Storing a fibrin bandage

Alan J. Hawk <hawk [at] afip__osd__mil> writes

>We are interested in collecting a fibrin bandage for the National
>Museum of Health and Medicine.  It is made from human blood proteins
>on a mesh and it is extremely hydroscopic.  It cannot be exposed to
>any moisture or oxygen or it will deteriorate.  We are interested in
>suggestions on materials for a container to store and possibly
>display the artifact over the long term. What plastics or other
>materials have an extremely low transmittibility of moisture?

The correct barrier film and oxygen-scavenger combination can
provide a solution for this kind of storage problem. When a properly
formulated barrier film envelope and oxygen removal procedure are
used, an oxygen-free atmosphere can be created and maintained for an
extremely long period.

A few general notes on anoxic packaging:

General uses: In the real world, anoxic packaging is used in the
food industry for a wide range of products (wet and dry)  to extend
shelf life. It is also used in the metals and electronics industries
to protect finished parts and other materials prone to oxidation.
The conservation community is beginning to use it for storage of
sensitive organic materials (hair, rubber, pelts, plastics, etc.)
Anoxic packaging is also widely used to safely destroy infestations
in museum objects.

Rigid vs flexible containers: Almost all anoxic packaging uses
flexible barrier films rather than sealed rigid containers. Changes
in volume due to atmospheric effects make the sealing of a rigid
container very challenging.

Barrier films: Almost all barrier films consist of (at least) three
layers: The outer layer (usually transparent polypropylene, Mylar,
and sometimes Nylon) provides a strong substrate. The middle/inner
layer (often extremely thin) may consist of a metal foil (eg
Marvelseal), EVOH, Saran, or a transparent vacuum deposited ceramic
(eg Escal)- this inner layer forms the gas barrier. The inner layer
is usually low density polyethylene, which melts at a lower
temperature that the other layers, and can therefore be used to
provide an efficient method of sealing. EVOH films are advisable for
short term storage, foil and ceramic films are designed for
long-term storage. Aclar is a good moisture barrier, but does not
match the performance of foil or ceramic based films.

Oxygen scavengers: Oxygen scavengers are now widely available. Most
formulations rely on the oxidizing of a chemical in a semi-permeable
sachet or packet to bind oxygen. Ageless by Mitsubishi Gas Chemical
uses iron to bind the oxygen, the RP System (also made by MGC) uses
an organic deoxidizing chemical, and will also bind many corrosive
gases. Both Ageless and RP are available in various formulations-
most notably RP-A type, which will also reduce the RH in a sealed
container to less than 1% as well as absorbing the oxygen. RP-K type
will not affect the RH within the sealed container.

Ease of use: With only a little practice, barrier films are easy to
manipulate. Once an envelope is made, it is only a matter of
including a measured amount of the correct oxygen scavenger and
sealing the envelope. Envelopes can be sealed with a tacking iron or
home iron, although a sealing machine may be useful when volume work
is done. Snap on sealing clips are available for use "in the field"
and temporary storage. Anoxic atmospheres can also be generated by
flushing with gas (eg nitrogen) or by combining active and passive
techniques (flush and scavenger). Flushing will be more cost
effective for larger projects.

Advantages: Anoxic packaging will protect an object from oxidation,
corrosion from air-borne corrosive gases, water and smoke damage,
and has other advantages (security for infestations, discrete
collections, labelling, tampering protection, etc.) Transparent
barrier films allow visual inspection, photography, radiography,
inventorying, and cataloguing without opening the envelopes.

For more detailed information on these materials and anoxic
packaging in general, please visit <URL:http://www.keepsafe.ca>.  We
are in the midst of a web site "makeover", and welcome comments and
questions about what you would like to see on the site, or
suggestions on how to make it more useful for your work would be
very much appreciated. Please respond directly to info [at] keepsafe__ca

Jerry Shiner
Keepsafe Systems
Microclimate and Oxygen-free storage supplies and solutions
800-683-4696
Fax: 416-703-5991


                                  ***
                  Conservation DistList Instance 15:21
                  Distributed: Friday, August 31, 2001
                       Message Id: cdl-15-21-003
                                  ***