National Library News July/August 1999 Vol. 31, nos. 7-8

Challenges in Mass Deacidification

Photo: Stephen Homer

The mass deacidification system has been in operation for 18 years, implemented by the then Conservation Division of the National Archives of Canada, and, since October 1, 1997, run by the National Library of Canada. Over the course of these years, mass deacidification has faced many ongoing challenges. The first and overall challenge is addressing the slow deterioration and changes in molecular structure occurring in the acidic paper that had been used for publishing many of the items in the Library’s collections. Equally important have been the tasks of analysis and experimentation, the establishment of criteria and procedures, the building of custom-made equipment, and the evolution and development of appropriate solvents to be used in treatment. These challenges need to be met in order to achieve the level and quality of deacidification necessary to preserve and protect Canada’s published heritage in print form.

Securing resources to exploit the full potential of the system has also been a major challenge. Because of the nature of the deacidification process, it has been necessary to ensure that whatever treatment processes used for the mass treatment of printed materials respect the evolving legislation and regulations that the Government of Canada and the Province of Ontario have put in place to address ozone depletion and global warming. Until December 1997, when a new solvent was introduced for treatment purposes, the reduction of ozone-depleting substances (ODS) was a major preoccupation. Carrying out this public good of ensuring the long-term availability of Canadian print publications has to be balanced against societal concerns regarding the protection of the environment.

At the end of the 1970s, to conserve the Canadian printed heritage more quickly than through conventional methods, a mass deacidification program was introduced with the purpose of protecting our books and documents against the damaging effects of acid in paper. Therefore, from 1981 to 1986, mass deacidification efforts were directed mostly towards research and development. We had to be cautious with regard to the materials to be treated, since certain inks and binding materials could be altered by the treatment, particularly at one critical stage where documents are immersed in a solution of liquefied gases. During this period, we had to individually test all documents undergoing treatment so as to prevent irreversible damage. That would enable us, at the same time, to become familiar with the materials capable of undergoing treatment and also to identify non-treatable materials. At the very beginning, predictions regarding the production capacity of the system had been set at approximately 240 000 documents per year on the condition that it operated 24 hours per day with sufficient personnel and treatment solvent. The system was used to full capacity from 1992 to 1995 only. Because of budget reductions, in April 1995 the National Library was forced to limit the use of the system to only one shift per day. Table 1 shows the variations in annual productivity.

Table 1

*For consistency reasons, this data is established according to calendar year.

Since the system was put in place, over 925 000 items in the Library’s collections have been deacidified. To date, close to one million documents have undergone treatment. While significant, there are many other documents which remain at risk of deteriorating if they are left untreated.

The importance of solvent recovery is twofold: as the purchase price of the solvent is high, for purely economic reasons, wastage must be kept to a minimum; but equally significant are our environmental responsibilities, as laid out in the Montreal Protocol. In order to maximize overall solvent recovery, different solvents have been developed over the years.

The first deacidification solution formula used the specially blended gas cfcs 12/13 to disperse the methoxy magnesium methyl carbonate (MMMC). This solution was used until 1993. During testing, we had thought that we could obtain better results if the pressure of the chamber used for treatment was lowered. We looked for a liquefied gas that was compatible and could be used under much less pressure in order to give the desired results. The supplier therefore added a percentage of another coolant, which made operations safer for staff while offering acceptable results. However, because of the slower evaporation process, it was more difficult to recover the solvent and to control the release of gas into the atmosphere.

Over the course of 1993, a feasibility study was undertaken on the replacement of chlorofluorocarbons (CFCs), which were scheduled to be banned in January 1996 ¹. The latter were replaced by hydrochlorofluorocarbons (HCFCs) ², the only other product successfully mixed by the manufacturer at the time. This change slightly increased the quantity of recovered solvent. With all the experience acquired over the course of the previous 12 years, followed by the modifications made to the adjustment of electrical controls, we were able to overcome the difficulties caused by the pressure and we gradually began to increase our solvent recovery rate.

In December 1995, it was necessary to purify the system of any trace CFCs and to start using only the HCFC formula. Use of the HCFC formula resulted in improved recovery. However, we could not recover major quantities of solvent without prolonging the time of each treatment cycle, resulting in a decrease in the number of cycles from five to four per day. And in 1996-1997, all system components were examined for leaks, no matter how minor. By studying all possibilities, we once again prolonged the recovery stage of the solvent, which consequently reduced the number of cycles to three per day.

We could have used the HCFC formula until the year 2000, when Ontario planned to ban its use. The supplier of the solution suggested testing a chemical formula using hydrofluorocarbons HFCs ³. Tests proved to be fruitful and even beneficial. In fact, inks affected by the previous solutions remained stable in the new solution, which was named the "Good News Formula." Materials such as polyvinyl chloride (PVC) bindings, mimeograph pamphlets and, of course, alkaline paper, make up the list of materials presently excluded from treatment. It is believed that system modifications will eliminate these exclusions.

Table 2