Vacuum packing

David Kerr <d.kerr [at] nls__uk> writes

>I am experimenting with vacuum packing as a means of storing
>newspapers and I would like to find out more about other peoples
>experiences using vacuum packing technology as a means of storing
>library material.  I know the benefits of anoxic packaging to
>prevent chemical and biological reactions but there are a few areas
>in which I'd like find out more on ...

The British Library ran a pilot project to look at the use of vacuum
packing for newspapers and low-use collections. The new newsprint we
vacuum packed did not change colour when exposed to high levels of
UV light, increased temperature and higher humidity levels.
Alteration in colour can be indicative of cellulose degradation.
More recent tests in Sweden have shown that new newsprint retains
more of its mechanical strength when stored in an anoxic
environment.

The tests we undertook did not show the same benefits for acidic
papers, as yet no tests have been conducted by us on paper that has
been de-acidified then placed in an anoxic environment or vacuum
packed.

Vacuum packing and anoxic storage are not the same process, in
anoxic environments you can control humidity, the gas levels,
scavenge any off-gassing, but you do not make a 'hard vacuum'.

However, as in most things in conservation, the issue of vacuum
packing/anoxic storage is not that straightforward, so a few
questions need to be considered by anyone undertaking this type of
project:

    *   Do you intend to use vacuum packing purely as a storage
        method? We as yet do not have enough evidence to show vacuum
        packing can be recommended for archival storage.

    *   Do you intend to pack new editions and/or your existing
        collections? It is thought to be best that you deacidify
        before vacuum packing.

    *   Will you microfilm the newspapers before vacuum packing?
        Makes sense to do this, as you do not want to have to open
        the enclosures too many times.

    *   Are you concerned with how the newsprint will react in a
        vacuum pack or anoxic environment over the long term? It has
        been shown that degradation processes can speed up when
        acidic paper is in airtight enclosures. More research is
        needed on what happens inside the anoxic enclosures and
        vacuum packs.

    *   Paper can profit from low-oxygen atmospheres but other
        reaction mechanisms like hydrolysis are as important as
        oxidation. Tests have shown that hydrolysis can still occur
        in vacuum packages.

    *   Anoxic atmospheres can be generated by various means not
        just by vacuum packing. These modified atmospheres do not
        give a hard vacuum (package) and offer no space saving
        benefits.

Anoxic microclimates are commonly generated by purging or modifying
the air within a well-sealed environment to exclude oxygen. Common
gases for replacing the oxygen by purging are nitrogen and CO2,
although argon is sometimes used. Oxygen absorbers will scavenge the
oxygen from the atmosphere in a barrier film envelope leaving
(essentially) nothing but nitrogen. Each method has its advantages
and drawbacks. Combination techniques can be more effective than
purging or using oxygen absorbers alone.

>What barrier films should we be looking at for long term storage of
>material and what shelf life do these barrier films have?

At the moment the 'best' barrier films we have for low-oxygen
storage or treatments are made from low oxygen-permeable
multi-layered films such as aluminium laminates or ESCAL. The oxygen
permeability of the ceramic deposited, transparent ESCAL-sheet
amounts only to 0.05 cc/m2/day/atm. The clear barrier films are not
particularly robust, even a deep scratch into the package can result
in loss of vacuum (puncture resistant SuperEscal is available but
very expensive). Large vacuum packets (broadsheet newspapers) are
difficult to physically handle and store. To protect the package it
would be best to box the vacuum package.

The sealing of the bag is very important it is the weakest part of
the structure.

The seals of the sheets must be around 8 mm and gas tight. For
long-term storage, make three seals behind each other.

>If newspapers are vacuum packed, making them a solid block, can they
>be stored vertically or is there still a risk of distortion if
>stored this way?

Handling and storage of large vacuum packages is difficult, when
vertical must make sure no stress is placed on the sealed edge. If
the vacuum fails the package can collapse.

>Should we put a buffer, such as acid free paper, between the item
>being stored and the barrier film?

No one has studied the long-term effect of contact between barrier
films and the objects in the package. The buffer may eventually
degrade and stop absorbing any off-gassing and may even when 'full'
leak degradation products back into the enclosure. Tests with
Corrosion Intercept products look to be more useful than other
options such as Micro-chamber papers.

>Should oxygen scavengers always be used?

Ideally as a safeguard against leakages in anoxic housing, but puts
the cost up,  if  the  vacuum pack leaks you lose the vacuum, and
would need a lot of scavengers to keep a hard vacuum in a large
package. No tests have been done on how effective scavengers are in
a vacuum pack.

>Has anybody carried out a study to find out how much shelf space is
>saved when vacuum packing as opposed to boxing material?

Not as far as I know--you could contact Stuart Welch at Conservation
by Design: he may know more.

Jerry Shiner, Keepsafe Systems, Anoxic and Microclimate Storage
Solutions, found the volume of a stack of paper was generally
reduced to 60% or so in vacuum packing.

With reference to the question of aging, Dr John B.G.A. Havermans of
TNO Industry in the Netherlands has carried out some work. This
project was looking at the possibility of enclosing acid material in
a partial vacuum with a special gaseous atmosphere intended to raise
the pH of the material in the enclosure to create a kind of
suspended animation without permanently and physically altering the
composition of the paper.

   "Based on the approach that the in-pouch environment has to be
    equal to the outdoor environment during ageing studies, in our
    case 24 days at 70 deg. C and 55% RH, the conclusion can be
    drawn that encapsulation of paper using laminated uncoated
    polyester pouch and a slight vacuum, will neither influence the
    mechanical paper properties in a positive or negative way in
    time. However, paper deterioration will continue and paper
    acidification will even be enhanced by the paper encapsulation.
    It is suggested therefore that only for deacidified papers this
    accelerated acidification will not occur. Based on the
    artificial ageing experiments, care has to be taken for storing
    acid papers encapsulated."

        Extract From: Ageing Behaviour of Encapsulated Paper, John
        B.G.A Havermans, Restaurator 20 1999-108-115

There are still some fundamental questions to be answered before I
would recommend vacuum packing for archival storage.

David Jacobs
Senior Conservation Officer
The British Library
96 Euston Road
London NW1 2DB
+44 207 412 7897


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                  Conservation DistList Instance 18:2
                   Distributed: Friday, June 18, 2004
                        Message Id: cdl-18-2-001
                                  ***