PRESERVATION RESEARCH RELATED TO THE SWEDISH R&D PROJECT ON PAPER PRESERVATION
Ingmar Fröjd, National Archives of Sweden
The Swedish R&D Project on Paper Preservation (FoU-projektet for papperskonservering) is conducted by major public institutions concerned with the preservation of archival and library material. The main aims of the project are: to build up knowledge and competence in the field of preservation of paper, to evaluate available conservation methods, and to initiate and promote the production of long-lasting printing and writing paper grades.
The recently closed Nordic Fine Paper Project was initiated by, but not subordinated to the Swedish R&D Project on Paper Preservation. It was carried through by major cooperating Nordic research institutes and the R&D Project.
The project Effects of Air Pollutants on Cellulose Containing Materials is carried through by cooperating Dutch, French and Swedish participants within the STEP (Science and Technology for Environmental Protection) programme. The R&D Project on Paper Preservation is involved as a sponsor on behalf of Swedish interests.
The following presentation covers completed and current research within the framework of the Swedish R&D Project on Paper Preservation or research programmes linked to it through partner- or sponsorship, in order to give a complete overview of all related activities. Planned but not yet initiated tasks or tentative subprojects are not included.
1 The state of the art
1.1 Literature survey
By way of introduction, a literature survey was carried out to review the most important factors affecting the ageing and degradation of paper. The survey also included a short appraisal of test methods, effects of the papermaking process and printing, a comparison between natural and accelerated ageing, and a short introduction to some deacidification methods.
The survey resulted in a general assessment stressing the importance of initiating basic research to develop greater competence in the field of paper preservation, to improve storage conditions, to develop diagnostic methods for assessing the conditions and ageing stability of papers, to evaluate deacidification methods and, finally, to develop ageing stable wood-based papers. According to this assessment the project programme was set.
Status: Completed and reported by STFI under the leadership of Tom Lindstrom in Ageing/ Degradation of Paper —A literature survey.
1.2 Damage survey
A damage survey has been completed at the National Archives, the Royal Library and the University Library of Gothenburg. The survey was carried out as an Uppsala Variant of the so called Stanford method, which had been established at a previous study at the University Library of Uppsala. This study had confirmed by chemical analysis that a simple test procedure based on folding by hand reflected the properties of the paper.
The results showed that the largest proportion of weak paper is in the material from 1860-1890, and that the average proportion in the investigated collections is about 20%. Brittle books are rare. The proportion of weak paper and the dating are considered to be representative on a national level.
Our experience of this method is that it is simple to use and gives reliable results when making a damage survey. The Uppsala Variant has later been used in a major survey at the Dutch National Archives and the Royal Library in the Hague, the Netherlands. The results were similar to the Swedish.
Status: Completed andreported by Jonas Palm and Per Cullhed (Uppsala University Library) in Deteriorating Paper in Sweden — A Deterioration Survey of the Royal Library, Gothenburg University Library, Uppsala University Library and the National Archives.
2 Methods for the characterization and
evaluation of paper ageing
2.1 Natural ageing of paper
A collection of naturally aged papers, kept at the Swedish National Testing and Research Institute (Statens Provningsanstalt), has been investigated. The papers, manufactured from 1908 up to present time, had been tested within a couple of weeks after manufacture. These papers were reinvestigated with respect to strength properties, degree of sizing, and for some papers, copper number and acidity.
The retention of tensile strength is high, often more than 90% even after 80 years. The retention of elongation at break is around 70%. The fold numbers of papers manufactured up to roughly 1950 have changed considerably with retentions less than 20% for papers made from rag or from chemical pulp. The fold numbers were, however, approximately ten times higher for the rag papers. The changes are attributed to the acid sizing and, in some cases, to the low fibre quality. There is some correspondence between low copper number (low contents of easily oxidized components) and high retention of fold.
The properties evaluated in this subproject cannot account for all differences between papers on ageing. General descriptions in such terms as fibre composition and acidity are insufficient to predict permanence. A fair correlation between natural and accelerated ageing was observed, but the choice of ageing conditions is important. Accelerated ageing without moisture is apparently of limited value.
Status: Completed by Statens Provningsanstalt (Swedish National Testing and Research Institute) and reported by Marie Louise Samuelsson and Karin Sorner in Naturligt aldrat papper - Svenska papper 1908-1988, with a summary: Natural Ageing of Paper — Swedish Papers 1908-1988.
2.2 The physics and chemistry of paper ageing - A comparison between accelerated and natural ageing
Accelerated ageing at an increased temperature is generally used for the evaluation of ageing properties. There is however, no investigation that justifies
the underlying assumption that accelerated ageing actually induces the same type of changes that a natural ageing process would do. Therefore, data from other subprojects within the Swedish R&D project on paper preservation together with additional chemical spectra (e.g. CP/MS NMR) will be subjected to multi-variate data analysis in order to reveal the process of accelerated ageing in a few "latent" variables. Some selected series of old papers are evaluated in order to describe the natural ageing in a similar manner. The development of accelerated ageing will then be compared to that of natural ageing, and the relevance of accelerated ageing may be assessed.
Status: Carried out by STFI and still in progress. Coordinator Tommy Iversen.
2.3 Accelerated ageing of paper - A criti-
cal review of methods and evaluation
The effects of different ageing conditions on a wide range of paper samples have been investigated. The paper samples range from archival grades to unbleached kraft paper. The ageing conditions chosen are not only the widely used 80 C/65%RH and 90 C/ 50%RH, but also the more extreme conditions 95'C/ 65%RH. Several mechanical properties have been determined. Standard methods are used for tensile testing (incl. strength, stretch, elastic modulus, tensile energy absorption), tear testing and folding endurance. In addition to these methods, the Pulmac zero-span tensile strength and a so called fracture toughness test, developed at STFI, are included. The optical properties are also determined. The effects on paper properties of the different ageing conditions are compared, and the suitability of the various mechanical tests for monitoring these changes will be assessed.
Status: Carried out by STFI and the Swedish National Testing and Research Institute in cooperation. Almost completed. Coordinator Petter Kolseth.
2.4 Accelerated ageing of paper – The influence of papermaking variables
The ageing of paper is generally looked upon as a process in which the sheet becomes brittle. This embrittlement, or loss of toughness, is often monitored by measuring folding endurance or tearing resistance. The new method, the fracture toughness developed at STFI, measures a more well-defined fracture resistance of paper, which has been shown to work well in other situations where brittleness is a critical prop-erty. We know of several papermaking variables that can make paper tougher (less brittle), but very little about how these variables affect the ageing process. In this subproject, the influence of several of these variables and of others, such as fibre furnish, beating, wet pressing, shrinkage during drying and calendering, on the accelerated ageing of paper are investigated.
Status: Carried out by STFI and still in progress. Coordinator Petter Kolseth.
2.5 Characterization of low molecular weight substances formed in aged paper and their correlation with strength loss
The natural ageing processes in paper lead to the formation of several low molecular weight compounds. However, knowledge of the composition of these compounds and their correlation to strength loss in aged paper is incomplete. In this subproject, aqueous extracts from aged paper samples are analysed in order to identify and quantify the formation of such compounds. Several analytical techniques including gas chromatography (GC), liquid chromatography (LC) and ion chromatography (IC) are used. The compounds identified so far include several low molecular acids, e.g. acetic acid, propionic acid and levulinic acid. The correlation between these and other cellulose and hemicellulose degradation products and paper strength parameters will be tested using multivariate data analyses. Further, the formation of low molecular weight compounds in natural and artificial ageing processes will be compared. This will provide insight into similarities and differences between the mechanisms leading to strength loss in these processes. The potential of using chemical analysis of minute paper samples to predict the condition of aged paper will be evaluated.
Status: Carried out by STFI and still in progress. Coordinator Marianne Bjorklund Jansson.
2.6 Correlation between ageing of paper and developed chemiluminiscence
Ageing of paper is mainly an oxidative process. In many oxidation reactions, reactive intermediates or the excited products formed may give rise to chemiluminiscence. The chemical reactions that occur during ageing sometimes leave traces of reactive structures like peroxides or excited carbonyls in the paper. In the methods that we use these unstable chemical groups are forced to relax. If the paper is treated with
heat or with oxidation agents like hydrogen peroxide or oxygen in alkali, chemical reactions occur and if some of the energy is released as light it can be detected. Very weak light emission can easily be quantitatively determined using sensitive photomul-tipliers.
Samples of different origin and age have been examined. Chemiluminiscence was obtained by treating the paper sheets at an elevated temperature. The light is weak but measurable. The goal is to find a correlation with the degree of ageing. Since paper samples of a well-defined composition and history are not readily available, the absolute calibration on a realistic time scale of ageing is not a straightforward process.
Status: Carried out by STFI and still in progress. Coordinator Nils-Olof Nilvebrant.
3 Evaluation of conservation treat-ments
3.1 Effects of deacidification
The purpose of this subproject was to examine whether there were any differences in the effects of preventively or retrospectively deacidified papers exposed to simulated air pollutants (SO2 and NO2) and accelerated ageing. Effects of calcium hydroxide and magnesium methyl carbonate (MMC) were studied.
The results did not answer the question as to which treatment is generally to be considered the best. The additional alkali reserve created in the samples was about 1% unit carbonates, no matter which paper or treatment was used. There are however indications, that calcium hydroxide works better in preventive treatment whereas MMC works better as a retrospective treatment with respect to strength properties. There was a low correlation between pH, the rate of yellowing and the rate of degredation. Finally, the results indicate that certain air pollutants maybe react with the paper itself instead of with the buffer of magnesium carbonate.
Status: Completed by the Conservation Departement of Uppsala University Library with the assistance of the Departement of Inorganic Chemistry of Uppsala University, the Swedish National Testing and Research Institute, and STFI. Reported byJonas Palm inPreventiv och retroaktiv avsyrningavpapper, with a summary: Preventive and Retrospective De-acidification of Paper.
3.2 Evaluation of available mass treat-ment methods
A lot of data from different evaluations of mass treatment methods are now internationally available in the literature, and it appears not to be necessary to repeat all these tests. An independent evaluation based upon our own choice of test material and relevant methods is however, still required.
A selection of well characterized samples will therefore be treated (which naturally presupposes vendor cooperation) and evaluated with respect to immediately observed effects, and the properties determined by physical tests and chemical analysis. The long-term effects will be determined by physical characterization after accelerated ageing. The outcome of the evaluation of the effects of the treatments will create the necessary base for the next step in a total assessment, including cost accountings, logistics etc
Status: A recently initiated cooperative subproject. Coordinator Petter Kolseth.
4 Storage conditions and environ-mental effects on paper ageing
4.1 Storage conditions in archives and libraries
In order to obtain a picture of the general storage conditions in Swedish archives and libraries, the climate and common air pollutants were measured in some institutions. The institutions chosen were the same as in the damage survey (section 1.2) together with the Uppsala University Library.
With regard to one of the most interesting questions, it was established in the study that a considerable proportion of the incoming SO2 and NO2 in the supply air was deposited in the store rooms/ stacks. No certain correlation between percentage SO2 or NO2 deposited and outdoor temperature, relative humidity or degree of air pollution was, however, established.
The results are compared with a study at Dutch archives and libraries which show some similarities with the Swedish study.
Status; Completed by the Swedish Environ-mental Research Institute (IVL) and on its way towards being published. Coordinator Ann-Beth Antonsson.
4.2 Effects on paper ageing of air pollu-
tion
4.2.1 Effects of nitrogen dioxide
Several studies have discovered the effects of sulphur dioxide on the ageing of paper and have clarified the mechanisms. The effects of nitrogen dioxide, which can attain considerable concentrations particularly in urban areas where most archives and libraries are located, is less clear.
The study shows, that the effects of the gas exposure and accelerated ageing depend on the composition of the paper. Acid-sized papers from chemical pulp lose their strength but the optical properties are affected to only a small extent. The mechanical properties of acid-sized wood-containing paper were not affected either, but the optical properties were strongly affected leading to discoloration. Neither the mechanical nor the optical properties of neutral-sized paper from chemical pulp or rag were affected by the exposure and ageing, apparently because the calcium carbonate filler neutralized acid substances. The study indicates the importance of further research on the effects of interaction between nitrogen dioxide and other pollutants, e.g. sulphur dioxide.