Volume 08, Number 2
Jun 1995

Letters

To the Editor:

We have been reading with interest the Alkaline Paper Advocate for the last two years but we felt compelled to respond to your recent article, "Aging Behavior of Groundwood and Freesheet, Part 2" (The Alkaline Paper Advocate, Vol. 7, No. 5-6, Dec. 1994). In your article, you selected some data published by Daniel et al. (Restaurator, Vol. 11, No. 3, p. 179-207, 1990) and replotted them to support your opinion that the groundwood sheets age more rapidly than freesheets.

Indeed, the work of Daniel et al. and their conclusions on the effects of pollution on deacidified paper is interesting and very useful. However, since their study was only intended to evaluate effectiveness of various deacidification methods under the influence of air pollutants, their sample selection and experimental treatments were designed to achieve that purpose. Therefore, any interpretation of their results to current or future manufacture of alkaline lignin-containing paper products requires careful consideration and may in fact be irrelevant. For example, the following points should be considered:

1. Coated paper vs. uncoated paper: In the work of Daniel et al., book paper is made of 100% bleached chemical pulp sized with rosin and starch and coated with clay. On the other hand, newsprint (60% mechanical and 40% bleached kraft) is neither sized nor coated. When paper is coated, coating materials can account for as much as one third of the total paper weight. Therefore, the base paper may be protected from the attack of air pollutants because air pollutants cannot have much access to paper. As a consequence, the comparison of coated paper with uncoated paper may give misleading conclusions. In fact, Iverson and Kolar reported that wood-containing paper is less affected by nitrogen dioxide than wood-free paper (uncoated)¹.

2. Papers with different pH values: The original paper samples in the study of Daniel et al. were not sufficiently acidic (particularly newsprint) to study the effects of pollution on deacidified papers. Therefore the authors acidified the samples by exposing them to air pollutants. In the case of comparing aqueous deacidification methods, only the newsprint was acidified because of its neutral pH. In the case of comparing alcoholic deacidification methods, both samples were acidified but the final pH values were different (5.1 for book paper and 4.7 for newsprint). These treatments and different pH values may cause different responses of book paper and newsprint to air pollutants. Furthermore, it is not clear how the pH value of coated paper is defined and determined. On the other hand, in the STEP project, it was found that acidic groundwood-containing papers had a comparable relative degradation rate to the acidic woodfree papers².

It has been generally accepted that all permanent papers should have an alkaline reserve. One of the functions of the alkaline reserve is to protect paper from air pollutants. This has been demonstrated in recent studies and the results have shown that lignin-containing papers can be as stable as lignin-free papers when exposed to air pollutants, as long as there is a sufficient alkaline reserve (such as CaCO₃)^{1, 2, 3, 4}. For example, from the STEP project, Havermans concluded that calcium carbonate can be seen as a fiber protective agent against the attack of air pollutants². From the chemical data, he found that the relative deterioration rate of deacidified groundwood paper was comparable with deacidified copy paper². In a very recent study, Ziesler and Hamm of Germany compared various controlled sheets with different fiber composition and different additives. Their results showed that lignin had no negative effect on the permanence of sheets containing calcium carbonate under a pollutant atmosphere.

A Canadian cooperative project is currently under way to study the impact of lignin on the mechanical permanence of paper. One of the key objectives is to look at the effect of air pollutants on the permanence of lignin-containing and lignin-free papers. We are hoping to resolve this debate through this thorough study with controlled samples and conditions. As this joint work with Canadian Conservation Institute (CCI) develops, we will be glad to update you further.

References

1. Iversen, T. and Kolar, J., "Effects of Nitrogen Dioxide on Paper," FoU-Projektet för papperskonservering, Rapport Nr. 5 - ISSN 0284-5636, Stockholm (February 1991).

2. Havermans, J.B.G.A., "Main Conclusions of the STEP 90-0100 Project. Influences of Air Pollutants on the Accelerated Aging of Cellulose Based Materials: Paper." TNO Center for Paper and Board Research, Delft (June 1994).

3. Zeisler, P. and Hamm, U., "Physical Properties of Papers with and Without Wood under the Influence of Air Pollutants," Final Report, AIF Research Project No. 8698, Technical University of Darmstadt, Germany (Sept. 1994).

4. Zou, X. and Gurnagul, N., "The Role of Lignin in the Mechanical Permanence of Paper: Part III, Effect of Sulfur Dioxide," report in preparation, Paprican (1995).

Editor's response:

Perhaps I have not made myself clear. I am not saying that all mechanical-pulp paper is impermanent. I am saying that in the acid range (which is where nearly all papers were made until recent decades), newsprint-type paper deteriorates much faster than paper made with chemical pulp. This is a well-known phenomenon, confirmed by research and surveys of naturally aged papers, as well as by common experience. I have been reprinting reports of earlier research by the Bureau of Standards in this newsletter, to keep it from being forgotten or overlooked.

Contemporary research data on the rapid aging of newsprint has been accumulated as a byproduct of deacidification research, which often includes an acidic newsprint sample along with other papers to be aged before and after deacidification. The untreated newsprint typically shows a steep decline in strength as it ages, but after treatment it deteriorates slowly like the other samples.

The protection offered by alkaline salts in paper is not perfect, however. Studies in Sweden and France about six years ago showed that the period of stability for deacidified papers comes to an abrupt end as soon as the alkaline buffer is used up by interaction with pollutant gases.¹ These accelerated aging studies used high pollutant concentrations, so the aging conditions were admittedly extreme--but they do demonstrate that groundwood's stability depends on that alkaline buffer, not on its own stability.

As for carbonate-filled mechanical-pulp paper, industry studies show that calcium carbonate protects this paper nicely against deterioration. However, since this kind of paper has not been made commercially for much longer than five years, it does not have a track record. This makes it hard to say whether a given set of accelerated aging conditions can cause the same changes in the paper that natural aging does. The ASTM/ISR research program will look into this and a number of other questions that must be answered concerning the permanence of carbonate-filled groundwood. Other research is going on, or has been concluded recently, which will help fill out the picture.

Zou objects that the Daniel study was not intended as a comparison of papers made from mechanical and chemical pulps. Of course not. But one can legitimately do further analysis of someone else's data, even when the data was originally gathered for a different purpose. Science would be unnecessarily handicapped if this were not possible.

It is objected that the two papers in the graph were not perfectly comparable, since they had slightly different pH levels to start with, and the paper made with bleached chemical pulp was coated. The effect of coating is generally slight or variable (see the two abstracts in the literature section of this issue, classified under 3B1.8), and the pHs of these papers are so close that they might even have been identical or switched if another test method had been chosen (see "An Annotated Bibliography on Variations in pH Measurement," Alkaline Paper Advocate, v. 4 #1, Feb. 1991, p. 4-5).

On the other hand, the aging effect is very impressive--the one paper ages hardly at all, while the other loses virtually all its bursting strength (measured, by the way, as bursting number). The same magnitude of effect can be observed in most or all aging studies that compare acidic mechanical and chemical pulp papers, regardless of what test is chosen to indicate degradation, or what weight of paper is used, or whether moist or dry heat is used for aging. If there were only one such study, one could say that the comparison is invalid, because of this or that consideration; but when the great majority of such studies say the same thing, the evidence is overwhelming.

One last point: Iverson and Kolar did study the effect of nitrogen dioxide on paper, but it is an oversimplification to say they found wood-containing paper to be less affected by it than wood-free paper (uncoated). There were positive and negative effects on both kinds of paper, and the effects were not comparable; that is, the chemical-pulp paper was unaffected or even slightly improved by exposure to low concentrations of NO₂, up to a certain point, then deteriorated fairly quickly, while the mechanical-pulp paper yellowed but did not weaken.

Since the little article and graph that Zou his colleagues are replying to was published some time ago, it is reprinted below for reference.

1. F. Daniel et al., "The Behavior of Papers Deacidified under Pressure by Ethylmagnesium Carbonate as Regards Two Kinds of Accelerated Ageing: Wet Heat and Simulated Pollution" [and] Jonas Palm, "The Effect of Deacidification on Different Types of Paper Exposed to Air-Pollution and Accelerated Aging." Both papers presented at the Conference on Book and Paper Conservation, Budapest, Sept. 4-7, 1990. Pages 471-482 and 483-490 in the preprint volume (ISBN 963 8271 46 9. Published by the Technical Association of Paper and Printing Industry and the National Széchényi Library).

Aging Behavior of Groundwood and Freesheet, Pt. 2

A graph that showed groundwood aging more rapidly than freesheet was printed in the October issue of this Newsletter, to show that the impermanence of groundwood paper has been demonstrated not only in daily experience but also in research settings. (At the ISR workshop in July, reported in the July issue, evidence for groundwood impermanence was dismissed as "anecdotal" by one or two industry scientists. The fact that newspapers have been deteriorating rapidly ever since they started being made of groundwood 125 years ago was attributed to a lower pH.)

The graph below is presented as an example of evidence that is available in the literature. It is based on data from the same study as the one published in July: "The Effects of Pollution on Deacidified Paper," by Floréal Daniel, Françoise Flieder and Françoise LeClerc, Restaurator 11 #3, 179-207, 1990. Data for the earlier graph were taken from graphs on p. 199, and for this graph, from p. 200. Both graphs show values only for the two control papers, which like the test sheets were aged in polluted atmospheres (13 ppm SO₂ and4 ppm NO₂) at 28°C and 90% RH. The papers were 1) rosin-sized, clay-coated book paper and 2) newsprint (60% groundwood); both had an initial pH of 5.

Fig. 1. Effect of pollution on strength of newsprint and freesheet.

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To the Editor:

I coordinate a project to preserve old photographic collections. In Argentina archival quality papers and boards are neither manufactured nor available. In order to carry out preservation projects, we need to import them. Buying them through distributors makes these products very expensive for us. I am interested in getting some of our local library suppliers in touch with the mills that manufacture archival corrugated board and phased box board suitable for making boxes. Would you or one of your readers be able to send me the name, addresses and fax numbers of these companies?

Thank you very much for your help. I would appreciate it if you could send me the information as soon as you can.