NBSIR 73-155 iS)

Accelerated Aging of Commerciai

Papers in Dry Air, Compared with

Natural Aging

E. J. Parks, R. L. Hebert, and Mrs. Catherine Feasenmyer

Paper Evaluation Section

Product Evaluation Technology Division

Institute for Applied Technology

*Keuffel & Esser Company

Morristown, New Jersey 07960

March 30, 1973

Technical Report

Prepared for National Archives and Records Service

General Services Administration

Washington, D. C. 20408

NBSIR 73-155

ACCELERATED AGING OF COMMERCIAL

PAPERS IN DRY AIR, COMPARED WITH

NATURAL AGING

E. J. Parks, R. L. Hebert, and Mrs. Catherine Feasenmyer*

Paper Evaluation Section

Product Evaluation Technology Division

Institute for Applied Technology

*Keuffel & Esser Company

Morristown, New Jersey 07960

March 30, 1973

Technical Report

This document has been prepared for the use of National Archives and Records Service. Responsibility

for its further use rests with that agency.

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Note:

or

CONTENTS

Page

1. INTRODUCTION AND SUMMARY 1

2. RESULTS AND DISCUSSION 3

2.1 Results 3

2.2 Discussion 6

3. DTA 9

4 . pH 10

5. APPENDIX 11

5.1 Samples and Aging Conditions 11

5.2 Methods of Test 11

6. CONCLUSIONS 13

7 . REFERENCES 14
> 1
1. INTRODUCTION AND SU^4MARY

A reliable accelerated aging method would be desirable

for determining paper permanence, since natural aging requires

long periods of time to generate meaningful trends in the

decrease of paper strength. However, it is questionable

which is better suited to simulate natural aging--a dry or

a humid accelerated aging environment. It has been shown

that the presence of a high percentage of moisture promotes

oxidative degradation of paper at 90°C [1] . It is known,

furthermore, that paper retains a significant amount of

moisture at ordinary temperatures and relative humidities.

It is not known whether the same chemical reactions which

occur in paper at an elevated temperature also occur at an

ambient temperature.

The surest way to resolve this and related questions

would be to age a supply of papers covering a wide range of

stabilities in a humid and in a dry accelerated aging

atmosphere, then store other representative samples for

natural aging, to be tested periodically over a number of

years. Correlations of the results of selected physical

tests before and after all types of aging might indicate

which accelerated aging environment is more suitable for

forecasting paper permanence in natural aging environments.

T'nf ortunately , the few systematic comparisons which are

currently available are based only on short-term dry accelerated aging versus natural aging for periods of time up to

about 30 years, and are usually limited to fold, burst, and

tensile tests. There are no data with which to compare humid

accelerated aging and natural aging.

The present report describes the results of tests performed on 13 samples of drawing and tracing papers for which

data on dry accelerated aging were obtained in 1940. The

papers include commercial rag and sulphite papers. It has

been shown previously that decreases in MIT folding endurance,

observed after the dry accelerated aging of a number of rag

and sulphite papers, were highly correlated with natural

aging processes for periods of 4, 8, and 26 years [2]. Data

included in the present report complement the older study,

since changes in tearing resistance observed after accelerated

aging are similarly correlated with changes observed after

natural aging.
2

This report also discusses results of differential

thermal analysis (DTA) on aged papers. DTA has been shown

to be very sensitive to the presence of trace amounts of

metals in paper [3] and to functional groups such as aldehydes

and carboxylic acids in modified cellulose [4]. Thus, it was

of considerable interest to note that the present work shows

a high correlation between a DTA parameter, T2 (the temperature

at which massive decomposition of cellulose begins), and the

changes in tearing resistance observed after natural aging.

Since the samples were not analyzed by DTA in 1940, soon

after they were manufactured, it was impossible to know

whether their thermal stability had changed. The absence of

a correlation between T2 and the magnitude of tearing resistance also implies the absence of correlations between T2 and

those structural factors that determine tearing resistance.

The only evident correlation involves T2 and the magnitude

of change in tearing resistance and, therefore, relates DTA

to pern.anence.

The pH of the aged papers is included in this report,

as tne pH of paper is thought to influence permanence. The

data do not support this correlation. However, since pH may

change as a paper is aged, the data cannot be interpreted

with complete confidence.
3

2. RESULTS AND DISCUSSION

2 . 1 Results

Initial Properties

The sample numbers, fiber content, and the initial

bursting strength, folding endurance and internal tearing

resistance of all of the papers, as determined in 1940, are

given in Table 1. Tables 2, 3, and 4 summarize the changes

in physical properties due to accelerated and natural aging.

Correlation of Accelerated and Natural Aging

Bursting strength . Both increases and decreases in

bursting strength are observed after 20 and 32 years of

natural aging, and are plotted in Figures 1 and 2, against

the decreases observed after 72 hours of accelerated aging.

No correlation is evident.

Schopper folding endurance . Decreases in Schopper

folding endurance observed after 20 and 32 years of natural

aging are plotted in Figures 3 and 4 against the decreases

observed after 72 hours of accelerated aging. Again, no

correlation between natural and accelerated aging is evident.

However, the original tests were interrupted at 2500 double

folds. Only a limited number of samples, which had an initial

folding endurance below 2500 double folds in at least one

direction, can be used in calculating changes in folding

endurance, and the useful data are limited to the weaker paper

direction. For these reasons, little meaning can be attached

to the changes in folding endurance.

Internal tearing resistance . The data listed in Table 4

indicate a high correlation between the changes in tearing

resistances observed after 20 years of natural aging and

changes observed after 72 hours of accelerated aging. One

of the samples (No. 178) is extremely resistant to accelerated

aging but does not prove to be especially stable under natural

aging conditions, and a second (No. 58) is exceptionally

unstable under accelerated aging conditions but not under

natural aging conditions. Omitting these two extremes, the

linear correlation of the data plotted in Figure 5 has a magnitude of about 0.89, which implies an explained variation

of about 80 percent. The linear correlation of 0.67 for the
4

data plotted in Figure 6, involving measurements taken after

32 years of natural aging, is considerably lower probably

because of the use of different instruments in making the

measurements. It is also possible that the rates of decrease

in tearing resistance are significantly changed after a given

aging period, and that the 32 year data do not correlate as

well as the 20 year data for reasons involving inductive

processes that became important after 20 years. This point

can be surmised but not verified at present. Very few data

are available on natural aging periods beyond 25 years.

Differential thermal analysis (DTA) . The DTA thermograms

of various types of paper are usually characterized by a

decomposition endotherm beginning and ending within the

temperature range of about 220 to 400°C. A typical thermogram

is shown in Figure 7. The first endotherm (range about 90°

to 200°C) is due to desorption of moisture and gases and is

not important. In the decomposition endotherm, there are at

least three transitions: the beginning of the endotherm (T2);

the approximate end of exothermic reactions (T^, located at

the intersection of the straight portions of the slopes just

above the lowest point in the endotherm) ; and the highest

point on the curve just after T-,, which is usually the peak

of a mild exothermic reaction (T^).

Figures 8-10 show the relation of T2 to the magnitude

of changes in internal tearing resistance. One sample (No. 22)

for unknown reasons shows an extremely high resistance both

to natural and accelerated aging, but not an exceptionally

high T2. This point is taken to be nontypical and is omitted

from the calculated slopes. Considering the data obtained for

the other 12 samples after 20 years of natural aging, the

correlation with T2 is remarkable.

Tearing resistance depends partly on the weight of paper

per unit area [5]. For example, the plot of tearing resistance in grams against basis weight, in grams, shown in

Figure 11, roughly indicates a one-to-one correspondence.

T2 is independent of weight but might conceivably be affected

by structural variables that also affect strength. In order

to compare T2 directly with tearing resistance, all of the

tearing resistance data were placed on a common weight basis.

The calculated tearing resistances are plotted in Figures 12

and 13 against T2. The result is a nearly random scatter of

points showing that T2 is not correlated directly with the

magnitude of the tearing resistances of these papers either

before or after aging. The only evident correlation involves

T2 and the percent of decrease in tearing resistance or, in

other words, the permanence of the papers.
5

It would be very desirable to know whether or not T2

has changed since 1940. If T2 were essentially constant

over the years. Figure 8 indicates that the thermograms could

have been used empirically, in 1940, to predict the relative

aging stability of these samples. If T2 has changed concurrently with tearing resistances, however, the thermograms

and the attendant correlation indicate properties as they are

now and are not necessarily closely related to properties as

they were 32 years ago.

The correlations between T2 and the tearing resistance

changes after 32 years of aging and after accelerated aging

both are relatively low. For the 32-year samples, the

reason may be that the calculations are based on data obtained

with two different instruments. For the accelerated aging

data, however, all of the data were obtained with the same

tearing tester, and one could expect a higher correlation

with T2 . The situation is seriously impaired by the low

correlation between T2 and accelerated aging data because an

accelerated aging method might have provided an empirical

means to check out correlations of DTA and changes in tearing

resistance with a number of papers tested before and after

aging. Figure 10 shows that this approach might not work

very well.

Figure 14 shows no correlation between To and changes

in tearing resistance, in marked contrast to T2. The

resistance to pyrolysis of the 32~year old papers is more

closely related to T^ than T2 since extensive pyrolysis

precedes T^ and little or none precedes T2. A logical

inference is that permanence and resistance to pyrolytic

decomposition are not closely related.

pH . Paper pH is often considered to be a criterion of

paper stability, and acid paper is generally less stable

than neutral or alkaline paper. However, the original pH

values of these papers are unknown. The pH values listed

in Table 7 were determined on the present set of papers after

32 years of aging. Paper pH can change substantially during

accelerated aging, and probably also during natural aging,

so that the values listed in Table 7 may reflect the original

pH only approximately. Positive rank correlations between

the pH values, tearing resistances, and Schopper folding

endurances are still evident after 32 years of aging, but

they are too weak to indicate whether the original acidity

or the amount of acid generated in the present case has anything to do with stability.
2 . 2 Discussion

The question of what type of accelerated aging environment is best suited to simulate natural aging is a very

important one that has not been successfully resolved. It

may be addressed in a number of different ways.

One of the ways is to characterize the types of change

that actually occur in the different aging environments and

then examine old papers for evidence of similar types of

change. For example, it has been shown in recent studies

[1, 6, 7] that the accelerated aging process in a dry air

environment leads to increases in the wet tensile strength

of laboratory handsheets which are concurrent with slight

loss of dry tensile strength, and that MIT folding endurance

and internal tearing resistance decreases as wet strength

increases. In humid air, at the same temperature, the

principal change is a rapid decrease in dry tensile strength,

with consequent very rapid decreases in folding endurance,

tearing resistance, and bursting strength. One seldom knows

the initial wet strength or tensile strength of an old paper,

but if old paper should prove to have a much higher wet

strength than papers of their composition usually have initially, but a normal tensile strength for papers of their

type, it might be inferred that their natural aging process

was similar in type to dry accelerated aging. But, if the

dry tensile strength were quite low, it might be inferred

that humid accelerated aging processes more closely resembled

natural aging than dry accelerated aging processes.

A second approach is to determine if the nature of

changes and the rates of change in a number of physical

properties observed in a given type of paper during accelerated aging can be correlated with changes occurring over a much longer period of natural aging. This might involve

tests after several accelerated aging periods and over

several decades of time.

The third approach is used in the present study. That

is, to subject a number of papers, having widely different

stabilities, to natural and to accelerated aging and then

try to develop correlations between the amount of change

detected after one or two periods of accelerated aging and

after natural aging.
7

All three approaches have advantages and disadvantages,

and a combination of the three would certainly be preferable

to any single approach. A rational choice of testing methods

also is important for a fine perspective on the aging process.

Decreases in folding endurance and tearing resistance, for

example, can provide only crude information. These changes

may be observed after either dry or humid accelerated aging,

as a consequence of very different types of reactions. Dry

aging results in crosslinks that can cause fold and tear

both to drop because of the embrittlement of paper. Humid

aging results in fiber degradation that also causes fold and

tear to decrease. While the rates of decrease are quite

different, it would not be surprising if either aging method

could be correlated with natural aging. It is more significant

that tensile strength declines very slowly in dry aging and

very rapidly in humid aging. Therefore, if folding endurance

should drop rapidly while tensile strength changes much more

slowly, or not at all, during natural aging, a similarity to

dry aging would be indicated. But if both fold and tensile

strength should decline fairly rapidly, a parallel with humid

aging would be indicated. This is not to imply that fold,

tear, and tensile tests are recommended by the present authors,

but that several different tests may provide a much finer

perspective on aging than a few conventional tests can possibly

provide

The stumbling block in deciding which type of accelerated

aging method to employ is the very reason that an accelerated

aging method is needed: it takes so long to determine the

stability of paper by natural methods. One must put some of

the paper through an accelerated aging process, test it, and

store other samples against future testing after natural

aging processes. While it is true that experiments of this

type were initiated long ago—in the thirties and forties

all of them have involved dry oven aging. No data are

presently available that would permit a correlation of the

effects of humid accelerated aging and natural aging.

In their study of the aging of a number of rag and

sulphite papers, Wilson, et al [2] reported changes in the

tensile strength and the MIT folding endurance determined

before and after accelerated aging at 100°C in dry circulating

air for periods of 24, 48, and 72 hours, and after 4, 8, and

26 years of natural aging. Significantly, they found little

change in tensile strength, but a whole spectrum of changes

in folding endurance, suggesting a similarity to dry accelerated aging. The samples which were least stable in the
8

accelerated aging environment also were least resistant to

natural aging, and for both rag and sulphite papers, there

was approximately the same equivalence between accelerated

and natural aging times —i.e., 48 hours of accelerated aging

produced about the same amount of decrease in folding endurance as 12.5 years of natural aging.

Some of Wilson's data are replotted in Figures 15 and 16,

in order to show the fit of points determined by all of the

papers to a common slope*. Fold is more sensitive to aging

than is tear. Nevertheless, there is a remarkably similar

correlation between the effects of natural and accelerated

aging for both folding endurance and tearing resistance.

Together with the lack of change in tensile strength, the

coefficients of linear correlation strongly indicate that

dry accelerated aging and natural aging are comparable.

Wilson's data include a comparison of rates; a test

which may differentiate between dry and humid aging processes

(the dry tensile test) ; and a selection of samples having a wide variety of stabilities. His tests permit all three of

the types of comparison listed at the beginning of this

discussion. Unfortunately, his data are limited only to two

physical tests —fold and tensile. It could be especially

interesting to know what changes in wet strength may have

occurred.

The present experiments are also limited in range but

complement Wilson's data in that the correlations are equally

high. The same conclusions can be drawn from them, even though

they involve a different physical property.

*It should be noted that the high intercept apparent in

Figure 15 means little. It is due to the fact that the

least stable of the samples had suffered a loss of more than

90 percent of their folding endurance after 8 years, at the

same time that the more stable samples had lost less than

20 percent. The more stable samples continued to lose folding

endurance during the next 18 years of aging, whereas the

least stable ones are unable to sustain much more loss after

8 years. So the slope determined by changes in the folding

endurance of all of the papers decreases with time, and the

intercept increases. This is immediately evident in comparing

Figure 16 for the 8 year term and Figure 15 for the 26 year

term
9

3. DTA

The time required to obtain a DTA thermogram is less

than 1 hour. Because of the rapidity of the method, any

reproducible type of correlation between permanence and DTA

would be very useful, however empitical it might be. The

principal difficulties lie in the interpretation of thermograms. DTA is sensitive in different ways to many components

of paper. For example, aluminum metal can promote endothermic

reactions. Mineral acids also do this. T2 may be affected

by functional groups located in cellulose chains and by

hemicelluloses in paper in qualitatively similar ways.

Most of the DTA performed in this laboratory has tended

to show a correlation between T3 and aging stability. The

correlation between changes in internal tearing resistance

and T2, especially as indicated in Figure 8, was not anticipated. It is significant that T2 is not related to the

magnituae of the tearing strength of paper, but instead to

the rate of change during natural aging. It also is interesting that Wilson's samples, which are quite similar to the

ones tested by DTA, show little change in tensile strength.

Where tensile strength is constant, fiber strength is nearly

so, and the observed T2-tear correlation evidently is not

related to changes in fiber strength. This is helpful

negative information, even though no explanation of the

correlation is directly suggested by the present data.
10

4. pH

The pH data are of little value in the absence of

knowledge of the original pH data for comparison. It would,

for example, be possible for acid to be generated during

the aging process. This is particularly characteristic of

humid, accelerated aging, though not dry accelerated aging

[1].
11

5. APPENDIX

5 . 1 Samples and Aging Conditions

The sample numbers, fiber content, and the physical

properties that were determined in 1940 are listed in

Table 1. The samples were subjected to accelerated aging

at 100°C for 72 hours in circulating air. They were

conditioned prior to tests according to recommendations

given in TAPPI Method T 402 [8]

For natural aging, the samples were stored in the dark

at ordinary temperatures and relative humidities for 20 and

32 years, respectively.

5.2 Methods of Test

Schopper folding endurance . Schopper folding endurance

was determined in machine and cross directions according to

TAPPI Method T 423 [8]. Originally, folding endurance

measurements were interrupted at 2500 double folds. Most of

the samples exceeded 2500 double folds in the stronger

direction, but in the weaker direction, 10 out of 13 had

folding endurances below 2500. Only those measurements, in

the weaker direction, which were below 2500 are used in the

cal':ulations of subsequent changes in folding endurance.

Internal tearing resistance . Internal tearing resistance

was determined according to TAPPI Method T 414 [6]

Bursting strength . Bursting strength was determined

according to TAPPI Method T 413 [8].

pH, hot extraction . The hot extraction pH was determined according to TAPPI Method T 435 [8].

pH, cold extraction . The cold extraction pH was determined according to TAPPI Method T 509 [8]

Differential thermal analysis . A commercial differential

thermal analyzer was used which has a temperature range of

-100° to +500°C with a precision of 0.2°C and a sensitivity

of 0.0025°C, according to manufacturer's data. Glass beads

served as the reference material. The specimens and reference

material were heated in a dry nitrogen atmosphere at a flow

rate of 1.0 liter per minute and a heating rate of 2Q°C per

minute
12

Calculation of percent change in physical properties . The calculations of percent change in tearing resistance are

based on measurements taken in both directions. Those

Schopper folding endurances which were interrupted at 2500

double folds, however, are considered to be undefined, and

the changes are calculated only for measurements in the

weaker direction, which are usually less than 2500 double

folds. The original data do not indicate whether measurements taken in the weaker direction were in the cross or the

machine direction; but for the naturally aged papers, it was

found to be the cross direction. It is assumed that, originally, the weak direction always refers to the cross

direction.

Constancy of testing conditions . The same industrial

laboratory and the same instruments were employed for Schopper

folding endurance, internal tearing resistance, and bursting

strength determinations throughout the first 20 years of

this study, but the tests after 32 years of aging were performed with different instruments in a laboratory at the

National Bureau of Standards.
13

6. CONCLUSIONS

1. Correlations of the accelerated dry aging of rag

and sulphite paper and their natural aging are discussed.

2. Changes in the internal tearing resistance indicate

a wide range of stabilities in both accelerated and natural

aging.

3. Changes in internal tearing resistance indicate a

high correlation between dry accelerated aging and natural

aging

.

4. Changes in Schopper folding endurance indicate no

correlation between dry accelerated aging and natural aging,

but these are of little value because many tests were interrupted before completion.

5. Changes in bursting strength are low, both in dry

accelerated aging and natural aging.

6. Pata on changes in the MIT folding endurance of the

same types of paper used in this study are cited in the

literature showing that a high correlation exists between

dry accelerated aging and natural aging [2]

.

7. Differential thermal analysis indicates a surprisingly

high correlation between T2 and the magnitude of changes in

tearing resistance due to natural aging.

8. Positive rank correlations between the pH of aged

papers and rates of decrease in folding endurance and internal

tearing resistance exist but are too weak to be meaningful.
14

7. REFERENCES

1. E. J. Parks and R. L. Hebert, Accelerated Aging of

Laboratory Handsheets : Changes in Acidity, Fiber Strength,

and Wet Strength, NBS Report 10 627 to National Archives.

2. William K. Wilson, Jack L. Harvey, John Mandel, and

Thelma Worksman, Tappi 38 , 543 (1955) .

3. E. J. Parks and R. L. Hebert, Tappi 55 (10), 1510 (1972).

4. E. J. Parks, Tappi 54 (4), 537 (1971).

5. E. J. Parks, R. L. Hebert, and G. H. Limparis, Develop-

. ment of Specifications for Bond and Ledger Papers, NBS

Report 10 844 to National Archives.

6. E. J. Parks and R. L. Hebert, Accelerated Aging of

Laboratory Handsheets: Retention of Folding Endurance,

Internal Tear, Bursting Strength, and Tensile Strength,

NBS Report 10 628 to National Archives.

7. E. J. Parks and R. L. Hebert, Accelerated Aging of

Laboratory Handsheets: Reflectance, Moisture Regain,

Sonic Modulus, and Differential Thermal Analysis, NBS

Report 10 687 to National Archives.

8. Standard and Suggested Methods of the Technical Association of the Pulp and Paper Industry (TAPPI) , 1 Dunwoody

Park, Atlanta, Georgia 30341.
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Table 2. Bursting strength observed after aging

paper for 72 hours at 100°C and after

20 and 32 years of natural agina,

and changes as a percent of the original

bursting strength.

Aging Conditions

72 hours

at 100°C

20 years,

natural

32 years,

natural

Sample

No

.

Bursting

Strength

( points

)

Change

(%)

Bursting

Strength

(points

)

Change

(%)

Bursting

Strength

(points

)

Change

(%)

22 75 0 72 -4 70 -6.7

2 5

• 86 0 94 + 8.5 99 + 15.1

5 3 74 - 5 78 0 75 +4.0

D28 57 -3 60 + 1.7 57 -3.0

802 \J \J £j 3^ 56 -8 60 + 1.6 56 -8.0

58 49 -39 63 -21 56 -3.0

181 29 -3 31 + 3.0 31 + 3 . 3

D172 13 : -7 14 0 13 -7

N176L 14 0 16 -14.3 17 + 21.4

D179L 17 0 17 0 20 + 17.6

178L 32 -6 26 -23.5 34 0

19 5M 49 0 45 -8.2 42 -14.3

198 36 -14 31 -26.2 40 -4.8
Table 3. Schopper folding endurance observed after aging

paper for 72 hours at 100°C in dry air and after

20 and 32 years of natural aging and changes

as percent of the original folding endurance.

Aging Conditions

72 hours

at 100°C

20 years , natural

32 years

,

natural *

Sample

No.

Folding**

Endurance

(double

folds)

Change***

(%)

Folding

Endurance

(double

folds)

Chanae***

(%)

Folding

Endurance

(double

folds)

Change***

(%) a **** b a b a b

22 7 9 -30.0 1 1 -90 1 1 -90

O TT TT 25H 1764 2500 779 1216 981 1216

5 3 2500 2500 59 346 513 545

D2.0 338 439 -73.8 10 28 -99 19 46 -98. 6

O A O O o02 J 760 790 -41.0 3 7 -99. 7 33 60 -97. 6

58 5 570 -99.9 19 29 -99. 0 14 32

181 429 2500 -33.5 396 662 -33. 3 154 599 -76. 1

-^172 32 344 -66.7 26 64 -72. 9 12 29 -87. 5

Nl7eL 37 203 -24.5 23 49 -53. 1 14 66 -71. 4

D17SL 104 1058 -60.2 64 133 -75. 4 76 365 -70. 9

1781 1227 2500 + 19 105 233 -89. 6 500 674 -51. 6

195^ 669 2500 -47.2 233 283 -47. 2 221 256 -82. 6

198 171 1200 -48.3 187 354 -43. 5 182 349 -45. 0

* Tests after 32 years performed with a different instrument

from that used originally, after accelerated aging and after

20 years of natural aging.

** Tests were interrupted at 2500 double folds.

*** Each value represents change in the weaker direction.

****(a) and (b) refer to either machine direction or cross

direction, not specified in the original data.
Table 4. Percent change in internal tearing resistance

observed after aging paper for 72 hours at 100*'C

in dry air and after 20 and 32 years of natural

aging.

Aging Conditions

72

at

hours

100°C

20

of

years

storage

32

of

years

storage*

Sample

No

Tearing**

Resistance

(g) (%)

Tearing

Resistance

(g) (%)

Tearing

Resistance

(g) (%)

22 i J D - 3.7 X1 4T Ro - 9.2 X J o -15.1

25H . 384 -13.7 252 -34.5 278 -27.8

53 . 20 5 -10.7 151 -25.4 153 -25. 3

D28 172 - 9.6 127 -24.2 116 -32.6

8023 l^Q -14.

134 -32.7 135 -32 . 2

S 8 186 -45.4 104 -44.1 100 -46.3

181 46 - 3.3 39 -15.2 33 -28.3

D172 22 -16. 3 14 -37.2 12 -44.2

F176L 25 - 6.0 20 : -18.0 18 -40.0

D179L 20 -12.2 12 -41.5 11 -46.3

178L 20 - 2.5 14 -32.5 13 -35.0

195M 65 -13.0 49 -25.2 46 -29.8

198 59 - 7.1 42 -14.3 37 -24.5

* Tests performed after 32 years with a different instrument than

that used originally, after accelerated aging and after 20 years.

**Average of two directions.
Table 5. Half-lives calculated from decreases in

internal tearing resistance observed

after aging paper for 72 hours at 100°C

in dry air and after 20 years and 32 years

of natural aging.

Aging Condition

Sample

No.

Accelerated*

(half-lives, hours)

20 years

(half-lives, years)

32 years**

(half-lives, years)

22 975 116 104

25H 260 29 58

53 334 39 63

D28 364 38 48

8023 256 31 50

58 96 23 34

181 900 66 57

D172 251 30 35

N176L 450 56 54

D179L . 240 25 35

D178L 1440 31 45

195M 265 39 53

198 445 70 66

* 72 hours at 100°C in a laboratory oven with circulating air.

**Data obtained after 32 years performed with a different

testing instrument from that used for earlier tests.
Table 6. Differential thermal analysis (DTA) of

13 samples of commercial paper after

natural aging for 32 years.

DTA Parameters

Sample

No.

T^*

(°C)

rp * *

3

(°C)

np * * * ^4

(°C)

22 260 338 372

25H 245 332 377

5 3 255 339 380

D28 255 327 372

8023 240 308 333

58 223 341 360

181 287 ' 363 385

D172 255 347 380

N176L 262 321 368

D179L 235 372 392

178L 240 308 333

195M 267 372 392

198 295 369 391

* T2 is the approximate temperature of the

onset of the principal decomposition

endotherm.

** T3 is the intersection of extrapolated

slopes preceding and following the nadir

of the decomposition endotherm.

***T4 is the temperature of the exothermic

peak immediately following T3.
Table 7. pH values (cold and hot extraction)

for 13 samples of commercial paper

tested after natural aging for 32 years.

pH pH

Sample

No

(cold

exti'action)

(hot

ext Tact ion )

22 4.90 4.42

25H 4.50 4.20

5 3 4.64 4.36

D28 4.41 4.18

8023 4 .75 4.34

58 4.70 4.14

181 4.80 4.53

D172 4.40 4.14

N176L 4.68 4.22

D179L 4.80 4.47

178L 5.04 4.38

195M 4.09 3.98

198 5.40 5.01

I

i

1
Table 8. Rank correlations of pH (hot extraction,

32 years) with physical and thermal

properties of the aged papers.

Parameter

Ranked

Against pll

Aging Condition

Accelerated 20 Years Natural 32 Years Natural

Rank Correlation

tear .45 51 .43

fold .21 29 .54

burst -.03 09 .24

T

2

.25

^3 .41

.17
0 -10 -20 -30

CHANGE AFTER ACCELERATED AGING,

I Figure 1. Relation of changes in bursting strength observed

after accelerated aging to the changes observed

after 20 years of natural aging.
iD

Z

o

<

<

D

<

Z

u.O

</) <

>-,

<>J fO

q:

111

o

z

<

I

o

-10 —

-20

0 -10 -20 -30 -40

CHANGE AFTER ACCELERATED AGING, 7o

Figure 2. Relation of changes in bursting strength observed

after accelerated aging to the changes observed

after 32 years of natural aging.
o

z

o

<

<

<

Z

Ul

o

</) <

UJ

o

(VJ (T

Id

Iu.<

UJo

z

<

I

u

-100 —

-20 -40 -60 -80 -100

CHANGE AFTER ACCELERATED AGING, %

Figure 3. Relation of percent decrease in Schopper folding

endurance after 20 years of natural aging to

percent decrease after accelerated aging.
o

z

o

<

-I<

q:

100 —

I 80 —

<

z

u.o

(/) a:<

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to

q:

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o

-60

-40 —

-20 —

-20 -40 -60 -80 -100

CHANGE AFTER ACCELERATED AGING, 7o

Figure 4. Relation of percent decrease in Schopper folding

endurance after 32 years of natural aging to

percent decrease after accelerated aging.
Figure 5

Relation of decreases in internal tearing resistance

observed after accelerated aging to the decreases

observed after 20 years of natural aging.
CHANGE AFTER ACCELERATED AGING,7o

Figure 6. Relation of decreases in internal tearing resistance

observed after accelerated aging to the decreases

observed after 32 years of natural aging.
o

4-1

C

-HcC 0) •H x;

0) X! tn

O £ H 4-1 -P o .

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-p

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!h H 1

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CSJ 1 > ( oooo

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ro _,

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O

LO LU

CM "5 Ooo

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0X3 i V OQNB
Figure 8. Half-lives in internal tearing resistance plotted

against DTA T2 in degrees Centigrade. The calculated

half-lives are based on decreases in tearing resistance observed after 20 years of aging.
1

\ \ \

\—I

\—\—

100

z

o

<

-J <

D

I-<

Z

u.O

(/) o:<

UJ

>-

lij 50

-J

I li. -J<

X

''CORR.^O-^O

200 220 240

DTA T.2*

260 280 300

Figure 9. Half-lives in internal tearing resistance plotted

against DTA T2 in degrees Centigrade. The calculated

half-lives are based on decreases in tearing resistance observed after 32 years of aging.
1500

1 \ r-pn \

I

\ r

5

>-

a:o

oOO

cco

X

m UJ

iv-J

u.<

X

1000

500

200 220 240 260

DTA Tg.'^C

280 300

Figure 10. Half-lives in internal tearing resistance plotted

against DTA T2 in degrees Centigrade. The calculated

half-lives are based on decreases in tearing resistance observed after 72 hours of accelerated aging.
Figure 11. Internal tearing resistance, as a function of

weight per unit area.
150

O

u.Q

IJLJ CVJ <^

< o

- u. o> o

lJ <

U Ul

Z X

< <

CO 2

UJ 3

a:

a: Z CLy- <

LlI O

z <

UJ

I100 —

igure 12. Relation of magnitude of the tearing resistance

of unaged samples to DTA T2 , °C, of same samples

aged 32 years.
q:

o

Q

5 -

u

< c

o O

- o

100 —

LUo

<

(/) _

(/) 2

UJ =>

£r q:LU

<

UJ<

q:

<

UJ< <

q:UJ

ql ou —

I

o

igure 13. Relation of the magnitude of the tearing

resistance of samples aged 20 years to DTA

°C, of same samples aged 32 years.
380

Figure 14 Half-lives m tearing resistance clotted aaainst DTA T3 m degrees Centigrade. The calculated

half-lives, in years, are based on chances

observed after 20 years of natural aginc.
or

1

1 1

I

1 1 1

1 1 1

UJ

1-

Ll<

-100 —

• U <s 2 z

<

UR o

< -80

Q

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•

•

•

H -40 • <

UJ

>- • • Z •

UJ CM o -20

z

<

X

o

0 I 1 1 1 1 0 -20 -40 -60 -80 -100

CHANGE IN MIT FOLDING ENDURANCE AFTER

72 HOURS OF ACCELERATED AGING,

Figure 15. Relation of decreases in MIT folding endurance

after accelerated aging (72 hours at 100°C, dry

air) to decreases observed after 26 years of

natural aging. Data of Wilson, et al [2] .
UJ

LU <^ U Z

<

Q

Z

UJo

z

Q

_Jo

LUO

z

<

I

o

<

<

3

I-<

Z

u.O

CO

en<

UJ

>-CD

-20 -40 -60 -80 -100

CHANGE IN MIT FOLDING ENDURANCE AFTER

48 HOURS OF ACCELERATED AGING,

'igure 16. Relation of decreases in MIT folding endurance

after accelerated aging (48 hours at 100°C, dry

air) to decreases observed after 8 years of

natural aging. Data of Wilson, et al [2].
FnayA NgS-lJA^ (1.71) 'U.S. DEPT. OF COMM. 1 . PU B LIC ATION OR RE PORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA m^ctd -7-3 i c c SHEET NBSIR 73-155

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Accelerated Aging of Commercial Papers in Dry Air,

Compared with Natural Aging

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

E. J. Parks, R. L. Hebert, & Catherine Feasenmyer

8. Performing Organization

MnCTXJ 7*3—1 t^t:

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No. 4110442

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

National Archives and Records Service

Washington, D.C. 20408

13. Type of Report & Period Covered

iecnnica± Keporu

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16- ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) An accelerated aging method is necessary for determining the

permanence of paper, since natural aging requires long periods of

time to generate meaningful trends in the decrease of paper strength.

It is questionable which would be better suited to simulate natural

aging—a dry or a humid accelerated aging environment. This report

describes correlations of the dry accelerated aging of rag and sulphite

oaper and their natural aging for periods up to 32 years.

The tests performed include internal tearing resistance, Schopper

folding endurance, bursting strength, differential thermal analysis,

and pH determinations.

Changes in internal tearing resistance indicate a high degree of

correlation between natural aging and dry accelerated aging. Differential thermal analysis is correlated with the change in tearing

resistance. Bursting strength changes little during either natural or

accelerated aging. The original acidities (pH) are unknown, but the

acidities of the aged papers show little or no correlation with aging,

"chopper folding endurance cannot be correlated with aging, perhaps

because of interruption in the initial tests.

Data on changes in MIT folding endurance of similar types of paper

are cited, which indicate an equally high correlation between dry

accelerated aging and natural aging.

17. KEY WORDS (Alphabetical order, separated by semicolons) Bursting Strength; differential

thermal analysis; dry accelerated aging; humid accelerated aging;

internal tearing resistance; MIT folding endurance; natural aging; pH;

raf^^^^£^er ;

Srhnppf^r fnldinq Pindnrance; sulph;Lte ^T paper,

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