Molecular Traps
As important as alkaline buffering is,
conservation scientists now realize it does have important limitations.
Alkaline buffering does not deliver the degree of protection we once assumed it
provide to our collections. If an acid migrates to, or arises from within (in
the form of a by-product of deterioration), or forms from a pollutant coming
into an alkaline buffered paper, and, if this acid is in contact with a
particle of alkaline buffer, the acid will be neutralized. However, if the deteriorative
molecule is an oxidative species such as a peroxide, or an acid precursor like
an oxide of nitrogen or sulfur dioxide, or a pre-acidic by-product of
deterioration, it will not react with the alkaline buffer. Instead it continues
through the paper housing (i.e, box, envelope, folder, mount board, etc.) and
damages the artifact you are attempting to protect. If a suitable molecular
trap is contained within the alkaline buffered paper, it can capture and remove
those harmful molecules which passed by the alkaline buffering. Our General
Purpose MicroChamber Paper and MicroChamber boxboards (except the
MicroChamber/Silversafe boards) contain both activated carbon and our SPZ
zeolite. The black side of the General Purpose MicroChamber paper (also used in
the MicroChamber boxboards) contains alkaline buffers and an especially
effective activated carbon. The white side of the paper contains alkaline
buffers and our modified proprietary hydrophobic, acid-resistant SPZ zeolite
which we developed and engineered after extensive research to perform the
specific functions necessary to protect your collections. Our SPZ zeolite
removes acids, aldehydes, ammonia, pollutants such as SO2 and NOx, and despite
the incorrect information seen in a competitor’s catalog, it does remove
oxidative gases, even in very low concentrations (see doorway and bus photos
subjected to ANSI standard IT 9.15-1992 oxidative gas tests in MicroChamber
test section on our website. This SPZ zeolite was engineered to remove all of
the known deteriorative molecules that threaten our collections, even those
with very low polarization levels.
Efficacy of Molecular
Traps in MicroChamber Papers
Acids:
It is
interesting to note that our molecular traps are significantly more effective than
an alkaline buffer at removing acids, and unlike buffered-only papers, they
will remove by-products of deterioration such as aldehydes which form acetic
acid. This is important because acetic acid is the primary by-product of
deterioration produced both by paper and by photographic materials. One
of the most dangerous pollutants to paper is acetic acid As the effects of
acetic acid build up in a paper artifact, it accelerates degradation My goal
was to identify materials that would be most effective at absorbing and
retaining acetic acid, and that would be suitable for use in preserving
artifacts. I looked at about 18 different materials, including activated
carbon, clays, calcium carbonate, and several zeolites The activated carbon and
one of the zeolites-called SPZ, (the zeolite Conservation Resources developed
for use in Artcare board, conservation boards, papers and materials) performed
significantly better than the other physical adsorbents … based on its
adsorption and retention of acetic acid-which can be assumed to inhibit
cellulose deterioration-the SPZ zeolite, incorporated in Artcare (and)
MicroChamber technology (products), is a very viable material for preventative
conservation applications. 1
The results
from our tests using gas chromatography show that if we have equivalent
papers-for example a 65 g/m2
interleaving paper, or a 130 g/m2, .006" thick envelope paper, or a
standard 250 g/m2 archival
file folder paper in both MicroChamber paper and buffered paper, the
MicroChamber papers have 170 times the acid-removal capacity of the buffered
papers. In other words, the buffered paper would have to be replaced 170 times
before you would need to replace the MicroChamber paper.
1.
From an interview with James Druzik, Senior Scientist, the Getty Conservation
Institute, printed in the October 2003 Decor magazine.
By-products of
deterioration:
MicroChamber papers are very effective
at removing pre-acidic by-products of deterioration, such as aldehydes. These
pre-acidic deteriorative by-products pass unaffected through traditional
buffered paper because the deteriorative by-products do not react with the
alkaline reserve in buffered papers. If we assume all of the acetaldehyde (a
precursor to acetic acid) removed as deteriorative by-products by the
MicroChamber paper will become acetic acid, we find the MicroChamber paper can
remove what would become 231 times as much acid as would form if only the
buffered paper were present.
Pollutants:
MicroChamber
products do provide protection against common oxidative and acid gaseous
pollutants such as ozone (O3), oxides of nitrogen (NOx, NO, NO2), sulfur
dioxide (SO2), as well as H2S, CS2, ammonia, formaldehyde, peroxides and a
great many other such molecules which can harm collections. The
traditional alkaline buffers in conservation papers do not react with or remove
these deleterious molecules. Furthermore, such molecules can pass unaffected
through even the thickest buffered boards 2,
where they can contact and damage collections housed within these buffered
boards and papers. If, for example, we look at New York City and at Los
Angeles, the EPA (The U.S. Environmental Protection Agency) gives us the
maximum hourly rate of a variety of pollutants measured in these two cities for
one year. Using these maximum concentrations, we can calculate the maximum
amount of a pollutant such as SO2 in one liter of air. Exposing a 24 x 36
MicroChamber folder to a fresh liter (slightly more volume than a quart container)
of polluted air every hour, we find, at the maximum hourly concentration level
of pollutants measured in New York and Los Angeles, the MicroChamber folder has
the capacity to remove the SO2 in NY city for 8219 years, and in LA for 26,224
years. Obviously if the air exchange is increased this figure will be lower.
For example, if the air flow rate into the folder was increased to 10 liters
per hour, the figures would drop to 1233 years for NY City and 3933 years in
Los Angeles, CA. Of course the MicroChamber product will also pick up other
harmful molecules, in addition to the SO2. Therefore to the extent these other
molecules are present and removed, the maximum quantity of SO2 which can be
removed will be lowered-but these figures do at least provide a point against
which you can form a comparison between the effectiveness (zero) of buffered
products and of MicroChamber products.
The preservation advantage offered by
our new MicroChamber boards and papers, which contain both specialized
proprietary molecular traps and alkaline buffers, is quite striking. While
traditional alkaline buffered conservation papers and boards do provide an
advantage over acidic commercial products, this improvement does not begin to
approach the phenomenal gain in protection offered by MicroChamber products
over traditional alkaline buffered products. Alkaline buffered paper is a
technology of the 1960s. MicroChamber materials give you the advantage of
technology from the 1990s. MicroChamber products offer new opportunities in
preventative conservation, increased life and thus reduced preservation costs
for all collections. See the MicroChamber product verses traditional
buffered-only test results on our website.
2. Guttman, C. M. and
Jewett, K. C. 1993 “Protection of Archival Materials from Pollutants: Diffusion
of Sulfur Dioxide through Boxboard”, Journal of the American Institute for
Conservation 32:81-91. Also, see MicroChamber test section on our website.