NBSIR 78-1443

The Effects of Temperature

and Moisture on the

Accelerated Aging of Paper

E. L. Graminski, E. J. Parks and E. E. Toth

Polymers Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

Progress Report Covering the Period

July 1 975 - December 1 976

Issued March 1 978

Prepared for National Archives and Records Service

Washington, D.C. 20408

NBSIR 78-1443

THE EFFECTS OF TEMPERATURE

AND MOISTURE ON THE

ACCELERATED AGING OF PAPER

E. L. Graminski, E. J. Parks and E. E. Toth

Polymers Division

Institute for Materials Research

National Bureau of Standards

Washington, D C. 20234

Progress Report Covering the Period

July 1975 - December 1976

Issued March 1 978

Prepared for National Archives and Records Service

Washington, D.C. 20408

U S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
.
TABLE OF CONTENTS

Page

SUMMARY 1

INTRODUCTION 5

EXPERIMENTAL 9

ACCELERATED AGING 11

TESTING METHODS 12

RESULTS 14

DISCUSSION 16

TEMPERATURE AND HUMIDITY 16

BOUND WATER 18

ALKALI SOLUBILITY , COPPER NUMBER AND ACID

GENERATION 20

STRENGTH PROPERTIES 21

PHYSICO-CHEMICAL PROPERTIES 22

WET STRENGTH 23

ESTIMATION OF PERMANENCE 25

CONCLUSIONS 27

BIBLIOGRAPHY 28
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1

SUMMARY

Tne purpose of an accelerated aging test is to predict the

useful life of the material in question. Investigations on the

permanence of paper by means of accelerated aging at elevated

temperatures have been conducted over the past 50 years.

The conventional method, quite prevalent in permanence

investigations, assesses permanence in terms of the extent of

degrauation occuring a fixed time after aging at a single

temperature. This method, however, has been criticized as being

potentially misleading (1) . It was argued that, altnough the

rate at which a paper degrades depends on temperature, this

temperature dependence mignt not be the same for all papers. In

sucn a case the degradation of one paper relative to another as

determined by accelerated aging would differ from the relative

degradation observed at room temperature. The suggestion was

made that permanence be assessed in terms of the degradation rate

at room temperature. This rate could be obtained from the

Arrhenius equation using rates determined at several elevated

temperatures

.

Although the Arrhenius approach towards estimating paper

permanence appears simple and straightforward, predictions of

permanence may be just as misleading as those obtained in the single

temperature method. More than one reaction contributes to the

degradation of paper wnile the Arrhenius concept is applicable

in a simple manner only to single reactions. The rates of
2

ue terioration of paper at elevated temperatures, estimated by

tne decline of physical properties with time of aging, are for

the system as a whole and unless the reaction rates for all the

aegradative reactions are increased in the same proportion with

temperature tne determined rates will be anamolously high or low

depenuing on a number of factors. Similarly, the slope of the

Arrhenius plot, generated from the determined rates, will be

anamolously high or low and extrapolation of the plot to ambient

conditions will yield degradation rates which are appreciably

different from the actual rate of degradation.

It has been known for some time that moisture has a profound

effect on the results obtained from accelerated aging tests for

paper (2,3,4). Eventually studies on the accelerated aging of

paper were conducted at some chosen relative humidity or at some

constant moisture content of paper. Accordingly, much disagreement arose between investigators since the results of an investigation were aepenaent on the environmental conditions of the

aging system. The only opportunity for agreement between investigators occurred when the moisture content of the papers used

by two investigators was maintained the same.

It became very clear that much information had to be

developed on the effect of moisture in accelerated aging of paper.

In order to develop such information it would be necessary to

age paper at a multitude of humidities and temperatures. Such a
3

stuuy would not only provide critical information on a very

important variable in accelerated paper aging but the data might

be also used to evaluate the validity of using the Arrhenius

concept for assessing paper stability.

riandsheets were prepared from a Northeastern softwood kraft

pulp wnich has been aeashed with 0 . IN HC1 . The handsheets were

aged at 60°, 70°, 80°, and 90°C and at 0, 10, 25 and 50% RH for

all temperatures except 60° where the humidities were 0, 25, 50

and 75%. The reason for the change in humidity conditions at

60 °C was oecause the partial pressure of water at 10% RH was so

low very little increase in rate could be expected over that

occurring at 60°C and 0%Rh. The rates of deterioration were

determined by plotting the log of the property in question

against time for all properties except alkali solubility, copper

number, hydrogen ion concentration and wet strength which were

plotted on a linear scale against time. The slope of the plot

was considered to be a measure of the degradation rate. Linear

relationsnips were found between the degradation rate and the

amount of moisture in the aging atmosphere, expressed as the

partial pressure of water, for each temperature investigated.

The plots were expected to pass through the origin since little

if any degradation occurred at 0% R.H. regardless of the temperature. However plots for the 90°C series did not pass through

the origin for any of the properties investigated. In the 80°C
4

series the plots passed through the origin only for the chemical

properties and for brightness while all of the plots passed

through the origin for the 60°C and 70°C series. This suggests

that the mecnanism of degradation changes appreciably at some

temperature above 70 °C.

Although the results of this investigation indicate that

atmospneric moisture and not bound water affects the degradation

rate of paper it must be recognized a linear relationship usually

exists between relative humidity and the amount of water bound

to cellulose in the humidity range employed in this investigation.

In the two instances where the R.H. range was broadened the results conflicted with each other. It will be necessary to expand this study to include humidities substantially above 50%

for all the temperatures investigated before an indication of the

type of water affecting degradation rates can be obtained. The

expanded investigation should also provide additional information

on the possibility of a change in degradation mechanism above an

optimum temperature.

The results of this investigation clearly demonstrate the

need to establish the optimum temperature and moisture conditions

for accelerated aging tests for paper. Unless the functionality

of moisture ana the limits for temperature are established there

is little hope for obtaining agreement between investigations on

paper permanence or for designing an accelerated test for paper

wnich will produce meaningful results.
5

INTRODUCTION

For over fifty years attempts have been made to predict the

permanence of paper by means of accelerated aging. The earliest

accelerated aging involved placing paper in an oven at 100-105°C

for times ranging from 20 to 125 hours (5,6)

.

The decline

in physical properties resulting from exposure to elevated temperatures was considered a measure of paper permanence. The

papers naving a high retention of the original properties were

considered to oe permanent while those exhibiting an appreciable

decline in properties were considered to be impermanent. The

degree of impermanence was proportional to the extent of decline

in properties. No attempt was made at predicting the service

life of paper.

It was eventually recognized that the degradation rate for

all papers might not remain constant and that the estimated permanence of paper could change with longer aging periods. This

led to tne practice of aging paper for longer periods of time

with multiple withdrawals during the course of aging. The

physical properties were plotted for the various time intervals.

If necessary the data were suitably transformed in order to

ootain straight lines-. The slopes of these lines were considered

to be a measure of the degradation rate and were used to assess

the permanence of paper. The papers having the lowest degradation

rates were judged to be the most permanent.
6

Generally speaking it is assumed that the degradative reaction

in paper at elevated temperatures are not significantly different

from those at amoient conditions, because for an accelerated aging

method to oe valid it must duplicate the chemical and physical

changes occurring naturally. Within the limitation of this assumption attempts have been made at establishing a relationship

between natural and accelerated aging. The results of several

investigations concluded that three days oven aging at 100 °C

was equivalent to 20-28 years of natural aging (18,19). Barrow

suggested that for convenience three days oven aging could be

considered equivalent to 25 years natural aging (8)

.

However,

the most recent investigation comparing accelerated and natural

aging clearly indicates that the degradation occuring during

three days oven aging of paper frequently does not correspond to

a specific number of years of natural aging(9)

.

Tne situation became more complex when it was discovered

that moisture had a significant effect on the rate and extent of

degradation of paper (2,3,4)

.

To date no study, fully interpreting the relationship between moisture and degradation rate

in accelerated aging, has been conducted. For the most part the

choice of atmospheric conditions by various investigators has

been based on an empirical rather than on a fundamental basis.

Some investigators considered the control of relative humidity

to be most important with no consideration of the amount of
7

water Douna to cellulose. Other investigators considered the

"Dounu water" to be most important. At the present time there

appears to be no consensus as to the type and amount of water to

oe controlled in an accelerated aging test.

Most recently the single temperature aging methods have been

criticized as being potentially mis leading ( 1) . The decline in the

pnysical properties of paper is caused by a variety of chemical

reactions. Since different reactions that might occur in different

papers nave different responses to temperature it was argued that

aging at a single temperature does not provide a means for detecting

the differences in temperature dependence of the rate constants.

It was suggested tnat the rate of degradation be measured at several

elevated temperatures and that the well known Arrhenius equation

tnen he used to extrapolate to the rate of deterioration at room

temperature. In this way an estimate of the half-life of paper

could be determined and a predication of the lifetime of paper

could oe made.

Altnough the Arrhenius approach towards estimating paper

permanence appears simple and straightforward, predictions of permanence may be just as misleading as those obtained with single

temperature methods. As mentioned previously, more than one reaction contributes to the degradation of a paper while the Arrhenius

concept is applicable in a simple manner only to single reactions.

The determined rate of deterioration at elevated temperatures is

of tne system as a whole and unless the reaction rates of all of
8

tne degrauative reactions increase in the same proportion with

temperature the determined rate will be anamolously high or low

depenuing on a number of factors. Similarly, the slope of the

Arrnenius plot generated from the determined rates will be

anamolously high or low and extrapolation of the plot to ambient

conditions will yield degradation rates which are appreciably

different from the actual rate of degradation.

The question at hand is how do we evaluate paper permanence

witn precision? Essentially everything that has been said in the

literature adout tne factors affecting paper permanence has been

based on results obtained from accelerated aging tests. There is

no assurance that accelerated aging duplicates the chemical and

pnysical cnanges in natural degradation. Unless more fundamental

knowleuge of tne aging process is known, assessment of paper

permanence oy means of accelerated aging will be more empirical

tnan fundamental.

The purpose of this investigation was to develop information

on the relationship between moisture and degradation rates in

accelerateu aging and to determine whether the temperatures

commonly used in accelerated aging are excessive.
9

EXPERIMENTAL

Handsheets, prepared from a northeastern bleached kraft pulp

containing approximately 85 percent alpha cellulose and 15 percent

hemicellulose were used in this investigation. Six kilograms of

the pulp were torn into pieces of approximately two square inches

area and divided into three two-kilogram samples . Each sample

was demineralized by soaking in 0 . IN hydrochloric acid at a five percent consistency. After one hour the acid was drained and

fresh acid was added to the pulp. After the fourth acid treatment

the pulp was washed with distilled water on a large Buchner funnel

until the pH of the filtrate was identical to the pH of the distilled water and remained at that pH for an additional three to

four rinses.

Following demineralization, the three two-kilogram samples

were blended thoroughly, and washed four additional times with

carbon dioxide-saturated distilled water. The bulk of the water

was removed by filtration and the treated pulp was placed in a covered glass jar and stored at -18°C until used.

The pulp was beaten in a laboratory mill at 10 percent

consistency with no clearance between bedplate and roll for 5,000

revolutions at 33. 3N '(3.4 kilograms force) and a relative velocity

of roll to bedplate of 6m/sec. The beating was done in distilled

water using sufficient wet pulp to provide 40g of dry pulp for

each charge. One kilogram of pulp was beaten (25 beater charges)
10

and placed in a large stainless steel container, diluted to

approximately one percent consistency and blended for approximately one hour prior to preparing handsheets.

Aliquots, containing sufficient pulp to make a 30.5 x

2 30.5 cm handsheet having a weight of 70 g/m + 5% were placed

in a British Disintegrator, diluted with distilled water to a consistency of approximately 0.5 percent and disintegrated for

3000 revolutions. The disintegrated pulp was placed in a 30.5 x 30.5 cm deckle box containing approximately 28 liters of distilled

water. The contents were agitated by moving a perforated plate

up and down five times followed by a pause of approximately 10

seconds then drained through a 100 mesh monel wire screen. The

wire containing the formed sheet was placed on a blotter, covered

with wool felt and consolidated by pressing with a 33 cm long

roller weighing 22.5 kg. The sheet was carefully removed from the

wire, olaced between wool felts and passed through a roll press at

a oressure of approximately 7 kg/per linear cm. The pressed sheet

was then dried on a drum dryer at 95°C for approximately four

minutes. The tension on the endless felt of the drum dryer was

adjusted to restrict sheet shrinkage to a minimum. The sheets

were stress relieved by suspending them in a humidity chamber at

30°C and 95% relative humidity for approximately 16 hours.
11

Accelerated Aging

All of the handsheets were randomized out of the order in

which they were manufactured in order to obtain samples, representative of the lot, for the various combinations of aging time,

temperature and relative humiditv. All of the handsheets were

randomized into sets of 12 handsheets. Six sets of 12 handsheets,

selected at random, were designated for each of the four temperatures

Each sheet in the sets was cut into four quaters and each quarter

was designated at random. The quarters from each sheet having

the same designation were then grouped together and each set of

quarters were then aged for the same time period at four different

relative humidities. following aging the specimens were conditioned

according to TAPPI T402 0S-70 before testing.

Constant temperature oil baths of internal dimensions, 30 cm

in width by 60 cm length and 37 cm in depth, were constructed of

stainless steel. A heating coil, immersed in the bath, was an

auxiliary source of heat, with current input controlled by a variable transformer. An immersion heater controlled bv a relay

box and thermoregulator was the principal source of heat and provided the desired temperature control with ±0.1°C. The oil was

continuously pumped in the bath with an immersion type pump to

ensure uniform distribution of temperature.

Two baths were used in series. One bath (prehumidifier)

was maintained at a temperature that would provide the desired

partial pressure of water and the other (aging bath) was maintained at one of the four temperatures employed in this investigation
12

To provide a vented atmosphere at a specific relative humidity

3 in the aging vessels, 50 cm of air per minute was metered through

water in the prehumidifier, passed through glass tubing surrounded

by a heating jacket at a temperature somewhat higher than the

prehumidifier bath to avoid condensation, then through coiled

glass tubing immersed in the aging bath and finally through the

aging vessel containing the suspended paper specimens. To provide dry air (0% RH) , air was passed over silica gel through a flowmeter to the aging vessel. The temperatures, the aging baths,

the partial pressure of water vapor in the saturated air and the

relative humidities in the aging vessels are given in Table 1.

The baths were covered with black cloth to exclude light.

Testing Methods

The following Tappi methods were employed: Folding Endurance

T511 Sn-69, Brightness T452 OS-58, Alkaline Solubility T212 OS-54,

Cooper Number T430 M-52, Tensile Strength T494 0S-70 using 1.5 cm

wide specimens at a span of 10 cm and a rate of elongation of

1 cm/min, and pH by method T509 SU-68 with the exception that the

pH measurement was made on the decantate (20)

.

Internal tear was performed on an Elmendorf tear tester having

a 200 g capacity. A single ply was used unless the tear strength

deteriorated considerably necessitating three or four plies in

order to obtain a reading in the range suggested for the instrument.
13

Zero span tensile strength was determined on a commercially

availaole zero-span tester. Sample size was 2 cm x 11 cm. The

clamping pressure for each set of specimens was determined in

advance to determine the minimum pressure at which slippage did

not occur ana the maximum pressure where fiber damage occurred.

The clamping pressure chosen was midway between these two pressures.

We t tensile strength was determined on a constant rate of

elongation tensile tester using specimens 1.5 cm wide and a length

of 10 cm. The samples were soaked for two hours in distilled

water prior to testing.

Moisture regain specimens were first conditioned in a desiccator for 24 hours and then exposed to an atmosphere maintained at 23 ± 1°C and 50.0 ± 2.0% relative humidity for at least

24 nours. Specimens of approximately two grams were placed in

weighing bottles and the total weight was determined to the nearest

0.1 mg. The sample was then dried in a vacuum oven at 105°C for one

hour, covered immediately upon opening the oven, cooled in a desiccator for two hours and reweighed. This procedure was repeated

until constant weight was obtained. The difference in weight between

the conditioned and dried sample was due to the moisture in the

specimen. The specimen was then removed from the weighing bottle,

and the empty bottle was dried in the vacuum oven at 105°C for one

hour, cooled in a desiccator for two hours and weighed. The difference between the weight of the bottle containing the dried specimen,

and the empty weighing bottle was the weight of the anhydrous specimen. The weight of water divided by the weight of the anhydrous

specimen multiplied by 100 was the percent moisture regain.
RESULTS

The results for all of the properties investigated in this

study are given in Tables 2-12. Little if any change in physical

properties occurred at any of the temperatures investigated when

the aging atmosphere was desiccated. The one exception was a marked increase in wet strength. Possibly cross linking occurs

under these conditions. As the relative humidity was increased

to 25 ana 50% the rate of wet strength formation also increased as

snown in Figures 1-4. At the higher temperature and relative

humidities the wet strength reached a maximum then declined indicating that more than one reaction was having an affect on wet

strength.

In plotting the data it appeared that a better linear relation

ship was obtained by plotting the log of the property in question

against time, rather than by merely plotting the physical property

against time. Examples of this can be seen in Figures 5A, 5B, 6A

and 6B . However, alkali solubility, copper number, hydrogen ion

concentration and wet strength gave better linear relationships

when plotted on linear coordinates. Therefore, the degradation

rates were determined from the slopes of the plot of log property

against time for all but alkali solubility, copper number, hydrogen

ion concentration and wet strength. In every instance the rate of

degradation of physical properties or change in chemical property

increased with increasing relative humidity.
A plot of degradation rate as a function of relative humidity

(Figures 7 and 8) resulted in a good linear relationship. However,

relative humidity is not a fundamental expression for water vapor

concentration and it is much better to express the amount of water

vapor in the atmosphere in terms of partial pressure of water.

When the degradation rate is plotted against the partial pressure

of water an excellent linear relationship is also exhibited

(Figures 9-19). The lines connecting the data points in Figures

9-19 were fitted by the least squares method.
16

DISCUSSION

Temperature and Humidity

It is interesting to note that the plots of degradation rate

against the partial pressure of water for the 90°C series do not

pass tnrough the origin for any of the properties investigated.

In the 80°C series the y intercept is at or near the origin for

not alkali extraction, brigntness, copper number, pH, moisture

regain but not for zero span, fold endurance, tear, breaking

strength, wet strength and elongation to break. Inasmuch as

little if any degradation occurs in the absence of moisture at

each temperature investigated it would be reasonable to expect

the y intercept for the plots of degradation rate against the

partial pressure of water to be at or very near the origin. Since

none of the 90°C plots and only some of the 80°C plots have a y

intercept near zero it is possible that either the cellulosewater interaction or the degradation process changes at these

\ conditions. There are several possible explanations for this

phenomenon and it will be necessary to determine the exact causes

for tnis occurrence.

This investigation demonstrates clearly that water has a profound effect on the degradation of paper in an accelerated

test. The rate ana extent of degradation apparently are directly

dependent on the amount of moisture in the aging atmosphere. It

is quite clear that any accelerated aging method must include some

specification for moisture. Without such a specification the
17

results will vary from investigator to investigator, however, it

will be necessary to identify the role of moisture in the degradation process before it will be possible to specify the right

quantity of moisture to be used in accelerated aging.

The object of an accelerated aging test is to speed-up the

aegradative process sufficiently to enable assessment of the

stability of the material in question in a reasonable time interval. It is essential that only the aegradative processes of

interest are accelerated in the same ratio as they occur naturally

ana that degradative reactions wnich are insignificant at ambient

conditions ao not become significant at elevated temperatures.

Since there appears to be a linear relationship between the

partial pressure of water in the atmosphere and degradation rate

it could be argued that the amount of moisture to be employed in

an accelerated aging test should be identical to that which paper

is normally exposed to under natural conditions. The amount of

moisture which could be specified is that equivalent to TAPPI

stanuard conditions (50.0 ± 2.0% RH and 23.0 ± 1.0°C). In fact

accelerated aging has been conducted in which air from a room at

TAPPI stanuara conditions was piped into ovens to control the

moisture in the aging atmosphere (8). Oven aging is frequently

referred to as arid aging and the method has been criticized for

its lack of moisture (1,4). However, in a recent study on the

comparison of accelerated aging of book papers with natural aging

it was concluded that oven or dry aging appeared to correspond

more nearly to natural aging than accelerated aging at 90 °C and

50% RH (9) .
18

Bound Water

Some investigators consider that controlling the moisture

content of paper in accelerated aging tests for paper is most

important (1,10). The presumption here is that the water bound

to cellulose is the moisture in question and that atmospheric

moisture is important only in the sense that it must be present

in sufficient quantity to assure a prescribed moisture regain

(bound water) . This presumption is quite divergent from the

supposition that atmospheric moisture directly affects the

degradation rate of paper.

Tne moisture content of paper is dependent on the amount

of atmospheric moisture and on the temperature of the air in

contact with the paper. Furthermore, the quantity of sorbed

water at a particular set of conditions depends on whether the

equilibrium conditions were appproached from a high or low

relative humidity. A typical moisture sorption isotherm is

shown in Figure 20. It is important to note that the isotherm

is essentially linear between 10 and 50% RH which is the range of

humiaity conditions employed in this investigation with one exception. Consequently, the plot of degradation rate of paper as

a function of moisture would be the same whether the moisture

was expressed as relative humidity, partial pressure of water or

as water bound to cellulose, providing the moisture isotherm was

unchangeu over the range investigated. The range of relative

humidity employed in this investigation was too narrow to enable

establishment of the type of water affecting the degradation rate

of paper.
19

In one set of conditions in this investigation (60°C, 75% RH)

the relative humidity was outside the 10-50% range. It can be

seen in Figure 20 that the amount of water bound to cellulose

under these conditions is considerably greater than it would be

if the linear relationship between 10 to 50% was maintained.

However, the various degradation rates for paper at 60 °C and

75% RH fall very nicely on a straight line with the degradation

rates at 25 and 50% RH (Figures 9-19) . It might therefore be

argued that atmospheric and not bound water is most important.

Nevertheless it must be recognized that the slopes of the 60°C

series plots are low and it would be difficlut to detect divergence

from linearity unless the disparity were quite large.

In order to get a better insight into the type of water

affecting degradation rate it was decided to conduct an additional

experiment at 80°C and 75% RH. At these conditions the degradation

rates were much higher than predicted by linear extrapolation of

the rate-moisture plots. This result could be used to argue in

favor of bound water as the important variable. However there is

evidence that the degradation mechanism is different at 90° and

80°C and it may be that moisture may affect the degradation rate

at these temperatures differently. It will be necessary to determine the effect of relative humidity on the degradation rate at

several humidities above 50% RH before any conclusions can be

made on the importance of atmospheric moisture as opposed to

bound water.
20

Alkali Solubility/ Copper Number and Acid Generation

The bulk of material that dissolves in the hot 1% alkali

solubility test is low molecular weight carbohydrates consisting

mainly of hemicellulose and degraded cellulose. One might assume

then that the increase in alkali solubility which occurs during

accelerated aging in a humid atmosphere is a consequence of

hydrolysis. The increase in copper number which is also characteristic of accelerated aging would seem to support this premise.

However, the unusually high increase in alkali solubility at the

higher temperatures and humidities seems to indicate other

processes are occurring.

Tne degradation rate for paper is considerably lower in a moist nitrogen atmosphere than in moist air (11,12,13). Apparently,

cellulose is oxidized during accelerated aging with the formation

of 3-alkoxyl groups. The B-alkoxycarbonyl grouping occurs in all

possible situations where a carbonyl group is introduced into a cellulose molecule. Whenever a 3-alkoxycarbonyl group is present

in alkali, a rapid elimination of the alkoxyl group will occur

as follows:

H H H H H H

- C

O

It may be assumed that rapid chain scission will occur by the above

mechanism in dilute alkali. If 3 _ alkaxycarbony 1 groups do form

during aging chain scission will occur during the alkali solubility
21

test producing alkali soluble material exceeding that present

prior to chain scission. This could account for a significant

portion of the material dissolved in the hot alkali.

The copper number indicates the relative number of reducing

groups in paper. Aldehydes as well as the reducing end groups

of a number of sugars reduce copper but ketones do not. However,

tne copper number test is conducted under alkaline conditions and

ketones promote chain rupture in alkali by means of the beta

elimination mechanism described above. Chain rupture produces

new reducing end groups and increases the copper number. As in

alkali solubility, copper number is affected by a number of

variables and is not indicative of any one specific reaction.

The production of acidity during aging is likely to be caused

oy a combination of oxidation and hydrolysis. However, the

hydrogen ion concentration was derived from pH measurements and

the quantities reported do not necessarily represent the total

hydrogen ion concentration in the paper. A variety of acids are

probably formed during the aging process each having a different

pK value. Therefore, there is the possibility some weak organic

acids are not dissociated at the time of pH measurement and the

only way the total acidity could be determined is by complete

extraction of all acids and a titration of the extract.

Strength Properties

Folding endurance deteriorates at the fastest rate and to

the greatest extent of all the physical properties investigated.

There is even an appreciable decline in fold in desiccated air
22

at the higher temperature. This decline may be due to the

formation of crosslinks which appear to form quite prevalently

in the absence of moisture. Due to the great variance commonly

associated with folding endurance a specially designed experiment would have to be conducted to determine if the observed

differences are significant.

The deterioration of strength properties of paper during

aging is apparently due in large part to the decline in fiber

strengtn as assessed by zero span tensile measurements. The

decline of fiber strength is undoubtedly due to hydrolysis.

Oxidation may also be an indirect cause for fiber degradation.

It has been reported that the rate of hydrolysis of cellulose

is increased two to three fold by the introduction of aldehyde

groups in the 2 and 3 positions (14) . A carbonyl group in the

6 position can lead to an increase of from 20 to 70 times the

normal rate of hydroylsis (15) .

Physico-Chemical Properties

The decrease in brightness is probably due to hydrolytic

processes. The formation of uronic acids is know to cause color

reversion (16) . Oxidation may also play a role in color reversion not only tnrough an increase in hydrolysis rate because

of carbonyl formation at the 2, 3 or 6 positions but also by the

formation of chromophoric groups.

The decrease in moisture regain strongly suggests a decrease

in the accessibility of moisture in the amorphous regions of

cellulose. Apparently, strain induced by crystallization forces
23

is relieved by chain splitting during hydrolysis and a rapid

crystallization results (17). As crystallinity increases,

accessibility ana consequently the moisture regain will decrease.

This premise will have to be tested in specially designed

experiments

.

Wet Strength

Tne changes which occur in wet strength with time are

critically dependent on the temperature and humidity conditions.

In desiccated air as well as at 10% RH wet strength increased

continuously at all temperatures. There was very little difference in the amount of wet strength developed at 0 or 10% RH

for any of the individual temperatures investigated but the

rate of wet strength development increases with temperature.

As the humidity increased to 25 and 50% RH the rate of wet

strength development increases also. However, at 80° and 90°C

wet strength reached a maximum, plateaued and finally declined.

Plots of wet strength as a function of aging time are given in

Figures 1-4.

It is quite apparent that wet strength development is affected

by more than one process. It is reasonable to assume that the

eventual decline of wet strength under certain conditions is the

result of competing reactions. Since the decline in wet strength

occurs only at the higher humiaity conditions it may be assumed

hyurolysis is the cause for the decline in wet strength.
24

Frequently wet strength is expressed as a fraction of the

dry strengtn. When wet strength is expressed as fractional dry

strengtn and plotted against time (Figures 21-24) the character

of the plots changes appreciably. In fact a decline in wet

strength is observed only at conditions of 50% RH, 90°C and

75% Rii , 80°C after the paper has degraded extensively. In

expressing wet strength as fractional dry strength, some compensation for fiber degradation is made. This is an important

consideration as fiber degradation is extensive at the higher

temperatures and humidities.

Presumably the mechanisms for the fracture of wet paper

changes as the fibers degrade. Fracture of wet paper is presumed to occur primarily by breaking interfibers bonds as they

are quite weak in wet paper. As fiber degradation becomes extensive it is probable that an appreciable number of very weak

fibers break in wet tensile failure. This would especially

be true if inter- fiber bonds became more hydrophobic and fiber

strengtn decreased. This nypothesis could be verified by determining the ratio of broken to whole fibers at the fracture line

of unaged and highly degraded accelerated aged paper.

Rates for wet strength development may be obtained by plotting

wet strength as fractional dry strength against time. Only the

time intervals were used when a substantial increase in wet strength

development occurred over the preceeding time interval. For example, only time intervals 0-6 days were used at 90°C and 50% RH

while all but the 42 day interval was used at 80°C and 50% RH.
25

Plots of wet strength development rate versus the partial

pressure of water in the aging atmosphere were linear (Figure 19)

.

Neither the 80° or the 90°C plots passed through the origin indicating once again that the optimum temperature in accelerated

aging of paper is in the vicinity of 70°C.

Estimation of Permenance

Since moisture has a profound effect on the rate of degradation

of paper and possibly on the degradation mechanism itself it could

De anticipated that evaluation of permanence by the Arrhenius

approach will also be affected by the moisture conditions in the

aging system. The water in question, affecting the degradation

rate, is either atmospheric moisture or bound water. If atmospheric moisture is at issue then the partial pressure of water

must be kept constant at all temperatures. If bound water is in

question then the relative humidity must be set to provide a constant moisture content at every temperature investigated.

Neither bound water nor partial pressure of water was

maintained constant in this investigation. However, the degradation rates at a given partial pressure of water can be extrapolated from the plots in Figures 9-18. Furthermore, the moisture

content of paper, in the temperature range of this investigation,

should be approximately the same for each temperature at a constant

relative humidity (16). Therefore, it is possible to calculate an

approximate heat of activation and an ambient degradation rate at

a constant partial pressure of water or a constant moisture content

of paper from the data generated in this investigation.
26

It was impossible to extrapolate degradation rates at 1405

2 N/m , whicn is the partial pressure of water at 23°C and 50% RH

,

with any precision. However, since the plots are linear, extrapolation can be aone at higher moisture conditions since the rates

at one partial pressure are proportional to those at another

2 partial pressure. An estimate of degradation rate at 1405 N/m

and 23°C is also possible since the degradation rates are proportional to the partial pressure of water.

Arrhenius plots were made for zero span tensile strength

and brightness at 25% and 50% RH and at 5333 and 14932 and N/m2

(Figures 25 and 26) . The heats of activation and degradation

rates at 23° and 50% RH are given in Tables 13 and 14. It is

oovious that the heat of activation and the extrapolated degradation rate at ambient conditions are dependent on the amount

of water in the aging system.

At constant partial pressures of water the heat of activation

is approximately 13-18 kcal/mole while at constant relative

humidity it is between 25-29 kcal/mole. These heats of activation

should correspond to the heats of activation usually observed in

oven and humid aging respectively. In previous work the heat of

activation was reported to be higher in oven than in humid aging

in contrast to that seen here (1) . One possible explanation for

this divergence is that extrapolation from the rate-moisture plots

at a constant partial pressure of water gives rise to a significant

error in the estimated rates at 80° and 90°C as these plots do not

pass tnrough the origin. In actual oven aging the determined rates

may differ significantly from those obtained by extrapolation.
27

CONCLUSIONS

Moisture has a profound effect on the degradation rate of

paper. The exact relationship between moisture and degradation

rate must be established before a satisfactory accelerated aging

method for estimating paper permanence can be specified. Without

precise knowledge of the function of water in accelerated aging

the choice of moisture conditions will be based purely on empirical

rather than on a fundamental basis.

Evidence also exists which indicates that accelerated aging

should not be conducted at temperatures above 70 °C, however

additional work is necessary before an upper boundary on temperature

can be specified.

The likelihood of developing an accelerated aging method for

paper which will assess permanence in close agreement with actual

long term natural aging is critically dependent on establishing

the function of moisture and the limits for temperature in artificial

aging

.

G
28

J

BIBLIOGRAPHY

1. Gray, G. G. , TAPPI, Vol. 52, No. 2, p. 325 (1969).

2. Tongren, G. A., Paper Trade Journal, 107 (1938) TAPPI Section 76

3. McIntyre, J. W. , Paper Trade Journal, 109 (1939) TAPPI

Section 317.

4. Richter, G. A. and Wells, F. L., TAPPI, Vol. 38, No. 8, p. 603

(1956) .

5. Hall, G. , Paper Trade Journal, 82 (1926) TAPPI Section 185.

6. Rasch, R. H. , J. Res. Nat. Bur. Std. , 3:469 (1929).

7. Arrhenius, S. Z., Phys. Chem. , 4:226 (1889).

8. Barrow, W. J. , "Permanence/Durability of the Book, a Two-Year

Research Program," Richmond, VA, W. J. Barrow Res. Lab (publ.

No. 1, 1963)

*9. Wilson, W. K. and Parks, E. J. , Comparison of Accelerated Aging

of Book Papers in 1937 with 36 Years of Natural Aging, NBS

Report IR 74-632, Dec. 17, 1974, NTIS PB 246-554.

10. Browning, B. L. and Wink, W. A., TAPPI, Vol. 51, No. 4, p. 156

(1968) .

*11. Parks, E. J. and Hebert, R. L. , "Accelerated Aging of Laboratory

Handsheets: Changes in Acidity, Fiber Strength and Wet Strength'

NBS Report 10-627, Dec. 27, 1971, NTIS COM 75 10164.

*12. Parks, E. J. ana Hebert, R. L. , "Accelerated Aging of

Laboratory Handsheets: Rention of Folding Endurance, Internal

Tear, Bursting Strength, and Tensile Strength, NBS Report 10-628

Dec. 1, 1971, NTIS COM 75 10165.

*13. Parks, E. J. and Hebert, R. L. , "Accelerated Aging of Laboratory

Handsheets: Reflectance, Moisture Regain, Sonic Modulus, and

Differential Thermal Analysis, NBS Report 10-687, Feb. 22, 1972,

NTIS COM 75 10162.

14. Theander, 0., Acta Chem. Scand. , 12 (1958) 1897.

15. Lindberg, B. Chim. Biochim. Lingnine, Cellulose Hemi celluloses

,

Acta Symp. Inter., Grenoble, France, 303 (1964).
29

16. Urquhart, A. R. and Williams, A. M. , J. Textile Research 15,

T559 (1924).

17. Hermans, P. H. and Weidinger, A. J., Polymer Sci. 4_, 377 (1949).

IB. Wilson, W. K. , Harvey, J. L. , Mandel, J. and Worksman, T.

TAPPI 3Q, 543, Sept. 1955.

19. VanRoyen, A. ri. H., De Papierwereld, 12, No. 9, 219-22, April 1958.

*20. Parks, E. J. and Hebert, R. L. , "A Source of Error in Paper

Extract pH Determinations: Contact Between Paper and

Reference Electrodes," NBSIR 74-915, January 31, 1976,

NTIS PB 249-775

* Reports marked with an asterisk may be ordered from:

National Technical Information Service (NTIS)

5285 Portroyal Road

Springfield, Virginia 22161

Order number given at the end of reference.
V

."> ; i

[ .

• ; i

1 '«
Table 1. Partial Pressure of Water Vapor at Various

Temperatures and Relative Humidities

Relative Humidity - %

Aging

Temperature 10 25 50 75 100

°C N/m 2 N/m 2 N/m 2 N/m 2 N/m 2

90 7010 17524 35047 52571 70095

80 4734 11834 23672 35507 47343

70 3116 7789 15579 23368 31157

60 1992 4979 9958 14937 19916

23 281 702 1405 2107 2809
Table

2.

Effect

of

Aging

on

Folding

Endurance

O O O O un Ot CM cn

CVJ C\J r— rcn _Q -TD > 3

<£ O O Q <4- ^ O ^ (\j o r^. i— c\j CO CVJ ooVO O O O 00 vo

00 CVJ CVJ VO CO

r— CT> CO CVJ

00 i i

CD

I— </> -a -o

i 3o o Q <4-

O O O VO CVJ

CVJ VO vo

CO o o co i <3- CVJ CO

oo^-oo i"-. r^s. CVJ CVJ o o

O'

CVJ VO OdOO^f a> r— VO rr- 00 CVJ oI CVJ

CVJ

VO

VO O' LO • • CO LD r— o O

co co

00

-Q TD 3 I

o o O v*_

O O O tJ' N

o o o co cvj i

o o VO *3- r— CVJ o o o o

O I ^oco CO CVJ CVJ •—

CD

I— CO cn jo to > 3 »— cooQ *4-

O O O i— CO CO CO O'* r— VO O CVJ o o CO <3- lO co O 00 vo

CO VO

• vo O CO if) vo

r— o cvj

<y> ld i O' I LO I o o o oo o or— O'

I— vo LT) *3- CT> CT> CO vo CO CVJ I I I I I I

jQ -o 3 I

o o O <4-

o o o o o O CO Lf) Lf) N

CVJ CVJ I— I

o o 00 CVJ

CVJ o o o I VO r— r— — CVJ CVJ o o o o o VO I VO VO I VO CVJ

CVJ CVJ CO CVJ •—

o o o o o CO co vo vo

r- VO CVJ vo VO o o CO COvo O' o o o vo vo *3" «— o- o o o o 00 vo CO

i co cvj i at in

-O TD 3 «

o o Q ‘4— o o o o o o CO I- N o CO N CO *3- CO CVI CVJ CO o o VO VO o o o o I CVJ CVJ 00 CO

CO CO CO CVJ o o I VO O' o o o vo vo vo

CVJ CO CVJ ovo

O' o o o o I fOr- OCl

CVJ CO co

CD * <— V/1 cn_a -o >3 r- cooQ *4—

o o o o o o CVJ (O r- vo n vo co io a» o o VO CVJ 00 O' o o o o ON voo

VO 00 VO co o o I O VO

vo vo o o o r- VO O vo vo vo ooo o o o o o oo i ovo voai

00 CO vo vo vo

cn vo cvj co v COVOCTtCVJVOOOOCVJ l_ »- r- r- CO 4-J cr> co n cvj o vo i- r- c\j in n a> cvj *> r— Co

•- E

cn CD c »— o00

Average

of

12

specimens
Table

3.

Effect

of

Aging

on

Zero

Span

Tensile

Strength

ao

c: ^

OO <n CNJ O 3 co vo in Nr-^HN <n cn oo cn in

o> ac

co

i <u o s- lo .— 4-> in co •!— oj ^ E

CXJ 00 c\j 3 3 CO

co co 3 <3- cxj fN

lo o o oo o

N n cn lO io

cn>C

r- OJ ^ E

CT* LO r— CO i— Csj CO LO .— CO <3- CO

oo .— O'* in co 3

c^roc\ja>0 OOr-^fr- ^ ro c\i ro i

co

c

QJo

i-CD a.

O

E

<d>

CO

QJ Od

O'?

CO

i a> o O r— 4—

LO CO -r- <D ^ E

cn>

<3:

co

LO

C\J

V/l

i <d o i- cn#— > i- <c ^

a;E

co

c

CD

<D Cd

I— CO •#-

LO

i a» o i- cn i— -*-> > •#- CD C ^ E

co

4-> o? c

QJ 4-> CD Cd

co

I CD O O * — 4-J CD

co e

i * o

cn#— > •»- C ^

CO

CD

4-> CDE

CO Q

CO #— O 00 C\J

O'. 00 co oo co

co co co co in coo^cnco

cn co ro cxj .

OO 00 CO CO N

CO .— CO LO 3

.— 3 C\J ro CO O O* C0 CO LO

ONMino 3 CO LO cO Or

nr-r-LOO

fN in o c\j <\j 3 ro cxj cn co

oo .— oo n N

o o cn co oo

*3 O* i— CNJ LO co rv co co cn

O . r- Oi N o N CO CO CO

LO 3 3 CXI CXI

COMONN o o o cn o i

.— ex cxi ro co cxi co co 3 cn co 3

LO co co o CNJ CXI o oo lo cxi co co

LO «3 «3 LO «3

.— OO CO cxi co i-

.— .— -»-> coo

#— o

3 3

cn oo cn CO ro CO ro fN CO co IN CO CNJ LO 3 oo cn 00 N co LO cn i cn 1 |N rN CO

.— 3 co ro CO CO CNJ LO LO o CNJ 3 O

CO *3

- CXI cn CO CO r— CNJ LO 3 rN CO IN *“

LO CO CO IN cn co ro CNJ fN O 3 CNJ CXJ *3- cn lo LO CO 00 LO cn CO '

CO o

00 co LO CXI #— cn co CO ro O <n

<3- O 3 CO lo cn 3 3 CO CO CO fN 00 IN VO cn 1 cn oo i CO CO o i cn i <n co oo

ro cn *3

- LO LO IN *3 *3 CO IN CO rN oo

*3" LO CO in* 00 LO 3 LO CO co cO cn

r_

LO CO O LO cn co LO O CO co co CNJ r- OOJ ro ro .

IN CO cn 00 oo co oo o cn 3 ro cnj o cn •3 CO CO CXI CXJ

CXJ 3 IN 00 lo cn CO CNJ cn cn oo cn 1 cn oo i oo co l 1 1 i i 1 1

lo cn cnj co .— ro •— oo

cn co cn LO

1 LO INi oo co

l 1 1 i i 1 1

CNJ LO r— rN LO *3 cn ro

ro LO co oo 3 LO O LO ro ro CNJ 3 3 ro CO CXI

OOn- 00 O 3 o #— CXI *3 cn rN o o cn i cn 1 o cn i cn <n i o I O 1 o cn cn

o cxi cn oo ro cn lo CO i— CXJ oo IN LO CNJ CNJ 00 O'- cn CNJ IN CO CXJ cn CO cn LO •— co rN *“ r” •—

cn co 3 3 in 3 in cxj ro CXJ <3 o ro rN IN 00 3 roo 3 00 cnj ro IN oo CNJ CO •

O LO CO 3

3 *3- 3 3 3 lo *3

- co ro LO <3 3 LO 3 3 3 1 ' ' ' ' 1 ‘ 1 ' ' ' 1 ' ' ' '

, t o o O

00 O CNJ cn oo ix <3 CXJ O CO <3 CO CO O CNJ fN CNJ #— ro *3

- 4-> f— CNJ LO fN cn og 4—

CNJ ro *3 co rN , CO 4—

c <

c l C

cn • C Q.

•r- E CO

cn <d o C H- ocn o

00

* o o in co

*

*

Average

of

12

specimens
Table

6.

Effect

of

Aging

on

Wet

Strength

N t O rx

LD fO CO to I c\j co co cnj cnj O CT> f\J ON (T> LD tv | I Osj c\i ro ro ro

CM CM CM CM CM

CO LO OS LO LO O CNJ r— CNJ CNJ o o o o o

CNJ

I I O

O CNJ CNJ CNJ CNJ O O CO CO VO

CNJ CNJ CNJ CNJ CMI O O O O O I I

> Z

c

cnj ^ o so oo os ^ co oo

CNJ CNJ CNJ CNJ CNJ I I I O

N CO Or- CO

so cnj vO 00

•— CNJ CNJ CNJ CNJ I I

4-> Oi O 00 O C^r— C l/Mt^OO«t 00 O

<x> CNJ ^ CO CNI CNJ <3-

i— OS

OS CO VO ^ ^ CNI O O 00 O os OCO^^Oi

cnj cni co co co o i os

CNJ CNJ

LO VO CNJ OS r— CNJ co *3-

CD C£ O CO CNJ CNJ .

OID E co os lo .— co — r— CO CNJ CNJ CNJ WZ o o o o o _x

CNJ CNJ

cnj co o ooo CNJ oo

CNJ r— LO o o o

LO CO VO US N

— LO CNJ CNJ CO o o o o o

O os VO

CNJ CNJ CNJ o o o

E O 00 *— O CNJ os

cn \ os co co co os vo > Z i— CO CO CM r— r— CNJ c u* • •

r— OS O CO CO 00 CO CNJ i—

co cn os O LO 00 VO OS CNJ C"* «— CNJ CNJ CO CO

CNJ CNJ O VO r— r— CNJ CO OO CO

co

4-> CO OO CO I— o c fc-S o-. r— o

<u cnj co LO lo oo

CO os

CO CO

CNJ CO

VO O r- VO VO US US US

OS O 00 ^ os

vo i r>* i os n r— CNJ CO CO co O OS

co i lo

r- CNJ

co vo CO

os os CNJ

CNJ CO ^3’

<u or c

CDu

L.CD Q_

>>

LO

CNJ C

E O co N PS N \ CNJ CO *3- CO CO

oo Z O O O O O -X

CNJ CNJ

r—*— CNJ o o

CNJ r- CNJ CNJ CNJ CNJ CNJ CNJ CNJ CNJ CNJ CNJ CNJ

CO *3- r^

CNJ CNJ CNJ O O O

oo o

o o

CNJ OO oo oo

I o o

o LO

CNJ o

OS VO LO

CO CNJ r— o o o

TDi

E CNJ o us vo LO cn\ co oo CO O N LO CNJ > Z 1— CNJ CO CO f— CNJ <X -* . .

vo LO 00

oo oo co

os ^ O vo

LO LO CNJ N LO

r— I CNJ OO I CO CO

CO r— LO

CNJ O CNJ

CNJ OO CO

<u c

> o

4—> O vo '— vo OS C 6^ CNJ Os i— .— Os

<D CNJ CNJ cf LO ^ 00

cnj r*» CNJ CNJ

VO rv. co ^ co o

^ LO VO

CO VO VO r— i

LO I r— 00 I CO

i— CNJ CNJ CO

CD an

CNJ CNJ .— CNJ OCNJ CNJ CNJ CNJ CNJ CNJ CNJ

E CO N r- vf \ .— CO co CO LO

oo z o o o o o -X

r— CNJ r— CO o o

co lo ^r

CNJ CNJ LO o o o

co cnj co cn Kt

CNJ CNJ CO CO LO O I O O I o o

E LO CNJ oo O vO

CD \ VO CNJ O CO N LO 00 > z ,— CNJ CO CO CO .— r-

<C -* • •

OS CO CNJ Os Os CNJ

cnj co

Kj- CO os *— LO

Vf O VO r—

r— I CNJ CNJ | CO«t

co

4-» 00 LO VO ^ CNJ C ** r- CNJ r- o N

<u cnj co lo lo

LO CNJ *— oo

CNJ CNJ

VO CNJ CO

r— LO O LO U3

vo o cnj

*3- i o to i o lo

CNJ CNJ CO CO

cnj VO I O «— CNJLO VO vo

OS os i CNJ CNJ CNJ

OJ QC

o

CD OS E 4- c

•*- o •*- h- os

•X.

OS • C CL

•r- E

os QJ c —

CNJ CNJ CNJ CNI CNJ CNJ CNJ CNJ CNJ OO CNJ

CNJ CNJ CNJ CNJ CNJ CNJ CNI i— CNJ CNJ CNJ r— Os i f— 1 r— r— »— i— 1 r— | r— » r— r—

*c

' ' * r~“ ' r~~ .— 1 1 • ' * ' '

E O VO CO o CO 00 oo LO vo CNJ VO OS CO ^ o LO CO Os CO

* 'N. CNJ CO co CO o CNJ LD CO <

r— CO CNJ CO CNJ f— CNI us z O o o o o o o O I 1 i o o o O O l O O i o o o o • O I O O o o , -V _x X

(-J

i E co CNJ co OS LO os Os o r^. LO vf LO vo <— nr CO VO LO LO VO 1 c

OS \ VO rv CNJ *3- CO rv. o vo co Os CO oo co OS CNJ LO 00 CNJ cnj CN > z r— CNJ co CO O «— 1 1 1 CNJ CO O CNJ 1 CNJ CO O r— CNJ CNJ O X c

<c -X r-1C

r— ,

O o O o US i— co vo CNJ 00 L. 3 6 9 2 us co o CNJ i- os co CNJ O vO V. VO 00 o cnj CNJ V.

4-> CO *3- 4-> r- CNJ LO r-. Os CNJ 4-> CNJ CO VO r— VO 4-> <v c c *— c *— c II O o o o o

<-> V_) o o US *

II c

* o o o o os 00 o o r-* vo

number

of

specimens
Table

7.

Effect

of

Aging

on

Elmendorf

Tear

Co

CO O'* C\J LO NinOICvJr- co cn cn <

oo n*. lt> ld lt> i i

CD cl

O'* Lf> (\J r— f— O lD to Z I I I I I OOOOOliif

rv O ^ N N 'T

r- O O O O I I

cn lo o o <3- lo > Z II I II LO lo c\j OO .— I I I CO

«=£ N CT> Lf) OT N

LO LO Lf) I I

co

+-> vd rv O' n oo CO c cn lo oo co lo

07

<? m CT) oo i— co o O0 i— 00 00 LO co CO

CO OO r— <0

co i n*. i lo ro

<D cl

LO LO OO OO •— CO LO o </>z ooooo oo lo • •

r~~ CXI •— CO CO OO ooo ooooo o cn lo r— I o i o o o

cn> Z N UD Csj N V£l LOCO

<t r^^-oooo i— lo

OO OO CO OO O

.— O •— lo U) N If) CO OO x co oo

i lo i ^ ro

co

C o3

QJ LO O'* 0"> O LO O'*

-*-> cn co lo co oo co x

a> CL

cn r-. cj- LO CO OO O 00 co lo

i r- i *3

- co lo co oo n-. c\j cn i oo i n lo lo

c

a;u

s-07

Ol. LO U0 OO

cr* co lo co co oo o> ooooo o oLO oo oo O r- o

<t* lo lo co o i o o i o o

co o co co co r— 1 r— I O O O

*oi

3

cn cn co oo lo o ooco > z rs n inco oo c-*. C

Lf C\J LO CO OO

oo O o 00 I VO LO I OO CO

co oo X oo oo

CO I CO I LO LO LO

07> co

C lO CO *3" O'* OO

07 o (Tt CO N N

CO f—

cn cn

lo cr* i—

cn co cn

co an co o i cn cn i go lo

07 07 CL CL

o o o co cn r- r— o o

r- cn

r- O

lo OOO O r— o lo

r~ I O r- I r- O

cn x o ouf) a> vo^r > z co co lo lo lo co co C • •

CO oo

co co oo

lo O o oo

co i con i Mfi

<3- lo cn o co o o co cn cn *— ^ cn co O *3- r-v cn co cn

co

cn

oo o lo o cn <— i o cn i cn o <— cn lo

oo i cn i cn co oo i

* o *

1/7

oo cn cn r- o o *— co

<— O O r- r- O

^ o oo cn cn cn

*— r— «— o o * O r- cn i

o o

00 OOOr-O O I

• f~ '

*

cn io x co lo oo co n cn oo o oo r^^oo co lo co o co > z oo co x rs. x co cor^i i i oo x co cn co i co cn i co x co co i co i co co co cn <

07 cn E <*- c

•r- O

f— cn

<c

LO20

«T5 O

CO LO OO CO i- r- f— 4-> coo

co lo cn cm in co o oo l_

i— .— co coo

<n co n

i- oo o *o l_

I— C\J Lf) X Oi OO 4-* I— c

oo

cn • C CL

•r- E

cn 07 c t—

L_7 O o cn o00

+ * o o r— lo

Average

of

12

specimens
Time

Aging

of

Relative

Humidity,

Percent

Temp.

Aging

vO in C\J «3- 00 +

n: CM *3- 00 <J> 1 i i r*^ rv in cm cm Oi

•

1 r— co «3 in .— CM CM CM

..—

>

CO co r— in CM 08 CO CO CO r— in m o o o O i o o o o o in o.

- r- r*^ O O 00

-—

*

O vo O vo CM CTv (j\ vo in in co cm LO CO CM »— o o*> > Q. C —

*3 <3" ^3- *3

l 1 «3- <3 v3 <3 «3

i—i VO vO co -<3 O r— VO CM ^3 CO *3 CO r— in VO CO

n= VO CO O 00 *3 i 1 1 CM 00 in 00 , , co m i i <3

*

1 CM i _ co o L—l •— CM *3 r*^ c*. r— *3 «t3 vo r— CM CO co CM CM «3

•3CMCOVOO r- O r— CO O .— r— in in n •3- CM o O 3 zn o o o o o O O i • i o O o o o o O O i i O i o 1 o o o in Cl

CM VO CO CM O'* O CM O'* m c- <3-

-—

-

00 r- oo CO o o> 00 CM o ows m n cm • i r— i in «3 CM cm pvin r- Oi O c3 VO • 1 1 i • > CL < — «3 «3 ^ co <3 *3

*3 *3- <3 *3- *3- ^3 «3- *3- in <3- <3- C3 «3

O VO 00 c\j CO vo c- co co

vj I VO I O' in 00

r— co vo vo c\j o o o o o

cm co o l o o

> CL

<3- «3- *3- ^3 *3- ^ o •— <T> vO K3 CO O • • • • • • • • in *3 *3" ^ ^ LD

in i*"* o> r— cm

in r- c\j

VO CM I— CO O . . Ill ... co vo o co incm in c\j o

c\j oo

o o o o o

CM CO CO O co .— r— OO*— OOl I lOOO OlOOlOO I I I I I I

> CL <

Oi Oi if) O VO 1-OOiCON

in n vt S

cvj vo

*3“ ^ ^

co

in

i i i i i i

oovt vrcon co vo vo <— in vo cm o *3 •— r-^ oo c\j •— vt in co

• • iii.... • i • • i . i . i . . . . ^ in in vo ^ (\j cm co in in vo cm in in ^3 vo cm cm kj-^-^-cm

TjOOVOOCOr- O r- o r- O O S p-i-n in co op >— r— co in cm <— cm <— oo OOO O too lOOO O lO lOOOO

o>:r > cl < ^

>»

ro Q

OVO

[H

]

calculated

from

pH

values

and

expressed

in

mi1

1

iequi

val

ents

per

hundred

grams

of

paper.
Table 9. Effect of Aging on Solubility in Hot 1% Alkali

Time

Aging of Relative Humidity, Percent

Temp. Aging

90

80

70

60

0 10 25 50 75

Avg* Avg Avg Avg Avg

% % % % %

1 3.51 3.66 5.14 7.29

3 4.49 4.76 7.04 12.87

6 4.18 5.79 11.68 21.51

12 4.82

4.52'

3.50

7.43 17.88 31.38

18

Control

7.54 21.42 32.69

3 3.92 4.23 5.07 7.46 9.63

6 4.01 4.42 5.96 9.93 15.02

9

- - - - 19.90

12 - - - - 24.17

15 - - - - 27.69

18 4.23 6.56 9.46 20.70 - 30 4.98 9.07 16.06 28.23 - 42

Control

5.14

4.00

8.50 18.05 31.00

4.49

9 4.73 5.28 6.62 8.52

18 - - - 9.25

27 3.97 4.96 7.57 13.85

54 4.80 6.28 9.22 18.40

72

90

126

Control

4.80

4.82

4.17

7.67

9.41

14.98

22.91

26.50

24 3.84 _ 5.16 5.80 6.88

36 - - - - 10.08

48 4.42 - 6.50 7.97 12.84

60 - - - - - 72 4.43 - 7.80 13.50 13.52

117 4.45 - 11.49 15.64

162

Control

4.57

3.30

- 10.18 20.85

* Average of 2 specimens
Table 10. Effect of Aging on Copper Number i

Time

Aging of Relative Humidity, Percent

Temp. Aging

°C Days 0 10 25 50 75

Avg* Avg Avg Avg Avg

Cu No. Cu No. Cu No. Cu No. Cu No.

90 1 .72 .82 1.20 1.63

3 .73 .88 1.32 3.04

6 .85 1.13 2.42 6.06

12 .81 1.44 4.79 10.39

18 .80 1.39 5.99 13.13

Control .61

80 3 .73 .76 .89 1.60 3.19

6 .65 .85 1.18 2.40 4.14

9

- - - - v 5.49

12 - - - - 6.51

15 - - - - 8.58

18 .72 1.00 1.86 5.50 - 30 .73 1.36 3.65 8.44 - 42 .79 1.76 4.72 10.62 - Control .61 0.58

70 9 .70 .71 .81 1.40

18 - - - 2.30

27 .66 .92 1.23 3.37

54 .70 1.00 2.47 5.04

72 - - - 5.82

90 .84 1.31 3.37

126 .79 1.90 4.46

Control .61

60 24 .76 _ .82 1.03 1.39

36 - - - - 2.33

48 .68 - 1.17 1.61 2.95

60 - - - - 2.97

72 .62 - 1.23 3.47 3.60

117 .60 - 1.87 4.28

162 .60 - 2.05 6.15

Control .54

* Average of 2 specimens
Table

11.

Effect

of

Aging

on

Brightness

C b-'S <D

VO O' VO O O' O' VO i— O C\J

oo r— co co O O r— r— i— ^ ^ N

r— O O

>c

O' co O' < O cnj o O'

rs, vd m m ^

to 01 O'

£Z<D

cnj r— co lo

CO I VO i vo cnj O'

lo vo co lo co O •— <— CNJ CNJ

<3- cf o o

NOM

r— CNJ CO

vo lo co o cr* O O O C\J •00 O O' CJ- O r— O O

IT) in CO N

> b^ c

to .— O'* lo

c frS

<

co co oo oo o r-^ i

cr* co co vo vo

CO CO O'* 00 vo

CO LO CNJ CNJ 00

.— CNJ CNJ

LO CO VO CNJ CNJ

• • III ... O r- rVOO

LO VO O O'* CO > S'*

•=c O N I I I CNJ I 00

00

^ ^ f">- cr* lo CNJ O' oo

O' O'* O'* 00 00

CO vo

o' co

co<j in<t n d d d d d

lo ^ d dlo o d oVOoLO o dLO vo d d

O' LO O'* LD O'

CNJ <— CO lo lo COCO fNfN N

CNJ CNJ 00 00CO I CNJ O I O' CO

Or-N^-

oo co • • i lo ^ in

co LO LO d o o o o o

LO

. .Ill ....

o o o o o o

LO «3- o oLO «

o o o

VOo

^ LO 00 o o o o

O'> S-9 c

CNJ O CNJ O CO *3- CO CNJ r- o O' LO

CO CO 00 00 00

00 CNJ LO VO CO CNJ I I I co co

r— •— .— LO

oo co co co

CO CNJ I CNJ o ^ oo co co oo oo

I CO

oo

I co co CO LO

00 CO 00 co

<U O' E c

•r- O rI— CO V£> CNJ CO t- r— r— 4-> coo

CO VO O' CNJ LO 00 O CNJ i_ I— , i CO *-> CTiOOl^^-CNJOvO V- *— CNJ LO O' CNJ 4-> »— coo

cr> . C Cl — E

O' CD C h- o00

Average

of

12

specimens
Table 12. Effect of Aging on Moisture Regain

Aging

Temp.

Time

of

Aging

Relative Humidity,

°c Days 0 10 25 50

Avg* Avg Avg Avg

% % % %

90 1 6.87 7.06 6.81 6.66

3 6.73 6.80 6.62 6.63

6 6.63 6.63 6.18 5.40

12 6.42 6.53 5.39 4.48

18 6.21 6.77 5.50 5.32

Control 7.37

80 3 6.64 6.67 6.47 6.23

6 6.74 6.66 6.27 6.25

9

- - - 6.03

12 - - - - 15 - - - - 18 6.68 6.68 6.48 5.72

30 6.60 6.43 6.07 5.22

42 6.49 6.43 5.74 5.02

Control 7.17

70 9 6.80 6.58 6.58 6.38

18 - - - 6.53

27 6.68 6.29 6.20 5.89

54 6.58 6.55 6.66 5.80

72 - - - 5.40

90 6.88 6.57 5.51 - 126 6.44 6.22 5.79 - Control 7.26

60 24 6.82 _ 6.69 6.52

36 - - - - 48 6.83 - 6.40 6.50

60 - - - - 72 6.66 - 6.55 6.03

117 6.80 - 6.56 6.21

162 6.96 - 6.30 5.87

Control 7.03

Percent

75

Avg

%

6.35

5.86

5.9

6.69

6.74

6.91

6.47

6.16

6.00

Average of 2 specimens
Table 13.

Moisture

Conditions

25% RH

50% RH

1405 N/m 2

14932 N/m2

29330 N/m2

Heats of Activation and Degradation Rates

for Zero Span Tensile at Various Conditions

Heat of Degradation

Activation Rate at 23 °C 50% RH

kcal/mole

29.0

26.5

xlO6

1.7

7.8

*4.6 - 6.8

18.3 49.8

16.3 141.1

Estimated
Table 14. Heats of Activation and Degradation Rates

for Brightness at Various Conditions

Moisture

Conditions

Heat of

Activation

Degradation

Rate at 23 °C

kcal/mole xlO6

25% RH 27.3 2.16

50% RH 25.4 8.06

1405 N/m2 *11.7 - 12.8

14932 N/m2 13.2 136.1

29330 N/m2 13.8 243.9

Estimated
Fig.

1

Change

in

wet

breaking

strength

of

paper

with

time

when

aged

at

60°C

and

various

relative

humidities.

w/N>fl ‘Ml6udJis 6ui>jB8jg

10

o

120

160

200

Aging

Time,

Days
Fig. 2

Change

in

wet

breaking

strength

of

paper

with

time

when

aged

at

70°C

and

various

relative

humidities.

Aaina

Time,

Days
Fig. 3

Change

in

wet

breaking

strength

of

paper

with

time

when

aged

at

80°C

and

various

relative

humidities.

Aging

Time,

Days
Fig.

4

Change

in

wet

breaking

strength

of

paper

with

time

when

aged

at

90°C

and

various

relative

humidities.
Fig.

5A.

Linear

plots

of

zero

span

tensile

strength

of

paper

versus

time

when

aged

at

90°C

and

various

relative

humidities.

co

in

CM

CD

CO

CO

Aging

Time,

Days
Fig.

5B

.

Semilogrithmic

plots

of

zero

span

tensile

strength

of

paper

versus

time

when

aged

at

90°C

and

various

relative

humidities.

GO

in

CM

o>

co

co

ui)| ‘ij)6ue-| 6uj)|eejg

Aging

Time,

Days
Fig.

6A.

Linear

plots

of

Elmendorf

tear

of

paper

versus

time

wnen

agea

at

90°C

and

various

relative

humidities.

\

I

CC

lO

CM

cr>

co

- co

N ‘Mi6uejjs Buueax

Aging

Time,

Days
Oi3

.

Sendlogri

thmic

plots

ol"

Elmendorf

tear

of

paper

ve

time

when

ayed

at

90°C

and

various

relative

humidities.

T>

•Du

_ CN4

00

lO

- o>

- <o

CO

M'(q;6u0ns) 6uuedj_

Aging

Time,

Days
g

sAbq ‘9ui|i 6ui6v/ui)| ‘i|)6ue~| Su^eejg 6o~|

U

<DO.

rcQ. • U)

4-( (D O U

3 G -p

-U ro

O -C

•H 2

4-> 3 >1

-P

rtf H

P 3

cn h o

TJ 3

G

H 1)>

d) H

O' 4-J G 3

rtf <—

.G 0» U P

r- -h2

O'

r-\ U.

Relative

Humidity,

%
.032r

Temp.

Fig.

8.

Change

in

uegraeatior.

rate

of

paper

brightness

wit!',

relative

nun.idity

wnen a

gee

at

various

elevated

temperatures
01 '0 ~U -3 3 O

-r-\ u

'.4 1

O >

Partial

Pressure

H

2

0,

kN/m
Temp.

O

CL

O

L CM

CO

sAbq ‘euiii BujBv/% ‘sseuu|6ug Bon

to •H

4-> U

(0

4-> -P

1

0

c S

•H

U-l <D o

cnC 0)

<tj i-i .c ^

L) in

</) v

. n o a,

CT» H

lu

Partial

Pressure

H

2

0,

kN/m
Temp.

i i 1

i - _J I I i- J ©i/>©io©tf>©®2 »

- • o

CO CO CM CM r- rsAea ‘eui|i BujBv/spioj jo on ‘eouejnpug pioj Boi

Partial

Pressure

H

2

0,

kN/m
,064r

Partial

Pressure H2

0,

kN/m
Cnanye

in

aegrauation

rate

of

paper

breaking

strengtn

wit:,

partial

pressure

of

water

when

aged

at

several

elevateu

temperatures.

sAea‘aui|i 6in6v/ Z iu/N>i ‘M»6u©j»s 6u|>|eajg 6o~|

Partial

Pressure

H

2

0,

kN/m
Temp.

i

•H

U to 0 0 a ^

0 D a 4-» 03

4-4 M o o

(/) 0 V)

cr» 0 cU -Ha

•H

. 4J 3" M

i-t <0a.

o> •H

Cn

04

sAea ‘euju 6u|6v/% ‘>|e9jg o\ uo!»e6uo|g Bon

Partial

Pressure

H

2

0,

kN/m
15.

Change

in

the

rate

of

alkali

solubility

of

paper

with

partial

pressure

of

water

when

aged

at

several

elevated

temperatures.

o

CD

CO

CM

CO

CO

CM

CM

CM

CD

CM

- CO

CO CM TsAbq ‘8UILL 6uj6v/% ‘A»mqn|OS !|B>||V

CM

Partial

Pressure

H

2

0,

kN/m
Temp.

o

o o o o

CO N 00 O)

O <3 O

L

CN

CDuo

Cfl U)

CDUa

c 2

fTJ .c ^

a o

VO

H

U-4

sAbq ‘euiji 6uj6v

/jequinN jeddoo

Partial

Pressure

H

2

0,

kN/m
7.

Change

in

the

rate

of

extractable

acidity

of

paper

with

partial

pressure

of

water

when

aged

at

several

elevated

temperatures.

Partial

Pressure H2

0,

kN/m
Fig.

18.

Change

in

the

rate

of

moisture

regain

of

paper

with

partial

pressure

of

water

when

aged

at

several

elevated

temperatures.

CD

CO

CM

CO

CM

CM

CD

CM

00

II

i

8 -

sAbq ‘auiji 6uj6v/% ‘Uje6dy djn)SjO|/\|

Partial

Pressure

H

2

0,

kN/m
o

O

C

o

4-> U •

4-1 G

G

03 4J

03

CO G

03 03a

j: a

4-> 03

O'* 4-) c

a;

ra

U 03 *3 4-» (0 03>

>i 03 G •—{ J <u O »H

43 03G

jG (D -P >

CP a) C CO

03G 4->

4-> 03

(0 cn

4-» G

03 H

2 CP

03

4-|O GO

O ^4 •H

4-4 G

03 03 G 4-3 03

4-4 >

O

4-4 03 O

CPG 03

03 G

.G G

U COW

4-4 03 O Ga

03

4-3 '—

1

03 03 Oh -H

43

• 03 cp cu

CP •H

Cn

oo

Q.

c o o o o

5

(O N 00 O)

H

O <3 O

i 1 _—i_ ^

CM O

CM

o o o o o o o

iAbq ‘auiji 6u|6v/m6uaJ4s Ajq o) m6udJis IBM |0 oijeu

Partial

Pressure

H

2

0,

kN/m
Moisture

Content

%

1

Fig. 20. A typical water sorption isotherm for paper.
c

<y x

zp

0) a

03a

<4-4 ox w

-p qj Cn-H C -P

(3 *H P T3

-P -H

U) g

D

>,-c p

03 CD>

O -H

-P 4-1 03 X i—

l

4-) (D cn P

G

(U W

p a

-p o

in -Hp

4-1 03 0) >

03

<44 G

O 03 O U

-H o

4-J O

03 X

4-J 03

1—i 03

04 0) Cn

• 03 Cn •Hx

qiBueJis AjQ/i|}Buej)S OM ojjeu
qiBueJis AjQ/q)Buej)S »em oqeu

•rH

Cu,

I

.

22.

Ratio

of

wet

strength

to

dry

strength

of

paper

when

aged

at

70°C

and

various

relative

humidities.
*3

*

c

CD x:Zu

CDa

fda

4-1o

jC co -p cd Cn -h C -P

&) *H P 'V

-P -H

CO ^

P

Td CD> O -H

-P 4-> id £ >H

-p aj Cn p c

CD (0 p a

-p o

CO -Hp

-P id

CD >

s

4-1 C

o (d o u H o

-P O

cd oo X

-p

fd m T3

og (Dcn

• fd

<r> •HX

L

CM

CO

CO

00

CM

CM

(jlBueJis AjQ/mBuajJs 1&M oijbu

L

Aging

Time,

Days
The

ratio

of

wet

strength

to

dry

strength

of

paper

when

ageu

at

90°C

ana

various

relative

humidities.
Fig. 25. Arrhenius plot for the degradation rate of

zero span tensile strength for various

environmental moisture conditions.

o 50% R.H.

& 25% R.H.

0 14932 H/m2 H

2 0

O 5333 N/m 2 H^O

<

O

<

DC

C9

CO

N

.0001
Fig. 26. Arrhenius plot for the degradation rate of paper brightness for various environmental moisture conditions.
N 8S I I 4 A iR£< /. / i) U S. OEPT. OF COMM

BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC A HON OK l< I POR I NO. 78-1443

4. TITLE AND SUHTITLI

2. Gov’t Accession

No.

The effects of Temperature and Moisture on the

Accelerated Aging of Paper

3. Recipient's Accession No.

5. Publication Hate February 28, 1978

6. Performing Organization Lode

7. A UTHOR(S)

E. L. Graminski, E. J. Parks and E. E. Toth

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME ANO ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project /Task /Work Unit No. 3110442

11. Contract /Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP) 13. Type of Report & Period Covered

July 1975-Dec. 1976

14. Sponsoring Agency Ciode National Archives

15. SUPPLEMENTARY NOTES

16. AHS| RAC 1 (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The rate of paper degradation at elevated temperatures appears to be directly

proportional to the partial pressure of atmospheric water up to 50% relative humidity.

This linear relationship continues to exist at higher humidities at 60°C but not at

80°C. It is uncertain at this time whether the water in question is bound to

cellulose or is atmospheric moisture. Additional degradation studies at relative

humidities above 50% must be conducted in order to identify the type of water

affecting the degradation rate. There is also an indication that either an optimum

temperature exists for accelerated aging of paper or that the cellulose-water

interaction at the higher temperatures and lower humidities differs significantly from

that at ambient temperatures.

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; alkali solubility; fiber degradation; paper degradation; paper

permanence; wet strength

18. AVAILABILITY Qc Unlimited

I For Official Distribution. Do Not Release to NTIS

Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C . 20402, SD (.at. No. C U

(X 1 Order From National Technical Information Service (N I IS) Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

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21. NO. OF PAGES

72

22. Price

$ 5-25

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