Volume 18, Number 6
Oct 1994

EC's STEP Project on Pollution & Paper Permanence is Finished;

Report will Exceed 500 Pages

The objectives of the EC (European Commission) research project, STEP CT 90-0100, have been to determine effects, especially synergistic effects, of air pollutants and environment on the stability of cellulose materials, in particular paper used and stored in museums, archives and libraries. The research was carried out by four European research institutes: TNO Centre for Paper and Board Research, Delft, The Netherlands; Centre de Recherches sur la Conservation des Documents Graphiques, Paris, France; Department of Inorganic Chemistry, Chalmers University of Technology and Göteborg University; and the Swedish Pulp and Paper Research Institute, Stockholm, Sweden.

To reach the objectives, a number of paper grades were selected and reference papers were manufactured. The investigation was not limited to newly made materials; old and naturally aged papers were also used. Three mass deacidification processes were evaluated with respect to their ability to protect against further acidification of the papers. These processes were: the DEZ (DiEthylZinc) gas phase process as run by Akzo Chemicals, Texas; the solvent-based Methyl Magnesium Carbonate (MMC) process, a modification of the Wei T'o process used at the Bibliothèque Nationale in Sablé, France, called the Sablé process; and the Magnesium Butoxytriglycolate solvent-based process used at the FMC Corporation, MG3-Lithco (FMC).

The papers were thermally aged (12 days at 90°C/50% relative humidity), artificially polluted (4 and 12 days exposure using 20 ppm NOx and 10 ppm SO₂), and thermally aged after the pollution. In a selection of the papers, the deposition of SO₂ and NOx took place at ambient pollutant concentrations and different levels of relative humidity (RH). The chemical, mechanical and physical changes in the materials were measured and evaluated.

It was concluded that the relative humidity played an important role in the uptake of the air pollutants and it is therefore recommended not to store papers at RH levels higher than 50%. At all levels of RH investigated, there was a synergistic effect of NOx (= NO₂ and NO) on the SO₂-induced deterioration of paper. It is therefore recomended to store paper at an NOx level as low as possible.

It was shown that all three deacidification processes protected paper against the attack of air pollutants, although some quantitative differences occurred. However, it was also shown that the protection by the three processes was not the same. The permanence of the deacidified papers was increased by all three deacidification methods used. Modern acid papers benefitted more from deacidification (were better protected against acid attack) than acidic naturally aged papers.

In general, the acid wood-containing papers (those made with mechanical pulps, such as groundwood) showed a relative rate of deterioration similar to that of the acid woodfree papers (those made from chemical pulps). After DEZ- and FMC-deacidification and subsequent pollution, the rate of deterioration of wood-containing papers was comparable to that of the deacidified acidic copy paper. However, after the Sablé deacidification and subsequent pollution, they showed a greater rate of deterioration than the woodfree papers. Care must therefore be taken in the deacidification of wood-containing papers, because protection against acid attack depends not only on the alkalinity, but also on the amount of active alkaline compounds.

To protect paper against air pollutants, it is not necessary to have a perfectly homogeneous distribution of the active compounds. To protect papers against internally generated acid, however, the distribution of the alkali reserve has to be as homogeneous as possible.

Deacidification improved the durability of the paper. Deacidified papers will have good protection against acid attack under the archival storage conditions usually recommended (50% RH and 23°C).

All alkaline papers were well protected against acidification, but it was shown that the protection level differed according to the type of alkaline compound. The presence of an alkaline reserve is no guarantee that the paper will not be degraded by acid attack. More research therefore has to be carried out on the use of inorganic compounds and their protection against acidification.

Because of the (synergistic) effects found on accelerated deterioration of paper using SO₂ and NOx as pollutants, it is recommended to include other outdoor air pollutants (ozone) and/or indoor pollutants (formaldehyde) in future research programs.

From a comparison of the characteristics of naturally aged papers and new thermally aged papers, it was concluded that thermal aging seems to be a reasonable method for evaluating paper permanence. Also, the characteristics of naturally aged papers and artifically polluted papers were comparable. It is therefore recommended to use artificial pollution as a supplement to thermal aging, especially when deacidification and/or added alkaline inorganic compounds are to be evaluated. If an artificial pollution test method is to be standardized, it is recommended that mild exposure conditions should be used and that a time effect should be included.

Paper stocks of the grades investigated have been stored and may be obtained from the TNO for reference purposes in future research. Contact John Havermans, TNO Centre for Paper and Board Research, Schoemakerstraat 97, P.O. Box 6034, 2600 JA Delft, The Netherlands, tel. 31.15.69 66 74; fax 31.15.69 65 11.