16 The Effects of Varying Relative Humidity Conditions on the Folding Endurance of Aged Paper Samples ADRIAN C. SCLAWY Preservation Office, Library of Congress, 10 First Street, SE, TJB G-1008, Washington, DC 20540
The MIT folding endurance testing machine was used to show the effects of varying relative humidity conditions in the range of 20% to 80% on aged and unaged paper sam ples. The aged and unaged samples showed significant im provement of folding endurance test results when the paper was initially of a good quality. One set of Foldur Kraft paper samples was deacidified by washing in a solution of magnesium bicarbonate. The results show that the deacidi fication process improved the folding endurance test values. Ύ ibraries today are filled with brittle books. Many volumes are in such bad condition that they cannot be circulated, and some can hardly be consulted. Deacidification slows the rate of degradation but does little or nothing in the way of restoring vanished physical properties. Crook and Bennett (1) showed that great increases in folding endur ance were obtained by humidifying new paper. The objective of this work is to learn if raising ambient humidity will restore enough pliability and fold that brittle books may again become useful. This is of particular interest with regard to deacidified papers. Barrow (2) classified papers according to their folding endurance strength as follows: 1) high strength, 1000 or more folds; 2) moderate strength, 300-1000 folds; 3) low strength, 10-300 folds; 4) weak strength, 2-10 folds; 5) unusable, 1.0-0.1 fold; and 6) brittle, 0.1-0.01 fold. Experimental In this experiment, four types of papers were subjected to accelerated aging. The papers, Foldur Kraft, newsprint, JCPA-60 (Government Print ing Office property No. 16929), and Allied Superior were placed in a This chapter not subject to U.S. copyright. Published 1981 American Chemical Society
218
P R E S E R V A T I O N
Table I. Paper Sample
O F
P A P E R
A
N
D
T E X T I L E S
I I
Specifications of the Papers Used in the Experiment Pulp Composition
pH
Internal Size
Newsprint
80% ground wood, 20% bleached sulfite
5.1
unknown
Foldur Kraft"
90% southern pine, 10% hardwood
JCPA-60
30% bleached southern Kraft, 70% bleached hardwood Kraft
Allied Superior 90% softwood bleached Kraft, 5% hardwood bleached Kraft
4.9-5.0 0.5% rosin 3.0% titanium 6.5
13 parts clay
6.1
unknown
"After magnesium bicarbonate washing, the p H of the Foldur Kraft paper was 9.2 with a 1.69 alkaline reserve value.
constant humidity oven at 50% relative humidity and 90°C temperature. The specifications of the papers used in the experiment are shown in Table 1. The papers were aged at time intervals of seven, fourteen, and twenty-one days. One set of each type of paper was left unaged as a control group. Two different sets of Foldur Kraft papers were used. One set was prewet with a solution of 1:1 denatured alcohol to distilled water and then treated with a wash of 10 g/L (1% ) magnesium bicarbonate solution for thirty minutes. The other set of Foldur Kraft papers was left untreated. After the paper samples were removed from the humid oven, they were placed in a drying oven at 100 °C for one hour to remove all moisture. The samples were transferred immediately from the dry oven to specifically labeled, widemouthed, airtight containers for storage until folding endurance tests could be conducted. Relative humidity conditions ranging from 20% to 80% with 10% increments were produced in a controlled atmosphere glove box. The temperature was held constant at 78°F throughout the experiment. Various saturated chemical solutions were used to maintain the relative humidity conditions in the glove box. The folding endurance testing values of the paper samples were determined by using an MIT folding endurance tester. The tests were conducted at a tension of Vi kg with an angle setting of 135°. The tests were performed in the machine direction of the paper only. The ten best trials were used per sample; fifteen trials per sample were conducted, the five lowest values were dropped. The paper samples were conditioned in each relative humidity range for a period of forty-eight hours prior to conducting the folding endurance tests that were performed under the specific humidity conditions in the glove box. Results and Discussion 1. The data in Table II show that the Foldur Kraft paper that was treated with a magnesium bicarbonate solution con-
16.
Relative Humidity and Folding Endurance
S C L A W Y
219
Table II. Comparison of Aged Foldur Kraft Paper Treated with Magnesium Bicarbonate Solution with Aged Untreated Foldur Kraft Paper Under Various Relative Humidity Conditions, Average Number of Folds (MIT 1/2 kg Tension) 7 Days
Control
%
14 Days
21 Days
UnUnUnUnTreated treated Treated treated Treated treated Treated treated
RH
20 1291.1 30 1623.3 40 1855.5 50 1975.4 60 4006.1 70 8412.6 80 10,521.9
973.2 1052.8 1122.6 1203.2 1447.1 1529.3 1663.5
430.7 523.9 832.2 1114.5 3195.6 7510.6 9666.4
1.0 1.0 1.5 1.6 10.0 15.0 16.9
413.9 457.9 907.2 1064.9 2374.2 6479.8 8530.5
1.0 0.0 0.6 0.5 0.9 1.0 1.0
307.5 416.5 820.1 838.5 1635.5 2274.4 2592.9
0.6 0.0 0.4 1.3 0.4 0.1 0.4
sistently showed higher folding endurance test values than the untreated Foldur Kraft paper at the corresponding relative humidity ranges. Table III is an analysis of the data in Table II. Values are expressed as the number of times that the folding endurance increased or decreased from 20% to 80% relative humidity. 2. The data in Table IV show that the folding endurance values for the control group of newsprint paper were never improved enough by exposure to the varying relative humidity conditions to reclassify them into a higher strength group than the low strength category. There were not any significant changes in folding endurance test values by exposing the aged newsprint samples to higher relative humidity conditions. A l l of the aged newsprint paper samples could be placed in either the weak or unusable categories. 3. The data in Table V show that the control group for JCPA60 paper had low strength folding endurance test values at 20% and 30% relative humidities. At 40% relative humidTable III. Number of Times Folding Endurance Increased for Foldur Kraft Paper Samples for the Relative Humidity Range of 20% to 80% Control 7 Days HDays 21 Days UnUnUnUnTreated treated Treated treated Treated treated Treated treated 8.15
1.71
22.4
16.9
20.6
1.0
8.43
-0.67
220
P R E S E R V A T I O N
O
F
P A P E R
A
N
D
T E X T I L E S
Table IV. Average Number of Folds (MIT 1/2 kg Tension) for Aged Newsprint Paper Samples Subjected to Varying Humidity Conditions % RH
Control
7 Days
14 Days
21 Days
20 30 40 50 60 70 80
12.8 22.6 37.1 48.2 52.3 53.7 58.1
1.8 1.0 1.2 2.0 1.9 2.5 3.1
0.4 0.7 0.2 0.6 1.0 1.6 1.8
0.0 0.4 0.2 0.8 0.0 0.0 0.0
ity, there was a significant enough change in folding endurance test values to reclassify the paper into the moderate strength category. At 70% and 80% relative humidities, there was a slight decline in folding endurance but the paper still maintained a moderate strength. The folding endurance test values for the JCPA-60 paper aged seven days at 20%—50% relative humidities show that the paper falls into the low strength category. At 60% relative humidity, the paper is raised to the moderate strength category, and at 70% -80% relative humidities, folding endurance declines and the paper is again categorized as low strength. The data for the JCPA-60 paper aged fourteen and twenty-one days show that for the 20%-80% relative humidity range, the paper was of low strength. However, the highest folding endurance values were between 50% and 60% relative humidity. All of the JCPA-60 papers showed an increase in folding endurance testing values up to 60% relative humidity. A slight decline occurred for all JCPA-60 samples at 70%80% relative humidities. Table V. Average Number of Folds (MIT 1/2 kg Tension) for Aged JCPA-60 Paper Samples Subjected to Varying Humidity Conditions % RH
Control
7 Days
14 Days
21 Days
20 30 40 50 60 70 80
278.2 294.1 356.2 550.6 631.3 582.2 495.8
261.4 282.8 291.6 293.5 376.4 222.3 177.7
93.8 129.5 148.3 249.0 254.2 137.8 123.8
62.8 66.4 80.3 136.4 137.9 96.0 85.9
I I
16.
S C L A W Y
221
Relative Humidity and Folding Endurance
4. The data in Table VI shows that the Allied Superior paper improved in folding endurance test values as the relative humidity was increased. This occurred in all instances except for the paper that was aged seven days and tested at 30% relative humidity. The control group of Allied Superior paper was categorized as high strength at 20% relative humidity, and at 80% relative humidity, the folding endurance test values had increased 9.56 times. The Allied Superior paper aged seven days at 20% relative humidity was categorized as moderate strength. At 50% relative humidity, the folding endurance had more than doubled and the paper could be reclassified as high strength. The Allied Superior paper samples aged fourteen and twenty-one days at 20% relative humidity were classified as low strength papers. At 40% relative humidity, both groups were reclassified by the folding endurance test values. The paper sample aged fourteen days achieved high strength classification. The paper sample aged twenty-one days was reclassified as high strength at 80% relative humidity. Table VI. Average Number of Folds (MIT 1/2 kg Tension) for Aged Allied Superior Samples Subjected to Varying Humidity Conditions % RH 20 30 40 50 60 70 80
Control 1215.2 1229.2 1758.6 2516.3 5012.1 9504.2 11,627.0
7 Days
14 Days
21 Days
534.3 515.5 913.8 1207.3 2487.9 4592.4 6707.8
177.8 273.9 354.1 356.4 945.4 1317.2 1502.9
172.2 250.6 305.9 418.1 727.3 914.3 1007.4
Conclusions The results of this experiment show that folding endurance values for certain types of paper, both aged and unaged, can be improved by exposing them to atmospheres of increasing relative humidities. The use of magnesium bicarbonate solution as a deacidifying agent with Foldur Kraft paper increased the folding endurance of the paper when it was exposed to increasing relative humidity conditions.
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PRESERVATION OF PAPER AND TEXTILES II
Literature Cited 1. Crook, D. M.; Bennett, W. E . "The Effect of Humidity and Temperature on the Physical Properties of Paper," Br. Pap. Board Ind. Res. Assoc., 1962, 3.21. 2. W. J. Barrow Research Laboratory "Test Data of Naturally Aged Papers" Permanence/Durability of the Book 1964, Vol. 2, 41. RECEIVED October 23, 1979.
