Ethafoam

The following discussion took place in private mail and is reproduced
here in edited form with the permission of the corespondents.  I am
posting it not only in order to nip a possible rumour in the bud, but
for the valuable technical information transmitted in the process; many
thanks to Jessica and Doug for all the work they put into this.

    Date: Wed, 3 Feb 93 11:41 CST
    From: Jessica Johnson <tqaa345 [at] utxvm__cc__utexas__edu>

    At a recent meeting of the Collection Managers Committee of the
    Texas Association of Museums a rumour was circulating that Dow had
    changed the blowing agent for Ethafoam (because of problems with
    CFC's) so that it was now "acid".  Questioning a few people, I think
    that the concern is that now a layer of fatty acids is left on the
    surface so that it's not safe to put materials directly on the
    surface.  Does anybody know anything about this?  Are fatty acids a
    concern because of deterioration of Ethafoam, or damage to objects?
    Does anybody have a good contact at Dow I can question?

    Thanks,
    Jessie Johnson
    Texas Memorial Museum

    Date: 05 Feb 1993 11:36:29 -0400 (EDT)
    From: Doug Nishimura <dwnpph [at] ritvax__isc__rit__edu>

    I called two people at CCI with regard to Jessie Johnson's question
    about the Ethafoam rumours.  Scott Williams is really not involved
    in plastics and storage anymore, but I thought I would see if he had
    heard anything.  His successor is Jean Tetreault and I contacted him
    also.  Scott had heard the rumours but had no confirmation at all.
    Jean Tetreault hadn't really heard anything about it, but said that
    if anyone had actually had a problem with the new Ethafoam, he would
    like to hear about it and possibly initiate a project to determine
    the cause of the problem (or at least contact Dow Canada about it.)

    The three of us were speculating about the "fatty acids" part and
    couldn't come up with any reasonable source for such chemicals. Jean
    had suggested that the carboxylic acids, if they existed, were
    likely low boiling such as formic and acetic and I have to admit
    that such a thought hadn't occurred to me.  (Sources of such LB acids
    are more common than the usual longer ones.)  Usually "fatty acids"
    are very long chain acids such as oleic acid, etc.  (Fats themselves
    are esters of "long chain acids" and glycerol thus fatty acids are
    usually thought of as being "long chain" also.)  Jean and Scott also
    thought that if indeed hydrolysis of glycerol esters were the
    problem, they would result in yellowing of the foam and messy
    deposits.  (Guess they wouldn't make ethafoam out of used bacon
    grease.)  It also seems much more likely that if Dow was already
    using a physical blowing agent like CFCs that they would be more
    likely to switch to a more acceptable physical blowing agent such as
    pentane (very commonly used right now) rather than going through all
    the expense of adding chemical blowing agents and reformulating the
    plastic to handle such blowing agents.

    All in all, it just sounded like a weird problem.

    -Doug

    Date: Mon, 8 Feb 93 03:18 CST
    From: Jessica Johnson <tqaa345 [at] utxvm__cc__utexas__edu>

    I've spoken to the source of the rumour on Ethafoam.  Her name is
    Milly Walker the Collections Manager of the Dr. Pepper Museum in
    Waco.  She has correspondence with F. Douglas Wilson, Product
    Steward for Ethafoam from September 1992.  In this letter he
    explained that in 1990 Dow Chemical changed their blowing agents
    from CFCs to stearamids or fatty-acid derivatives.  According to him
    they have the unfortunate effect of migrating to the surface of the
    Ethafoam over time and leaving a soapy feeling residue.  He did an
    informal pH test of the surface of the foam by placing a water
    droplet on the surface and measuring pH with pH paper.  Ethafoam
    products with no additives (slip agents, anti-static) have a pH of 6
    in his test; those with additives gave a pH of 5.  Milly Walker says
    her samples seem to feel more soapy over the time she's had them.
    Does anybody know what blowing agents Sentinal Foam uses?

    Jessie Johnson

    Date: Mon, 15 Feb 93 16:19 CST
    From: Jessica Johnson <tqaa345 [at] utxvm__cc__utexas__edu>

    ... I spoke to Douglas Wilson, Product Steward for Dow Ethafoam.  He
    was the one who wrote the letter to Milly Walker at the Dr. Pepper
    Museum, and the original source of information that's floating
    around.  According to Wilson, early in 1990 the blowing agent for
    Ethafoam was changed from CFC 114 to HCFC 142B because of concerns
    about the damage to the ozone layer.  HCFC 142B (and most other
    blowing agents that aren't CFCs) require "perm select additives"
    which maintain a pressure balance between the off-gassing blowing
    agent and the air permeating into the structure and keeps the cell
    structure from collapsing.  This is where the "fatty acids" come in.
    The additive they use is stearyl stearamid, a fatty acid derivative
    (I think).  In the pink anti-static Ethafoam they use glycerol
    monostearate.  Because of tighter government regulations they will be
    changing the blowing agents again within the year, however, whatever
    they use will probably require a "perm select additive".

    So what does this mean for those of us that depend on Ethafoam?
    Wilson doesn't know how stable stearyl stearamid is and whether it
    will go through chemical/physical changes over time that might
    affect objects in contact.  He thinks there must be a molecular film
    of stearamid on the surface of Ethafoam, but that it probably
    doesn't migrate towards the surface, but stays dispersed in the
    foam.  That last statement was just a guess he made though.  He also
    did an informal pH test (I reported it in another message) that
    showed the surface pH to be about 6, this is probably wildly
    inaccurate though.

    I've talked to Jean Tetreault at CCI about this some more, and he's
    going to look into it further.  I also plan to talk to people at
    Sentinal and find out if their polyethylene foams have the same
    additives.

    I'd appreciate any ideas or feedback anybody has.  Is pH 6 too
    acidic for sensitive objects, are we going to have to go back and
    cover all of our ethafoam.  Will paper work, or does it have to be
    impermeable (another use for Tyvek!) Should we worry about fatty
    acid deposits even on non-porous stuff like porcelains, will it
    attract dust?  Is it volatile, another source of acidic vapors in
    storage.  What else should I worry about?

    Jessie Johnson

    Date: 09 Feb 1993 10:38:09 -0400 (EDT)
    From: Doug Nishimura <dwnpph [at] ritvax__isc__rit__edu>

    ... I went back to notes from Scott Williams at CCI from 1988/1990
    (a week session on plastics in Toronto at the ROM and the AIC
    pre-session) and noted that from his work that Dow (Canada) (I
    assume) said that Ethafoam was "pentane replaced by air".   In the
    same notes he says that Sentinel is "butane then air."  Since
    physically blown foams don't leave chemical residues, I can only
    assume that CCI got this information from Dow Canada and Sentinel
    respectively although it does leave the question that if pentane/air
    was used in Ethafoam before, then why does Dow need to change the
    blowing agent.  Stearamide is one of the compounds added (at least in
    Canada) as a slip agent for polypropylene films.  The other one used
    in Canada is oleamide.  Similar long chain amides of fatty acids are
    used in the US.  These substances (I have a bag full of one of the
    agents used) are waxes of sorts and considered to be chemically
    fairly inert.  The problem is that they leave a waxy coating on
    things in contact with them and tend to make PP films look cloudy.
    I've seen these compounds used in some PE films also.

    Stearamide will undergo acid catalyzed hydrolysis although it is very
    slow.  Even very small amides require a lot of work to react.
    Benzamide with ethanol (while not hydrolysis is a very similar
    substitution reaction) requires HCl at 75 C for 28 hours and
    produces about 54% theoretical yield.  Stearamide is very insoluble
    in water and would be very slow to react.  Even if you did get
    stearic acid out of this, it too is very very insoluble and has a
    pKA of 198.6.  Jean Tetreault raised the point that if large chain
    fatty acids are formed, that Ethafoam will have a yellowing problem
    that would not be acceptable to Dow or the public.  Stearic acid can
    undergo oxidation in the air forming a yellow residue with a rather
    rancid odor to it....

    One last thing:  the difference in pH between a 5 and a 6 with
    plastic materials is pretty iffy in significance.  Even using a
    three hour soak time with partly degraded cellulose acetate (good
    water penetration, reasonably fast diffusion and very soluble acid)
    three specimens from the same piece of film (no gelatin) results in
    a wider than 1 pH unit variation.

    -Doug

    Date: Tue, 9 Mar 93 16:40 CST
    From: Jessica Johnson <tqaa345 [at] utxvm__cc__utexas__edu>

    I have just received CCI Analytical Report EDR No. 1883 from Jean
    Tetreault.  In it he describes tests he did evaluating Ethafoam
    (Dow), Polyplank (Astro-Polyfoam Ltd.) and Sentinel foam (Sentinel)
    in response to my questions and those of other individuals.  To
    quote his cover letter ..."The conclusion of this report shows that
    there is no fatty acid inside the foam.  Ethafoam uses stearyl
    stearamide a fatty amide as blowing "control" agent to slow down the
    blowing process.  Because amide compounds have been used for years
    in the past as slipping agent(s) without reported damages, we still
    consider polyethylene foam as suitable material." ....

    Jessica Johnson

                                  ***
                  Conservation DistList Instance 6:49
                  Distributed: Friday, March 12, 1993
                        Message Id: cdl-6-49-005
                                  ***