Alkaline Paper Advocate

Volume 1, Number 4
Nov 1994


Letters

To the Editor:

A few weeks ago, we received the July issue of Alkaline Paper Advocate which reported the ISR Workshop held in Philadelphia on July 6-8, 1994. On page 13, you dealt with the presentation of the German DIN 6738 standard. Unfortunately, your report contains several inaccuracies. Since our [the Papiertechnische Stiftung's] Dr. Wilken did not have an opportunity to discuss the DIN standard with you personally during the Symposium at the time, we would like to give you our comments on the report as follows:

In actual fact, DIN 6738 was not prepared by several German papermills, but by a standardization committee of DIN in the course of several years of painstaking work and controversial discussions. Apart from representatives of the German paper industry as well as numerous renowned experts from research institutions and official authorities, this committee included librarians and archive keepers.

During the opposition proceedings, all seven objections were discussed, one of which was endorsed with 96 signatures. After a detailed discussion, the standard was finally issued in its present form. Since this was the regular procedure, there was no need to expressly mention it in the presentation. Bringing up the question of acceptance of the standard by the "cultural community" means to venture into the field of philosophy. However, the standard defines a system to classify papers in terms of their lifespan strictly in accordance with the principles of the engineering sciences. Its underlying concept is a logical and stringent one which rules out preconceived opinions or prejudices. The frequently claimed lack of acceptance may sometimes originate from a basic inability to follow the lines of scientific thinking. The ever-increasing number of inquiries for test certificates definitely proves that the standard is being accepted. Incidentally, the demand for test certificates is another point which was covered incorrectly in the report.

Admittedly, testing according to DIN 6738 is a somewhat lengthy procedure. On the other hand, there exist quite a number of typical paper testing methods that are equally time-consuming (e.g. hygroexpansivity measurements) and none of them has ever given rise to complaints on account of this fact alone. Depending on the kind of type tests, the test only needs to be performed once at the beginning and at large time intervals thereafter. Only in case the paper manufacturer decides to modify the formulation--thus changing the type--will the testing procedure have to be repeated.

We trust that these brief comments will help to clarify a few points which have remained open. We welcome any response to the German standard and will be pleased to answer additional questions that may arise in this context.

Dr. R. Wilken

In my report of the ISR symposium, I wanted to make the point that DIN 6738 is hard for the customer to use, and that librarians and archivists, who represent the interests of the ultimate end-users, had had minimal influence in writing the standard. -Ed.

To the Editor:

I have been reading with interest your useful booklet "North American Permanent Papers" (May 1994). But I feel compelled to write to you to correct a misleading statement made regarding the effect of lignin on paper permanence.

Your text on p. 36 states that lignin degrades and discolors cellulose.* It was stated at the ASTM/ISR July workshop on paper permanence that lignin does no such thing but quite the reverse. Perhaps your views have changed since the workshop. I would like to reiterate that and encourage you to make a correction to the booklet when it is reprinted.

Cellulose is actually protected from degradation by the presence of lignin. This happens naturally and in lignin-containing papers. Plants without lignin are very vulnerable to biological attack and protection of cellulose is one of lignin's natural functions. The cellulose in lignin-containing papers is protected against free radical oxidation.

Nor is cellulose discolored by lignin. Cellulose discolors quite rapidly on its own in the presence of acid or heat. As far as we can tell the heat or acid induced discoloration or loss of strength of cellulose continues independently of the presence or absence of lignin. Newsprint, which is usually acid-sized, loses its strength on aging because of the acid degradation of cellulose not because it contains lignin.

Lignin can itself be degraded or discolored. In the presence of cellulose lignin acts as an anti-oxidant, thereby protecting the cellulose from some forms of attack, particularly by air pollutants like ozone or nitric oxide and any agents that produce free radicals. In other circumstances (e.g. treatment with acid) both the lignin and the cellulose may degrade independently.

Unlike cellulose, lignin is susceptible to discoloration by light. This causes lignin-containing papers to yellow and is probably what has given lignin a bad reputation with archivists. But the discoloration that occurs when lignin-containing papers yellow in light is confined to the lignin and it is not accompanied by a loss of paper strength or degradation of the cellulose component. If paper containing lignin is not exposed to light it should retain its color as well as a lignin-free paper of comparable pH.

Our Mechanical Pulps Network is carrying out research that aims to stop the light-induced yellowing of lignin-containing papers. When we are successful we hope there will no longer be a prejudice against the use of lignin-containing papers, but they will be judged on the basis of their true properties. Wider use of lignin-containing papers would additionally be beneficial because it would lead to a more efficient use of the world's forests in the production of paper.

Gordon Leary, Executive Director
Mechanical Wood-Pulps Network

*(The text on p. 36 of the booklet reads, "The first edition of this standard required only 'no groundwood or unbleached pulp.' This was an indirect way of excluding lignin, which degrades and discolors cellulose.")

Editor's reply:I remember that several people at the ISR symposium said that lignin protected cellulose, but I did not believe it, of course, because I am fairly familiar with a large body of evidence to the contrary. I attributed the statement I heard to the speakers' lack of familiarity with the field of permanence research, and their desire to open more markets to mechanical pulps.

It is widely recognized that lignin is chemically stable in wood, but unstable in paper. If a new way of refining wood has indeed been found that permits lignin to retain that stability in paper, under all conditions of use and storage, then the people who developed it can take a lot of credit. However, the characteristics of this new kind of paper are not yet established beyond doubt.

It is very easy to prove that something is unstable or destructive; all you need is a few examples. It is very hard, on the other hand, to prove that something is not destructive, because you have to be very familiar with its chemical and physical characteristics, and you have to be able to predict the ways in which it is likely to be used and stored over the next few hundred years. Leaders in the cultural community (scientists, conservators, curators) know this. The literature of conservation contains evaluations of materials (e.g., soluble nylon) that were originally endorsed by leading authorities and accepted as stable, but which ultimately damaged the paper they were used on. So they are pretty cautious, preferring to use materials with known characteristics, and demanding credible evidence before they accept new claims of permanence for a material they have had bad experience with.

In permanence research, it is not enough to work with handsheets, though they have their place. Commercial papers must be tested too, and (sometimes) historical papers. To omit them from consideration would be like investigating a disease without studying its effect on people.

Not only physical tests, but chemical and optical tests must be performed, in order to fully understand the aging process. Physical, chemical and optical properties are just as important in permanence work as they are in the pulp mill, where these properties are regularly monitored.

It is important not to represent something as established fact when it is really unknown, unclear, controversial, or under investigation. You say in your fifth paragraph that lignin, in the presence of cellulose, acts as an anti-oxidant, thereby protecting the cellulose from attack by air pollutants like ozone or nitric oxide and any agents that produce free radicals. Actually, this is not known. A research project on free radicals and permanence is under way at Queen's University, and a first report will be presented at the CPPA meeting in February. The work breaks new ground, but the report also makes clear how much we still do not know.

Regarding the permanence and degradation of paper containing mechanical pulps, it is still too early to make many generalizations. This topic has seen little work (except on color reversion) before now, and virtually nothing has been done on how the different kinds of mechanical pulps behave in a neutral or alkaline environment. The purpose of the ISR symposium, we were told, was to plan research that would fill in these areas of ignorance, and lay a more solid foundation for standards work. We cannot pretend to know what answers will be found before the research is done. And even after it is done, much of it will have to be reviewed or replicated independently, as research findings usually are (or should be), before it can be accepted without question in the field.

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