Polyvinyl acetate and offgassing

Alexandra Greathead <mcard.pro.kew<-a t->gtnet< . >gov< . >uk> writes

>I am in the process of making boxes in which rolls of 35mm negative
>film strips will be stored.  I am using PVA in the process of making
>the boxes and am wondering what the consensus of opinion is
>regarding the length of time the boxes should be left open and
>unused until offgassing no longer occurs.

Polyvinylacetate is, effectively, acetated vinyl polymers.  In
simple terms each polymer holds 'acetate units' which will, in time,
be broken away by reaction with air/moisture as acetic acid vapour.
This loss continues throughout the life of the material; acetic acid
is a decay product of polyvinylacetate.

This fact means that the adhesive will not simply stop off-gassing
after a short period, but will continue to do so as long as there is
acetate present, which means probably as long as you expect your box
to last!  If you do not wish to risk acetic acid vapour effecting
your photographs, do not use polyvinylacetate as your box adhesive.

Presumably an institution of the size and complexity of the Public
Record Office must hold a considerable quantity of 35mm material,
not least as microfilm?  In theory the PRO will be housing such
material in suitable, commercial photosafe storage packages, rather
than actually making each box by hand?

Your query raises an important question.  What adhesives are being
used in commercial photo-storage boxes?  The adhesive on the
microchamber boxes looks very much like a PVA; could Mark Vine
clarify this for us?

We use a polyvinylalcohol solution which does not contain acetate.
It can be bought as granules and if takes about 5 minutes to make in
a microwave oven, twenty minutes or so on a hot-plate.  Anyone
wanting a recipe and details of where to get the material can
contact me here at Dorset Record Office.

Chris Woods
Senior Conservator, Dorset County Council
Chairman, Photographic Materials Conservation Group
+44 1305 250550

                                  ***
                  Conservation DistList Instance 11:13
                  Distributed: Friday, August 1, 1997
                       Message Id: cdl-11-13-007
                                  ***