04:33 AM
Subject: FW: [Nhcoll-l] Potential problem with older PE jar lid liners

  _____  

Hi Scott,
I don’t know if you would have seen this or not.  This could be a huge problem for natural science museums.  Is there any chance you could look at exposed and non-exposed samples from Paul to see whether this might be expected to affect all PE foam liners or just one batch?  Any guidance on that as soon as possible would be of great benefit to natural science museums in Canada as well as elsewhere.
I know you are always busy and backed up with requests but I think this one is scary important so I hope you can slip it in.
Thanks,
Rob

From:  <mailto:nhcoll-l-bounces at mailman.yale.edu> nhcoll-l-bounces at mailman.yale.edu [ <mailto:nhcoll-l-bounces at mailman.yale.edu> mailto:nhcoll-l-bounces at mailman.yale.edu] On Behalf Of Paul Callomon
Sent: July-30-12 9:56 PM
To: NH-COLL listserv ( <mailto:nhcoll-l at mailman.yale.edu> nhcoll-l at mailman.yale.edu)
Subject: [Nhcoll-l] Potential problem with older PE jar lid liners

Colleagues,

I have today found a severely deteriorated jar lid liner in our alcohol collection. The liner is made from polyethylene foam. It was sold to us in 1999 and installed in 2000. The material has failed completely, with crazing and cracking of the surface and tearing along the compression face. The foam has become weak and powdery in places. The jar was filled with 70% ethanol.

The manufacturers have suggested that the use of this liner for long-term storage of alcohol is responsible for the deterioration. If this is true, the implications for our collection – we have about 20,000 bottles that use these liners – are potentially serious. 

Does anyone have experience with this problem? Are Teflon liners a better alternative? 

Paul Callomon
Collections Manager in Malacology, Invertebrate Paleontology and General Invertebrates
The Academy of Natural Sciences of Drexel University
1900 Benjamin Franklin Parkway
Philadelphia, PA  19103
callomon at ansp.org
Tel. 215-405-5096
ansp.org
Follow us: Facebook <http://www.facebook.com/AcademyofNaturalSciences>  | Twitter <http://twitter.com/#!/AcadNatSci> 
Join us as we celebrate the Academy’s 200th anniversary with a year of exciting events, special programs, and our bicentennial exhibit, The Academy at 200: The Nature of Discovery.  <http://www.ansp.org/> www.ansp.org

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