Morpholine Deacidification of Whole Books - Advances in Chemistry

5 Morpholine Deacidification of Whole Books

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 15, 2016 | http://pubs.acs.org Publication Date: December 17, 1978 | doi: 10.1021/ba-1977-0164.ch005

BERNARD F. WALKER W . J. Barrow Research Laboratory, Inc., Richmond, Va. 23221

A process for deacidifying whole books has been developed, based on impregnation with a mixture of morpholine vapor and water vapor. Even after accelerated aging at 100°C for 8 days, the paper from processed books maintains a pH close to neutral; the rate of folding endurance loss during accelerated aging is retarded by a factor of about 3.5, showing increased life expectancy for the treated paper. Aging in moist air containing sulfur dioxide indicates that the treated paper also has a degree of resistance to polluted atmospheres. The process is currently being demonstrated at the Virginia State Library in Richmond, Va. on 250 books per day. The equipment is fully automated; present estimates show a total deacidification cost of about $0.32/lb.

he problem of deteriorating books i n library and archival collections has been described by many authors; the severity and the urgency of the problem have long been apparent, but more detailed information is available i n articles by L o w e ( I ) and Williams ( 2 ) . Several useful deacidification processes are available which can be applied to sheets of paper or to single book pages, but the labor-intensive nature of such page-at-a-time procedures limits their use to relatively small numbers of the more valuable books. The objective of the present work was to develop a deacidification process which could be applied simultaneously to a substantial number of books and be much more reasonable in time and cost than the singlepage procedures. The exploratory phase of the project was started i n 1970; the past six years' work have culminated i n a process which inex pensively deacidifies about 85 lb of books i n 60 m i n and which substan tially retards their subsequent deterioration rate. F r o m the information generated since 1970 only two main aspects are dealt with here: a description of the process i n its current form and 72 Williams; Preservation of Paper and Textiles of Historic and Artistic Value Advances in Chemistry; American Chemical Society: Washington, DC, 1978.

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Morpholine Deacidification of Whole Books

73

the effect of the process on the properties of the paper. The data pre sented is only a small fraction of the available data but is adequate for illustrative purposes.


Analytical Methods In testing morphohne-treated paper samples and their corresponding untreated controls, the standard methods of the Technical Association of the Pulp and Paper Industry ( T A P P I ) were used with few exceptions. In evaluating the permanence of paper, both dry and moist aging pro cedures were used, both of which were somewhat more elaborate than the dry aging method specified by T A P P I . The residual nitrogen content of treated paper was measured by an Antek digital nitrogen analyzer. Monitoring and controlling the concentrations of free morpholine which could be found i n the vicinity of the processing unit and i n the air around processed books were done with a M i r a n infrared spectrometer. During development, the processing parameters were adjusted so that the Occupational Safety and Health Administration ( O S H A ) require ments for morpholine concentrations i n the atmosphere were met fully. Since the term paper covers a wide range of material compositions and since even a single lot of the same paper shows great variability when the samples tested are small i n area (as is the case i n testing samples cut from book pages), statistics were used extensively to select the number of replicate tests to be made i n relation to the scatter of each test and to evaluate the significance level of the differences between treated and untreated samples. As an example, the folding endurance test on papers of poor uniformity requires a minimum of 50 replicates if the difference between average folds of, say, 250 and 350 is to be just significant at the 95% confidence level. Appropriate statistical programs were developed for use on a Hewlett-Packard 9810A calculator. Process and Equipment The process is simple; it consists of placing the books to be deacidified in an air-tight container, then removing most of the air with a vacuum pump to an absolute pressure of 0.5-1.0 torr. A mixture of morpholine vapor and water vapor is admitted to the container for about 10 min, during which the alkaline vapors completely penetrate each book. Evacu ation to 2-3 m m H g removes most of the residual morpholine, and the remaining chemical is flushed out b y letting i n air to 7 0 0 m m H g and evacuating the chamber to 20 m m H g ; these last two steps are repeated several times. A l l morpholine removed is disposed of through a waterspray scrubber to the sewer so that at no time during processing can free morpholine escape into the room. Figure 1 gives an overall view of the appearance of the equipment currently used for 80 lb of books. The unit was manufactured by Vacu-

Williams; Preservation of Paper and Textiles of Historic and Artistic Value Advances in Chemistry; American Chemical Society: Washington, DC, 1978.


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PRESERVATION O F P A P E R A N D TEXTILES

Figure 1.

Deacidification unit

dyne/Altair, Inc. i n Chicago. It occupies about 10 ft X 12 ft and w i l l readily fit into a small room. The unit has four main parts: the chamber to contain the books, the evaporator, the control panel, and the vacuum pump. T h e process controls were subsequently modified extensively b y this laboratory. Figure 2 shows the books loaded onto the shelves with the door open. Figure 3 shows the control panel. The process is initiated b y turning the handle i n the upper right-hand corner toward "Evacuation." T h e fully Table I.

Classification of Books Processed Years of Publication

Before 1900

momo

1940

1%

8%

15%

19411960 29%

1961Present 47%

Type Fiction 8%

Bound Nonfiction 44%

Government Periodicals 15%

10%

Foreign 23%



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75

automated process runs by itself for the 60 m i n of processing time. F i nally, the door is opened, and the books are removed. Automation of the unit permits operation by semiskilled labor. D u r i n g developmental work, thermistors taped to several of the book pages inside the processor allowed monitoring of temperature changes at the actual site of deacidification, the paper itself. Temperature changes arising from moisture loss by the paper and from morpholine-watercellulose interactions could be detected readily. The books used were obtained from the Exchange and Gifts Division of the Library of Con gress. Table I shows their distribution by type and by year of publication.

Figure 2.

Books loaded ready for processing


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PRESERVATION O F PAPER A N D TEXTILES

Figure 3. Table II.

Control panel

Effect of Morpholine Treatment on p H of Book Pages

Book No.

Before Treatment

Immediately after Treatment

Stored Several Weeks

Oven-Aged Equivalent of 100 Years

31 24 21 68 14 17

5.5 5.1 5.6 5.9 5.1 5.2

8.4 8.0 8.2 7.8 8.0 8.2

6.5 6.4 6.3 6.4 6.7 6.7

6.3 6.0 6.0 6.1 6.3 6.5


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77


Experimental Data p H . Table II shows that treatment causes the original p H of about 5 to increase to about 8. After standing several weeks i n the room, residual traces of free morpholine dissipate, and the p H stabilizes at about 6.3-6.7. E v e n after accelerated aging, the average p H remains above 6.0. This numerically modest increase i n p H reflects a substantial decrease i n acid content. Fold Loss Rate. A direct way of evaluating the effect of the morpho line process on the stabilization of paper is to measure the rate at which its folding endurance deteriorates before and after treatment. Figure 4 typifies the effect. The two lines are for the same paper aged i n a dry oven at 100 °C; the line with the lesser slope reflects morpholine-treated

2 DAYS

Figure 4.

4 AGED

6 AT

100°

C.

Effect of morpholine treatment on rate of fold loss

paper and that with the steeper slope is the untreated control. The con verging lines are 95% confidence limits around the slopes. In this case, the p H of the paper was raised 1.5 units by the morpholine process, and the change i n slope shows that the aging rate was substantially reduced. This graph is a composite of several sets of data from the control book used i n comparing a smaller laboratory processor with the present 50-book processor. Since the reactivity of paper towards deacidifying processes varies greatly with the type of paper and its condition, one would expect that the improvement i n aging rate would vary from one paper to another. T o illustrate this, Figure 5 shows a small improvement i n aging rate, and Figure 6 shows a greater improvement. These last two figures also



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PRESERVATION

2

Figure 5.

DAYS

4

AGED

6

AT

OF

PAPER AND

8

10

100°

C.

TEXTILES

12

Change in aging rate resulting from morpholine treatment

show the dispersion of the data points about an individual regression line when using 50 replicate fold tests for each point. L i f e Expectancy Estimates. If the end of the useful life of a paper is arbitrarily defined as a folding endurance of one double fold, rate-offold-loss fines such as those i n Figure 4 can be extrapolated until they reach one double fold, and the corresponding accelerated-aging inter cepts on the time axis can be compared directly. This gives a measure of the extent of improvement resulting from treatment. 400. r

2

4 DAYS

Figure 6.

6 AGED

8 AT

10 100°

C.

Change in aging rate resulting from morpholine treatment



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79

F r o m the conservators point of view, it would be useful to convert these accelerated-aging times to equivalent years of natural aging so that estimates could be made of how many additional years of life expectancy are provided by applying the morpholine treatment. Unfortunately, it is not yet possible to do this unequivocally because of the uncertainty of the relationship between accelerated aging at elevated temperatures and natural aging at ambient temperatures. Estimates of the length of natural aging equivalent to 72 hr at 100 °C of accelerated aging vary from 18.5 years to 306 years; many published values center around 25 years. Although the relationship appears to vary widely with the type of paper and the exact test conditions used, it seems certain that a relation ship does indeed exist. Thus, as shown in Figure 4, morpholine treatment prolongs the useful life of paper under conditions of accelerated aging and also corresponds to an increased life expectancy under conditions of natural aging. The significance of these findings is that from all the tests made on the morpholine treatment, an average book is estimated to last about 2V2 times longer than its untreated counterpart. More recent changes in processing procedure have increased this factor to 3—5. Paper Property Changes. Tables III, I V , and V show evaluations of possible changes i n the properties of paper which might be caused by the morpholine process. As to folding endurance, of the 36 books tested, five showed higher fold after treatment, six showed lower fold, and 25 were unchanged. Table III indicates that the changes resulting from treatment can be either positive or negative. However, as shown in earlier figures, even when the fold strength decreases after treatment, the rate of fold loss also decreases so that after extended aging, the treated sample exhibits the better fold characteristics. Table I V shows changes i n tear strength resulting from morpholine treatment. They are insignificantly small. Another set of tests was made for tensile strength; Table V shows no measurable change. The last three sets of data indicate that morpho line treatment does not harm the strength of paper significantly. Color Changes. Amines can cause color changes i n paper; the extent of the possible changes was estimated by measuring brightness according to T A P P I standard T-452. The data are given i n Table V I and indicate that before oven aging, brightness reductions do not exceed 3—4 points. This is a consequence of the low concentration of morpholine used i n the process; only occasionally is a brightness change observed. Although Table V I shows a detectable change i n two of the samples, with the last 3,000 books processed such changes have been apparent in less than 1% of the cases. Permanence of Deacidification. If paper were composed of chemi cally inert fibers, one would expect that a brief exposure to the alkaline vapor of morpholine would have no appreciable effect since there would


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PRESERVATION

Table III.

Fold Change from Morpholine Treatment

Sample No.


OF PAPER AND TEXTILES

Folding Endurance

95% Confidence Limits

Results

1752-2286 1849-2183

no change

116 132

106-125 118-146

no change

Untreated Treated

8 12

7-9 10-14

increased

Untreated Treated

114 49

76-151 27-70

decreased

38

Untreated Treated

2019 2016

2

Untreated Treated

5 66

Table

IV. Effect of Morpholine Treatment on Tear Strength of Book Paper Tear Resistance (0)

Book No.


Results

54

Untreated Treated

64 63

65-63 64-61

no change

66

Untreated Treated

28 27

28-27 29-26

no change

19

Untreated Treated

49 46

50-48 48-45

decreased

22

Untreated Treated

49 50

50-48 51-49

no change

Table V . Effect of Morpholine Treatment on Tensile Strength Tensile Strength (kg/m)

Book No.


Results

66

Untreated Treated

214 201

187-241 184-217

no change

19

Untreated Treated

384 388

367-400 377-399

no change

21

Untreated Treated

368 381

354r-383 368-395

no change

54

Untreated Treated

462 423

424^501 395-452

no change


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Table VI. Effect of Morpholine Treatment on Brightness


Book No.

Unaged

Observable Yellowing

10

Untreated Treated

58 55

none

66

Untreated Treated

68 64

slight

54

Untreated Treated

77 75

slight

76

Untreated Treated

83 83

none

be no specific affinity between morpholine and such fibers. However, cellulose has properties which strongly favor the adsorption and retention of morpholine. Since it has a very large specific surface, it contains appreciable amounts of adsorbed moisture and is often acid-sized; even pure cellulose contains acidic groups. Also, under mildly swelling condi tions, cellulose can form the so-called "inclusions" with molecules the size of benzene or morpholine. During deswelling of cellulose, such molecules can be more or less firmly held or "included" within the paper structure. Morpholine itself has three characteristics which favor its adsorption and retention by paper: first, it is an amine, and amines are known to adsorb tenaciously on many surfaces; second, it is alkaline; and third, it has a m i l d swelling effect (3) on the less-ordered regions of cellulose. W h e n one considers these characteristics of paper and the known char acteristics of morpholine, it is easy to see how paper could bind morpho line with some tenacity. Morpholine is probably adsorbed on the large specific surface of cellulose, and it w i l l certainly react with accessible Table VII. Morpholine Retention by Treated Books Aged in Ambient Air°

Book No. A B C D a

Increase in Nitrogen Content (as Morpholine)

Nitrogen Content Untreated (ppm)

1 Mo after Treatment

713 529 643 649

833 1440 1443 1145

3 Mo after Treatment no no no no

change change change change

Each sample is an average of 20 tests.



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AND

TEXTILES

acidic constituents of the paper. As a m i l d swelling agent, morpholine has the possibility of being included within the cellulose structure. For these reasons, one would expect that morpholine-treated paper would more or less firmly retain some morpholine. In fact, this does happen. Table V I I illustrates tests of morpholinetreated paper corrected for the nitrogen content of untreated controls; a significant increase i n residual nitrogen is apparent, which i n this case can originate only from retention of morpholine. After a 3-mo additional exposure to ambient air, no change was detected, and it is therefore concluded that exposure to ambient air at normal humidity does not reduce the bound morpholine content. Resistance to Polluted Atmospheres. There is general agreement that it is desirable for a deacidified paper to have built into it some degree of protection against future inadvertent exposures to acidic atmospheres. The buffering capacity of a paper above p H 7.0 is termed "alkaline reserve." There is no consensus as to the necessary extent of this reserve, but the Preservation Office of the Library of Congress has suggested 3 % as a reasonable level for reserve alkalinity, expressed as calcium carbonate. Using the normal titration method on morpholine-treated paper samples, reserve alkalinity levels of less than 1% are found. However, i n view of the previously mentioned possibilities for interaction between cellulose and morpholine and the observed reduction in the aging rate of morpholine-treated paper, it was thought likely that morpholine could be present i n a form not immediately titratable but which might still offer some degree of protection against acid attack. It was therefore considered useful to age under conditions which would simulate the effect of exposure to a polluted urban atmosphere. This was accomplished by aging paper in 60% relative humidity air containing 5 ppm sulfur dioxide, the most common urban air pollutant. Table V I I I shows that morpholine-treated paper possesses a significantly improved resistance to acidic atmospheres. The extent of this protection varies; comparing it with the Barrow two-bath process which is a calcium hydroxide—calcium bicarbonate system, it ranges from about the same to half that much. This conclusion is based on the retention of fold during accelerated aging at 60% r.h. and 75°C. About the same degree of pro tection was conferred upon the tear resistance, which further supports the finding that morpholine-treated paper indeed possesses a reduced sensitivity to acid-induced degradation. Odor. To arrive at a usable process, it was essential that the mor pholine concentration i n the air around the processor and around proc essed books should be reduced to a level where neither odor nor health hazards would be a problem. Measurements of both the odor and the


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Morpholine Deacidification of Whole Books Table VIII. Resistance of Morpholine-Treated Paper to an Acidic Atmosphere 0


Paper No. 45 (pH 5.1)

Loss Tear drop Loss F o l d drop

Untreated

Morpholine Treated

Barrow Two-Bath Treated

24% 58.0 - » 44.3 67% 225 -> 75

13% 58.3 - * 50.9 48% 184^-95

8% 61.8^-56.9 26% 265 -> 195

Paper No. 50 (pH 4-5) Loss Tear drop Loss Fold drop a

37% 58.3 -> 36.5 84% 87-+ 14

16% 60.4 -> 50.7 25% 69-^53

9% 62.6 56.6 33% 74->50

At 75°C, 60% r.h., and 5 ppm S0 . 2

morpholine concentrations would allow the process conditions to be adjusted to meet requirements. Measurements of morpholine concentra tion were made with the Miran infrared analyzer, calibrated over the range 1-100 ppm of morpholine i n air. The applicable O S H A healthrelated standard is defined as an upper limit of 20 ppm for a weighted 8-hr exposure. The ability to detect odors varies widely from one individual to another, depending on factors such as age and smoking. It is therefore necessary to express the relationship as a proportion of the population which can detect a given concentration. In Figure 7, the horizontal scale is probability, the vertical scale is concentration. The graph is interpreted to mean for example that 50% of the population can detect 0.7 p p m and that 89% of the population can detect 21 ppm. These data were devel oped for the project b y the Illinois Institute of Technology Research Institute using a smell panel. O n the basis of these measurements, process conditions were adjusted to meet two criteria: 1. T o satisfy OSHA's requirements, the morpholine concentration i n the air around treated books and during processor operation should never exceed 20 ppm. 2. The atmosphere around freshly treated books should never exceed more than 10 ppm. After making suitable process adjustments, morpholine concentra tions were measured around the processing equipment immediately after a batch of books had been treated. F r o m Table I X , it is apparent that the concentrations even immediately after processing are i n a range con sidered safe b y O S H A rules. These levels drop to undetectable levels a


83

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PRESERVATION OF PAPER

Table IX.

Morpholine Concentrations around Processor Morpholine Concentration (ppm)


Area 6" in front of processor Door opened after run Shelf areas inside processor after run 4 ft above work area 3 " from freshly treated books A t nose level above freshly treated books

5 a.

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Morpholine Deacidification of Whole Books - Advances in Chemistry

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