NBSIR 78-1459

Characterizing the Interfiber

Bonding of Paper Pulps: Effect

of Preparation Pressure on

Tensile Test Specimens.

Jack C. Smith and Edmond L. Graminski

Polymer Science and Standards Division

National Measurement Laboratory

National Bureau of Standards

October 1 5. 1 977

Progress Report Covering the Period

October 1, 1976 through March 31, 1977.

Prepared for U.S. Department of Energy

Washington, D.C. 20234

NBSIR 78-1459

CHARACTERIZING THE INTERFIBER

BONDING OF PAPER PULPS: EFFECT

OF PREPARATION PRESSURE ON

TENSILE TEST SPECIMENS.

Jack C. Smith and Edmond L. Graminski

Polymer Science and Standards Division

National Measurement Laboratory

National Bureau of Standards

October 1 5, 1 977

Progress Report Covering the Period

October 1, 1976 through March 31, 1977

Prepared for U.S. Department of Energy

Washington, D.C. 20234

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, Acting Director

TABLE OF CONTENTS

Page

SUMMARY AND CONCLUSIONS i

INTRODUCTION 1

EXPERIMENTAL 5

ANALYSIS OF THE DATA . 4

RESULTS AND DISCUSSION 9

REFERENCES 14
... .
1

SUMMARY AND CONCLUSIONS

Handsheets In the form of low-density open webs of

2

grammage 2.5 g/m were prepared from Northern and Southern

softwood kraft pulps, unbeaten and beaten for 5000 revolutions

in a PFI laboratory beater. These webs were formed on filter

paper and pressed for five minutes against a ferrotype backing

p plate. Webs were prepared at pressures of 44 kPa (6.4 lb/in ),

550 kPa (51.2 lb/in2

) and 660 kPa (96 lb/in2

).

Specimens selected from these handsheets were tested to

the breaking point in a tensile tester. The resulting forceelongation curves were analyzed to obtain a characteristic

energy interpreted as the average energy lost per interfiber bond break by fibers in the vicinity of the break. The

average initial percent elongation per bond break was also

determined for each handsheet. These two parameters are used

to characterize the relative strength of the interfiber bonds

in the web. The objective of this work was to determine if

values of the parameters obgained were dependent on the pressure

used in the preparation of the webs.

Handsheets formed from the beaten pulps were coherent

and well bonded. It was found that for the beaten Northern

pulp webs, the value of E-^ and the initial elongation per

break obtained were independent of the pressure used during

preparation. The corresponding values of these parameters for

beaten Southern pulp webs were also independent of preparation

pressure. However there was evidnece that the Southern pulp

web prepared at 660 kPa pressure was of slightly inferior

quality. It may have been damaged when it was peeled from the

ferrotype backing plate after pressing.

The handsheets formed from the unbeaten Northern and

Southern pulps were weak and flimsy. Values of the parameters

obtained for the Northern pulp webs were not dependent on

preparation pressure. Values of E

1

for the unbeaten Southern
ii

pulp webs were not dependent on pressure, but values of

initial elongation per break for the webs prepared at 330 kPa

and 660 kPa were excessively large, indicating that these

webs had a very loose structure. Presumably these webs,

possessing intrinsically weak bonding, were easily damaged

by removal from the ferrotype backing plate.

In general it seems that the quality of bonding between

fibers in these handsheets is not affected by preparation

pressure between 44 kPa and 660 kPa. However webs which are

weakly bonded intrinsically may stick to the backing plate

at preparation pressures of the order of 350 kPa and may be

damaged upon subsequent removal.
1

INTRODUCTION

If a specimen from a handsheet of pulp fibers formed into

a low-density open web is elongated to break in a sensitive

tensile tester, a force-elongation curve containing numerous

jags is obtained. Each jag is caused by the breakage of a bond

between fibers constituting the handsheet network. Data for a

curve of work of extension versus number of bond breaks can be

obtained by integrating under the force-elongation curve and

counting the discontinuities in slope caused by the bond breaks.

A characteristic energy E, interpreted as the average stored

energy lost per break by fibers in the vicinity of the broken

bond, can be determined from this curve. This energy is used as

a measure of the bond adhesion between two fibers.

From the force-elongation data a curve of percent elongation of the specimen versus number of bond breaks can also

be plotted. The initial slope of this curve, or initial

percent elongation of the specimen per break, is a measure

of the tightness of the web structure, or density of bonds

per unit area of web.

Relative bond adhesion and web tightness have been

measured on handsheet webs prepared from Northern and Southern

softwood kraft pulps, unbeaten and subjected to various

amounts of beating. Details of this work have been given in

the two previous reports [l,2].

In the previous work experiments were carried out on

webs prepared by two different methods. In the first method

cotton linters pulpsheet was used as a forming medium, and

the web was pressed against a ferrotype plate at 660 kPa

(96 lb/in ) for 5 minutes. In the second method filter paper

was used as a forming medium, and the web was pressed against

O

a ferrotype plate at 44 kPa (6.4 lb/in ) for 5 minutes.

Handsheets were easier to prepare by the second method,

and appeared to be well bonded and uniform in texture. However
2

the curves of work of extension versus number of bond breaks

obtained by tests on these handsheets had a scalloped appearance with many changes in slope. As a rule the minimum slopes

that occurred extended over only a few bond breaks so the

values of these slopes were uncertain. It was not possible to

obtain a good estimate of E by averaging these minimum slope

values. This difficulty was not so prevalent in the webs formed

at higher pressures by the first method.

It is important to know if forming pressures affect the

test results so that a procedure for preparing standard handsheets can be established. A low forming pressure would be

desirable in order that the web can be peeled easily from the

forming medium and the ferrotype backing plate. This report

therefore gives the results of tests on webs formed at several

different pressures.
3

EXPERIMENTAL

p Handsheets of 2.5 g/m mass per unit area were prepared

from Northern and Southern softwood kraft pulps used previously

[1,2]. The pulps were unbeaten and beaten for 5000 revolutions

in a PFI laboratory beater. The method of preparation was the

same as that reported previously. Filter paper was used as the

forming medium. Pressing in a hydraulic press was carried out

at room temperature for five minutes.

The following handsheets- were prepared from unbeaten

pulps

1. Northern pulp, pressed at 350 kPa (51*2 lb/in2

) p 2. Northern pulp, pressed at 660 kPa (96 lb/in ) 2

3 . Southern pulp, pressed at 350 kPa (51*2 lb/in ) p

4. Southern pulp, pressed at 660 kPa (96 lb/in )

.

The following handsheets were prepared from pulp beaten

for 5000 revolutions:

p

5 . Northern pulp, pressed at 44 kPa (6.4 lb/in ) p 6. Northern pulp, pressed at 350 kPa (51.2 lb/in ) p

7. Northern pulp, pressed at 660 kPa (96 lb/in ) 8. Southern pulp, pressed at 44 kPa (6.4 lb/in2

) 9 . Southern pulp, pressed at 350 kPa (51*2 lb/in2

) p

10.

Southern pulp, pressed at 660 kPa (96 lb/in )

.

The procedure for preparing, mounting and testing of the

specimens from the handsheets was unchanged. Specimen dimensions

were 1 cm width by 2 cm length. The specimens were tested at

a crosshead speed of 0.2 cm/min and a chart speed of 20 cm/min.

Load cell sensitivities ranged between 0.02 N (2 g) full scale

for handsheets of unbeaten pulp and 0.2 N (20 g) full scale

for handsheets of beaten pulp.
4

ANALYSIS OP THE DATA

Figure 1 provides an illustrative example of the forceelongation curve obtained by testing one of the web specimens,

in this instance specimen number 12 from the handsheet of beaten

Southern pulp pressed at 44 kPa. Figure 2 is the corresponding

plot of work of elongation versus number of bond breaks, and

figure 3 the plot of percent elongation versus number of

bond breaks.

According to the argument used in a previous report [l],

energy is stored in the web during the elongation process, and

some of the store of energy is dissipated when a bond between

fibers breaks. In order to estimate the average energy dissipated per bond break it is necessary to make some assumptions

about the relationship between the force sustained by a network

and the energy stored in it.

There is a functional relationship between the stored

energy and the force sustained by the web. In an extension

process in which none of the interfiber bonds are broken this

relationship could be found by integrating under the forceelongation curve to obtain data on work of extension versus

force. During the extension, part of the work done would be

dissipated by the friction involved in aligning fiber segments,

but if the extension were removed and the web specimen then

re-extended, the frictional dissipation would not recur and

the work of extension would all be stored as energy in the

network.

The analysis to follow is based on the assumption that

the force resisting extension of a web is sustained by only

a small fraction of the fiber segments between bonds. It follows

from this assumption that in many instances the force-energy

relationship can be regarded as unchanged by a bond break.

To see this consider a typical web in which the fiber segments

between bonds have all possible orientations. It seems reasonable to assume that when the web is extended most of the
5

resisting force will be borne by those relatively few fiber

segments that are straightest and best aligned in the direction

of extension. There is a redundancy of unloaded fiber segments.

Most of these segments bear little or no load, because they are

unaligned, or because most of the load is borne by adjacent

fibers with shorter straighter segments between bonds. When a

bond breaks leaving a small or moderate-size hole in the network other fibers in the vicinity of the break assume the load

relinquished by the broken bond. Thus the web can be expected

to behave as though the force overall were sustained by the

same number of load bearing elements before and after the break.

The force-energy relationship therefore should be the same

except for very small changes due to improved alignment of the

load bearing segments.

If the web structure has changed significantly as the

result of many bond breaks, or has incurred significant damage

such that portions of the web are torn away and can no longer

store energy, the force-energy relationship applying in this

case will differ from the relationship applying in an earlier

stage of the extension. However if the load bearing portions

of the changed web still retain a large fraction of unoriented

unstressed segments between bonds, the force-energy relationship

should still remain essentially the same over a subsequent

series of bond breaks that result in small or moderate-size

holes. It follows from these assumptions that, if in a series

of breaks the forces after break drop to approximately the

same level, the total energy stored in the web just after each

of two successive breaks is the same, and the energy dissipated

during the second break is equal to the increment of energy

stored during the transition between the two breaks.

Figure 2 is a plot of cumulative work of extension versus

number of bond breaks. The slope of this plot between successive

breaks thus is equal to the work of extension per bond break.

In many instances when a bond breaks the force after break is
6

greater than the force after the previous break. In such a case

the slope of the plot, figure 2, has a high value, because only

part of the work done is dissipated during the second break,

the rest is stored as strain energy in the network. When in a

series of two or more breaks the forces after break return to

approximately the same level, the work done per break is equal

to the energy dissipated per break. In these cases the slopes

of the plot, figure 2, have a lower value. These slopes have

been indicated by the short line segments drawn in the figure.

Slopes of lower value however can also occur when the force

after a break is less than that after a previous break. If

such is the case, as determined from the original data of

figure 1, it is necessary to exclude these slopes from consideration.

The average energy dissipated per break, E, is estimated

as the average slope of the line segments such as those sketched

in figure 2. This graphical procedure is the one that was used

to analyze data of the previous two reports. Results given in

the first report [l] were obtained from tests on handsheets

prepared by the first method using cotton linters pulpsheet

as a forming medium and pressing at 660 kPa. Curves of work of

extension versus number of breaks had relatively few regions of

low slope but of much longer duration, so that fairly reliable

estimates of E could be made. Results given in the second

report [2] were obtained from tests on handsheets prepared by

the second method using a filter paper forming medium and

pressing at 44 kPa. Curves of work of extension versus number

of breaks were similar to figure 2, and estimates of E obtained

from these curves were less reliable than those of the first

report

.

Obtaining values of E by the graphical method just described

is a tedious and highly subjective process. Although some of

the results reported here were obtained in this way, most of

the results were computed directly by another method which is
(

more objective and avoids curve plotting. These computed values

of average energy dissipation per break are designated by the

symbol E^.

In the force-elongation curve, figure 1, drops in force

resulting from bond breaks are distributed through a wide range

of values. The small drops presumably represent breaks in which

the network is left essentially intact; i.e., other fibers in

the vicinity assume the load relinquished by the fibers involved

in the break. Large drops presumably represent breaks in which

the network incurs significant damage. such as a large hole or

torn portions. By considering only those force drops equal to

or less than an arbitrary value D, attention can be focussed on

those breaks resulting in damage sufficiently slight that the

same force-energy relationship applies before and after the break.

Figure 4 depicts two "jags" in a force-elongation curve

that are suitable for calculating the energy parameter E^ • In

the two diagrams point 0 designates the force and elongation

values prevailing just after a bond break. As the specimen is

elongated the force increases up to its value at point 1, where

the next break occurs and the force drops to point 2. (Elongation

ep is greater than elongation e^ because the specimen is being

elongated at a constant rate and the drop in force occurs over a

finite time). Elongation e^ is the elongation attained during

the extension, at which a force equal to the force after break

Fp is attained. Presumably the energy stored in the network at

elongation e^ .is the same as the energy remaining in the network after the break at elongation e^* The quantity D shown in

the figure represents the maximum force drop used in the calculation of energy dissipation.

Only selected regions of the force-elongation curve are

used in the calculations. Situations in which the force drop

Fl - F2 exceeds D or situations in which the force after

break is less than a certain minimum value H are excluded

because of the possibility that the network may have been

excessively damaged. Situations in which the force drop
b

- f is less than 0.1D or in which the force rise F

1

- F

Q

is less than 0.2D are also excluded. These cases in which

the change in force is not well defined represent situations

in which the processes occurring in the network are not well

understood. Thus only the two situations depicted in figure 4

are used in the calculation. In situation a the energy

dissipation is taken as the area under the force-elongation

curve between points 0 and 2, and in situation b as the area

between points 3 and 2. The energy dissipations calculated

in this way from a given force-elongation curve are averaged

to obtain the value of A computer program was devised

to perform these calculations.

The curve of percent elongation versus number of breaks,

figure shows that the initial portion is essentially

linear over a large range, except for the first five points.

This behavior was true in general for the specimens of handsheets prepared from the beaten pulps. Some of the results

reported here were obtained graphically from plots similar

to the one shown in figure but in order to eliminate the

necessity for these plots, a computer program was devised

that provided a least squares fit to those elongation points

ranging between a minimum break (MINBK) and a maximum break

(MAXBK) . The value of MINBK was usually 5. The value of MAXBK

was usually 50 , but could be less depending on the total

number of bond breaks incurred by the specimen in tearing

completely apart.
9

RESULTS AND DISCUSSION

Specimens of handsheets formed from beaten Northern pulp

pressed at 44 kPa and at 350 kPa were tested. The data were

analyzed graphically, and the results are given in tables

1 and 2. Values of average energy dissipation per break E

and initial percent elongation per break for the two handsheet samples are the same, indicating that these mechanical

properties were not affected by forming pressure. Results of

similar tests on beaten Southern pulp handsheets are given

in tables 3 and 4. Again the values of E and of initial

percent elongation per break for these samples are the same,

indicating that these mechanical properties do not depend

on forming pressure.

Tables 5* 6 and 7 present the results of tests on handsheets of beaten Northern pulp pressed at 44 kPa, 350 kPa

and 660 kPa respectively. The tests listed in table 5 are

the same as those in table 1, but the values of E^ and of

the initial elongation per break were obtained by a computer

program. Similarly the tests of table 6 are the same as those

of table 2.

In tables 5> 0 and 7 the value of E

1 given for each

specimen is the average of the energy dissipations calculated

for each of a number of situations such as those depicted

in figure 4. The number used in each average is given in the

column headed "Number of breaks" . For instance in table 5

E^ for specimen number 1 is the average of dissipations

calculated from 18 situations. The average of the E-^ 1 s given

in each table is the unweighted average of the E-^ values

tabulated for the different specimens. The standard deviation

is calculated from the deviations of the specimen E-^s from

this average. This particular method of averaging is thus

the same as that used to calculate the average E's given in

tables 1 and 2. Computer analysis values of the average energy

dissipation per break and the initial percent elongation per
10

break for the beaten Northern pulp handsheets of tables 5,

6 and 7 appear to be independent of forming pressure.

The results of all the tests on beaten Northern pulp

handsheets are summarized in table 11. For completeness this

summary table includes results reported previously [2] for a

beaten Northern pulp handsheet pressed at 44 kPa. The value

of E (obtained graphically) by measurements on this different

handsheet has a somewhat lower value than the value given in

table 1. Sample to sample variation may account for some of

this discrepancy but most of it should be attributed to

subjectivity of the graphical measurement process.

Tables 8, 9 and 10 present results of tests on handsheets

of beaten Southern pulp pressed at 44 kPa, 950 kPa and 660 kPa

respectively. The values of E

1

and initial percent elongation

per break given were obtained by a computer program. The tests

in table 8 are the same as those in table 5, ant the tests of

table 9 are the same as those of table 4.

Computer analysis of tests on beaten Southern pulp handsheets pressed at 44 kPa and 550 kPa (tables 8, 9) gives values

of E-^ and Initial elongation per break which are independent

of the forming pressure, as does the graphical analysis of tests

on these handsheets (tables 5> 4). The average values of E-^ and initial elongation per break for the handsheet pressed at

660 kPa (table 10) are both higher than the values obtained

for the handsheets formed at the lower pressures, but the

standard deviations are also larger. The higher forming pressure

probably has not directly affected the E-^ and elongation values,

but has affected the uniformity and consistency of the test

results. The higher more erratic value (0.217 ± 0.044 $/break)

for the initial elongation per break suggests that some of the

test specimens had a looser network texture in which some of

the fiber crossings were not bonded. This may be attributed to

damage incurred by the handsheet when it was separated from

the ferrotype backing plate after pressing. The results on
11

beaten Southern pulp handsheets are summarized in table 12.

For completeness table 12 also includes results reported

previously [2] on a different beaten Southern pulp handsheet

pressed at 44 kPa.

In table 11 listing results for the beaten Northern pulp

handsheets the average values of energy dissipation per break

E (tables 1, 2) obtained by graphical analysis are close to the

values of E

1

obtained by computer analysis. This correspondence

in value must be regarded as somewhat fortuitous, as the E^

value obtained depends on the parameters D and H chosen for the

computer calculation. This same correspondence of E and E

1

values

is also noted in the results for beaten Southern pulp handsheets

(table 12), and must also be regarded as somewhat fortuitous.

The results listed in tables 11 and 12 also confirm results

reported previously. The initial elongation per break for the

beaten Southern pulp handsheets is larger than that for the

beaten Northern pulp handsheets. This is interpreted to mean

that the beaten Southern pulp web has a looser more open texture.

This interpretation seems reasonable because it is known that

the Southern pulp fibers are coarser than the fibers of Northern

pulp. Thus although the beaten Northern and Southern pulp

handsheets have the same mass per unit area, the Southern

pulp web comprises fewer fibers per unit area.

According to the results of tables 11 and 12 the average

energy dissipation per break is the same for the beaten Northern

and Southern pulp handsheets. This equality of E or E^ values,

which has been reported previously, does not necessarily mean

that the strength oF bonding between the Northern pulp fibers

is the same as that between the Southern pulp fibers. The

values obtained for E or may depend upon the mesh size

of the network, and in this instance the Southern pulp network,

as noted above, has the larger mesh size. The effect of mesh

size is not known at present, but it is planned to investigate

it in some future work.
12

Handsheets formed from unbeaten pulps were weak and flimsy,

especially those formed from the unbeaten Southern pulp. As an

example figure 5 is the force-elongation curve obtained in the

test of specimen number 11 from the handsheet of unbeaten

Southern pulp pressed at 660 kPa. Throughout the course of the

elongation the force never exceeds a value of 2.0 mN (0.2 g),

and the specimen is torn completely apart after approximately

25 bond breaks. The breaking of this specimen is also characterized by relatively large elongations between breaks, as compared

to the elongations per break observed when specimens from beaten

pulp handsheets are tested. Force-elongation curves that resulted

from tests on each of the unbeaten pulp handsheets were similar

to figure 5*

Inasmuch as many specimens obtained from the unbeaten pulp

handsheets had a very loose texture it would seem that the force

sustained by the network was channeled through relatively few

effective bonds. Thus the assumption that the force-energy

relationship remains the same over a series of breaks might not

be valid on this account. However in figure 5 it should be noted

that the slopes of this curve in the intervals between breaks

are all approximately the same. Similar behavior was noted in

the force-elongation curves for the other specimens. This implies

that the force-energy relationship does remain constant, so that

a value of can be calculated. The calculated values of E^,

and of the initial elongation per break, that were obtained

however were not very consistent or reliable, but are presented

here notwithstanding, as they provide some useful information.

Results from tests on unbeaten Northern pulp handsheets

are presented in tables 15 and 14. These results were obtained

by a computer analysis of the force-elongation curves. Average

values of E-^ and the initial elongation per break for the two

handsheets, one pressed at 550 kPa and the other at 660 kPa,

are approximately the same, but the standard deviations particularly for the initial elongation per break values are large.
13

A summary of results is given in table 1J, where data on a

handsheet pressed at 44 kPa from a previous report [2]

(analyzed graphically) is also included. The summarized results

do not indicate that there is any systematic effect of forming

pressure on the values of (or E) and the elongation per

break for these handsheets of unbeaten Northern pulp.

Computer analyzed data from tests on unbeaten Southern

pulp handsheets are presented in tables 15 and 16 and summary

table 18. The summary table includes previously reported [2]

results (obtained graphically) for a handsheet pressed at 44 kPa.

According to these results the handsheets pressed at 330 kPa

and 660 kPa are of inferior quality. The initial elongation

values obtained for these handsheets are excessively large

and have very large specimen-to specimen variation, suggesting

a very loose and flimsy network structure. When these handsheets

were prepared, it was difficult to separate them from the

ferrotype backing plate, and it is probable that they were

damaged in the process.
REFERENCES

1. J.C. Smith and E.L. Graminski, Characterizing the

Interfiber Bond Strengths of Paper Pulps in Terms of a

Breaking Energy, Progress report covering the period

January 1, 1976 to June 30, 1976, NBSIR 76 - 1148.

Available from National Technical Information Service

PB 264,689.

2. J.C. Smith and E.L. Graminski, Characterizing the

Interfiber Bond Strength of Paper Pulps in Terms of a

Breaking Energy, Progress report covering the period

July 1, 1976 through September 30, 1976, NBSIR 77 - 1286.

Available from National Technical Information Service

PB 276,473.
15

Table 1.

Graphical Analysis of Tests on

Beaten Northern Pulp Handsheets Pressed at 44 kPa

Specimen E Init. elong.

per break

10

-7 J/break $/break

1 4.52 0.128

2 6.48 0.145

5 4.10 0.124

6 5.17 0.127

7 4.80 0.186

Average ± standard deviation

E (4.97 ± 0. 94) xlO -7 J/break

Initial elongation per break 0.142 ± 0.026 $/break

Table 2.

Graphical Analysis of Tests on

Beaten Northern Pulp Handsheets Pressed at 550 kPa

Specimen E Init. elong.

10

" 7 .J/break

per break

$/break

1 5.20 0.144

2 4.88 0.150

5 5.00 0.157

4 4.60 0.144

7 5.00 0.126

Average ± standard deviation

E (4.94 ± 0.22)xl0

~ 7 j/break

Initial elongation per break O.I56 ± 0.008 $/break
16

Table 3*

Graphical Analysis of Tests on

Beaten Southern Pulp Handsheets Pressed at 44 kPa

Specimen

2

3

4

7

12

E Init. elong

per break

j/break ^/break

4.50 0.200

4.80 0.192

5.36 0.190

5.30 0.184

5.00 0.155

Average ± standard deviation

E (4.99 ± 0.96)x10

' 7 j/break

Initial elongation per break 0.184 ± 0.017 $/break

Table 4.

Graphical Analysis of Tests on

Beaten Southern Pulp Handsheets Pressed at 550 kPa

Specimen

10 7 j/break

Init. elong.

per break

$/break

2

4

5

6

11

5.60 0.198

5.40 0.174

4.76 0.162

5.10 O.I85

5.60 0.180

Average ± standard deviation

E (5.29 ± 0

.

36 ) xlO

~ 7 J/break

Initial elongation per break 0.180 ± 0.013 $/break
17

Table 5»

Computer Analysis of Tests on

Beaten Northern Pulp Handsheets Pressed at 44 kPa

Specimen E

1 ± std. dev. Number of Init. elong

breaks per break

10" j/break $/break

1 508 ± 2.87 18 0.125

2 5.41 ± 2.08 21 0.144

5 6.64 ± 4.18 20 0.154

6 4.76 ± 2.47 18 0.141

7 5.15 ± 0.82 15 0.195

Average ± standard deviation

Ei (5.10 ± 1 . 29 )xl0

"' j/break

Initial elongation per break 0.147 ± 0.028 $/break

Table 6 • Computer Analysis of Tests on

Beaten Northern Pulp Handsheets Pressed at 550 kPa

Specimen ± std. dev. Number of Init. elong

10

7 J/break

breaks per break

^/break

1 5.11 ± 2.50 27 0.155

2 6.55 ± 507 28 0.158

5 4.28 ± 2.12 42 0.125

4 6.08 ± 2.95 25 0.141

7 4.91 ± 2.06 21 0.127

Average ± standard deviation

E

1 (509 ± 0.92) x10' 7 j/break

Initial elongation per break 0.155 ± 0.007 %/break
18

Table 7»

Computer Analysis of Tests on

Beaten Northern Pulp Handsheets Pressed at 660 kPa

Specimen E

1 ± std. dev. Number of Init. elong.

breaks per break

lO' 7 j/break $/break

1

2

3

4

5

5.22 ± 2.58

4.95 ± 2.28

5.39 ± 2.72

4.99 ± 1*96

5.20 ± 2.46

23

14

25

32

24

0.149

0.151

0.159

0.140

0.119

Average ± standard deviation

( 5 • 15 ± 0.l8)xl0~^ J/break

Initial elongation per break 0.144 ± 0.016 $/break

Supplementary Information - Tables 5* 6 , J.

For computation of E^:

Maximum force drop D O. 98 I mN (0.1 g)

Minimum force H 9*81 mN (1.0 g)

Average is unweighted average of E^ values

for each specimen.

Initial elongation per break:

Values of initial elongation per break were obtained

by a least squares fit of data points ranging from a

minimum break (MINBK) of 5 through a maximum break

(MAXBK) of 50.
19

Table 8.

Computer Analysis of Tests on

Beaten Southern Pulp Handsheets Pressed at 44 kPa

Specimen E-, ± std. dev. Number of Init. elong.

breaks per break

10 "

' j/break $/break

2 4.66 ± 2.08 20 0.188

3 4.41 ± 1.49 52 0.172

4 4.99 ± 2.17 22 0.181

7 4.64 ± O .96 11 0.186

12 4.32 ± 1.94 37 0.151

Average ± standard deviation < E

i (4.60 ± 0.26) x10~^ j/break

Initial elongation per break 0.176 ± 0.015 $/break

Table 9 • Computer Analysis of Tests on

Beaten Southern Pulp Handsheets Pressed at 350 kPa

Specimen E

1 ± std. dev. Number of Init. elong.

breaks per break

10”^ J/break $/break

2 4.81 ± 2.21 22 0.208

^

4 4.87 ± 1.95 22 0.179

5 3.65 ± 1.07 • 11 0.149

6 4.65 ± 1.51 21 0.222

11 4.30 ± 1.86 36 0.179

^

Average ± standard deviation

E

x (4.46 ± 0 . 50 )xl0" 7 j/break

Initial elongation per break 0.187 ± 0.028 ^/break

I
20

Table 10.

Computer Analysis of Tests on

Beaten Southern Pulp Handsheets Pressed at 660 kPa

Specimen E

1 ± std. dev.

10-7 j/break

Number of

breaks

Init. elong.

per break

$/break

1 5.71 ± 2.35 20 O .185

2 5.04 ± 1.89 31 0.252

3 7.07 ± 2.44 26 0.179

4 4.57 ± 1.95 13 0.196

5 4.84 ± 2.04 17 0.276

Average ± standard deviation

(5*45 ± 1 . 00 )xl0”7 j/break

Initial elongation per break 0.217 ± 0.044 $/break

Supplementary Information - Tables 8 , 9 > 10

.

For computation of E^s'

Maximum force drop D O .981 mN (0.1 g)

Minimum force H 9*81 mN (1.0 g)

Average is unweighted average of E

1

values

for each specimen.

Initial elongation per break:

Values of initial elongation per break were obtained

by a least squares fit of data points ranging from a minimum break (MINBK) of 5 through a maximum break

(MAXBK) of 50, except where noted.

1. MINBK 10, MAXBK 100

2. MINBK 5, MAXBK 100
21

Table 11.

' Summary of Results for Beaten Northern Pulp Handsheets

Identification Forming E or E

i Init. elong.

pressure ± std. dev. per break

kPa 10

~

{ j/break $/break

Graph i/ 3.36 + 0.79 0.133 ± 0.022

Table 1 (graph) 44 4.97 + 0.94 0.142 ± 0.026

Table 2 (graph) 350 4.94 ± 0.22 O.I36 ± 0.008

Table 5 (comp .

)

44 5.10 + 1.29 0.147 ± 0.028

Table 6 (comp.

)

350 5.39 + 0.92 0.133 ±. 0.007

Table 7 (comp .

)

660 5.15 + 0.18 0.144 ± 0.016

Table 12.

Summary of Results for Beaten Southern Pulp Handsheets

Identification Forming E or E

i

Init

.

elong.

pressure ± std. dev

.

per break

kPa 10

"

j/break $/break

Graph 1/ 44 4.09 + 0.53 0.160 ± 0.023

Table 3 (graph) 44 . ^.99 + O .36 0.184 ± 0.017

Table 4 (graph) 350 5.29 ± O .36 0.180 ± 0.013

Table 8 (comp.) 44 4.60 + 0.26 0.176 ± 0.015

Table 9 (comp.) 350 4.46 + 0.50 0.187 ± 0.028

Table 10 (comp.) 660 5-^5 + 1.00 0.217 ± 0.044

1. From previous report [2].
Table 13

.

Tests on Unbeaten Northern Pulp Handsheets Pressed at 350 kPa

Specimen E

i

Number of Init. elong . MINBK,

± std. dev.

IQ

' 7 j/break

breaks per break

$/break

MAXBK

3 0.94 ± 0.46 15 0.331 10,40

5 1.13 ± 0.46 26 0.194 5,50

7 1.08 ± 0.45 25 0.162 5,40

8 0.92 ± 0.30 19 0.149 5,50

10

Average

Ei

1.13 ± 0.44 12

± standard deviation

(1.04 ± 0.10)xl0

‘ 7 J/break

0.213 5,50

Initial elongation per break 0 .210 ± 0.072 $/break

Table 14.

Tests on Unbeaten Northern Pulp Handsheets Pressed at 660

Specimen E

i

Number of Init. elong. MINBK,

breaks per break MAXBK

10 7 J/break $/break

2 0.88 ± 0.43 9 0.245 5,35

3 0.82 ± 0.19 8 O.I65 5,35

4 0.56 ± 0.23 13 0.145 5,35

8 0.99 ± 0.57 10 0.207 5,35

11 O .96 ± 0.43 15 0.180 5,35

Average ± standard deviation

(0.84 ± 0 . 17 )xl0‘ 7 j/break

Initial elongation per break 0.188 ± O.O39 $/break
2 ^

Table 15.

Tests on Unbeaten Southern Pulp Handsheets Pressed at 350 kPa

Specimen E^ Number of

± std. dev. breaks

10-7 j/ti reak;

Init. elong.

per break

//break

MINBK

MAXBK

4 1.29 ± 0.47

^_ / 13 0.873 5,15

6 1.30 ± O.58 y 13 O.836 5,15

11 1.36 ± 0.70 9 1.811 0

1

—

1

1

—

1

14 2.01 ± O.56 11 1.171 1,15

15 1.20 ± 0.54 9 2.019 0

1

—

1

1

—

1

Average ± standard deviation

E

1 (1.43 ± 0.33)xl0" 7 j/break

Initial elongation per break 1.342 ± 0.544 //break

Table 16.

Tests on Unbeaten Southern Pulp Handsheets Pressed at 660

Specimen E

i Number of Init. elong. MINBK,

± std. dev.

10"7 j/break

breaks per break

//break

MAXBK

3 1.89 ± 0.83 15 1.500 1,15

6 1.37 ± 0.43 8 2.157 1,10

10 0.77 ± 0.41 10 1.172 0

1

—

1

1

—

1

11 1.20 ± 0.87 13 1.003 1,15

19 1.83 ± 1.14 13 2.219 1,15

Average ± standard deviation

E

1 (1.41 ± 0.47)xl0" 7 J/break

Initial elongation per break 1.610 ± O.557 //break

Mi
24

Supplementary Information - Tables 13, 14, 15, 16.

For computation of E^s

Maximum force drop D 0.196 mN (0.02 g)

Minimum force H (Tables 13, 14) O. 98 I mN (0.1 g)

Average E^ is the unweighted average of values

for each specimen.

Initial elongation per break:

Values of initial elongation per break were

obtained by a least squares fit of data points ranging

from a minimum break (MINBK) through a maximum break

(maxbk)

,

(Tables 15, 16)

1 .

0.0 mN except for

0.592 mN (0.04 g)
25

Table 17.

Summary of Results for Unbeaten Northern Pulp Handsheets

Identification Forming

pressure

kPa

E or E

1

± std. dev.

10-7 j/break

Init. elong.

per break

$/break

(graph)

^

44 0.76 ± 0.10 0.164 ± 0.039

Table 13 (comp.) 350 1.04 ± 0.10 0.210 ± 0.072

Table 14 (comp.) 660 0.84 ± 0.17 0.188 ± 0.039

Table 18.

Summary of Results for Unbeaten Southern Pulp Handsheets

Identification Forming

pressure

kPa

E or E-^

± std. dev.

10"7 j/break

Init. elong.

per break

$/break

(graph) 44 0.88 ± 0.31 0.520 ± 0.240

Table 15 (comp.) 350 1.43 ± O .33 1.342 ± 0.544

Table 16 (comp.) 660 1.41 ± 0.47 1.610 ± O .557

1. From previous report [2].

i
CHART

TRAVEL

,

cm

Figure

1.

Tracing

of

force-elongation

curve

for

specimen

12

of

the

beaten
WORK

DONE*

Figure 2. Plot of work of extension versus number of bond

breaks for specimen 12 of the beaten Southern

pulp handsheet pressed at 44 kPa.
ELONGATION

,

Figure Plot of elongation versus number of bond breaks

for specimen 12 of the beaten Southern pulp

handsheet pressed at 44 kPa.
d ‘30HOd

Figure

4.

Situations

encountered

in

calculation

of

energy

dissipation.

a.

Force

rise

F-^

- Fq

is

less

than

force

drop

parameter

D.

b.

Force

rise

F,

- F

n

exceeds

D.
ai

NW 1 30d0d

Figure

5*

Tracing

of

force-elongation

curve

for

specimen

11

of

the

unbeaten

Southern

pulp

handsheet

pressed

at

660

kPa.
MBS-114A IHCV 7 731

U.S. DEPT OF COMM. |. PUBLICATION OR RF.POR1 NO. 2. Gov’t Accession

BIBLIOGRAPHIC DATA

NBSIR 78-1459

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

CHARACTERIZING THE INTERFIBER BONDING OF PAPER PULPS:

EFFECT OF PREPARATION PRESSURE ON TENSILE TEST SPECIMENS

5. Publication Date October 15, 1977

6. Performing Organization Code

7. auihor(S)

Jack c Smith & Edmond L. Graminski

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Worlt Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, £ir)

U. S. Department of Energy

Washington, D. C. 20234

13. Type of Report & Period c °ve red Progress Rpt.

Oct. 1, 1976-Mar. 31.

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.) 0

Handsheets in the form of low-density open webs of g*ammage 2.5 g/m

were prepared from Northern and Southern softwood kraft pulps. These

handsheets, from pulps unbeaten and beaten for 5,000 revolutions in a laboratory beater, were pressed at 44, 350 and 660 kPa (6.4, 51.2 and 96

lb/inz

) during preparation. The relative density of bonding between fibers

and the relative strength of the bonds were estimated from tensile strength

data. It was found that the quality of bonding between fibers in the webs

was not affected by preparation pressures between 44 kPa and 660 kPa, but webs

prepared at the higher pressure tended to stick to the backing plate, thus

incurring some damage upon removal.

17. KEY WORDS (aix to twelve entries, alphabetical order; capitalize only tie Ural teller of the Ural key word iihleaa a ptnfiet name, separated by semicolons) p a per> interfiber bonding; paper, low-density handsheets;

paper, pulp characterization; paper, tensile testing; paper, recycling;

mixed waste paper.

18. AVAILABILITY [XT Unlimited

I

' For Official Distribution. Do Not Release to NTIS

QJ Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. C 1 3

I y Order F rom National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY ( LASS 21. NO. OF PAGES

(THIS REPORT)

IJN< LASSIE IF 1) 35

20. SE( IJKITY ( LASS 22. Pri« * (THIS PA(.K)

UNCLASSIFIED »v .50
. H