Volume 8, Number 3
Oct 1995

Letters

To the Editor:

Thank you very much for kindly publishing and responding to our letter (the Alkaline Paper Advocate, vol. 8, No. 2, p.20-21, June 1995).

As we read your response, we strongly felt that both end-user and paper industry communities should communicate well. In particular, we found a very significant difference in the ways of 1) how to extract scientifically-sound information from historic data, 2) how to compare samples, and 3) how to interpret pH values.

Since this is a very important issue requiring thorough discussion, we would like to invite you and your colleagues to the coming paper permanence seminar. This seminar is organized jointly by Paprican and CCI (focusing on deacidification) and will be held at CCI on December 1, 1995.

To the Editor:

Concerning your paper and the use of the data from my publication in Restaurator [APA, June 1995, p. 20-21], I have to say first, that it is not possible to generalize to all groundwood-paper types from the results on two particular papers. We have to consider that the difference between the two papers chosen in the research cited is not only the lignin content.

As Paprican researchers noted, the purpose of the study was to compare the efficiency of different deacidification methods used on different papers and not research on the comparison of the behavior of lignin-containing papers versus permanent or copy papers. Otherwise we would choose alkaline or acid papers with different amounts of lignin, in order to control the influence of each factor.

The CRCDG has been a partner in the STEP Project¹ on the effects of pollution on papers, and one of the conclusions of this research (based on the measurement of alkaline extractable fraction) was that the degradation rate is the same for a groundwood-containing paper (pH 5.9) as for a copy paper (pH 6.5). Considering a mechanical property of the papers (tensile energy absorption for example), after exposure of these two kinds of paper to pollutants² the % loss of tensile energy absorption (MD) is the same for both papers (60%). Nevertheless we have confirmed, as have other researchers before us³, that the deposition rate of pollutants (SO₂) on lignin-containing papers is higher than for pure cellulose papers. There is formation of acid groups with lignin and we know their destructive effect on cellulose⁴ during aging if they are not neutralized. Protection is given by neutralization of the acid groups by deacidification or by the neutral or alkaline papermaking process. That means that permanence is principally related with alkaline reserve.

However, in the STEP project, we have submitted the same papers (groundwood and copy paper), after deacidification by a mass method⁵ (pH 9.1 for both papers after treatment), to the same conditions of exposure to pollutants and we have noted that the % loss of TEA is lower for the groundwood paper (12%) than for the copy paper (60%). But after hygrothermal aging⁶ of these exposed samples the % loss is 90% for the first paper and less than 70% for the second. These are only examples of the difficulty of drawing conclusions about the effects of lignin in papers without a systematic study of the different parameters. Some research has pointed out that lignin doesn't affect the permanence of paper if neutral or alkaline papermaking conditions are used. To resolve this question, we are very interested in the conclusions of the Paprican/CCI project on the effect of lignin on paper permanence.

1. The Effects of Air Pollutants on the Accelerated Aging of Cellulose Containing Materials - Paper. STEP Project CT 90-0100.

2. 10 ppm SO₂, 20 ppm NO₂, t=23°C, rh=50%, 14 days.

3. Edwards, C.J., Hudson, F.I. & Hochey, J.A., "Sorption of sulphur dioxide by paper." In Journal of Applied Chemistry, 18, 1968, p. 146-148.

Langwell, W.H. "The Permanence of Paper, Part 4." In Technical Bulletin of Paper and Board Makers Association, 36. 1 Feb. 1955, p. 199-207.

4. Zou, X. & Gurnagul, N. "The Role of Lignin in the Mechanical Permanence of Paper: Part II. Effect of Acid Groups." In Environnement et conservation. Actes des journées internationales de l'ARSAG, Paris, May 1994, p. 161-165.

5. FMC method

6. t=90°C, rh=50%, 12 days.