The Abbey Newsletter

Volume 15, Number 8
Dec 1991

Three Deacidification Methods Compared

by Ellen McCrady

The Library of Congress (LC) has made available the report of tests performed by the Institute of Paper Science and Technology (IPST) on books deacidified by Akzo Chemicals, FMC Corporation and Wei T'o Associates. The test results for the physical properties of the treated books are set forth in great detail, but without evaluation in four large spiral-bound volumes. I will try here to compare and evaluate the results for the benefit of readers who do not have access to those volumes. My own evaluation does not reflect the thinking of the panel that evaluated the processes for LC, and will very likely differ from anybody else's evaluation in one or more respects.

Although reference will be made to "Akzo books" and so on, the books were actually furnished by the Library of Congress. Details of the testing procedures and criteria for acceptance are in LC's request for proposals (RFP), excerpts from which were published in the October 1990 issue of this Newsletter.

The first thing anyone wants to know about a mass deacidification method they are thinking about using is "Will it deacidify our books?" For all three of the processes tested, the hot and cold extraction tests performed gave the answer "Yes." In ten paper samples taken from each of ten old and new books for each process, the pH of the books tested 7.0 or higher. Akzo and Wei T'o raised it above pH 7.5. These all satisfied LC's criterion of an average pH value between 6.8 and 10.4.

Completeness of treatment was measured with chlorophenol red on a separate subset of books to identify areas still acid. For Akzo books, only 1% of the tested area was still acid, and for Wei T'o books, 2%; but for FMC books, it was 32%. The percentage of books with any part untreated was 10% for Akzo, 35% for Wei T'o and 95% for FMC.

At first it is hard to see how any book could have as much as a third of its page area untreated, according to the chlorophenol red pH indicator, and still test at pH 7.0 or above, according to hot and cold extraction tests. The nature of an alkaline reserve may be the key to this mystery. "Untreated" means a pH somewhere below about 6.8 (the upper end of the chlorophenol red visual transition interval), and, of course, lacking an alkaline reserve. "Treated" means above pH 6.8, and almost certainly this means the pH has been raised by the treatment, which also deposits an alkaline reserve. There may not be much of an alkaline reserve, but there is enough to raise the pH of the untreated part when it is all slurried together for the hot and cold extraction tests.

The next thing anyone wants to know about a deacidification process is, "Will it leave an alkaline reserve?" The target level most people have in mind (though I could not find any specification for this in the RFP) is usually 2%, expressed as calcium carbonate. (The salts deposited in the book are different for each process; what matters is how much acid they can neutralize.) None of the processes was able to do this consistently, at least not in the subset of eight old and new books tested for each supplier. Thirty-two samples from a total of eight pages in each book were tested, using titration. Akzo's books averaged about 1.2% calcium carbonate equivalent in six of those books; the other two books seem to have been either alkaline to start with, or very hospitable to deacidification chemicals. FMC's books averaged less than 0.3%; Wei T'o's books ranged from 0% to 4.5%, and averaged about 1.6%.

There were specifications, however, on the uniformity of distribution of the alkaline reserve. It was supposed to vary by no more than 20% between books or between or within pages. None of the processes came even close to this in any respect. Alkaline reserves varied by as much as 2.0% between pages and from one part of a page to another. Some books had very high alkaline reserves of about 10%, merely because they were on buffered alkaline paper to begin with. This of course affected the uniformity of pH from book to book.

There was also a maximum allowable decrease in alkaline reserve during aging. It was to be no greater than 0.5%, e.g a decline from 2% to 1.5%. This was apparently intended to rule out the processes that deposit fugitive alkaline reserves. The Akzo process came out best on this, especially with newsprint, which retained all or virtually all of its alkaline reserve. The FMC books satisfied the criterion, or nearly satisfied it, only because their alkaline reserve was so close to zero to start with. All the Wei T'o books but one lost over 0.5% of their alkaline reserve, or roughly half the original amount. Acid paper, surprisingly, retained its alkaline reserve better than the other three kinds of paper for both FMC and Wei T'o books.

If the books and papers had been aged with pollutant gases as well as with moisture and heat, perhaps these results would not have been so good, especially if aging had continued after the alkaline reserve was used up.

Other Effects of Treatment

All of the processes left the books drier. Moisture content of all the untreated books is described (somewhat unbelievably) as being in the narrow range of 5.0-5.5%. The treated books were supposed to have a moisture content of 3-5%. Treated Akzo books had a moisture content of 3.04.3%; treated FMC books, 4.0-4.8% (one was 2.5%); and Wei T'o books, 3.5% (one was 2.6%). The report does not say anything about how the books had been conditioned after treatment, or what their moisture content was after those four moist weeks in the oven. This would have given us some idea of whether the moisture loss was permanent, which some people worry about. At any rate, the low moisture content does not seem to have hurt them in any obvious way, and all but two books of those tested fell within the accepted range.

All the treatment methods involved heat, especially Akzo's, which got one book as hot as 220°F, far above the specified maximum of 70°C (158°F). FMC's method was the coolest: one book got up to 140°F, and the rest were below 120°F. These measurements were obtained from temperature sensors inserted in the books before treatment. There is no information on how long the books stayed at these elevated temperatures.

Smell was a problem. IPST had a panel of four people who assessed the books for odors and rated them on a scale running from "undetectable" to "overpowering." Their judgments on a given book differed widely from one another, but when you average them out, you see that the Akzo books were rated 6 on a scale of 1 to 10, FMC books were 5, and Wei T'o books 3. Untreated books were about 1. No information is given on the rate of decay of these odors, or what gases evolved to cause them, but the panel's work gave them headaches and sore throats. It was not possible to tell, because of the procedures used, which deacidification process or processes were responsible for their symptoms.

Bleeding and offset of inks and dyes was tested by examining filter papers inserted into or attached to some of the books before treatment. The percentage of the discolored area of each filter was measured for each deacidification process, and for untreated books with filter paper inserts as well. The FMC process produced the most bleeding (4% more than controls) and the Akzo process the least (1%).

Strengthening was not one of the requirements, but the data show both slight strengthening and weakening effects for all processes, probably all within the range of experimental error.

A panel evaluated the condition of the whole book, and found that all processes caused minor but sometimes annoying changes in the covers and spines, endplates, and textblocks. Only the shape of books was unaffected. So none of the three processes came close to leaving the books "essentially indistinguishable from their pretreated form," without markings on or changes in book covers, cockling of text block, damage to bindings, and so on, as specified.

Aging Results

You would not expect most papers with very low alkaline reserves to retain their strength after aging, but these did. The new test papers, bound in book form for treatment and aging, were aged at 90°C and 50% RH for 30 days. Each book contained a large number of papers, but only four of them were selected for testing: offset, alum-rosin sized, alkaline and newsprint. The following tests were performed at intervals over the 30-day period: fold, three tensile measures, brightness, opacity, hot alkali solubility (a measure of cellulose degradation), and retention of alkaline reserve. Results are presented in graphs with straight regression lines, without data points, for test and control papers.

Fold values for Akzo and Wei T'o books were retained well after aging, especially for newsprint. Two FMC papers just barely made it up to the criterion of a threefold reduction in the rate of deterioration. No process met that criterion for alkaline paper, perhaps because the paper was already so stable that it was hard to make it more stable by making it more alkaline. The Akzo process takes the prize in the fold retention category by making newsprint 11 times as stable as it was before. This particular newsprint may have been unusual, though, since it was by far the strongest of the four papers to start with.

Tensile values seem to have been well retained.

The hot-alkali-solubility test showed the papers to be minimally degraded by the aging they were experiencing, though there were a few exceptions.


LC rejected all three processes on the basis of these test results. Suppliers must be busy at the drawing board, preparing for the next RFP. The Library of Congress is also probably rethinking some of the requirements and test procedures.

In the next round, it might be useful to find the pH and alkaline reserve of books before they are treated, to compare with post-treatment values. Then the effect of treatment could be seen more clearly.

The requirement for uniformity of alkaline reserve may not be realistic. The distribution of calcium carbonate in papers from old books may not be even, either, but this may not make any difference to their stability. This topic bears investigation, in view of the recent finding that acidic encapsulated documents benefit from being next to a sheet of buffered paper. Uneven distribution of carbonate was reported in the May 1988 Alkaline Paper Advocate., p. 21-22, for Mohawk Superfine and Howard Permalife.

It would also help to learn how the different salts react to various pollutant gases. Three studies on aging with pollutant gases are briefly reported in the November 1990 issue of this Newsletter on p. 118, and other studies will be made, no doubt, in the future.

This was a massive project, involving a staggering amount of time, and it must have been very expensive for LC, but the report is a gold mine of basic information that will be consulted again and again.

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