NBSIR 74-632

Comparison of Accelerated

Aging of Book Papers in 1937 witli

36 Years Natural Aging

W. K. Wilson and E. J. Parks

Paper Evaluation Section

Institute for Materials Research

National Bureau of Standards

December 18, 1974

Interim Report

Prepared for National Archives and Records Service

Washington, D. C. 20408

-I

NBSIR 74-632

COMPARISON OF ACCELERATED

AGING OF BOOK PAPERS IN 1937 WITH

36 YEARS NATURAL AGING

W. K. Wilson and E. J. Parks

Paper Evaluation Section

Institute for Materials Research

National Bureau of Standards

December 18, 1974

Interim Report

Prepared for National Archives and Records Service

Washington, D.C. 20408

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

CONTENTS

Page

1. INTRODUCTION - 1

2. SAMPLES . , 3

3. METHODS OF TEST. . , 4

3.1 Methods Used in 1937 4

3.2 Methods Used in 1973 4

3.3 Statistical Treatment of Data 5

3.4 Sampling 6

4. RESULTS AND DISCUSSION 7

5. RELATIONSHIP TO SPECIFICATIONS 15

6. SHOULD AN ACCELERATED AGING ATMOSPHERE

BE MOIST OR DRY? 16

7. SUMi?RY 20

8. RECOMMENDATIONS FOR FURTHER WORK 22

9. ACKNOWLEDGMENT 22

10. REFERENCES 23

TABLES 1-31

FIGURES 1-12

APPENDIX. "Effect of Filling and Sizing Materials on

Stability of Book Papers," by M. B. Shaw

and M. J. O'Leary, J. Res. NBS , 2\_, 671

(1938) , Research Paper RP1149

1 . INTRODUCTION

The development of an accelerated aging procedure

requires information on the correlation between accelerated

aging and natural aging. Few successful studies of this

type have been made as (1) planning and executing an experiment over a period of 20-50 years is very difficult,

(2) test methods and their significance change with time,

and (3) materials of manufacture change so that one may be

evaluating the stability of materials that are no longer

manufactured. However, the development of information on

a continuing basis, with emphasis on (1) the examination of

characteristics of old papers and (2) the determination of

what actually happens--chemically and physically—during

accelerated aging of paper under various conditions, can be

very useful.

In 1937 a group of book papers made in the NBS paper

mill was tested before and after accelerated aging for 72

iiours at 100°C in a circulating oven. This work was

reported in a paper by Shaw and O'Leary entitled, "Effect

of Filling and Sizing Materials on Stability of Book Papers"

[1]. Although there was no plan to test these papers after

a period, or periods, of natural aging, a collection of some

these papers had been kept in an office for several years

for occasional evaluation, as the manufacturing history was

known ?nd the physical and chemical properties of the papers

had been extensively evaluated for that time. Out of a total

of 72 papers, 18 were found that could be assembled to form

a reasonably coherent set of samples.

A copy of the original paper by Shaw and O'Leary is

included as an Appendix to this report. For convenience, original

data are given in appropriate tables. Papermaking details

on the papers, made in the NBS mill in 193 7, that are included

in this report are given in Table 1. Chemical and physical

test data obtained in 1937 are given in Tables 2 and 3,

respectively. Data obtained after accelerated aging for

72 hours at 100°C in 1937 are given in Table 4.

A group of commercial papers was tested before and after

accelerated aging in 1929, and these papers were retested

after 4, 8, 22, and 26 years of natural aging [2]. Although

these data were useful, manufacturing data on the papers

were not available and, unfortunately, the papers were

accidentally discarded several years ago. Data on these

papers showed that an empirical correlation existed between
2

accelerated aging and natural aging. In general, rag papers

stood up better than wood pulp papers. Although the acidity

values did not vary sufficiently to enable much of a correlation between acidity and stability, it was obvious that

some sort of correlation did exist. The soda-sulfite papers

were especially vulnerable to acid. This probably can be

explained by recent work in this laboratory [3, 4, 5] which

showed that aluminum on the carboxyls in cellulose contributes

to the degradation of paper. These soda-sulfite papers

probably had a high carboxyl content, but they are no longer

available for examination.

Most accelerated aging has been carried out in dry

atmospheres, except that which has been directed towards

evaluation of brightness reversion. Work in this laboratory

has shown that significant differences exist between moist

accelerated aging and dry accelerated aging [3, 4, 5]. Therefore, it is desirable to obtain as much test data as possible

on papers that are still available that were subjected to

accelerated aging several years ago. A group of papers aged

in air at 90°C and 50 percent relative humidity 10 years ago

[6] has been tested, and it is expected that the data on

these papers will be the subject of a separate report.
3

2 . SAMPLES

The fiber furnishes fall into three categories (Table 1)

(1) 50-50 soda-sulfite

(2) purified wood pulp

(3) old rag

Chemically these furnishes are very different. The sodasulfite papers contain a high percentage of pentosans (hemicelluloses) (Table 2) . The purified wood pulp papers are

fairly low in pentosans, and rag papers contain no pentosans.

As the pentosans usually contain more functional groups than

the cellulose fraction, one would expect these papers, in

general, to be more vulnerable to degradation. Most of the

papers contain fillers. Number 1133 is very interesting

and useful as it contains no filler, alum, or rosin. Three

papers contain calcium carbonate. Most of the papers contain

clay and two are filled with titanium pigments, one of which

is a mixture of titanium dioxide and barium sulfate.

Varying amounts of alum were added to the papers during

manufacture. Greater variation in amounts of alum and rosin

would have been desirable, as well as information on the

natural mineral content of the pulps before they were processed into paper. For the time, however, the amount of

infor-nption available is considerable.
4

3. METHODS OF TEST

3 . 1 Methods Used in 1937

Filler was determined from the ash content and by use

of an empirical formula. In addition, titanium dioxide and

barium sulfate were determined on the papers containing

titanium pigment, and calcium carbonate filler was deterfrtined by a titration procedure. Rosin, acidity, and alpha,

beta, and gamma cellulose were determined by methods

developed by Launer [7-9] . pH at the headbox was determined by the Quinhydrone method except for the runs containing calcium carbonate for which a glass electrode system

was used. Ash and copper number were determined by TAPPI

methods that have not changed appreciably since that time.

Physical test data including weight, bursting strength,

tensil3 properties (pendulum tester), thickness, sizing

value, opacity (contrast ratio), Schopper fold, MIT fold,

and tearing strength were obtained using TAPPI methods.

These methods have not changed substantially since 1937.

MIT fold was performed at 0.5 kg tension. All physical

tests were made at 65 percent relative humidity and 70*^.

The papers were aged in a circulating oven maintained

at 100°C for 72 hours.

3.2 Methods Used in 1973

Tests that were repeated in 1973 were made under the

same conditions, as well as could be determined, as the

tests in 1937. Wet tensile properties (paper thoroughly

wetted before testing) were measured by TAPPI Method T 456

[10]. Zero span tensile was measured using a commercial

testing device made especially for the purpose. In this

test the jaws of the tensile tester actually touch at the

beginning of the test, and the values are considered to be

a function of fiber strength. Moisture regain (moisture

content based on the dry weight of the specimen) was determined at 50 percent relative humidity and 23*0 [11]. Brightness (reflectance using a blue filter with peak transmittance

at 457 nm) was determined by TAPPI Method T 452 [12].
5

3.3 Statistical Treatment of Data

The standard deviation, s, is a measure of dispersion

of the data obtained from n measurements {x^, X2 • • • x^^)

of the sample, and is estimated by means of the expression:

n-l

X is the arithmetic mean of n measurements.

Correlation coefficients were calculated according to

the following formula :

The slope of the regression line was calculated from the

formula

ZxEy

m = 1x2 . (^x)

N

A correlation coefficient is valid only if the data

come from the same statistical population. The latter

varies according to the test. For example, if thickness

were the only important parameter of a sample of paper,

reflectance might vary enormously, but as long as thickness

is maintained within allowable limits, the sample would be

from the same statistical population. On the other hand,

if the group of papers contained newsprint and a bond paper,

there would be at least two statistical populations with

respect to reflectance. In the set of 18 papers discussed

in this report, there are three subsets with respect to

fiber furnish. Each subset usually can be treated as

belonging to the same statistical population. For some

tests, one or more papers must be eliminated before the

subset can be treated as a separate statistical entity.

There is considerable scatter in most of the plots and one
6

cannot be sure that any relationship that may exist is a

straight-line relationship, although such a relationship

is assumed in calculating correlation coefficients.

A complex situation exists with respect to interactions

among the various physical and chemical properties of paper.

Correlation coefficients are useful as a rough guide in

separating the samples into homogeneous populations, identifying unusual situations, and indicating trends in the

data

.

3 . 4 Sampling

Sheets were selected at random from the supply of paper

at hand to create the sample. Unfortunately, paper frequently

was limited and most of the available paper constituted the

sample . •

.
7

4. RESULTS AND DISCUSSION

Data on the effect of natural aging on alpha cellulose,

copper number, acidity, tensile strength, elongation,

folding endurance, and internal tearing resistance are

given in Tables 5, 6, 7, 8, 9, 10, and 11, respectively.

Summaries of retention of various chemical and physical

properties after 36 years of natural aging and after accelerated aging are given in Tables 12 and 13, respectively.

Zero span tensile and moisture regain are given in Table 14,

and data on wet tensile properties in Table 15. Brightness

data are given in Table 16.

As the original data on individual specimens are no

longer available, it is not possible to calculate standard

deviations for the data obtained in 1937. However, some

data are available showing that standard deviations for

aged and unaged papers are not appreciably different [6, 131.

Correlations among various properties are given in Tables

17-21.

Alpha cellulose and copper number

Data in Tables 4-6, the plots in Figures 1 and 2, and

the correlation data in Table 17 show good correlations

between changes in alpha cellulose and copper number after

accelerated aging and natural aging. The correlations are

calculated for the collection of 18 papers and also for subsets of papers. The subsets usually show higher correlations

than the correlations for the complete set of 18 papers. The

correlation coefficients show that alpha cellulose and copper

number, based on the data from these 18 papers, are suitable

chemical tests for evaluating the stability of papers for

permanent records.

Figures 1 and 2 show that the decreases in alpha

cellulose and increases in copper number are much greater

during 36 years of natural aging than during three days of

aging at lOO^C. It is undesirable to place a value on the

number of years of natural aging that is equivalent to

three days of oven aging at 100°C. These values inevitably

would be quoted out of context, and they differ with different tests.
The slopes of the subsets of papers in Table 17 show

considerable variation. From this it is obvious that these

subsets do not belong to the same statistical population.

In general, the correlations between changes in alpha cellulose and copper number, after either accelerated aging

or natural aging, with cold pH are not as good as the correlations between changes after natural aging with changes

after accelerated aging. The correlations are fairly acceptable, with the exception of the correlation between pH and

copper number for the soda sulfite subset. The pH of paper

has been used for years as a rough guide to stability.

The relationship between cold extract pH and changes in

alpha cellulose and copper number after 36 years natural

aging are plotted in Figures 3 and 4. It is obvious that

a good straight line relationship does not exist but the

overall trend is unmistakable. This is borne out by the

correlation coefficients in Table 17.

It is not surprising that an alkali solubility test

appears to be useful in evaluating the stability of paper.

Alkali solubility is a measure of the short-chain material

that goer into solution during the test. The amount of

carbohydrate material dissolving depends, among other things,

on the strength of alkali and on whether the chain break

occurs near enough to the end of a chain for the fragment

to become soluble. Any alkali solubility test is strictly

empirical.

By today's standards, these tests are considered to be

archaic. Alpha cellulose [14] has been supplanted by other

more convenient and supposedly more meaningful alkali solubility tests. The copper number test [15] is not widely used.

Copper numbers are proportional to aldehyde content for

specific types of oxidation, but the slopes of the lines

relating copper number to oxidation level varies with the

location of the aldehyde group in the anhydroglucose ring [16]

In addition, the copper number reagent causes further degradation of alkali sensitive cellulose during the copper number

test.

Tensile strength

Tensile strength is not a particularly sensitive method

for detecting changes in paper after natural aging. This is

what one would expect from an examination of load elongation

curves for unaged and aged papers. Until the reduction in
9

elongation reaches the yield point, most of the deterioration shows up as a reduction in elongation. An examination

of the data in Tables 8 and 9 shows that the retention of

elongation with natural aging is appreciably lower than the

retention of tensile strength.

The three alkaline soda-sulfite papers, 1158, 1172,

and 1175, show good, but not outstanding, retention of

tensile strength, when compared with the other 15 papers.

The three acid soda-sulfite papers, 1129, 1130, and 1133,

exhibit comparatively poor tensile retention (70-85 percent,

MD) . With the exception of 1166 (79 percent, MD) all of the

other papers show retention values of 94 percent or above.

Number 1133 is a very slightly acid, waterleaf, shortfibered paper. As the fiber strength did not deteriorate

(shown later), the bonding must have deteriorated with time.

Elongation

The data on elongation after natural aging in Table 9

would be irore valuable if data on retention of elongation

after accelerated aging were available. Several correlations

of changes in elongation with natural aging are discussed in

connection with other tests. Correlations of retention of

elongation with cold pH are given in Table 20. Although the

corrslat-'on for all 18 papers is not good, the correlation

coefficients for the three subsets are much higher. Elongation is a fairly sensitive measure of the degradation of

polymeric materials, but this was not generally recognized

when the original testing was done on these papers.

Folding endurance

Data on folding endurance in Table 10 are not as useful

as they might be because of the high standard deviations.

More specimens would have been desirable but sufficient

samples were not available. Data on retention of folding

endurance after natural aging against retention of fold

after accelerated aging in 1937 are plotted in Figure 5.

The correlation coefficients in Table 18 are fairly good.

Differences in slopes indicate that the subsets belong to

different statistical populations.
10

Retention of fold after natural aging as a function

of cold extract pH is plotted in Figure 6 and retention of

fold after natural aging as a function of alum and rosin

added during manufacture is plotted in Figure 7. Correlation

coefficients in Table 18 show that correlations for the subsets are fairly high but correlations for the set of 18 papers

are very low. The fiber lengths and the chemistry of the

three paper subsets are quite different, so the three subsets could be expected to react differently.

Correlations in the paper subsets of fold retention

as a function of alum added minus rosin retained are surprisingly good. During manufacture, rosin size was added

first and alum was added later to precipitate the rosin

size onto the fibers. One would expect that carboxyl groups

in the cellulose would not have an opportunity to interact

with aluminum until the rosin size had reacted and an excess

of alum was available. The reactions of alum with rosin size

and with carboxyl groups in cellulose are quite complex and

probably nonstoichiometric . Subtracting the weight of rosin

from the weight of alum is hardly a stoichiometric approach,

but without information on the composition of the rosin size

precipitate (highly variable), metals on the carboxyls, composition of the natural resins in the pulp, and ratio of free

rosin size to rosin sodium salt in the size solution, nothing

more is warranted.

The pulps used in preparing the alkaline filled papers

first were sized (except 1158, which has no sizing) with

rosin and alum before calcium carbonate was added. None of

the three alkaline papers shows outstanding retention of fold,

either after natural aging (55-85 percent) or after accelerated aging (55-75 percent) . Several papers showed much

better retention of fold after accelerated aging in 1937 than

the three alkaline papers. After natural aging the three

alkaline papers, as a group, are good, but not outstanding.

Number 1161 shows 115 percent retention of fold after natural

aging, number 1191 also shows up well in both accelerated and

natural aging. Both of these papers are almost neutral,

although small quantities of alum and rosin were used during

manufactu re

The data show that pH is not the only indicator of

stability of paper and that folding endurance is not a universal method of measuring degradation. For example,

one would have expected the three alkaline papers to have

retained a much higher percentage of their initial folding

endurance. Number 1161 has a very high folding endurance,

so it has retained its bonding with time. It would appear

that some sizing material is desirable to maintain folding

endurance with time even though the acidity may be higher.
11

Data in Table 18 on correlations of fold after natural

aging with retention of elongation after natural aging are

very good for purified sulfite and rag. Elongation probably

could be used in place of fold as a routine test. This

would be especially desirable as (1) fold is a very timeconsuming test and (2) elongation usually is determined as

a part of the determination of tensile properties.

Internal tearing resistance

Data on retention of internal tearing resistance* after

36 years natural aging are given in Table 11. These data

are plotted against accelerated aging data in Figure 8 and

against pH in Figure 9. Two of the alkaline papers for

which data are available (insufficient sample to test 1158)

are superior to all others. Again, 1133 is somewhat exceptional, as one would expect a paper that has maintained its

fiber strength and folding endurance to have maintained its

tearing strength. Obviously, the bonding strength has

deteriorated. Some papers at the bottom of Figure 11 are

somewhat acid and show very poor retention of tear. However,

several other papers in the same acidity range retained a

much higher percentage of their tearing strength.

Correlations between internal tear after natural aging

with other parameters are given in Table 19. Correlations

between tear retention after natural aging and tear retention

a'f'ter (1) accelerated aging and (2) pH cold extraction, are

not especially good. Correlations for specific populations

are somewhat better. Correlations between retention of tear

after natural aging and retention of elongation after natural

aging are surprisingly good.

Change in Acidity

pH values, hydrogen ion concentrations [H"^] calculated

from pH values, and the changes that have occurred due to

natural aging are given in Table 7. It is obvious that most

of the papers, except the ones that are practically neutral,

exhibit significant changes in hydrogen ion concentration of

the extract after natural aging. it has been shown earlier

in this laboratory that significant changes in hydrogen ion

concentration of the aqueous extract of the paper, especially

As the name implies, internal tearing resistance is the

energy required to tear a specimen, under specified

conditions, after the tear has been started.
12

if the carboxyls are covered with aluminum, is a characteristic of moist aging. The magnitude of these changes in the

naturally aged papers is not nearly as great as the magnitude

of the acidity changes of handsheets with aluminum on the

carboxyls aged at 90°C and 50 percent relative humidity. It

appears, however, from these acidity data that some moisture

in an accelerated aging procedure may be indicated.

The data on acidity in Table 7 are not as meaningful

as they might be as pH values are expressed only to the

nearest 0.1 pH unit. Massive amounts of acid were not

generated during natural aging. Correlations between acid

generated and initial pH are very poor except for the three

acid soda sulfite napers. These correlations are not shown.

Poor correlation between initial pH and generation of acid

is not surprising. The acid may arise from hydrolysis of

aluminum on the carbo^yl groups in cellulose or rosin, from

hydrolysis of excess alum that may be in the paper, from

carboxyl groups, from acid-lignin residues, from oxidation

of cellulose, and probably others.

Zero span breaking length

Zero span breaking strength is considered to be a ^unction of the strength of the fibers in a paper. It is

conmon practice to convert breaking strength data to

breaking length by factoring in the basis weight of the

paper. Breaking length is defined as the length that would

cause the specimen to break under its own weight. Although

zero span tensile was not measured in 1937, differences

within the paper subsets, obtained in the current testing

program, may be meaningful.

Zero span breaking length data obtained after 36 years

natural aging (Table 14) are plotted against cold extract

pH, measured in 1937 (Figure 10) . The correlation coefficients in Table 20 show that it is fruitless to try to treat

all of the papers as belonging to the same statistical population. The subsets show fairly good correlations, but 1207

and 1208, both of which contain titanium pigment, cannot be

included in the rag subset.

An examination of papermaking procedures suggests that

the high zero span values of 1207 and 1208 may be indicative

of stable papers. The first three rag papers contain varying
13

amounts of alum, but no rosin. Number 1203 contains 2 percent rosin and a large amount (4 percent) of alum. Numbers

1207 and 1208 contain rosin and probably nearly stoichiometric

amounts of alum (with respect to rosin). Therefore, as there

is an opportunity for some of the carboxyls in the first four

rag papers to be covered with aluminum, and it is unlikely

that the carboxyls in 1207 and 1208 are covered with aluminum,

one would expect- the latter two papers to be more stable than

the other four. This is indicated by the much higher zero

span tensile strength of these papers. The papers that contain alum alone, and no rosin, (1129, 1130, 1191, 1192, 1193)

or an excess of alum (1203) exhibit lower zero span tensile

strength than the other papers in the subsets.

The three alkaline papers are somewhat higher in zero

span tensile than the other soda-sulfite papers. Data on

zero span breaking length were plotted (not shown) against

acid generated after 36 years of natural aging, but no

relationship was apparent.

Tensile properties of wetted specimens

Measurement of specimens in the wet state gives an

indication of the crosslinking that occurs in the aging of

paper. Paper in which no crosslinking has occurred has a very low strength when wet.

Data on wet breaking load as a percent of dry breaking

load (Table 15) are plotted against cold pH, 1937, in

Figure 11. As indicated in Table 21, correlations within

subsets are much better than the correlation coefficient

that includes all of the papers. As the development of

strength of wet specimens is a function of initial acidity

[17] , fairly good correlations of the development of breaking

strength of wet specimens with initial pH are to be expected.

Correlations between energy at break of wet specimens (Figure

12) and extensional stiffness of wet specimens with initial

cold extract pH show the same trends as correlations between

breaking strength of wet specimens and pH (Table 21)

Moisture regain

Papers within each fiber subset (Tables 14 and 15)

exhibit very similar moisture regains. Moisture regain of

the rag papers averages about one percent lower than moisture
14

regain of the wood pulp papers. This is in keeping with differences in crystallinity between wood fibers and cotton fibers. The data show no correlation between wet breakinq load as a percent of dry breaking load and moisture regain. This IS in keeping with data already reported [5] for drv aging of handsheets. i j ^ uxy
15

5. RELATIONSHIP TO SPECIFICATIONS

Specifications for permanent record papers should

include tests that indicate the quality of the paper for

immediate use, and tests that indicate the longevity of

the paper. Assuming that the physical and chemical tests

made in 1937 were adequate to indicate the performance of

the paper for immediate use, we are concerned today only

with the retention of properties with time. Indicators of

retention of properties with time are pH and retention of

properties after accelerated aging. On the basis of experience, one may make arbitrary decisions about minimum initial

pH values and retention of properties with accelerated aging

as indicators of stability. One thus can select one or more

indicators as requirements for a specification.

In Table 22 four categories have been arbitrarily

selected, based on pH data and changes after accelerated

aging, for possible specification requirements. The degree

of success depends on the restrictions placed on the definition of stable paper after natural aging as shown in the

right side of Table 22. From these data it is obvious that

one could have selected stable papers in 1937 with considerable success.

The ranks of the summations of retentions of properties

after accelerated aging and after natural aging (Table 22)

show that some relationship exists between accelerated aging

and natural aging. The correlation coefficient is 0.79.

Retentions for alpha cellulose and copper number were

obtained by expressing maximum change as zero percent

retention, no change as 100 percent retention, and normalizing the changes between these extremes. Retentions for

alpha cellulose, copper number, fold and tear were totaled

to obtain Z of retentions.

The correlation coefficient (0.79) or the ranks in

Table 24 may not be considered conclusive, as uncertainties

in sampling and uncertainties in laboratory technique spanning

almost 40 years must be kept in mind. The overall picture,

however, indicates that accelerated aging is useful in the

selection of stable papers for permanent records.
16

6. SHOULD AN ACCELERATED AGING ATMOSPHERE

BE MOIST OR DRY?

Data on accelerated aging of handsheets at 90°C and

at zero percent and 50 percent relative humidity already

have been reported [3, 4, 5] . Part of the data in these

reports, some of which have been recalculated to a different form, are reproduced in Tables 23-31. In the three

groups of handsheets (untreated, deashed, and alum-treated),

those made from untreated pulp were the most stable, those

made from deashed pulp were much less stable, and those made

from alum-treated pulp v;ere the least stable. Different

tests responded differently to moist and dry aging, but

moist usually resulted in much greater changes than dry

aging. It is not possible to draw definite conclusions from

these data and the data obtained on the 36 year papers regarding an accelerated aging atmosphere, but a trend is

obvious

Tensile strength

The data in Table 23 show that aging at 50 percent

relative humidity at 90°C seriously degraded the tensile

strength of handsheets made from deashed and alum-treated

pulps. Very little degradation occurred during aging in

dry atmospheres and the handsheets made from untreated pulps

vrere especially stable. The data in Table 8 indicate that

the degradation in tensile strength that occurred during 36

years o^ natural aging more nearly approximates dry accelerated aging than accelerated aging at 50 percent relative

humidity. A clear cut decision is not possible, but it would

appear that a small amount of moisture should be present in

an accelerated aging procedure.

Folding endurance

The data in Table 24 on changes in MIT folding endurance

with time of aging show that accelerated aging in a moist

atmosphere is devastating. On the other hand, even the alumtreated samples did not degrade as much during dry accelerated

aging as the NBS mill papers after 36 years of natural aging.

From this it appears that some moisture in an accelerated

aging procedure is indicated but not as much as is present

at 50 percent relative humidity.
17

Internal tearing resistance

The data on internal tearing resistance in Tables 11

and 25 lead to the same conclusion as folding endurance data.

Change in acidity

Data in Table 7 show that large amounts of acid were

not generated during 36 years of natural aging. The data

in Tables 26 and 27 show that little acid is generated

during dry aging, but massive amounts of acid are generated

during accelerated aging at 50 percent relative humidity.

Again this indicates that some moisture is desirable in an

accelerated aging atmosphere but not as much as is generated

at 50 percent relative humidity at 90°C.

Zero span breaking length

Data on zero span breaking length in Tables 14 and 28

cannot be conclusive because zero span data were not obtained

in 1937. The data in Table 28 show that the changes that

occur during accelerated aging in a dry atmosphere are not

great, but the changes that occur at 50 percent relative

humidity are considerable. The only way one can draw inferences from the data in Table 14 is to compare papers in the

same subset. Number 1129, a very acid paper in the sodasulfite subset, is decidedly lower in zero span tensile than

the other papers in the subset. Number 1130, also an acid

paper, is somewhat low. The three alkaline papers, 1158, 1172,

and 1175, are the highest in the group. Number 1133, a

slightly acid paper, lies between the alkaline papers and

the two acid papers. The average machine direction breaking

length of the three alkaline papers is about 12 km. The

breaking length of 1129 is about 80 percent of this average

value. A value this low does not appear in Table 28 except

with samples aged at 50 percent relative humidity. Again,

it appears that some moisture is desirable in an accelerated

aging atmosphere, but that 50 percent relative humidity at

90°C is too high.

Number 1166 in the purified sulfite subset is an acid

paper. Number 1161 and 1164 in the same subset are only

slightly acidic, and their zero span breaking lengths in

the machine direction are about 12.9 km. The zero span

breaking length of 1166 is about 75 percent of 1161 and 1164.
18

The zero span breaking length data for the six rag

papers are very interesting. The first three papers (1191,

11S2, 1193) contain increasing amounts of alum, but no

rosin. The fourth paper, 1203, contains 2 percent rosin

but a massive amount (4 percent) of alum. The zero span

breaking lengths decrease with increasing amounts of alum

from 1191 to 1203. The value for 1203 is about 85 percent

of that of 1191. Numbers 1207 and 1208 are different from

the other rag papers in that they contain titanium pigments

and were sized with rosin v/ithout an excess of alum. They

have outstandingly high zero span breaking lengths. It

would be difficult to attribute this to the presence of

titanium pigment. On the other hand, these two papers were

sized by a procedure that was not likely to allow appreciable

attachment of aluminum to carboxyls. Numbers 1191, 1192,

1193, and 1203 could have aluminum attached to the carboxyls.

Therefore, the values for 1207 and 1208 may indicate the

values that these rag papers would have if they were manufactured strictly with stability in mind. The zero span

breaking length values for 1191 through 1203 range about

65-75 percent of the average value of 1207 and 1208. In any

case, the data indicate that some moisture is necessary to

produce the changes that occur during natural aging.

Breaking strength of wet paper

Data on breaking load of wet specimens as percent of

dry breaking load in Table 15, when compared with tensile

prooerties of wet specimens in Table 29, are not definitive.

As strenrth when wet is developed during both moist and dry

aging, one cannot make a choice between the two by this test.

Moisture regain

The data in Table 30 show that great changes in moisture

content occurred during moist accelerated aging, but very

little change occurred during dry accelerated aging. Moisture regain data were not obtained in 1937. The moisture

regain data on the 36 year papers in Table 14 show that variations within each of the three subsets is not at all large,

and probably is within experimental error. As each subset

contains papers with a wide spectrum of stability, one would

expect much greater variation than the data show, when compared with the data in Table 30, if moist accelerated aging
19

were indicative of that which occurs during natural aging.

In terms of moisture regain, one can conclude that the

atmosphere should either be dry or contain only a small

amount of moisture.

Brightness

Data on changes in blue reflectance (brightness) of

experimental handsheets in Table 31 show very definite

differences between moist and dry accelerated aging. The

changes that occurred during dry accelerated aging are comparatively minor but the changes that occurred during moist

aging are massive. Data on brightness of the 36 year papers

in Table 16 are confused by the fact that (1) brightness

data are not available on the original papers and (2)^ the

presence of fillers in some of the papers. Comparisons

within subsets of the same fiber composition show that

differences in brightness are minimal, and that changes

due to differences in stability are more indicative of dry

accelerated aging than moist accelerated aging.
20

7 . SUMJ-IARY

Keeping in mind the limitations of correlation coefficients, discussed in 3.3, the following inferences may be

drawn from the data in this report:

(1) The changes in alpha cellulose that occurred

during accelerated aging for three days at 100°C correlated

well with changes in alpha cellulose that occurred after

36 years of natural aging. Alpha cellulose, or perhaps

some more convenient alkali solubility method, should be

suitable as a criterion of resistance to accelerated aging.

(2) The same is true for copper number.

(3) Correlations of retention of folding endurance

after natural and accelerated aging were fair only. Although

fold is useful as an evaluation method after accelerated

aging, one should not rely on it completely.

(4) Correlations of internal tear after natural and

accelerated aging were somewhat better than for folding

endurance, but still not great.

(5) Correlations between cold extract pH in 1937 and

changes after natural aging in alpha cellulose, copper

number, fold, tear, and elongation indicate that pH is a reasonably good criterion of stability.

(6) Retention of tear after natural aging correlated

well with retention of elongation after natural aging.

(7) Retention of fold after natural aging correlated

fairly well with elongation after natural aging, but not as

well as tear and elongation.

(8) Correlation between pH and zero span tensile data

for all 18 papers was very poor, but when the data were

separated into statistically homogeneous subsets, the correlations were better.

(9) The correlation between pH and breaking load of

wet paper as a percent of breaking load when dry for the

18 samples was fair only. When the data were separated into

statistically homogeneous subsets, the correlations were

better
21

(10) The correlation between pH and energy at break

for wet paper was fair only.

(11) The correlation between pH and extensional

stiffness for wet paper was very poor. When the data were

separated into statistically homogeneous subsets, the correlations were fair.

(12) It appears that pH , and changes in alkali solubility, reducing power and tearing strength after accelerated

aging for 72 hours at 100°C are reasonable indications of

stability. Fold is sensitive, but not as useful.

(13) Although changes after accelerated aging are not

available, it appears from data after natural aging that

zero span tensile and strength when wet as a percent of

strength when dry should be useful criteria.

(14) When data in this report are compared with data

in earlier reports, it appears that dry accelerated aging

more nearly corresponds to natural aging than accelerated

aging at 50 percent relative humidity. The data indicate,

however, that some moisture should be present.
22

8. RECOMMENDATIONS FOR FURTHER WORK

(1) Old papers that have been in storage from a few

(about ten) years to several hundred years should be examined.

T^reference should be given to papers on which some original

data are available. Papers in this age range that have

deteriorated should yield useful information. Older papers

would require more intensive study, as no original data

would be available.

(2) In order to finalize recommendations for an

accelerated aging procedure, handsheets should be aged at

low relative humidity (perhaps 5 and 10 percent) at 90''C.

9 . ACKNOWLEDGMENT

The authors are indebted to the writers. Merle B. Shaw

and M. J. C'Leary (deceased), of the original publication.

Effect of billing and Sizing Materials on Stability of Book

Papers. Their outstanding work and detailed reporting made

this report possible.
23

10. REFERENCES

1. Shaw, M. B. and O'Leary, M. J., Effect of Filling and

Sizing Materials on Stability of Book Papers, J . Re s

NBS 21, 671 (1938) .

2. Wilson, W.K., Harvey, J. L., Mandel, J., and Worksman,

T. L., Accelerated Aging of Record Papers Compared with

Natural Aging, Tappi 38 , 543 (1955)

3. Parks, E. J. and Hebert, R. L., NBS Report 10 627,

Accelerated Aging of Laboratory Handsheets: Changes in

Acidity, Fiber Strength, and Wet Strength (Dec. 1971)

4. Parks, E. J. and Hebert, R. L. , NBS Report 10 628,

Accelerated Aging of Laborato.ry Handsheets: Retention

of Folding Endurance, Internal Tear, Bursting Strength,

and Tensile Strength (Dec. 1971)

5. Parks, E. J. and Hebert, R. L., NBS Report 10 687,

Accelerated Aging of Laboratory Handsheets: Reflectance,

Moisture Regain, Sonic Modulus, and DTA (Feb. 1972)

6. Wilson, W. K. and Hebert, R. L., Evaluation of the

Stability of Record Papers, Tappi 52 , No. 8, 1523 (1969).

7. Launer, H. F., Simplified Determination of Resin in

Pulps and Papers, J. Res. NBS 18 , 227 (1937).

8. Launer, H. F., Volumetric Determination of Alpha, Beta,

and Gamma Cellulose in Pulps and Papers Containing

Sizing, Filler, and other Materials, J . Re s . NBS 2

, 87 (1938) . 9. Launer, H. F., Determination of the pH Value of Papers,

J. Res. NBS 22 , 553 (1939)

10. TAPPI Method T456 os-68. Wet Tensile Breaking Strength

of Paper and Paperboard.

11. ASTM Method D 1348, Standard Method of Test for Moisture

in Cellulose.

12. TAPPI Method T4 52, Brightness of Paper and Paperboard.

13. Wilson, W. K. and Hebert, R. L. , Evaluation of the

Stability of Manifold Papers, Tappi 55 , No. 7, 1103

(1972) .
24

14. TAPPI Method T429, Alpha Cellulose in Paper.

15. TAPPI Method T4 30 su-68. Copper Number of Paper and

Paperboard

16. Lidman-Safwat , S. and Theander, 0., Determination of

Carbonyl Groups in Modified Celluloses--A Comparison

^ of the Borohydride and Copper Number Methods, Svensk

Papperstidning 61 , 42 (1958).

17. Wilson, W. K. and Parks, E. J., An Analysis of the

Aging of Paper: Possible Reactions and Their Effects

on Measurable Properties, NBSIR 74-499 (April 1974)

.
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Table 2. Chemical test data obtained in 1937 on

book papers made in NBS mill in 1937.^

cold

pH

hot

Alpha

Cellulose

Copper

No. Pentosans

4.9

5.3

6.9

9.6

8.9

8.5

6.1

5.6

5.2

6.0

5.6

5.0

6.8

5.8

5.1

5.3

5.2

5.7

4.3

4.8

6.4

5,7

5.3

4.5

5.7

5.0

4 . 4

4.5

%

76.0

75.7

75.8

75.5

75.6

74.2

90.2

90.2

90.0

89. 8

89.9

89.6

92. 3

91.1

91.6

89.2

90.2

90.5

about 11

about 4

none

^Data taken from NBS Research Paper RP1149.
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Table 4. Effect of accelerated aging for 72 hours at

100°C in 1937 on book papers made in NBS

mill in 1937.

Machine

Run No.

Alpha^

Cellulose

Copper

Number

Fold

Retention

Tear

Retention

change change"^ a. s

1129 -7.6 +0.6 19 58

1130 -3.3 + 0.4 56 80

1133 + 0.1 -0.1 69 80

1158 -0.4 0 77 92

1172 -2.1 + 0.4 55 91

1175 -3.3 + 0.3 75 93

1161 -0.8 + 0.3 108 90

11C2 -3.6 + 0.5 97 90

1163 -4.6 + 0.7 81 80

1164 -1.8 + 0.2 93 91

1165 -2.9 + 0.4 95 80

1166 -5.0 + 0.5 62 74

1191 -3.1 + 0.1 114 97

1192 -3.0 + 0.1 114 92

1193 -8.1 + 0.2 95 90

1203 -9.6 + 0.9 100 91

1207 -4.4 + 0.5 96 91

1208 -3.7 + 0.4 107 94

^ Alpha cellulose value based on total cellulose;

change is decrease in analytical value.

^Change in analytical value.
Table 5. Effect of 36 years of natural aging on the alpha

cellulose content of book papers made in NBS mill

in 1937 compared with accelerated aging in 1937.

Machine

Run No.

Aipna

Cellulose, %

1937 1973

s\ %

1973 data

unange , %

Alter

36 Years

Natural Aging

Accelerated

Aging

1129 76.0 59.3 1.0 16.7 7.6

1130 75.7 62.3 0.8 13.4 3.3

1133 75.8 73.6 0.5 2.2 + .1

1158 75.5 68.6 0.3 6.9 .4

1172 75.6 70.2 0.6 5.4 2.1

1175 74.2 67.8 1.4 6 . 4 3.3

1161 90.2 86.3 0.4 3.9 .8

1162 90.2 84.4 0.4 5.8 3.6

1163 90.0 77.1 0.7 12.9 4.6

1 X o 't Q Q Q Q C Q u . / 1 Q

1165 89.9 77.8 1.9 12.1 2.9

1166 89.6 76.0 0.7 13.6 5.0

1191 92.3 85.3 1.0 7.0 3.1

1192 91.1 83.1 1.1 8.0 3.0

1193 91.6 76.5 1.5 15.1 8.1

1203 89.2 72.7 1.3 16.5 9.6

1207 90.2 81.1 0.4 9.1 4.4

1208 90.5 79.8 0.8 10.7 3.7

^Standard deviation. Three specimens for 1158; 4 for all others.

^Decrease in analytical value.
Table 6. Effect of 36 years of natural aging on the

copper number of book papers made in NBS

mill in 1937 compared with accelerated

aging in 1937

.

Machine

Run No

.

Copp

1 Q -J -7 er No. si Cu No.

ly / J data

Change

After:

36 Years

Natural Aging

Accelerated

Aging

1129 3.6 4.8 0.14 1.2 0.6

1130 3.6 4.4 .05 . 8 .4

1133 3.2 3.2 .14 ; .0 -.1

1158 3.3 3.9 .14 .6 .0

1172 3.4 4.2 .17 . 8 .4

1175 3,3 4.1 .22 , 8 .3

1161 0.8 1.8 .05 1.0 .3

1162 0.9 2.1 . 10 1.2 .5

1163 0.9 2 . 8 . 07 1 .

9

.7

1164 0.9 1.7 . 06 .8 .2

1165 0.8 2.4 .07 1.6 .4

1166 0.9 2 . 6 .07 1.7 .5

1191 0.3 0.9 .04 .6 .1

1192 0.4 1.1 .02 .7 .1

1193 0.5 1.6 .12 1.1 .2

1203 0.7 2.3 . 07 1.6 .9

1207 0.5 1.5 .07 1.0 . 5

1208 0.4 1.7 .04 1.3 .4

^Standard deviation. Five specimens for 1129, 1130, and 1133;

2 specimens for 1158; 4 for all others.

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Table 11. Internal tearing resistance, measured in 1937

and again in 1973, of book papers made in NBS

mill in 1937, and retention of tear after

accelerated aging for 72 hours at 100°C in

1937 and after 36 years of natural aging.

Tearing Retention of Tearing Resistance, %, after

Machine Resistance 36 Years

Run No. 1937 1973 ' Natural Aging Accelerated Aging

MD MD MD Ave . MD & CD

1129 46 20 43 58

1130 48 25 52 80

1133 55 29 53 80

1158 51 " 92

1172 50 38 76 91

1175 45 34 76 93

1161 82 49 60 90

1162 79 44 56 90

1163 77 35 45 80

1164 79 45 57 91

1165 83 33 40 80

1166 75 29 39 74

1191 55 97

1192 57 38 67 92

119 3 56 32 57 90

1203 54 31 57 91

1207 60 41 68 91

1208 54 35 65 94

^No standard deviation is reported because all

available plies of a given paper were torn

together in a single test.
Table 12. Summary of changes in various chemical properties

of book papers made in NBS mill in 1937 after 36

years natural aging and after accelerated aging

for 72 hours at 100°C in 1937.

Machine

Run No

.

Natural Aging, 36 Years

Accelerated Aaing

in 1937

Increase

in [H+]

Alpha

Cellulose

,

Decrease

Copper

Number,

Increase

Alpha

Cellulose , Decrease

Copper

Number

,

Cold Hot Increase

1129 190 293 16.7 1.2 7.6 0.6

1130 108 240 13.4 .8 3.3 .4

1133 49 75 2.2 0.0 + .1 - .1

1158 6.9 .6 .4 0.0

1172 5.4 .8 2.1 .4

1175 - - 6.4 . 8 3.3 .3

1161 92 138 3.9 1.0 .8 .3

1162 175 348 5.8 1.2 3 .

6

.5

1163 188 478 12.9 1.9 4.6 .7

1164 90 180 4.0 .8 1.8 .2

1165 226 531 12.1 1.6 2.9 .4

1166 151 233 13.6 1.7 5.0 .5

1191 3 7.0 .6 3.1 .1

11S2 63 8 . 0 .7 3.0 .1

1193 47 15.1 1.1 8.1 .2

1203 108 185 16.5 1.6 9.6 .9

1207 63 9.1 1.0 4.4 .5

1208 106 10.7 1.3 3.7 .4
Table 13. Summary of retention, %, of various properties

of book papers made in NBS mill in 1937 after

36 years of natural aging and after accelerated

aging in 1937.

Machine

Run No.

Natural Aging Accelerated Aging

Fold Tear Tensile Elongation Fold Tear

Ave

MD AveAve

Ave

MD

1129 10 43 76 58 19 58

1130 15 52 82 66 56 80

1133 4 53 70 56 69 80

1158 64 95 75 77 92

1172 55 76 102 111 55 91

1175 85 76 98 122 75 93

1161 115 60 98 85 108 90

1162 6f 56 101 84 9 7

1163 26 45 95 72 81 80

1164 68 57 102 83 93 91

1165 33 40 96 67 95 80

1166 17 39 88 62 62 74

1191 84 98 98 114 97

1192 78 67 98 95 114 92

1193 55 57 94 80 95 90

1203 56 57 101 78 100 91

1207 64 68 99 84 96 91

1208 72 65 100 84 107 94
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Table 16. Brightness of NBS mill papers after

36 years of natural aging.

Machine ~

" Standard

Run No . Brightness Deviation ^ %

112 9 6 0.9 1 . 6

1130 61.0 ^ " 2.9

113 3 : 60.0 0.9

1158 67.1 1.7

1172 6 7.1 0.42

1175 60.8 .85

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; 72.4 2.8

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1163 71.2 1.3

1164 7 5.6 1.0

116 5 . 74.3 2.5

1166 74.1 ; 1.4

1191 79.7 :

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1192 • 80.2 1.9

119 3 80.2 0.6

1203 73.5 0 .

9

12 07 78.6 ' 0.5

12 08 78.9 0.7

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Table 27^. Changes in hydrogen ion concentration ( [H"^] ) after accelerated aging of experimental handsheets in air or nitrogen at 90°C and 50% or

0% relative humidity.

Pulp Aging

Atmosohere

1 6 12 24

Chang e in fH+l X 107

Untreated Dry air 1 1 1 1

Dry nitrogen -1 0 , 0 1

Humid air 1 ,5 8 56

Humid nitrogen 1 1 1 3

Deashed Dry air 34 43 59 85

Dry nitrogen 13 82 30 38

Humid air 212 969 1199 1229

Humid nitrogen 35 222 367 679

Aluminum Dry air -10 48 37 59

Aging Period, days

treated

Dry nitrogen

Humid air

Humid nitrogen

71

197

91

59

857

303

27

1282

469

93

1562

518

^Data from Table 1, NBS Report 10 627.
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O 4J 0

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O LD

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H rH rH -P Q) U C 0

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C

C

C 0) U5

cn

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en <: >1 >1 6 B >t >( E iH ^ (Nj u ^1 13 :3 J-I J^ in M J-I XI 0 Q Q Q Q Q Q fd M-i Q) Eh iH e

X<

g fd

fd -p 0 J^ Eh c

Q)

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rr-^

g

H CP

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fd

C <D rH

i-H -P (D x:

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a Id

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w 6 fd •4-> QJ

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fdQJ Q 0 <u fH J-I < -p

fd Q r-i

CM
Table 29^. Wet breaking load as percent of dry breaking

load of experimental handsheets after accelerated aging at 90°C in various atmospheres.

Pulp

Treatment

Aging

Atmosphere

Aging Period, days

0 1 6 12 24

Untreated Dry air 0.8 1.5 1.7 2.8 3.7

Dry nitrogen .7 1.3 2 .

2.5 3.1

Moist air .8 1.3 2 . 0 2.9 4.8

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APPENDIX

EFFECT OF FILLING AND SIZING MATERIALS

ON STABILITY OF BOOK PAPERS, by Merle B.

Shaw and Martin J. O'Leary, Journal of

Research of the National Bureau of Standards, Volume 21, November 1938,

Research Paper RP1149.

U. S. Department of Commerce National Bureau of Standards

RESEARCH PAPER RP1149

Pan of Journal of Research of the }<{ational Bureau of Standards, Volume 21,

Hmember 1938

EFFECT OF FILLING AND SIZING MATERIALS ON

STABILITY OF BOOK PAPERS

By Merle B. Shaw and Martin J. O'Leary

ABSTRACT

The National Bureau of Standards has been carrying on research on the manufacture of papers to obtain information on composition and processes which have

an important bearing on the stability of pajier. Several publications have been

issued as a result of th€»e investigations. Three of them, Research Papers

RP372, RP574, and RP794, present data for writing papers. Another Research

Paper, RP949, reports the results on ox{)erimental unsized papers made from

pulps commonly used in book papers. The present publication i.s an extension

of the work on book paper, and relates primarily to the effect of fjlling and sizing variables introduced in manufacture.

The papermaking materials used were representative commercial products.

Four types of fiUers, including both natural materials and manufactured pigments, were used. They comprised one clay filler; two titanium dioxide pig- ments; two zinc sulfide pigments; and two calcium carbonates, one precipitated, the other a natural product, water-ground. The sizing agent, rosin soap pre- pared from rosin and soda ash, was precipitated by means of papermaker's alum,

aluminum sulfate. The fibrous nmterials covered the range of those commonly

used in the fine printing papers. They consisted of sulfite pulp and soda pulp of the ordinary book-paper grade; three "purified" wood pulps, produced by special

cooking and bleaching treatments to obtain high purity and strength; new rags, the grade known commercially a.s No. 1 white shirt cuttings; and two grades of old

rags. No. 1 old whites and "twos and blues." Seventy-two experimental papers were manufactured in the Bureau's semi- commercial mill. The papers were given extensive physical and chemical tests with particular reference to stability, both l^>cfore and after an accelerated aging

test made by heating the paper for 72 hours at 100° C. The strength of the experimental papers decreased with increasing filler content, and was influenced by the amount, not the tyix;, of filler present. There was

no pronounced difference in the relative effect of the nonalkaline fillers on sizing.

The nonalkaline fillers had less effect than calcium carbonate in reducing the degree of sizing. Although the sizing values of the carbonate-filled papers were

not high, the pai)ers were sized sufficiently to be written on with ink and for ordinary printing processes. Maximum clay retention was obtained in the

purified wood and the rag papers when the pH at the head box was approximately

5, and decreased as the amount of alum was increased. For the sulfite-soda stock, retention of all the nonalkaline fillers increa.sed as alum was increased. The pap)ers containing titanium dioxide, zinc sulfide, or precipitated calcium

carbonate pigments had the highest opacity. Preliminary printing tests made

on a few of the filled papers indicated satisfactory printing quality.

The rag and purifieid wood-pulp papers were more stable to the heat test than

the sulfite-soda. Nonalkaline fillers had no apparent harmful influence on the

stability of any of the papers, and the calcium carbonate pigments had a protective

or inhibiting effect in the aging test. Acidity was an important factor in deterioration. The attack on the cellulose was increased as the amount of alum was increased, in either the unsized or the

rosin-sized papers. The effect of increasing the amount of alum in the beater and then neutralizing

part of the alum with sodium carbonate as the stock was being pumped from

671
672 Journal oj Research oj the National Bureau of Standards ivoi.ti

the beater chest to the machine chest was practically the same as having had

the final pH value originally in the beater and maintamed throughout the preparation of the stock. CONTENTS

I. Introduction 672

II. Papermaking raw materials L 672

III. Papermaking equipment 673

IV. Papermaking processes 673

1. Preparation of rag half stuff 673

2. Beater and pajjer-machine operations 673

V. Testing methods 674

VI. Analyses of papermaking materials used 675

1. Fibers 675

2. Fillers _ 675

VII. Data on papers made 675

1. Physical and chemical measurements 675

(a) Clay-filled papers 676

(1) Sulfite pulp, 50 percent; soda pulp, 50 percent- 676

(2) Purified wood pulp: A, 75 percent; C, 25 per- cent... 686

(3) Purified wood pulp: D, 100 percent 686

!

, ; (4) Rags: No. 1 new whites, 100 percent 686

(5) Rags: No. 1 old whites, 60 percent; twos and

blues, SO percent.- 688

(b) Titanium-dioxide-pigmented papers 689

(1) Sulfite pulp, 50 percent; soda pulp, 50 percent. 689

^ V , (2) Rags: No. I old whites, 50 percent; twos and

; blues, 50 |>ercent 689

(c) Zinc-sulfide-pigmentcd papers 689

(1) Sulfite pulp, 50 percent; soda pulp, 50 percent. 690

(2) Rags: No. 1 old whites, 50 percent; twos and

blues, 50 percent 690

(d) Calcium-carbonate-pigmented pajjers 690

(1) Sulfite pulp, 50 percent; soda pulp, 60 percent. 691

(2) Rags: No. 1 old whites, 50 percent; twos and

blues, 50 percent. 692

2. Printing tests ._ 692

VIII. Discussion and conclusions 693

IX. References 696

I. INTRODUCTION

As a part of its program of research relating to the stability of

papers used for records, the National Bureau of Standards is making a study of the relation of papermaking materials and processes to the

strength, stability^ and other properties of book papers. Tliis publication is the fifth in the series planned to include the more important

types of fibrous and nonfibrous raw materials commonly used in the

manufacture of record papers. Of the preceding pubUcations, three

[1, 2, 3] ' related to writing papers and one [4] to fibers commonly

found in book papers. The present publication is an extension of the

work on book papers and deals primarily with the effect of filling and

sizing materials on their stability.

II. PAPERMAKING RAW MATERIALS

The fillers selected were representative of several types, both natural

materials and manufactured pigments, and were used as supplied by

the manufacturers. They comprised one clay ; two titanium pigments.

> Figures in brackets Indicate the literature referenoea at the end of this paper.
Skaw 1 O'Ltmti Stability oj Book Papers 673

titanium dioxide and a composite of titanium dioxide and barium sulfate; two zinc sulfide pigments, zinc sulfide and a composite of zinc

sulfide and barium sulfate; two falcium carbonates, one precipitated,

and one water-ground. Fillers are not added to book paper to adulterate it but to improve the printing Quality of the sheet. They

fill the interstices of the fiber network of the paper thus producing a more even surface, lend softness, and improve the opacity and,

generally, the color of the sheet. The number of types of important

fillers on the market has increased considerably in the last few years, but little is known about their effect on the permanence of paper. The

selection of fillers for the papermaking teets of this study was limited,

however, to oiUy the more important types, as a complete study of

fillers, as such, was not planned at tliis time.

The sizing agent was that most generally employed, rosin soap.

It was prepared from rosin and soda ash and was precipitated with

papermaker's ulum, aluminum sulfate. The fibrous materials employed covered the range of those com- monly used in the fine printing papers, and, like the fillers, were

obtained from commercial manufacturers. They consisted of sulfite pulp and soda pulp of the ordinary book-paper jgrade ; three "purified"

wood pulps produced by special cooking and bleaching treatment to obtain high purity and strength ; new rags, the grade known commercially as No. 1 white shirt cuttings; and two grades of old rags. No. 1 old wliites and "twos and blues."

III. PAPERMAKING EQUIPMENT

The Bureau paper mill is equipped for experimental manufacture

of practically all types of paper under conditions which in general

simulate those of industrial mills. A complete description and photographs of the equipment may be found in previous publications (5).

IV. PAPERMAKING PROCESSES

1. PREPARATION OF RAG HALF STUFF

The procedure followed in the preparation of the rag "half stuff"

(partially pulped rags that have been boiled, washed, drawn out of

weave, and bleaclied) was essentially the same as the general practice

in the commercial production of high-grade papers from rags. It was

described in a previous publication [3] of the series. The amount of bleacliing powder, containing 35 percent of available chlorine, required to produce the desired degree of whiteness

varied with the color of the rags. The amount used, based on the

oven-dry weight of the rags, for No. 1 white shirt cuttings was 0.1 to

0.2 percent; for No. 1 old whites, 0.3 percent; and for twos and blues,

1.0 percent.

2. BEATER AND PAPER-MACHINE OPERATIONS

To afford comparison of the papers made in the numerous experimental runs it was necessary to follow a uniform procedure for handling the papermaking materials and the paper machine. It was

desired that the procedure conform to customary or established

general mill practice, but inasmuch as different mills differ widely as
674 Journal oj Research of the National Bureau of Standards {voj. */

to the relative time of adding the pulps, fillers, rosin, and alum to the

beater, the method used was the one ordinarily followed at the Bureau

and previously found to compare favorably with commercial mill

methods.

The fillers were mixed with water (made into "slips") and the mixture agitated a fixed length of time and then run through an SO-mesh

screen to remove dirt and impurities before being added to the beater.

The procedure followed in furnishing the beater, unless noted otherwise elsewhere in the text, was as follows: The pulps or fibrous

materials and the filler slip were put in at the time of furnishing (which

required about 15 minutes), and the rosin size was added to the stock

1 hour, and the alum K hour, before it was dropped to the beater

chest. Variation from this procedure might have affected the

characteristics of the finished sheet as to bulk, opacity, etc., but it

is believed that it did not affect the permanence of the paper, which

is the property of primary interest in this study.

The beating procedure was adjusted to the peculiarities of the

different papemiaking fibers. The pap)er-machine operations were

the same for all runs. The methods of beating and paper-machine

operation followed very closely those described m the otlier pubUcations of this investigation [1, 2, 3]. The temperature of the stock at the head box of the paper machine was maintained at 90" F ±2°.

V. TESTING METHODS

All the physical and most of the chemical tests of the pulps and

papers were made by the official methods^ of the Technical Association

of the Pulp and raper Industry. For the determinations of the

amounts of alpha-, beta-, and gaimna-cellulose, pentosans, and acidity

in the cellulosic materials, the methods used were modifications re- cently developed at the Bureau [6].* Although all papers were

tested for acidity by the modified method (cold extraction), some of

them were tested also by the TAPPI method (hot extraction), and

for the latter the values obtained by both methods are reported. For

the mill waters - in the beater and the head box—the pH determinations were made electrometrically, using the auinhydrone method

except for the runs with calcium carbonate, for wnich a glass electrode was used because of the alkalinity.

The relative stabiUty of papers can be judged by determining their

chemical characteristics, but in addition it is desirable to subject

them to some form of accelerated aging. Therefore, the pertinent

physical and chemical tests were applied not only to the original

papers but also to samples that had been submitted to an accelerated

agmg test considered to closely simulate the effects of natural aging.

Tliis test is made by heating specimens of the papyers for 72 hours at 100° C and then conditionmg and determining to what extent the

paper has been altered in foldmg endurance, tearing strength, alphacellulose content, and copper number. For details of the accel- erated aging test the reader is referred to previous discussions of the

method [7].

Copies nf ttaa uiethods caa be obtained from the Technical AModatlon of the Pulp and Paper IndostiT,

i2 Esst 42d Street, New York. N. Y.

' Pentosans and acidity determined by unpublished method*.
Shaw 1 O'Ltarii Stability of Book Papers 675

VI. ANALYSES OF PAPERMAKING MATERIALS USED

1. FIBERS

Analyses showing the de^ee of celliilosic purity of the wood pulps

and the rag half stuffs used in the manufacture of the papers are given

in table 1. The fibrous material ranged in quality from 74 to 95

percent of alpha-cellulose and from 4.4 to 0.3 in copper number.

Table 1.

Chemical teat data on fibrous materiaU used

Fibrous material Alphacelluluse >

Betacellu- lose <

(Jamma

t-ellu- lose >

Pento- Copper

nuujber Ash > Resin'

%

or/O % Jo % %

Sulfite pulp - 82.0 6.8 12.2 6 8 3 4 0.

O.S Soda pulp 74.4 21 3 4.3 18.7 4. 4 .3 .2 Purified wood pulp A' 91.0 4.2 4.8 3.2 0.6 . 1 .3 Purified wood pulp C 88.3 6,3 6.4 4.3 .8 . I .3

Purified wood pulp D' M.Z 4.3 US 8.4 .6 .2 . 1 No. 1 new white rsRs, blearhed half 5tuff_ 04.8 4 7 a8 .3 . 1 .3 No. 1 old white rSK-s, bleached half stufl.

00. 3 0. 4 .3 .4 .2 .3 Twos and blues, bleached half stuff 91. 1 8.0 .3 .4 .3 .3

< Based on total cellulose.

' On oven-<lry basis.

' Produced commercially by special cooking and bleaching treatment to obtain Improved quality.

3. FILLERS

The chemical composition of the fiUors used is shown in table 2.

Table 2.

Composition of fiUerg used '

Test Clay

Titani- um diox- ide plR- ment A

Tluni- um diox- ide pig- ment B

Zinc

tulflde pigment A

ZIno

sulfide pigment B

Precipi- tated calcium

carbonate

Water- ground

natural calcium

carbonate

Loss at 106' 0

Further loss on ignition

Silica (8IO1)

0.3

13.7 46.3 0.3. sag

1.8

%

None

0. 16 \0.00 None %

0 00

IS. 1 %

0.07 0.0 \0. 16 43.6 %

0.03

43.8

Iron oilde (FeiOj) Alumina (AljOo

TiUnlum dioxide (Tld) 08.2 30.4 Calcium carbonate (CaCOi) 87.8 09.8 Barium sulfate (Ba.SOi).. 60.6 44.0 Zinc sulfide (ZnS) 00.8 64.8

' Analyses by Chemistry Division, National Bureau of Standards.

VII. DATA ON PAPERS MADE

1. PHYSICAL AND CHEMICAL MEASUREMENTS

Data relative to the composition of the beater furnishes (materials

blended in the beater) and the various physical and diemical measure- ments on the papers made are given in tables 3 and 4. The percentage of filler in paper is sometimes determined from the

ash content, and sometimes, when possible, by chemical analysis. In

the case of clay it was determined from the a.sh of the paper, corrected

for the loss of water of composition from the clay during ignition.

The values for the pigments were obtained by chemical analysis.
676 Journal oj Research of the Naiional Bureau of Standards ivoi.$t The amount of retention of filler is that proportion of the filler added

to the beater furnish which appears in the finished paper. The differ- ent methods used in different laboratories for computing retention

account in some degree for the varying results reported by them.

The formula used in this work was developed by Eidwin Sutermeister

of the S. D. Warren Co., Cumberland Mills, Maine, and has been used

in previous studies [8] carried on at the Bureau, in which it was found

to check the determinations by weight. The formula is: „ , . 0.94(100-C-^)

RetenUon= ^(joo-C-fi) '

in which A is the percentage of ash in bone-dry stock going to machine

(that is, the stuff box stock); B is the percentage of ash in bone-dry

paper at reel ; and C is the percentage of bone-drv filler lost on ignition.

Before being adopted for general use in a mill, however, this or any

retention formula should be tested to determine whether it is suited to the particular conditions with which that mill has to deal. Many

factors other than filler influence retention, but it is impossible to estimate their efi"ects except in a general way. Some of the conditions

which affect the retention of fillers are the kind of stock used, the extent of its beating (liydration), consistency of pulp and the amount of

filler added, acidity, weight of paper made, speed of machine, chemicals used (such as starch, sodium silicate, or viscose materials), the

use of save-alls, etc.

(a) CLAY-PILLKD PAPERS

(1) Sulfite pidp, 50 percent; soda vulp, 60 percent. —Two papermachine runs were made of sulfite ana soda pulps without filler—one

(run 1133), without rosin size or alum; the other (nm 1143), with

rosin size and alum added. The test data on the runs are given in

tables 3 and 4. For the paper made from pulp alone (run 1133) the

chemical test data for the heat-treated paper diner httle from those for

the original sheet, but when rosin and alum were added the alphacellulose content decreased and the copper number increased for the

aged or heat-treated paper. The stability as regards retention of

folding endurance and tearing strength is not high for either of the

papers, with or without rosin size and alum.
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Shaw ] OLearti Stability oj Book Papers 683

A series of runs (1134, 1135, 1130, and 1129) of unsized papers

containing clay was made in whicli the amount of alum added was

varied. The effect of acidity on tlie stability of the unsized clayfilled papers is shown by the decrease in alpha-cellulose content and

increase in copper number of the heat-treated papers as the amount of

alum in the furnish increased, and the decrease in retention of folding

endurance and tearing strength. In general, the agreement between

the pH values of the water from the stock at the head box and of the

hot-water e.xtraction of the finished paper was fairly good, the dif- ferences probably being due to differences in buffer conditions, the

head-box sample being well buffered and the water extraction of the

finished paper poorly buffered. The clay retention of the runs increased with increased amounts of alum.

To study the effect of rosin sizing on the stability of sulfite-soda

papers containing clay several machine runs were made in which the

amounts of alum and rosin size were varied.

The test data on the runs (1136 to 1138) in which the amount of

rosin was kept constant at 2 percent and the amount of alum was

varied show that the change in alpha-cellulose content of the heattreated papers increased as the alum was increased, but that the

increase in copper number remained constant, although large. The

percentage of retention of folding endurance and tearing strength

gradually decreased as acidity increased but to less extent than for the unsized papers, to which rosin was not added (runs 1134, 1135,

1130, and 112'J). The rosin seems to have hindered deterioration.

This phenomenon was noted also in a previous study [2] of sulfite pulps for writing papers. As a possible reason for this apparent dis- agreement, it is suggested that for pulps in the low stability range,

rosin sizing may actually have a protective effect. The indications

are that, within the range studied, the amount of rosin employed in sizing sulfite-.soda papers is not an important consideration as far as

stability is concerned. Retention of clay in runs 113(1 to 1138

increased as alum was increa.sed. For the series of papers (runs 1139 to 1141) in which the amount of

rosin was kept constant at 1 percent and the amount of alum was

varied, the stability falls between that of papers witli no rosin in the

beater furnish ajid those with 2 percent of rosin added. The data on the heat-trcuted papers of this series are shown graphically in figure 1. Although the folding strength of the original clay-filled papers

decreased as the amount of alum was increased, some of the decrease was due to the increased retention of clay. The increased filler content

should not affect tiie strength retention of the heat-treated papere,

however, since clay is an inert substance which has been previously

found to have no harmful effect on the stability of paper.

To determine whether paper made from stock having high acidity

in the beater but subsequently adjusted at the paper machine to low

acidity would remain stable, a paper-machine run (1142) was made

similar to run 1141 in the preparation of the stock in the beater. An

excessive amount of alum was added in the beater to give a pH of

4.2, but a solution of soda ash (sodium carbonate) was added to neutralize some of the acidity as the stock was being pumped from

the beater chest to the machine chest. The pH at the head box' of
684 Journal oj Research of the National Bureau of Standards \voi.ti

the paper nmcliine was 6.1. The stability of the finished paper

compared favorably with that of the run (1139) which had pH 6.2 at the head box without any treatment to reduce the original acidity.

The retention of folding endurance and tearing strength was as good

for the paper of the adjusted run as for the run in which only a small

amount of alum was used (run 1139), and the change in alphacellulose content of the heat-treuted paper was no greater. But the

increase in copp«'r number was the same as that of the paper with

high acidity at the head bo.x (run 1141). The sizing value was not

materially affected, but the clay retention was increased. The

improvement in day retention may be attributable to the presence of

< s 4 a.i or STOCK AT HCAO BOX

(•um MOS MM, 1140, 1141. »>I0 1141. MMlCTlVtLt)

Figure 1.

Effect of acidity on stability of rosin-sited, clay-JiUcd book papers made

frorn sulfite and soda pulps.

Points at (iH « I are di-^placcl t^i right of miiln graph Ui av iiil o-jJifution. For ihU run there was considorable

(lilTcreiice hetwueu the Initial and niml pll valim. An i^teerislva amount of alum wiu u<wd la the hnater

to give H pU of 4.2, but s<i(lium Ciirl)onat« was adileil t" nfiiiiralUe imrt of the acidity as the stock was

being pumped from the heater cheit to the machine i hest aluminum Hoc formed when the acidity caused by the excessive

amount of alum was neutralized with the soda ash. Retention has

been shown by a number of writers to be partly the result of occlusion

and fixation of the finer particles in the sheet by the rosin and the

aluminum hydrate floe formed in the sizing operation. In addition to the results obtained on the experimental paper,

tests at the Bureau on commercial papers of known history show that

with high acidity in the beater followed by treatment at the paper

machine to obtam low acidity, paper of fair stability, as far as acidity

is concerned, inay be produced.

The pentosan content of the different sulfite-soda papers was not

appreciably changed by the heat treatment. It is apparent that

pentosans do not contribute to the deterioration of cellulose to the

extent that modified celluloses do, and therefore that pentosan
S>iaw 1 0 Lenryl Stability of Hook Papers 685

determinations are comparatively unimportant in evaluating the

relative stability of papers.

(2) Furijied vood pulp: A, 75 percent; C, 26 percent.- in previous

work [4] !it the Bureau on purified wood pulps, papers made from pulp

A without rosin and alum were relatively stable but had comparatively

low folding strength. Pulp B produced a hard sheet, stronger but less stable to the heat test, and not as good in color as that made from pulp

A. The use of a small amount (25 percent of furnish) of pulp B with

the weaker but more stable pulp A increased the strength of the sheet

without appreciably lessening its stability. Paper made from pulp C

showed that although pulp (J was not so strong as pulj) li, it was considerably stronger than A and produced a S(jfter pai)er of better color

• S 4

f>H OF STOCK AT HEAD BOX

(HUNS ItOS li«4, lies. »N0 liM. »t5PtCIIVtl.Y) FiouRE 2.

Kjjcct of acidity on slabdily of rosin-sized, clay-filUd book papers made

from purified wood pulps A and C. and stability than B. Therefore, j>ulp C, rather than B, was selected

for mi.xture with purilled wood ])uli) A in the present study to obtain

improved strength.

One run (IKiO) was made of the mixture of pulj)H A and (^'with clay

filler but without rosin size or alum to obtain data on the quality of the

pulp mixture. To determine the effects of rosin size and alum on the

stability of pa})ers from the mixture, two series of runs were nuide—one

(runs l lfil to 1163), with 2 percent of rosin size and various amounts

of alum; the other (runs 1104 to llfifi), with 1 percent of rosin and

various amounts of alum. The data on the papers are given in tables

3 and 4. The stability of the second series (furnish containing 1 per- cent of rosin) is also shown graphically in figure 2. The stability of the papers to the heat treatment decreased as the

amount of alum was increased, and was little affected by rosin size. The clay retention was highest when the pH at the head box was 5.0 to 6.0 and lowest at the highest acidity, pll 4.2. The papers were of
686 Journal of Research of the NatioTuU Bureau oj Standards [vu-ti

good formation, color, and strength, showed little change in color

after oven-agin^, und compared favorably with those made from new

white rags, described herein later. (3) Purified wood pulp: D, 100 percent. —In ])revious work [4] pai>er

made from purified wood pulp D was hard, and therefore not suitable

for book paper, but some of the hardness was attributed to the beater

roll and beater tackle not being suited to produce from hard longfibered pulp the desired character of sheet for book paper. It was

believed, however, that if the beating could bo effected quickly enough

to preclude excessive hydrating or gelatinizing of the fibers without

pH OF STOCK AT HEAD BOX

(»ukS llui ut», II6», »N0 \I1Q. RfSPtCTIVELT; Figure 3. - Rffed of acidity on stability of rosin-sized, day-filled book papers made

from purified wood pulp I).

sacrificing the desired fraying and fibrillation, a soft bulky sheet would

result and would have the strongtli for severe service. Pulp D was

therefore included in the present study.

One ]>aper-machine run (11()7) was made from the pulp with clay

in<or])orated in the funiish but without rosin size or alum, and a

series of runs (11(18 to 1170) using 1 percent of rosin size and various

amounts of alum. The stability of the sized papers is shown graphically in figure 3. The papers showed less deterioration in the heat treatment than some of the other pulps, and better clay retention, but the retention

decreased as the acidity was increased. Perhaps because of the unfavorable beating conditions, the alum affected the hydrating or binding properties developed in the beater, thereby reducing the slowness

of the stock and the amount of filler retained mechanically. As would

be expected, the opacity was low and the paper was comparatively

hard—more like writing than book.

(4) Rags: No. 1 new whites, 100 percent.—Three series of papers were made from new rags and clay filler. One series (runs 1176 to
^"i^^^,] StaHlitij oj Book Papers 687

1178) was without rosin size but witli various amounts of alum; the

second (runs 1179 to 1182) contained 2 percent of rosin size and

various amounts of alum; and the third (runs 1183 to 1180), J percent

of rosin size and various amounts of uhim.

The preparation of the rag half stuff and tlie metliod of beating the

half stuff to prepare it for the paper nuirhine followed the procedure

described in previous publications (3, 4]. When beating the furnish

for the rosin-sized papers, however, the stock became very hot as a

result of hot weather and hard beathig. To preclude any harmful

influence of the high temperature on the sizhig effect of the rosin, part

of the stock was emptied into the chest after the beating was completed so that water could be added to the remauider ui the beater

before the rosin size was put in. After the rosin size was added, the

pH OF STOCK AT MEftD BOX

(runs MDb :'B1, I>t4, M«5, AND MSA, RCS^CTivELt) FioUHE 4.-- Effect of acidity on dahilily of ronin-itized, rlay-fiUcd booh papers viade from rtfic ragH.

stock was circulated about 15 minutes (with the beater roll off the

bedplate), the alum was added, and the stock filially mixed in the

beater chest. The folding endurance of the original papers decreased as the alum

was increusetl, the decrease being greatest for the series with the

highest rosin content. The unsized papers showed practically no

reaction to tlio lieat treatment in retention of folding endurance and

tearing strength, and the rosin-sized papers decreased only slightly.

An additional run in each of tlie sized series was made with the

amount of alum increased to 4 |)erceiit. The resultant papers also were fairly stable. As is apparent from the test data of tables 3 and 4

and the curves of figure 4, if new white rags are properly prepared and

the amounts of rosin size and alum added are not excessive, book

paper of high stability can be produced.
688 Journal of Research of the National Bureau oj Standards {Voi. ti The papers were not well sized hut were satisfactory iii this respect

for printing. Tlie color, formation, and finish were very good. The

retention of clay was niaxinium when the pll of the stock at the head

box was about 5.0. Also, at that acidity the tendency to foam was minimum, not only for the rag stocks but also for the other pulps

when rosin size and alum were added.

(5) Rags: No. 1 old whites, 50 percent; twos and blues, 50 percent.—

The preparation of the rag half stuff from No. 1 old whites and twos

and blues also was the same as tliat used in previous studies {3, 4). The half stuffs from the two kinds of rags were kept separate until

blended in the beater at the time of funiishing. Three series of runs, comparable to the runs described for the preceding pulps in respect

of the amounts of clay, rosui, and alum added, were made. One run

r

- 90

S«0

U 90

O

zeo

3*^ X

JO

pH OF STOCK AT HEAD BOX

, / (lIUNt not. I20«. 1105. mo l!Oi. MtHCTPVILr) FiGUKE 5. — Effect of acidity on stability of rosin-sized, clay-filUd bonk papers made

from old rags.

(1214) without clay filler but with rosin size and alum was also included.

The first two runs of old-rag papers (1191 and 1192) without rosin

size but with alum showed little change in physical and chemical tests after heat treatment, but the paper of run 1193, with pH 4.2 at the

head box, showed a decided decrease in alpha-cellulcse content and

retention of folding endurance. The clay retention was practically

the same for all tliree runs. For both series of the rosin-sized j)apers (2 percent, runs 1200 to 1203; 1 percent, runs 1204 to 1206) the measurements given in table

4 show increases in the change of alplui-cellulose and copper number

as the alum was increased, but the initial folding endurance (table 3)

of the papers was so low that the decrease for the heat-treated samples was not pronounced. Clay retention seems to be highest for the

old-rag papers when the pH value at the head box is approximately 5. Characteristics of the series sized with 1 percent of rosin are shown

in figure 5.
Shaw 1 O' Leartl Stability oj Book Papers 689

(b) TITANIUM-DIOXIDE-PIGMENTED PAPERS

Titanium dioxide pigments are manufactured pigments said to produce a liigli degree of opacity and brightness in paper. Although

tlie manufacturer reported that only small proportions of titanium

dioxide pigments are generally used in paper, since our study was

concerned iiuiiiily with the effect of the pigments on stability, 5 and

15 percent were each used in the experimental runs. The method of

furnishing the beater was the same for the titanium dioxide pigments

as for the clay filler. (1) Sulfite pulp, 1)0 percent; ftoda jndp, 60 percent.—Two papermachine runs (1147 and 114/)) were made with 15 and 5 percent of

titanium dioxide pigment A, at pH values 4.8 and 5.0, respectively, at the head box; and two runs (1148 and 1149) with 15 percent of

titanium dioxide pigment B but with different amounts of alum.

The beater furnishes all contained 1 percent of rosin size. The opacity of the paper for which 5 percent of titanium dio.xide pigment A was added in the beater was equal to that of the runs in

which 15 percent of clay was used; and when 15 percent of titanium

dioxide pigment, A or B, was used the opacity was better. The

papers containing titanium dioxide pigments were whiter and brighter

than the clay-lilled sheets. The relative cpiality of the clay and of

the other lillers should be regarded as applying only to materials

that were representative at the time the work was done. The relationship niay be changed with further improvement of fillers. The sizing

values were not affected by the pigments. Tlie stability of the

titanium-dioxide-pigmented papers was about the same as that of

The original folding endurance and tearing strength of the paper

in which 5 percent of pigment A (run 1 145) was used were higher than

when 15 percent of clay or titanium <lioxide pigment was used. To

maintain high strength and at the same time obtain high opacity is a

result desired in filled papers. Since strength is adversely affected as the amount of fdler is mcrease<l, relatively high opacifying power is a very desirable property. The retention of titanium dioxide pigment

B increased as the amount of alum added was increased.

(2) Rags: No. 1 old whites, 50 percent; twos and blues, 60 percent.—

Runs comparable to those made from the sulfite-soda pulps were made

from old rags also. The stock for one (run 1207) contained 5 percent

of titanium dioxide pigment A and was at pH 4.9 at the head box;

for two runs (1208 and 1209) the furnishes included 15 percent of

titanium dio.xide pigment B and varied amounts of alum. All contained 1 percent of rosin size. As with the sulfite-soda papers, the opacity of the paper (run 1207)

for which 5 percent of titanium dioxide pigment A was used was as high as tiiat of the papers in which 15 percent of claj was used, and was higher for the runs containing 15 percent of pigment B. The

finished titanium-dioxide-pi^nented papers also were whiter and

brighter. The effect of the titanium dioxide pigments on the stability

of the papers, and the degree of retention of the pigments, were about

the same as for clay.

Zinc sulfide pigments are manufactured materials said to have high

brightening and opacifying value.

(c) ZINC-SULFIDE-PIGMENTED PAPERS
690 Journal of Research of the National Bureau of Standards [Voi.u The supplier of the zinc sulfide pigments recommends as a precautionary measure that plants having considerable copper equipment

"avoid acid conditions so excessive as to attack this equipment and to form a dilute copper solution, as such a condition can dull dovm the

white pigment to an extent dependent upon the amount of copper in

solution and the time available for the reaction." The 50-pound

beater used at the Bureau is lined with copper, and the stock pipes

and screen plates are brass. Since the program of study included the

manufacture at [)H 4.2 of some papers with each filler, dulling of the

papers pigmented with zinc sulfide was expected.

The method of furnishing the beater was the same as that used with

clay and with titanium dioxide pigments. The papers were ail sized

with 1 percent of rosin.

(1) Sulfite pulp, 60 percent; soda pulp, 60 percent.—Paper machine

runs 1150 and 1151 were made with 15 and 5 percent of zinc sulfide

pigment A, at pH 4.9 and 5.0, respectively, at the head box; runs

1152 and 1153, with 15 percent of zinc sulfide pigment B and various

amounts of ulum.

All four papers were darkened somewhat, but this condition may

have been due to the copper and brass of the equipment and the degree

of acidity of the stock. (The odor of hydrogen sulfide was detected

at the higher acidities, lower pH's.) As a result the opacity would

naturally be slightly higher because relatively more light would be

absorbed thiin if the papers had been whiter and brighter in color. The opacity for the run using 5 percent of zinc sulfide pigment .4 is as high as that of papers made with 15 percent of clay, and the opacities

for the runs with 15 percent of zinc sulfide pigments, A or B, are

higher.

The stability of the zinc-sulfide-pigmented papers was as good as of

the papers containing the other fillers. The usual copper number

test as a measure of degradation is not applicable to papers containing

zinc sulfide because it interferes with the chemical reactions in the

test; therefore no values are given in the table. The retention of zinc

sulfide pigment B increased as the proportion of alum in the furnish was increased.

{2) Rags: No. 1 old whites, 60 percent; twos and blues, 50 percent. —

Runs comparable to the last three sulfite-soda runs with zinc sulfide

pigments were made with old-rag half stuff also. The test data indi- cate that as to stability the zinc sulfide pigments had no harmful

effect on the papers. But the papers were discolored, which could be

attributed in part at least to the copper and brass equipment and the

degree of acidity.

(d) CALCIUM-C^RDONATE-PIGMENTED PAPERS

Two types of calcium carbonate pigments were used in this study,

precipitated and water-ground natural material. When the work was

begun only two samples were considered, one of each kind, the precipitated and sample A of the natural. Later two more samples, B

and C, of the water-ground natural calcium carbonate were added.

'I'he producer of the water-ground natural pigments stated that the

three samples difiered only in fineness: "Sample A, average particle

size 10 microns, nothing larger than 30 microns; sample B, average

particle size 7 microns, notliing larger than 20 microns; sample C,

average particle size 2 microns, nothing larger than 7 microns."
Shaw 1 O'Ltary] Stability of Book Papers 691

The precipitated calcium carbonate was soft and bulky, was more

finely divided and more uniform in particle size, and when mixed with

water stayed in suspension for a comparatively long time. The waterground natural material was not so soft nor so bulky as the precipitated, and settled out of the water mixture more rapidly. The

analyses (table 2) of the two kinds of calcium carbonate show them

to be about the same chemically, and they were approximately alike

in color. Most book paper in which alkaline fillers are used is not sized, has no acidic material added, and consequently the stock is alkaline

during its manufacture into paper. The general manufacturing practice is very much the same as for the usual clay-filled sheet except for the omission of size and alum. In the experimental work at the

Bureau some of the calcium carbonate papers were made without

sizing materials, but the pulp for some was rosin-sized first and the

calcium carbonate was added later. Before calcium carbonate is used for commercial paper manufacture, however, the patent rights on

the use of the material in sized pajjers should be examined.

(1) Sulfite pulp, 50 percent; soda pulp, 60 percent.—In preparing

the sulfite-soda stock for the papermaking runs the pulp mixture was

beaten first, and the subsequent operations depended on whether the

stock was to be rosin sized. The procedure followed for each run is described under the discussion of the run. The precipitated calcium carbonate was used in runs 1158 and 1159

and 1172 and 1173. In run 1158 the calcium carbonate slip was

adfled when the stock was being discharged into the beater chest. No rosin size or alum was added.

The pulp for run 1159 was sized in the beater and the calciiim car- bonate was added later in the macliine chest. Two percent of size was used, based on the weight of pulp and calcium carbonate, or 2.3 percent if based on pulp alone. The sized stock was allowed to stand

overnight in the beater chest. The pH of the stock, before the calcium

carbonate was added, was 5.0. The calcium carbonate was added

1 hour before the stock was run over the paper machine.

Run 1172 duplicated run 1159 except for the interval between the

addition of the rosin size and the calcium carbonate. For run 1 172 the

rosin size was added to the pulp in the beater 1 hour before it was

discharged into the chest and Yi hour before the alum was added.

After being emptied into the beater chest the stock was agitated for a short time and then pumped to the machine chest. The pH of the

stock in the beater chest was 5.0. The calcium carbonate slip was

added in the machine chest and the stock was agitated for 1 hour to insure uniformity of the mixture. The pH of the stock at the head

box was 8.0. Run 1173 was similar to run 1172, except that 30 percent of precipitated calcium carbonate was added.

The water-ground natural calcium carbonate samples A and C

were used with the sulfite and soda pulp mixture. The stock for run

1 174 was prepared without rosin size or alum, but 30 percent of calcium

carbonate sample A was added in the machine chest. The stock was

then agitated for 1 hour to insure a uniform mixture for the paper

macliine.

For run 1175 rosin size was added to the pulp in the beater 1 hour

before the stock was emptied into the beater chest and hour before

the alum was put in. After being discharged to the beater chest
692 Journal oj Research oj the Natumal Bureau of Standards [Vot.ti

the stock was agitated for a short time and then pumped to the machine chest. The pll of the stock in the beater chest was 5.0. Fifteen

percent of natural calcium carbonate sample A was added in the

machine chest, after which the stock was agitated for 1 hour and then

pumped to the paper machine. The pH of the stock at the head box was 7.7. Run 1220 differed from run 1175 only in that 30 percent of calcium

carbonate sample 6' instead of 15 percent of sample A was added.

Natural calcium carbonate sample A (runs 1174 and 1175) settled

out of the stock somewhat in the rilfler, or sand trap, while being run

to the paper machine. This condition was not observed wlien either

the precipitated calcium carbonate or the more finely ground natural

calcium carbonate sample C was used.

The stock containing calcium carbonate, precipitated or natural,

but no size nor alum, did not foam on the paper machine. When

rosin size and alum had been added in the beater, however, followed

by calcium carbonate in the machine chest, there was foaming on the

paper machine, more for the precipitated than for the natural samples,

although the amount was not great and doubtless could have been

kept down satisfactorily with a fine water spray. There is, of course, always the possibility when foaming has occurred of foam spots

being left in the finished paper.

The sizing values reported in table 3 for the sized papers are not

high, but appraised by personal opinions and judgment the papers were sized sufficiently to be written on with ink and for ordinary

printing processes. There is no direct correlation between the

resistance of paper to water penetration and its ink-receptiveness.

The retention of the calcium carbonate and the opacity of the papers were good.

From the physical and chemical test data it appears that papers

containing calcium carbonate are more stable than the usual rosinsized papers, which are acid in character.

(2) Rags: No. 1 old whites, 60 percent; twos and blues, 60 percent.—

In the runs with old rags the calcium carbonate slip was added to the stock in the machine chest and the resultant mixture was agitated

for 1 hour before being pumped to the paper machine.

Precipitated calcium carbonate, 15 and 30 percent, respectively, was used in runs 1215 and 1216.

The three paper-machine runs (1217 to 1219) with water-ground

natural calcium carbonate comprised 15 percent of samples C, B,

and A, respectively. As previously stated, the only difference in

the three samples was the fineness to which they had been ground, A

being the coarsest and C the finest. In run 1219, as in the sulfite- soda runs with sample A, some of the carbonate settled out from the

stock in the rifller, or sand trap, but samples B and C (runs 1218 and

1217) seemed to remain in suspension.

There was no foaming of the stock on the paper machine in any of

the runs. The finish of the papers containing the carbonates was

satisfactory. All the carbonate-filled papers were comparatively

stable.

2. PRINTING TESTS

In the early part of the study, printing tests were made at the

Government Printing Office on the experimental papers that had
Shall' 1 O'Uaryl Stability oj liuok Papers 693

been iminufiuaiiroti ui> h) that time. The [)!ii)ers printed wore repre- sentative samples of sulfito-soda runs cuntainin<^ day (unsized and

sized sheets), titanium dioxide pigment A, zinc sulfide pigment A,

and calcium carbonate (precipitated and natural); and of purifiedwood-fiber and new-ra^; papers containing clay.

The papers were prmted from type on one side and by the offset process on the other. The fillers seemed well anchored to the fiber and did not dust out during printing. The papers caused no trouble

in the operations and the printings were considered very satisfactory.

Now that the experimental paper-mill work on the book papers has

been completed, extensive printing tests to evaluate the printing

quality of papers representative of all the different pulp and filler furnishes is in progress and the results obtained will probably appear

in a later publication. Final opinion as to the relative values of the

different fillers and of the other different papermaking details should

await the results of the printings.

VIII. DISCUSSION AND CONCLUSIONS

It is well known that fillers used in large amounts very appreciably

reduce the strength of paper. The strength of t!ie experimental papers

decreased with increasing filler content, but was influenced by the

amount, not the type, of filler present, liecause of their effective

opacifying quality, smaller amounts of titanium dio.xide and zinc

sulfide pigments than of clay were sufficient to obtain requisite opacity

for printing processes, and the resulting papers were less reduced in strength. All the papers had sufficient strength to withstand the

mechanical stresses to which book papers are ordinarily subjected.

There was no ])ronounced difference in the relative effect of the

nonalkaline fillers on sizing. The degree of sizing was very much

greater for the sulfite-soda pai)ers than for the rag papers, and the

purified wood-fd)er papers were in an intermediate position. The

nonalkaline fillers had less effect than calcium carbonate in- reducing

sizing. Although the sizing values of the carbonate papers were not

high the ])apers were sized sufficiently to be written on with ink and

for ordinary i)rinting processes. There was no direct correlation

between the resistance of the papers to water penetration and their

iuk-receptiveness.

When rosin size and alum had been added to the stock in the beater

and followed by calcium carbonate in the machine chest, the stock

foamed somewhat on the paper machine, although the amount of

foam was not great and doubtless could have been kept down satis- factorily with a fine water spray. Maxium clay retention was obtained in the j)urified wood and rag

papers when the pH at the head box was approximately 5. and decreased as the amount of alum whs irureaseu. For the snlflte-soda pulp, retention of all the nonalkaline fillers increa.sed as alum was

mcreased. Retention of the calcium carbonate was satisfactory.

The papers containing titanium dioxide, zinc sulfide, or ])recipitated

calcium carbonate pigments had the highest opacity values in the

experimental work, and, by personal judgment, gave the best printing

results. Only a few of the papers were submitted to the printing tests however. Further tests of the printability of representative samples

100021;— :;s —ii
694 Journal oj Research oj the National Bureau of Standards [Voi.tt

of all the papers are in progress, and rating of their printing qualities

will probably be reported in a subsequent publication.

Aside from natural aging the best information on the inherent permanence of paper is based on changes in phv'sical and chemical characteristics during accelerated aging tests. The Bureau believes that oven

aging rapidly accelerates tlie slow deterioration caused by impurities

in the paper, and that changes in alpha-cellulose content and copper

number and the percentage of the original strength retained indicate

the comparative resistance to degradation. The change in the

cellulose m the accelerated aging seemed to have been from alpha- to

beta-cellulose, with no appreciable difference in the percentage of

gamma-cellulose. The rag and i)urined wood-pulp i)apers were more

stable to the heat test tlian the sulfite-soda wood-pulp paj)ers. Nonalkaline fillers had no apparent influence on the stabihty of any of

the papers, and the calcium carbonate pigments had a i)r()tective or

inhibiting effect in the accelerat^'d a<^ing.

Acidity was an important factor in deterioration. Attack on the

cellulose was increased as the amount of alum was increased, in either

the unsized or the rosin-sized papers. The rag fibers seemed to withstand acidity better than any of the other fibers used. Contrary to the reaction with the pulps of higher initial purity, sulfite-soda papers were more stable to the heat test when containing rosin sizing than

when made with corresponding acidity but without size. The effect on the stability of increasing the amount of alum in the

beater and then neutralizing part of the alum with sodium carbonate

as the stock was being pumped from the beater chest to the machine

chest was practically the same as having liad the final pH value originally in the beater and maintained throughout the preparation of the

stock.

The necessity for employing only minimum amounts of rosin and

alum in the sizing of papers intended to be used for permanent records

is generally recognized. The optimum pll value for combining liigh

stability with adequate sizing of papers containing nonalkaline fillers, however, varies in different mills because of hardness of water, whitewater recovery, kinds of materials used, etc., but at the Bureau is appro.ximatcly 5 at the head box of the paper machine. The pH (hotwater extraction) of the finished papers is in approximate agreement

with that of the stock at the head box.

Resistance of paper to deterioration from internal causes is not

sufficient to insure its stability, however. The conditions under which

the paper is stored and u.sed must also be considered. For a discussion

of external deteriorative agencies—light, temperature, humidity,

acidic pollution of air—and recommendations as to storage conditions

for prolonging the life of paper, the reader is referred to a previous

Bureau publication [9].

The authors acknowledge their indebtedness to R. W. Carr of this

Bureau for the physical testing of the experimental papers, and to H. F. Launer, C. I. Pope, and W. K. Wilson, also members of the

Bureau staff, for the chemical testing of the pulps and papers.
Slmw 1 O'Learyl Stability of Book Papers 695

IX. REFERENCES

(1) R. H. Rasch, M. B. Shaw, and C W. Ricking, Highly purified wood fibers a» papermaking material, BS J. Research 7, 765 (1931) RP372.

[2] R. H. Rasch, M. H. Shaw, and G. W. Bicking, 4 study of some factors influencing

the strength and stability of experimental papers made from two different sul- phite vulps, BS J. Research 11, 7 (1933) RP574.

[3] M. B. Shaw, G. W. Bicking, and M. J. O'Leary, A study of the relation of some

properties of cotton rags to the strength and stability of experimental papers made from them, J. Research NBS 14, 649 (1935) RP794.

[4] M. B. Shaw and M. J. O'Leftry, Study of the effect of fiber components on the

stability of book pavers, J. Research NBS 17, 859 (1936) RP949.

[5] M. B. Sliaw and G. W. Bicking, Car'od fiber as a papermaking material, Tech.

Pap. BS 21, 338 (1927) T340; Further experimental production of currency paper in the liureau of Standards paper mill, BS J. Research 3, 904 (1929)

RP121; Equipment and research work of the Bureau of Standards paper mill. Paper Trade J. 89, 19, 60 (1929).

[6] H. F. Launer, Volumetric determination of alpha-, beta-, and gamma-cellulose

in pulps and tn papers containing sizing, filler, and other materials, J. Research NBS 20, 87 (1938) RP1068.

[7] R. H. Rasch, Accelerated-aging test for paper, BS J. Research 7, 465 (1931)

RP352; Estimating stability of paper by hrnting, Pai)er Trade J. 95, 4, 28

(1932); R. H. Rasch and B \V. Scrihner, Comparison of natural aging of paper with accelerated aging by healing, BS J. Research 11, 727 (1933)

RP620.

[81 M. B. Shaw and G. W. Bicking, Comparison of American and foreign clays as paper fillers, Tech. Pap. 18, 337 (1924) T262; A comparative study of paper

fillers, Tech. Pap. 19, 733 (1925) T301.

[9] A. E. Kimberlyand B. W. Scribner, 6'um;nory report of the Bureau of Standards

research on preservation of records, Misc. Pub. BS M154 (1937).

Washington-, August 10, 1938.

USC:OMM-NHS 0(
NBS-IUA (REV. 7.73)

U.S. DEPT. OF COMM.

DIOI t D A OLti ^ DATA

SHEET

1. in Hl.K A I ION OR Rl I'OR 1 NO,

NBSIR 74-632

2. Ckiv 't A< ( t- ss ion M . INO,3. Rccipit-nt's Accession No.

4. TITLF AND Slim ITl.H Comparison of Accelerated Aging of Book Papers

in Wi t-h "^6 Ypars Natural Aaina

5. Publication Date December 18, 1974

6. Performing Organization ( ode

7. Airi llOR(S)

W. K. Wilson and E. J. Parks

8* Performing Organ. Report No. NBSIR 74-632

9. PHRFORMINC; ORGANI/.A I ION .NAMh ANH APORI SS NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Pro)ect/Task/Work Unit No. 3000442

11. (ontract/Grant No.

12. Spciii sor 1 ng Org .111 1/ at uin N.im<- and < omph-ti Address (Strei-I. City, Sinte, ZIP)

National Archives and Records Service

Washington, D.C. 20408

13. Type of Report & Period

(-overed

Interim

14, Sponsoring Agency (ode

15. SUPPl.KMIiN TARY NOI i:s

16. ABS'I'RAf r (A 200-word or less (actual summary ol most si^ificanl information. If document includes a significant

bibliography or I iteraturc survey, mention it here.)

A group of 36 book papers made in the NBS paper mill in 1937 were

tested in 1937 before and after accelerated aging for 72 hours at lOO^C

and in 1973 after 36 years of natural aging. The data show that

fairly good correlations exist between accelerated aging and natural

aging when changes in alpha cellulose, copper number and, to a lesser

extent, tearing strength, were used as criteria of change. pH is a reasonably good criterion of stability. It appears that zero span

tensile strength, wet strength as a percentage of dry strength, and

brightness are useful criteria for evaluating the aging of paper.

When data in this report are compared with data from earlier reports,

it appears that dry accelerated aging at 100°C more nearly corresponds

to natural aging than accelerated aging at 90°C and 50 percent

relative humidity.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Accelerated aging; aging; natural aging; paper, permanent; paper,

stability; permanent papers; record papers; stability of paper.

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