NBSIR 76-1148 W)

Characterizing the Inter-Fiber

Bond Strengths of Paper Pulps

in Terms of a Breaking Energy

Jack C. Smith

Structural Analysis and Standards Section

and

Edmond L. Graminski

Polymer Stability and Reactivity Section

Polymers Division

October 15, 1976

Progress Report Covering the Period

January 1 , 1 976 to June 30, 1 976

Prepared for U.S. Energy Research and Development Administration

Washington, D. C. 20234

NBSIR 76-1148

CHARACTERIZING THE INTER-FIBER

BOND STRENGTHS OF PAPER PULPS

IN TERMS OF A BREAKING ENERGY

Jack C. Smith

Structural Analysis and Standards Section

and

Edmond L. Graminski

Polymer Stability and Reactivity Section

Polymers Division

October 1 5, 1 976

Progress Report Covering the Period

January 1 , 1 976 to June 30, 1 976

Prepared for U. S. Energy Research and Development Administration

Washington, D. C. 20234

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter. Under Secretary

Dr. Betsy Ancker-Johnson. Assistant Secretary for Science and Technology

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

Page

SUMMARY i

INTRODUCTION 1

EXPERIMENTAL 7 RESULTS 10

DISCUSSION 13

CONCLUSIONS 15

REFERENCES ..... 17

i

SUMMARY

Two of the most important factors influencing paper strength

are fiber strength and inter-fiber bond strength. Although tedious,

the average fiber strength can be determined by testing a large

i number of single pulp fibers. However, the measurement of interfiber bond strength is considerably more difficult to achieve. In

order to fully characterize a pulp, the quality of bondability must

be known, especially for pulps produced from a mixture of waste

paper in the paper recycling process . If a fiber network consists of a relatively small number of

fibers (2.5 g/m ) such that the area covered by more than two

fibers intersecting at a given point is negligible, then the forces

generated when a specimen is elongated will be significantly lower

than necessary to break fibers in the specimen. When the elongation

is performed in a sensitive tensile tester, the force-elongation

curve consists of jagged peaks. Each peak signifies the breaking

of a bond between two fibers. Integration under the curve produces

values for a second curve in which the cumulative work done on the

specimen is plotted against the number of bond breaks that have

occurred. Segments of this curve, usually occurring near the end,

have minimum slopes. The values of these slopes are equal to the

average energy dissipated per bond break by a few fibers near the

site of the break, and can be considered a measure of .bond strength.

2 Handsheets (2.5 g/m ) were prepared from beaten and unbeaten

Northern and Southern softwood kraft pulps. Specimens were tested

to tensile failure on a sensitive tensile tester. Plots of work
11

done as a function of the number of bonds broken were prepared

and slopes were determined.

The average energy dissipated per bond was similar for the

two unbeaten pulps, but differences were observed in the tensile

behavior of samples made from the two different pulps. Beating

resulted in approximately an eight-fold increase in the energy

dissipated per bond break. The bond strength for the beaten

Northern pulp appeared to be slightly higher than for the beaten

Southern pulp.

These preliminary results indicate that the proposed method

for measuring interfiber bond strength is feasible. However

additional work will be necessary to confirm the applicability of

the method and establish its usefulness. As a first step it is

proposed to test additional samples prepared from pulps subjected

to various degrees of beating. If sufficient time is then available,

tests will be performed on samples of different basis weights.

These latter tests should help determine whether the fiber density

of the sample influences its tearing behavior. These tests thus

might help explain the differences in tearing behavior observed

in samples made from the two unbeaten pulps.
INTRODUCTION

Consider a random fibrous network formed from the pulp to

be evaluated. The network should be thin; i.e., the number of

fibers constituting it shall be so small that the area covered bymore than two fibers intersecting at a given point is negligible.

The concept and statistical geometry of such "2-dimensional"

networks has been discussed by Kalmes and Corte [1]

.

If a specimen cut from this network is stretched to break in

a sensitive tensile tester, the force-elongation curve obtained

often looks something like the curve depicted in Figure 1. Each

jagged peak on this curve signifies the breaking of a bond between

fibers. (It is assumed the fibers are much stronger than the

bonds between them, so that the fibers themselves do not break.)

By integrating under the curve, Figure 1, it is possible to obtain

values for a second curve, Figure 2, in which is plotted the

cumulative work, U, done on the specimen as a function of the

number of bond breaks, n, that have occurred. It should be

noted that the slope dU/dn of this curve decreases and approaches

a constant value as n increases. This constant value is the

characteristic energy E proposed by Dodson as a measure of bond

strength.

During the straining operation the following behavior sequence

is observed in the fibrous network. The fibers gradually align

themselves in the direction of strain with the straightest and most

perfectly aligned fibers bearing most of the load. Initially

breaks occur at random points throughout the network, but

eventually they become concentrated in the vicinities of pre-

4 existing or developing flaws. As the extension continues the

network is gradually destroyed. In the final stages of the breaking

process, portions of the network often coalesce into long threadlike structures that sustain relatively large elongations before

breaking.

In order to provide some understanding of this extensional

behavior the following network response mechanics is postuated.

It is assumed that initially the force borne by the network is

sustained by a relatively small number of fiber segments roughly

oriented in the direction the network is being stretched. The

forces in these fiber segments range from small values up to

magnitudes large enough to break the bond at either end of the

segment. Most of the fiber segments in the network bear no load

at all, because they are unaligned, or because the load is borne

by adjacent fibers with shorter segments between bonds. When a bond breaks the network opens up in the vicinity of the break.

This permits new fibers to become better aligned and to carry

some of the load. During early stages of the extension the

number of load bearing fibers increases as a result of this process,

the load distribution among the fibers becomes more uniform, and

the force sustained by the network tends to increase.

During the stretching process part of the work done is stored

as potential energy and part is dissipated when bonds break.

Initially most of the work is stored as energy in the network.

When a bond breaks some of this energy is dissipated, but if the

level of force after break then increases in a series of successive

breaks, there is a net increase in energy stored. Because of this
5 increase in stored energy, the curve of work done U versus number

of breaks n has a large positive slope during the initial stage

of the stretching process. At higher forces the fiber bonds tend

to break more readily, and the increase in force before another

break occurs is not so great. Less additional energy is stored

between breaks, and the slope of the U,n . curve becomes less positive.

In those stages of the extension when the stretching force is

large and the network remains intact, each time a bond is broken

other previously unloaded fiber segments in the vicinity assume

some of the load. Under these conditions there is an approximate

one-to-one relationship between the level of force and the energy

stored in the network. In particular, if during extension the

force sustained by the network returns to the same value after

each of a series of breaks, the average energy stored in the

network remains constant. The work of extension is completely

dissipated; that is, it merely replaces the stored energy lost by

each bond break of the series. The slope of the U,n curve then has

a constant minimum value, and represents the average energy

dissipated per bond break. This dissipated energy is the energy

that was stored in a few fibers near the site of a broken bond,

and is equal to Dodson's characteristic energy E.

If during extension the force sustained by the network

diminishes appreciably between two consecutive breaks a flaw

has probably developed and the network has become partially

destroyed. The functional relationship between force and stored

energy that held in the previously intact network no longer

applies, but it is still true that the energy stored has been
6 diminished, and consequently all of the work done in extending

the network between breaks has been dissipated. Thus if the

force after break has a decreased value in each of a series of

successive breaks, the cumulative work done to produce the breaks

is all dissipated, and the average value of the work of extension

that is dissipated per break is given by the slope of the U,n

curve in this region. This slope will have a decreased value,

but this value may be greater than Dodson's characteristic energy

E.

Often after a network has been partially destroyed it again

begins to store energy, and the level of force rises after each

of a series of successive breaks until further deterioration

occurs. The force-elongation curve thus may rise and fall through

a series of peaks, and the corresponding U,n curve will have a scalloped appearance. The decreased slopes at each scallop can be used to estimate E; the minimum of these slopes is ordinarily

a good estimate. However the regions of the force-elongation

curve corresponding to these decreased slopes should always be

carefully studied in order to judge, in the light of this

discussion, how good this estimate is.

In the final stages of the extension portions of the network

may coalesce into long threadlike structures consisting of

several strands of fibers bonded end to end and cross linked at

intervals by other fibers. The presence of these structures would

be manifest in the force-elongation curve as a series of breaks

at low forces with relatively large elongations between breaks.

The curve of percent elongation versus number of breaks would
7 have a sharp increase in slope when these structures occur.

In the long narrow networks of these threadlike structures

the stretching force is sustained along a straight-line path

consisting of fiber segments bonded together in series. When one

of these bonds is broken, other slightly longer and previously

unstressed segments in the vicinity assume the load. The energy

stored in a structure such as this is a function of the applied

force. Thus by using the previous arguments it is seen that if

the force after break has the same or a decreased value in each

of a series of successive breaks, the cumulative work done to

produce the breaks is all dissipated, and the slope of the U,n

curve will have a decreased value. Ordinarily these final

threadlike structures do not suffer drastic deterioriation as a result of bond breaks, nor are they often capable of storing energy

over a successive series of breaks; thus the forces after break

stay within reasonable bounds. In most cases, then, the final

portion of a U,n curve should have a long constant minimum

slope that would provide a reliable measurement of E.

EXPERIMENTAL

2 Handsheets having a weight of 2.5 g/m (2-D sheets) were

prepared from beaten and unbeaten Northern and Southern softwood

kraft pulps. Beating was performed in a PFI laboratory beater

at a consistency of ten percent for 10,000 revolutions with no clearance between bed plate and roll at a force of 33N (3.4 kg)

and a relative velocity of roll to bed plate of 6 m/s.
8 The standard method for preparing handsheets was unsatisfactory for the preparation of 2-D sheets. A microscopic study

indicated that the fibers followed the undulations of the wire

xcreen used as the forming medium resulting in an entanglement of

the fibers with the wire screen. This made it virtually impossible

to remove the handsheet from the wire without damaging it. It

became obvious a smoother forming medium was necessary in order

to prepare the 2-D handsheets uniformly and reproducibly

.

In the course of evaluating several different forming media,

it was found that cotton linters pulp was superior to the ordinary

forming wire. Its performance was further enhanced by treating its

surface with a fluorocarbon release agent.

The procedure for forming 2-D handsheets is as follows: A

33 x 33 cm piece of cotton linters pulp treated with a fluorocarbon

release agent is placed on top of the support wire of the deckle

box of the handsheet machine and wetted. The pulp expands upon

wetting. The deckle box is then closed, clamping the pulp firmly

at the bottom. Water is then added to -the box from the top being

careful not to damage the pulp surface.

An appropriate amount of pulp to be tested is placed in

approximately one liter of water and disintegrated on a British

Disintigrator for 7,500 revolutions for beaten pulp or 25,000

revolutions for unbeaten pulp. Whenever unbeaten pulp is used

it is first soaked in one liter of water overnight prior to disintegration. The disintegrated pulp is added to the water in the

deckle box, agitated carefully and then drained through the pulp

sheet.
9

The pulp sheet is removed from the deckle box and placed

on top of a fresh sheet of pulp. A 33 x 33 cm ferrotype plate

is then placed carefully over the top of the wet pulp sheet so as not to disturb the fibers of the 2-D sheets. After placing another

pulp sheet over the ferrotype plate the entire sandwich is

2 placed in a hydraulic press and pressed at 0.66MPa (96 lbs/in ) for

five minutes.

During the pressing the 2-D sheet is transferred to the ferrotype

plate. It is allowed to dry while still adhered to the ferrotype

plate. When dry, the 2-D handsheet is carefully removed from

the plate without any damage to the sheet.

The handsheet samples were fragile so special handling and

mounting procedures were used to prepare and test the specimens.

The sample to be tested was sandwiched between two sheets of

paper and a 1 cm ribbon cut using a scalpel guided by a straight

edge. The ribbon was transferred, using forceps, to a paper

mounting frame, and taped at top and bottom with masking tape.

A frame for mounting the 1 x 2 cm specimens tested is shown in

Figure 3.

The frame and specimen were mounted in the tensile tester.

The top of the frame was held between two small strips of

aluminum suspended by a wire from the load cell. The bottom was held in an air clamp. After mounting, the strips of paper on each side of the frame were carefully cut with scissors.

All tests were conducted using a cross-head speed of 0.2

cm/min and a chart speed of 20 cm/min. For tests on the unbeaten

samples of Northern and Southern pulps, the load cell sensitivity

was 0.02N (2 g) full scale. Load cell sensitivity was 0 . 2N
10

(20 g) full scale for tests on the beaten samples of Northern

pulp and 0.1N (10 g) full scale for beaten samples of Southern pulp.

RESULTS

Results of the tests are given in Tables 1 through 4. In

these tables the quantities labeled E are the estimates of average

energy dissipated per bond break by a few fibers near the site of the

break. The values of E.were determined from the constant slope

portions of the U,n curve. N is the number of breaks that occurred

in the specimen tested. The quantity U

t/N is the total amount of

work done in breaking a specimen divided by the number of breaks

that occurred. Its value provides an upper bound to the estimate

of E. Most of the energy is dissipated by the collapsing network

rather than by the fibers located at the breaking sites. This is

why the value of U

t/N is greater than E.

The fifth and sixth columns in the tables provide qualitative

information about the force-elongation curves and the U,n plots

respectively. The fifth column gives estimates of the number of

peaks apparent in the force-elongation curve. This should correlate

roughly with the number of flaws in the specimen about which the

breaks were concentrated, and the number of scallops that might

appear in the U,n plot. In those cases where the symbol 00 is

given, the force at which breaks occurred was approximately constant

throughout most of the curve, and no peaks could be distinguished.

The U,n plots derived from these curves usually contained many

scallops.
11

The quality of the U,n plot as graded in the sixth column

is a rough evaluation of the reliability of the E value determined

from the U,n plot. For instance, a plot graded A usually resulted

from a test in which bond breaks occurred in the vicinity of a single flaw, and a long portion at the end of the U,n plot was

linear. In contrast, a plot graded D contained many scallops in

which the linear portions were not well defined.

Figures 4 through 7 are tracings of typical force-elongation

curves obtained in the tests. Each curve represents the behavior

of a different pulp sample. For instance, Figure 4 is a curve of two

peaks obtained in a test of specimen 4 of the unbeaten Northern

pulp sample. Column 5 of Table 1 indicates that multipeak curves

are usually obtained in tests of this sample. The corresponding

U,n curve is shown in the plot of Figure 8. Two pronounced

scallops corresponding to the two peaks in Figure 4 are the dominant

features of this plot. As the character of this plot was so definite the quality of the plot was assigned a grade of A.

In tests on the beaten Northern pulp, single-peak forceelongation curves are frequently obtained. Figure 5 is a tracing

of one of these curves. The corresponding U,n plot is given in Figure 9 The monotonic dependence of U upon n culminating in a long region

of constant minimum slope provides a good illustration of breaking

behavior in the vicinity of a single flaw.

Tests on specimens from the unbeaten Southern pulp sample

resulted in curves in which the magnitude of the breaking force

remained the same over much of the elongation. A force-elongation

curve of this type is given in Figure 6. The corresponding U,n

plot, shown in Figure 10, has many scallops of short duration.
12

The value of E derived from this plot is not very reliable, and

the quality of the plot was graded D.

Tests on beaten Southern pulp spcimens yielded multi-peak

force-elongation curves similar to the one shown in Figure 7. The

corresponding U,n curve plotted as Figure 11 shows multiple scallops.

Plots of elongation versus number of breaks are given in

Figures 12 through 15, for the same specimens whose force-elongation

and U,n curves were given previously. The curves for the unbeaten

and beaten Northern pulps tend to be linear throughout most of the

range of the number of breaks n, and to have a gradually increasing

slope when n is large. The increased slope at the end of the test

indicates that in the final stages the breaks are occurring within

a long thread-like structure formed by the specimen. Curves for

the beaten and unbeaten Southern pulps usually have two linear

portions with an abrupt change in slope occurring near the middle

of the range of n. This indicates that the Southern pulp specimens

have a greater tendency to form thread-like structures than do the

Northern pulp specimens.

Elongation is more compactly presented in columns 7 and 8 of

Tables 1 through 4. In column 7 total elongations are given, and

in column 8 elongations per break are tabulated. The values of

elongation per break were found from slopes of the elongationbreak curves. Those curves with two slopes have two values

tabulated. If the change of slope is gradual or occurs near the

end of the range of n values as in Figure 12, the value of the

second slope is not given in the tables. Similarly as in Figures

14 and 15 the very large slopes occurring at the end of the n value

range have been omitted from the tables.
13

DISCUSSION

According to Tables 1 and 3 it is not possible to distinguish

between the unbeaten Northern and Southern pulps by comparing

their E values, as the Northern pulp average value of 0.85 x 10 "^J -7

is almost the same as the Southern pulp average value of 0.82 x 10 J.

Nor do the average U

fc /N values afford a clear cut distinction, as

_ 7 the U

t/N value of 1.72 x 10 J for the unbeaten Southern pulp is

only slightly but not significantly higher than the value of

-7

1.30 x 10 J for the unbeaten Northern pulp.

The breaking behaviors of the two pulp samples however are quite different. Breaking in the unbeaten Northern pulp specimens

usually occurred only in the vicinity of a few flaws, as may be

seen from the small number of peaks observed in the force-elongation

curves, and the good reliability with which E could be determined

from the U,n curves. The low value of elongation per break averaging

to 0.15% break suggests that the network was firmly connected with

only short distances between fiber bonds. Thread-like structures,

if they developed at all, occurred only near the end of a test, as only one set of values of elongation per break is tabulated in

column 8 of Table 1.

In contrast, the unbeaten Southern pulp specimens had many breaks

occurring at random throughout the network. The U,n curves had

many scallops and E values could not be determined with good

reliability. The high initial values of elongation per break of

0.43 %/break suggest that in many of the specimens the network was not firmly connected; that is, there was a longer distance on the

average between fiber breaks. The occurance of multiple values of
14

elongation per break tabulated in column 8 of Table 3 suggests

that thread-like structures frequently developed about midway through

the breaking process.

It was noted during sample preparation that the unbeaten Southern

pulp sample was very fragile and difficult to handle. It is

therefore possible that further tests on different samples will

give results different from the ones obtained here.

Beating the pulp strongly affects the ability of the fibers

to bond together. In the case of the Northern pulp, the beating

-7

treatment produces a rise in the values of E from 0.85 x 10 J for

-7

the unbeaten pulp to 7.3 x 10 J for the beaten pulp. There were

also minor changes in the character of the force-elongation curves

and U,n plots. Beating tends to reduce the number of random fiber

breaks throughout the network and localize them to the vicinity

of a flaw. Fewer flaws develop in the beaten pulp network, and

the number of scallops appearing in the U,n plots are less, so

that more reliable values of E can be obtained.

Beating produces similar changes in the Southern pulp samples.

_7 The value of E is increased from 0.82 x 10 J for the unbeaten

pulp to 6 . 8 x 10 J for the beaten pulp specimens. The beaten

pulp network has more of a tendency to break in the vicinity of

a flaw, and the U,n curves have fewer scallops so that better

determinations of the value of E can be made. For the southern

pulp beating also causes the network to be more firmly connected,

as noted by the significant decrease in the value of 0.43 percent

elongation per break for the unbeaten pulp to 0.18 percent

elongation per break for the beaten pulp.
15

Although beating produces more strongly bonded networks in

both the Northern and Southern pulp samples, the breaking behaviors

of the two pulps are still different. The beaten Southern pulp

specimens have multiple-peak force-elongation curves, and the

reliability of the E values determined from the correspondingly

scalloped U,n curves is only fair. Moreover the beaten Southern

pulp specimens frequently form threadlike structures midway

through the tests. In the beaten Northern pulp specimens the forceelongation curves have fewer peaks, the U,n curves have fewer scallops

and the thread-like structures that form do not appear until the

end of the test. Evidently the differences in behavior between the

Northern and Southern pulp networks cannot be completely overcome

by a beating treatment.

CONCLUSIONS

From the preliminary work reported here it appears that

interfiber bond strength can be characterized by Dodson's energy

parameter E. Definite differences in bond strength have been

observed between beaten and unbeaten soft wood kraft pulps. The

effect of beating on bond strength therefore should be studied by

additional tests on samples prepared from pulps subjected to

various degrees of beating.

No significant difference in bond strength was observed

between samples prepared from Northern and Southern soft wood

kraft pulps, although differences in tensile behavior were observed

in the tests. The differences in tensile behavior may be due to

differences in the morphology and coarseness of the two pulp samples.
16

so these quantities should be characterized to help interpret

the test results. The effect of fiber coarseness should also be

investigated by tests performed on samples of different basis

weight

.
17-

REFERENCES

1. O. Kallmes and H. Corte, TAPPI 4_3, 737 (1960) .

2. C. T. J. Dodson, Brit. J. Appl. Phys. 1_8, 1199 (1967)
Tests

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Sample

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Table

21

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to cm

'3- (M

Or-H A

LOA

A

A

(M tO

VO r-H

to CM oo LO

vO o

oo

LO

to

LO to to

to

Tj» to vO rH vO LO LO 00i-H vO

to

vo

^5mou0 o a u •"D 0 1 "a oi-H Td 1 p o X 0

tH

LO

XJ0 X

CM P

LO rH 0 A A A i-H Co * p 8-« c p oo o cd •HP

a3 >0 o

•d "O -X

vO

O 0 TD 00

LO T) P0

td

u

r-H i-H i-H X) P

cd •ac §p0

fl

(Ua.

CM

O cd * co

i-H CO *“D r>*

p 1 0

•-D o 00

r*. i-H c 1 o X o

LO oo •—i

LO 0

00 LO VO

X LO i-H

r-H 0

00 •rH • 2 P

'O •H p e

tu => •H

<U 0 0

00 00 00 o r-H vO cd 0 0

i-H i-H r-H Jh (H (-4 0 0 0 > > > < < <
WORK

DONE

U

FORCE

CHART TRAVEL

Figure 1: Idealized force-elongation curve for a "2-dimensional" paper

network.

NUMBER OF BREAKS , n

Figure 2: Plot of work of extension U versus number of bond breaks n for

the force-elongation data of Figure 1.
TOP CLAMP

Guide lines

for specimen

PAPER MOUNTING FRAME

Figure 3: Mounting frame and clamp for testing paper specimens.
20 15 10 5 0

CHART TRAVEL , cm

Figure 4: Tracing of force-elongation curve for specimen 4 of the unbeaten

Northern pulp sample.

FORCE
150

100

50

0

100

50

0

55 50 45 40 35 30

CHART TRAVEL , cm

30 25 20 15 10 5 0

Figure 5: Tracing of force-elongation curve for specimen 10 of the beaten

Northern pulp sample.

FORCE

,

mN
Figure 6: Tracing of force-elongation curve for specimen 9 of the unbeaten

Southern pulp sample.

4

2

0

4

2

0

4

2

0

2

0

2

0

2

0

FORCE

,

mN
Figure 7: Tracing of force-elongation curve for specimen 3 of the beaten

Southern pulp sample.

FORCE

,

mN
NUMBER

OF

BREAKS

,n

Figure

8:

Plot

of

work

of

extension

U

versus

number

of

bond

breaks

n

for

specimen

4

of

the

unbeaten

Northern

pulp

sample.

WORK DONE. , UjJ
Figure

9:

Plot

of

work

of

extension

U

versus

number

of

bond

breaks

n

for

specimen

10

of

the

beaten

Northern

pulp

sample.

WORK DONE . U . mJ

P o P P P c> O — r\) oj cn
NUMBER

OF

BREAKS

,n

Figure

10:

Plot

of

work

of

extension

U

versus

number

of

bond

breaks

n

for

specimen

9

of

the

unbeaten

Southern

pulp

sample.

WORK DONE , U , pJ _ _ ro O cji o cn o
NUMBER

OF

BREAKS

,n

Figure

11:

Plot

of

work

of

extension

U

versus

number

of

bond

breaks

n

for

specimen

3

of

the

beaten

Southern

pulp

sample.

WORK DONE , U , m J

o

o

o o

fv>
CO

<

LU

CC

CD

Ll_

o

crLU

OD

0//o

c N0I1V9N013

Figure

121

Plot

of

elongation

versus

number

of

bond

breaks

n

for

specimen

4

of

the

unbeaten

Northern

pulp

sample.
lO o to o LO o

CM CM — —

% ‘ N0I1V9N013

NUMBER

OF

BREAKS

, n

Figure

13:

Plot

of

elongation

versus

number

of

bond

breaks

n

for

specimen

10

of

the

beaten

Northern

pulp

sample.
Figure

14:

Plot

of

elongation

versus

number

of

bond

breaks

n

for

specimen

9

of

the

unbeaten

Southern

pulp

sample.

ELONGATION O/

/o

a

00

m

x

o

~n

CD

XI

m

>

x

CD

13

o o

no oj o o o

o o o o o
NUMBER

OF

BREAKS

,n

Figure

15.

Plot

of

elongation

versus

number

of

bond

breaks

n

for

specimen

3

of

the

beaten

Southern

pulp

sample.

ELONGATION , %

_ — — TM

ro O (ji O cn O (ji
NBS-U4A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 76-1148

2, Gov't Accession

No.

4. TITLE AND SUBTITLE

Characterizing the Inter-Fiber Bond Strengths of Paper

Pulps in Terms of a Breaking Energy

3. Recipient's Accession No.

5. Publication Date October 15, 1976

6. Performing Organization Code

7. AUTHOR(S)

Jack C. Smith and Edmond L. Graroinski

8. Performing Organ, Report No, NBSIR 76-1148

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10, Projeet/Task/Work Unit No. 3110443

11. Contraet/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP

)

U* So Energy Research and Pevelopment Administration

Washington, D. C. 20234

13. Type of Report Si Period Covered PrOgTOSS Rpt

Jan 1, 1976 - June 30, l|97

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.)

The inter- fiber bond strength of paper is an important but an arduous property

to measure. In order to characterize a pulp completely, the quality of bondability

must be known especially for pulps produced from a mixture of waste paper. It has been

postulated that a measure of bond strength can be obtained by measuring 2.5 g/nr

handsheets to tensile failure, recording the number of bonds broken with a sensitive

tensile tester and plotting a curve of number of bonds broken as a function of

cumulative work done on the system. The value of the minimum slope of this curve is

equal to the average energy dissipated per bond break. Results obtained on two

different softwood kraft pulps indicate the proposed method may be useful in

assessing bond strengths.

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

)

Breaking energy; inter- fiber bond strength; mixed waste paper; paper recycling;

pulp characterization; 2.5 g/m2 handsheets

18. AVAILABILITY [j? Unlimited

I For Official Distribution. Do Not Release to NTIS

I

1 Order From Sup. of Doc., U.S, Government Printing Office Washington, D.C, 20402, SD Cat. No. C13

I X1 Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

38

22. Price

$4.00

U8COMM-DC 29042- P 74
A