The Abbey Newsletter

Volume 23, Number 1
1999


ASTM/ISR Paper Permanence Research

by Ellen McCrady

The ASTM's research arm, the Institute for Standards Research (ISR) has two big research projects underway. The first one, now nearing completion, uses accelerated aging. (Arnold 1996) The most recent one, launched in April 1999, will let an identical set of papers age naturally for 100 years , so that the results can be compared. (ASTM 1999) Fifty well-characterized lignin-free and lignin-containing papers have been prepared for this purpose, to see whether lignin interferes with permanence in any way--or, depending on the results, to demonstrate that it does not interfere. This is a gross simplification, but the idea is not as crazy as it seems.

The project was advocated and planned largely by the manufacturers of lignin-containing pulps, although collection-holding institutions have been involved too. What got it all started was a confluence of developments and conditions:

A wood shortage in most countries

Economic recession in Canada, where the pulp industry is very important

The development of a new kind of calcium carbonate that neutralizes the effect of lignin on paper strength and cuts the cost of paper production by allowing the use of cheaper pulps

The production of white office paper made with various amounts of high-lignin pulp

If the pulp industry can provide compelling arguments for the safe use of lignin in fine papers, and if they can get the restriction on lignin removed from the permanence standards, then they can use a cheaper and more plentiful raw material to produce printing and writing paper, and sell it for purposes that require permanence.

Industrial and Chemical Background

Pulp mills take trees and turn them into pulp by separating the fibers. The pulp is then sent to paper mills, which make paper using chemical pulp (processed to remove the lignin) or groundwood pulp (processed to retain the lignin) or both. Since it is impossible to remove every bit of the lignin from wood pulp without damaging the cellulose, even chemical pulp contains some lignin, but not usually enough to shorten the life of the paper significantly.

Groundwood pulp is made from mechanically separated fibers; nowadays this process is facilitated by the use of heat, fungal enzymes ("biopulping") and/or chemicals. They are referred to sometimes as mechanical pulps. Some of them are brown, some are white, but all contain lignin.

Since 1990, more and more papermakers have been adding the newly-developed "acid-tolerant" calcium carbonate to different grades of lignin-containing paper, including fine office paper as well as newsprint. (Before 1990, calcium carbonate could not be used in the paper machine with groundwood pulp.)

What Kind of Permanence will Carbonate give to Groundwood Papers?

These new buffered groundwood papers keep their strength for as long as the carbonate lasts (until it has been neutralized by acidic gases), but their brightness declines as a result of exposure to light, heat, pollutant gases or high humidity, depending on how much lignin they contain. The paper industry takes this darkening seriously, judging by the amount of research on "optical permanence" and "brightness reversion" reported monthly in the abstract journals. However, the industry does not perceive loss of brightness as a permanence issue.

Now the question is whether these alkaline papers can be considered permanent. The lignin content is all that keeps them from meeting ISO or NISO standards. Does it matter if they darken prematurely? Does it matter if the alkaline reserve reacts with gaseous pollutants and disappears before the art work or archival record has reached the end of its useful life?

The answer to both these questions is yes. Both flat paper and bound volumes lose an important aspect of permanence when they darken. If the paper on which a print, drawing, pastel or water color is executed yellows with age, the work will lose both market and esthetic value, especially if the paper cannot be bleached without damaging the image.

It might be argued that books are less vulnerable, because their pages are not normally exposed to light, but they are still degraded (and yellowed) by heat, gaseous pollutants and humidity. (Porck 1990) If they are exhibited, the pages at the opening will also be affected by light and possible exposure to pollution. If they are shelved where light falls on them, the edges of the page will yellow more rapidly than the rest of the page. Microfilming costs for a book with yellowed or darkened pages can double, rising from about $100 to $200, because the exposure level has to be continually reset. Presumably the cost of scanning would also go up.

As for the alkaline reserve, yes, it can be used up. Several studies have been done since 1990 in the U.S., France and Sweden, on buffered or deacidified paper that was exposed to concentrated pollutant (acidic) gases until the alkaline reserve was gone. The paper then returned to a reactive, vulnerable state close to the one it had been in before the buffering compound was added. These studies point up the fact that an alkaline reserve only plays a sacrificial role, buying time for the paper rather than giving it immortality. It follows that a minimal alkaline reserve, say 2% or 3% on the weight of the paper, will lose its effectiveness long before an alkaline reserve of 15%, which is close to current practice.

The manufacturers of groundwood pulps hope that the outcome of ASTM's accelerated-aging and natural-aging studies now underway will demonstrate to their customers that paper made from their product has been "scientifically proven" to be permanent. They rarely if ever qualify this statement to say that it is permanent provided the paper is also buffered with calcium carbonate or some other alkaline compound; their press releases and newspaper stories never mention the stabilizing effect of the alkaline buffer. This is a form of deception, for no good purpose.

Whether the "scientific proof" referred to by the manufacturers can make the public forget what they have learned from their experience with groundwood paper is something that remains to be seen. A factor working against the public's acceptance of calcium carbonate-filled groundwood paper on the market is that yellowing has always been taken as a sign of poor quality, weak and short-lived paper. This perception is based on universal experience over the last 130 years or so, even though the correlation between strength and color was never perfect. (Overbleaching, for instance, can leave paper white but tender.)

We now know that yellowing and weakening are caused by different chemical reactions. Nevertheless, the public is likely to prefer white paper that stays white. International Paper tried to sell its grayish-tan 100% recycled paper to the U.S. government a few years back. They got the contract, all right, and all the agencies were ordered to use it, but the agency staffs thought it was ugly, so they refused to use it. They bought the kind of white paper they wanted on the open market. The grayish-tan recycled paper was never bought again by the government.

Natural Aging Project

Here is a description of the new natural aging project, from the April 6 news release from ASTM:

"For the next 100 years, ten North American facilities [libraries] in a variety of climates will store volumes of 50 experimental paper types, and submit monthly/yearly storage condition reports to the U.S. Library of Congress, and National Archives and Records Administration. At ten intervals throughout the century, specimen pages will be extracted from each site and tested for optical and physical durability by [Arizona State University, CCI, Columbia University, NARA, National Library of Medicine, and the universities of British Columbia, California at Berkeley, Florida at Gainesville, Texas at Austin, and Washington University at St. Louis]. Ongoing results of this first-ever, scientifically-based study will be shared worldwide with industry, academia, and governments...."

This last statement implies unfairly that the ASTM study is the first-ever scientific study of natural aging. The ASTM project will not be a pioneer study of natural aging. Earlier studies were done by Wilson and Parks (1980) and Samuelsson and Sörner (1990). Furthermore, newsprint has been used as a control in aging studies in conservation labs for at least 20 years, with and without alkaline reserves, usually in connection with research on deacidification.

ASTM's news releases on this topic seem to be written by biased industry spokespeople. The research now being carried out, however, is expected to be objective and sound, because of the reputation of the labs carrying out the work. (Arnold 1996)

Buffered Groundwood and Permanence Standards

The paper industry favors accelerated aging over composition as the basis for a paper permanence standard. As one industry representative put it, "The papermaker ought to be able to make paper from elephant shit if he wants to [as long as the paper meets the customer's performance specifications]." The first phase of ASTM research, which began with a planning workshop in 1994, is well underway, with work ongoing in the Library of Congress, Image Permanence Institute, and the Forest Products Lab (and CCI?). It focuses on accelerated aging and is checking out effects of new as well as routine aging conditions, using a large number of paper samples containing different amounts of lignin and carbonate, in different kinds of paper. The results are expected to be used by the industry to persuade standards organizations to specify accelerated aging results, rather than maximum lignin content. (Germany already has a standard like this, a very lax standard, which the librarians refuse to use.)

Whether accelerated aging tests can give a reliable estimate of a paper's lifespan is still an open question, which is one reason the natural aging project was set up by ASTM. Tom Lindström, in his contribution to the TAPPI conference on paper aging, said, "It is obvious that paper aging is a continuously accelerating process, with cooperative and competing chemical and physical reactions, all having different activation energies and which change with the state of deterioration of the material. Thus, from a theoretical point of view, it is only a naive hope that it would be possible to estimate the life length of books by means of accelerated aging tests and Arrhenius approach." (Lindstrom 1990)

There are two problems with using retention of strength after accelerated aging as a measure of permanence. First, aging takes a long time and is expensive. It requires special equipment, facilities and trained personnel, especially if the effect of air pollutants is to be taken into account. The paper mills are not likely to do it very often (they even object to the fold endurance test because it takes a few hours), and most customers are not able to do it at all, much as they would like to. How will permanent papers be identified?

The second problem is brightness loss ("optical permanence"). If groundwood papers are to be represented as permanent, the standard should specify a certain level of calcium carbonate, high enough to control the effect of pollutant gases and reactive components within tar paper. An alternative would be for the accelerated aging to be carried out for long enough to tell whether the carbonate will last 300 years, or however long the paper is required to last.

Light-aging tests will have to be added to the list of tests in the standard in order to detect the papers with unacceptable brightness loss due to high lignin content. It would be irresponsible to publish a standard for permanent paper if strength retention was its only criterion. For at least some customers, it will be crucial to know how long the paper will remain white.

Perhaps the new or revised permanence standards can have a second part in which brightness retention can be specified. Or a second standard can be put together that will cover brightness retention as well. A third alternative would be to specify either a maximum lignin content or retention of characteristics after accelerated aging.

(Buffered groundwood paper, when it becomes more common, will certainly be useful for magazines and journals, because it is much longer-lasting than groundwood without buffering, and it has the advantage of being more opaque than fine paper. Printers like to use opaque groundwood paper, because it can be incredibly thin without showing the type on the other side, which lets them get more pages into a given book. Buffered groundwood paper is much longer-lasting than unbuffered groundwood, other things being equal, and it deserves to be used much more than it is right now.)

It is not likely that the ISO permanence standard, ISO 9706, will be revised until the results of the first ASTM research project have been published and studied, about two years hence. Findings from individual studies may appear before that.

References

Arnold, R. Bruce, 1996. "Update: ASTM/ISR Paper Aging Research Program," Alkaline Paper Advocate, v.9 #2, July, p. 24.

ASTM (American Society for Testing and Materials). "Century-Long Paper Study Launched." News Release #5532 [May 1999]. 2 pp.

Lindström, Tom, 1990. "Discussion Contribution: 'Slow Fires'--Its Paper Chemistry, Physics and Biology." Paper Preservation: Current Issues and Recent Developments (Papers presented at the TAPPI Paper Preservation Symposium Oct. 19-21, 1988, Washington, DC), edited by Phil Luner. p. 74-75.

Porck, Henk J. et al., 1990. "Research on Mass Conservation of Archival and Library Materials." Ibid., p. 71-73.

Samuelsson, Marie Louise and Karin Sörner, 1990. Naturligt Äldrat Papper: Svenska Papper 1908-1988 (Natural Aging of Paper: Swedish Papers 1908-1988). FoU-Projektet för papperskonservering, Rapport nr 4 - ISSN 0284-5636.

Wilson, William K. and E.J. Parks, 1980. "Comparison of Accelerated Aging of Book Papers in 1937 with 36 Years Natural Aging." Restaurator v.4 #1, p. 1-55.

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