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A 1 L1G1 7 2-A732

NAT L INST. OF STAND & TECH R.I.C.

A11105 037230

IMBSIR 79-1914

Assessment of the Quality of

Pulp Fibers by Short Span

Tensile Analysis

Edmond L. Graminski and Keith Bonin

Polymer Science and Standards Division

Center for Materials Science

National Bureau of Standards

Washington, D C. 20234

Progress Report Covering the Period

October 1, 1977 through September 30, 1978.

October 1979

Prepared for: ~QC " U.S. Department of Energy

]_QQ Washington, D.C. 20545

. U56

79-1914

NBSIR 79-1914

« * A ASSESSMENT OF THE QUALITY OF

PULP FIBERS BY SHORT SPAN

TENSILE ANALYSIS

1979

<\ot ft cc - IH-C P

sicuoo

use*

Edmond L. Graminski and Keith Bonin

Polymer Science and Standards Division

Center for Materials Science

National Bureau of Standards

Washington, D C. 20234

Progress Report Covering the Period

October 1, 1977 through September 30, 1978.

October 1979

Prepared for: U.S. Department of Energy

Washington, D.C. 20545

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

Luther H. Hodges, Jr., Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

Contents

Page

1 . Summary 1

2. Introduction 3

3. Experimental 4

4. Results and Discussion 5

5. Conclusions 8

6. Bibliography g

1. Summary

The strength of paper is dependent to a large extent on the strength of

individual pulp fibers. Regardless of its importance, however, fiber strength

is almost never determined as it necessitates the testing of single fibers which

is very tedious and time consuming. Fiber strength is usually assessed only

when it is critical as in the evaluation of a new pulping process.

Recent studies have shown that the tensile strength of softwood fibers depends

not only on the fibril angle of the S

2 layer, but also on the defects in fibers

which are distributed randomly within and among fibers. The defects are formed

during the pulping and mechanical action processes. When waste paper is recycled,

the fibers are subjected a second time to chemical and mechanical action processes

increasing the possibility of forming fiber defects.

Understandably, there is considerable uncertainty about the fiber quality

of recycled pulps and unless the waste paper quality is quite well known in

advance, it will not be used to make anything other than low grade paper products.

Unfortunately, most waste paper is not well characterized and frequently is

contaminated, and even though the waste paper may consist of high quality fibers,

the waste paper will be used only for low grade paper products. Since the supply

of low grade waste paper exceeds the demand, means will have to be developed for

optimizing the utilization of low grades of waste paper if the rate of paper

recycling is to increase. Much of the uncertainty of fiber quality could be

dispelled if a rapid and reliable method for assessing fiber quality were developed.

In short span tensile testing of paper the failure load decreases as the span,

or initial distance between grips, of the specimen increases, because the number

of fibers traversing the span decreases. The rate of the decrease in failure load

is dependent on the fiber length distribution. For a given fiber length distribution,

the rate of decline in failure load with increasing span should be minimal if all

of the fibers are perfect. As the quality of the fibers decreases, the rate of

decline in failure load with increasing span should increase. It would appear, then,

that the slope of a failure load-span length plot for a pulp, having a specific

fiber length distribution, would be a measure of fiber quality.

A kraft and a sulfite wood pulp, prepared from a common wood source, were used

in this investigation. The purpose of this was to evaluate two pulps having

nominally identical fiber length distributions^but greatly different fiber qualities.

Handsheets, having a weight of 2.5 and 5.0 g/m , from unbeaten and beaten pulps were prepared and tested to tensile failure at spans ranging from 5--500 ym. The

instrument used to determine the short span tensile strengths was specially

designed to provide a nominally constant rate of jaw separation. Transducers for

the simultaneous measurement of load and jaw separation were suitably located on the instrument.

Good linear plots were obtained when the log of the failure load was plotted

against span length. There was essentially no difference in the slopes for the

unbeaten kraft and sulfite pulps but there was a large difference in the slopes

for the beaten pulps. This difference in behavior between the beaten and unbeaten

pulps may be due to the differences in the wet plasticity of the unbeaten fibers

at the time of handsheet preparation.

1
As bonding increases, more and more fibers become load-bearing, resulting in

higher loads at the break, especially at the larger spans. In addition, the

probability of finding a defect within a bonded area increases as the relative

bonded area increases. Defects located within a bonded area are likely to respond

to tensile stresses differently. Furthermore, the defect might even become "repaired

or "healed" when located within a bond area. Because of these factors, it is

essential that the interfiber bonding in all test handsheets be at an equivalent

level for all pulps. Otherwise, the test results could be deceptive.

There appears to be little, if any, fiber slippage from under the clamps with

the low density sheets. Extrapolations of the log failure load-span length plots

to zero span are in good agreement with the failure loads obtained at 5 ym spans

which are very close to a zero span.

The results of this investigation indicate that short span tensile analysis

can be used to assess the quality of pulp fibers. Additional work will be necessary

to establish a standard procedure for preparing the handsheets and for conducting

the short span tensile test.
2.

—

Introduction

One of the more important fiber properties affecting the mechanical properties

of paper is single fiber strength. In order to assess the mean fiber strength of

a pulp, it has been necessary to determine the strength of a large number of

single pulp fibers. The precise measurement of the strength of single fibers

involves a tedious and careful preparation of specimens and specialized equipment

for measuring the load-elongation curve for each fiber. The time required to make

evaluations for single fiber strengths of pulps is very lengthy and, because

of this, single fiber strength evaluations are made only when a critical evaluation

of experimental pulps or pulping techniques is necessary.

Recently, single fiber studies have shown that the tensile strength of

softwood fibers depends not only on the fibril angle of the S 2 layer, but also

on defects which are distributed randomly along the fibers (1). The probability

of a defect occurring within the length of a fiber increases with increasing test

length of a fiber test specimen with the result that the mean fiber tensile strength

of pulp fibers decreases with increasing test length.

The occurrence of fiber defects depends largely on the chemical and mechanical

action process of pulp and paper manufacturing. When paper is recycled, the fibers

are subjected to chemical and mechanical action processes a second time, increasing

the probability of finding defects in the fibers. Since single fiber strength has

a great influence on the strength properties of paper it is desirable to have an estimate of the fiber quality of recycled pulps. Much energy and capital would be

wasted if the paper made from a recycled pulp resulted in a paper not being able to

meet specific strength specifications. Certainly, the usual single fiber techniques

cannot be used for the assessment of fiber quality of recycled pulps. What is

needed is a test method which is rapid and simple, yet reliable and reasonably

accurate.

As the probability of a defect appearing in a fiber is proportional to the fiber

length, it appeared that short span tensile analysis might be a useful technique

for assessing pulp fiber quality. In short span tensile testing of paper, the load

at failure decreases with increasing span (2). The reason for the decline in load

' at failure is the decreasing number of fibers traversing the span as the span increases.

The rate at which the strength decreases is also believed to be dependent on the

average fiber length (expressed as a length weighted average). A pulp having a low

j weighted mean fiber length would be expected to exhibit a faster rate of decline in

load at failure than a pulp with a high weighted mean fiber length. For a given

length distribution the load at failure will not decrease as rapidly when the fibers

are bonded because bonded fibers will continue to be load bearing when they no longer traverse the span between the clamps.

Consider, then, two pulps having similar fiber length distributions, but one

pulp has nearly perfect fibers while the second pulp contains fibers with many

defects. The rate of decline of the load at failure in a short span tensile test

would be much greater for the pulp containing fiber defects. As a consequence, the

slope of the failure load-span length plot would be more negative for the pulp

| containing fibers with defects than for the pulp with nearly perfect fibers. The

object of this investigation was to determine whether short span analysis could be

used to assess the quality of pulp fibers.

3
3. Experimental

A bleached kraft and a sulfite pulp from a common wood source were used in

this investigation. Sulfite pulp fibers generally contain more defects than do

kraft pulp fibers. The probability of having a similar fiber length distribution

for the two pulps was good because they originated from the same wood source. The

fiber length distribution was determined for each pulp with the aid of image

analysis (3) and the histograms for the pulps are given in Fig. 1.

Handsheets having a weight per unit area of either 2.5 or 5.0 g/m were

prepared according to the procedure described in an earlier report (4) except

that Whatman filter paper no. 541 was substituted for the cotton 1 inters pulp sheet

previously used as the forming medium. Pressing was carried out at 350 kPa (51

lb/in2) for 5 minutes. Specimens were 15 mm wide and approximately 4 cm long. The

specimen was placed in the jaws of the instrument so that one end was centered

between the jaws. After the specimen was strained to tensile failure, the jaws were opened and the specimen was moved approximately 1 cm from the previous test

area, reclamped and strained to tensile failure once again. In this manner, it was possible to obtain five to six test results from one test strip.

The instrument used for making the short span tensile tests was specially

designed for the purpose. The instrument was designed to provide a nominally

constant rate of jaw separation. Transducers for the simultaneous measurement

of load and jaw separation were suitably located on the instrument and the signals were recorded on an X-Y recorder. The instrument was previously calibrated for

load measurement with dead weights while the linear transducer was calibrated with

feeler gauges. The clamping pressure was 70 psi and was determined by observing

the zero span load as a function of clamping pressure. At pressures below 70 psi

slippage occurred and the zero span load value was low. At pressures substantially

above 70 psi, considerable fiber damage occurred and, again, the zero span load

value was low. The pressure chosen was at a point where the zero span load value

was at a maximum.

The rate of jaw separation was adjusted for each span length so that the

rate of elongation was 3% per second. This was the lowest strain rate possible

which would allow for an identical strain rate for all of the span lengths

investigated. Load elongation curves were obtained for span lengths of 25, 50,

75, 100, 200, 300, 400, and 500 ym. All tests were conducted in a room having

a controlled atmosphere of 23°C + 1 °C and 50% RH + 2% RH. The results of this

investigation are given in Tables 1-4.

4
4. Results and Discussion

There are four factors which affect the failure load in short span tensile

testing of paper, fiber strength, fiber length distribution, interfiber bond

strength. and fiber orientation. It has been speculated that these four factors

could be assessed by means of short-span tensile testing (5). During the course

of this discussion, an attempt will be made to demonstrate that the assessment

of these four factors by short-span tensile testing may be deceptive.

Most paper consists of multiple layers of fibers. As the thickness of the

paper increases it is quite possible that a significant number of fibers, at or near the center of the paper, are not clamped sufficiently resulting in fiber

pull-out. Fibers which are pulled out instead of broken in tensile failure contribute

little to the breaking load and as a consequence, the test results will be lower

than expected. The obvious procedure for avoiding fiber pull-out is to increase

the clamping pressure, however, high clamping pressures result in fiber damage which,

in turn, culminates in low tensile failure loads. An apparent alternative is to use very low density paper, consisting of very few layers of fibers, thus avoiding

poorly clamped fibers. Such paper is commonly referred to as

? a 2-D sheet. In this study, handsheets having a mass per unit area of 2.5 g/nr and 5.0 g/nr were used.

A second important variable in preparing paper for short-span tensile testing

is interfiber bonding. As bonding increases, more and more fibers become load-bearing

resulting in higher loads at the break, especially at the longer spans. This means

that the slope of the breaking load-span length plot would increase (become less

negative) as the amount and strength of interfiber bonding increased. Since the

object of this investigation was to determine whether the fiber quality of a pulp

could be assessed by the magnitude of the slope of the breaking load-span length

plot it is essential that the interfiber bonding of the test sheets be at an equivalent level for all test sheets.

Interfiber bonding may affect the slope of the breaking load-span length plot in

yet another way. All things being equal, the slope of the breaking load-span

length plot should decrease with increasing number of defects in the fibers. In instances where defects are located within the bond area, it is very likely that

the response of the defects to tensile stresses will be appreciably different than

when located outside the bond area. In fact, in certain instances, a defect might

be essentially "repaired" or "healed" when located within the confines of an interfiber bond.

The wet plasticity of pulp fibers, at the time of sheet preparation, should

be equivalent for all pulps to be tested. If the wet plasticity for two or more

pulps is significantly different, then the bonded area will be greatest for the

pulps having the highest wet plasticity as the ability of one fiber to conform

with another fiber increases with wet plasticity. For pulps having an equivalent

number of defects, the probability of finding a defect in an unbonded area is

greatest for the pulp having the lowest wet plasticity since less fiber area is

involved in bonding. Unless the relative bonded area is at an equivalent level

for all pulps, assessment of fiber quality by short span analysis could be illusory.

5
The results of failure load for the various span lengths are plotted in

Figs. 2 and 3 for 2.5 and 5.0 g/m^ sheets respectively . The failure load

declines as the span increases from 100 to 500 ym, however, the failure load

at 50 and 75 ym was usually lower than at the 100 y m span length. This behavior

between 50 and 100 ym was not as apparent with the 5 g/m^ sheets. The reason

for this behavior is not known at this time. There is a possibility that the

tensile response to straining may change appreciably as the span length approaches

the width dimensions of the fibers. The results from this investigation suggest

that span lengths less than 100 ym should not be used in short-span tensile analysis.

When the results were plotted on a semi-log scale, good linear plots were obtained (Figs. 4 and 5). Presumably, extrapolation of the plot to zero span

approximates the true zero span strength of the sheets. The coefficient of

correlation, slopes and y intercepts for all of the plots are given in Table 5.

The y intercepts for the 5.0 g/m2 sheets are approximately twice that for the

2.5 g/m^ sheets which indicates that no fiber slippage occurred during the

straining of the sheets.

The slopes for the failure load-span length plots for the unbeaten pulps were essentially the same regardless of the mass per unit area of the sheets or

the type of pulp. This would indicate that the fiber quality of both pulps was the same. However, since sulfite pulp fibers are weaker than kraft pulp fibers, some factor previously unaccounted for must have had an effect on the test results.

Unbeaten sulfite pulps swell more readily in water than do kraft pulps (6). As

a result, the sulfite pulp fibers have a greater wet plasticity than the kraft

pulp fibers and the sulfite fibers are able to conform to each other better during

wet pressing. This results in better bonding between the fibers of unbeaten

sulfite than in unbeaten kraft pulp. Therefore, more load bearing fibers are present in unbeaten sulfite sheets at the longer spans than in the kraft sheets

and the slope of the log failure load-span length plots for the sulfite sheets

should be less negative than the slope for the kraft sheets. The fact that the

slopes for both the unbeaten sulfite and kraft sheets are nearly identical may be

fortuitous. In light of the large impact interfiber bonding apparently has on short-span testing, it is imperative that all test sheets have an equivalent degree

of bonding, otherwise the results could lead to illusory conclusions.

Upon beating both pulps in a laboratory beater in order to have both pulps

at more nearly the same wet plasticity, great differences in slopes were observed

between the sulfite and kraft pulps. The slope for the kraft pulp increased

appreciably after beating while no change in slope occurred for the sulfite pulp.

One could argue that beating had no effect on the wet plasticity of the sulfite

pulp and no decrease in slope would be expected after beating. However, the

breaking strength for 10 g/m2 sheets of unbeaten sulfite was 58g before and 246g

after beating. Similarly, the unbeaten kraft had a strength of 1 21 g before beating

and 544g after beating. The breaking strengths were determined on a commercial

constant rate of elongation tensile tester according to TAPPI T494 0S-70 with the

exception 15mm and not 25mm wide specimens were used. The mean breaking strengths

reported above were based on a minimum of eight specimens.

6
I The data for the 100-500 ym range were reanalyzed since the results indicated

that spans less than 100 ym ought not be used. The results of that analysis are

an increase in the coefficient

eciable increases in the y intercept,

handsheet results. Although

increases in slopes were observed when only the 100-500 ym range was analyzed,

the ratio between the sulfite and kraft slopes was essentially unchanged, indicating

the range of span lengths investigated will not affect the assessment of fiber

quality providing the span length range is identical for all the pulps.

given in Table 5. In most instances there was of correlation, increases in the slope and appr

The greatest changes occurred with the 2.5 g/nr
5. Conclusions

The results indicate that an assessment of fiber quality by short span tensile

analysis is feasible providing the wet plasticity of the pulp fibers at the time

of handsheet preparation is such as to provide equivalent interfiber bonding

for all types of pulps. It also appears that fiber slippage can be virtually

eliminated by using very low density sheets in the range of 5.0 g/m^ . It appears

that span lengths less than a certain minimum value should not be used as fiber

dimensions become a factor in the test results. In this investigation, the

minimum span length appeared to be 100 ym. Since the assessment of fiber quality

by short span tensile analysis is approximately identical for both 2.5 and 5.0 g/rrr

sheets, the easier to prepare 5.0 g/m^ would be preferred.

8
6. Bibl iography

1) Page, D. H. and El-Hosseiny, F. , Svensk Papperstidning No. 14, 471 (1976).

2) Cowan, W. F. and Cowdry, E. J. K., TAPPI 57, No. 2 90-93 (1974).

3) Graminski, E. L. and Kirsch, R. A., Image Analysis in Paper Manufacturing,

Proceeds of IEEE Computer Society Conference on Pattern Recognition and

Image Processing, p. 137-143, June 6-8, 1977.

4) Smith, J. C. and Graminski, E. L., Characterizing the Interfiber Bond Strengths

of Paper Pulps in Terms of a Breaking Energy. NBSIR 76-1148, Oct. 15, 1978.

5) Cowan, W. F. , Short Span Tensile Analysis, Pulmac Instruments Ltd., Montreal,

Canada, 1975.

6) Scallan, A. M., In "Fiber-Water Interactions in Paper-Making", Trans, of the

Symposium held at Oxford: September, 1977. Edited by the Fundamental Research

Committee, Technical Division, The British Paper and Board Industry, Federation

London, pp. 9-27, 1978.

9

CNI O OO CO OJ

saaaid do HiONdi “ivioi do %

Figure

1.

Frequency

Distribution

of

Fiber

Lengths

for

the

Kraft

and

Sulfite

Pulps

Used

in

this

Investigation.

1000

800

600

<

o

<

2 400 I— A

A

o

o

o o

0 o

200

KRAFT, UNBEATEN

0 SULFITE, UNBEATEN

a KRAFT, BEATEN

o SULFITE, BEATEN

A

A

0 o

0

A

a

0

A

8

100 300 500

SPAN, |im

2 Figure 2. Change in failure load with increasing specimen length for 2.5 g/m

handsheets made from unbeaten and beaten pulps

LOADAT

FAILURE,

1000

800

600 _

400 -

200

-

o

0

0

8

KRAFT, UNBEATEN

0 SULFITE, UNBEATEN

a KRAFT, BEATEN

O SULFITE, BEATEN

o

0

o

0

1

©

0

100 300

SPAN, |lm

500

Figure 3 Change in failure load with increasing specimen length for 5.0 g/m*

handsheets made from unbeaten and beaten pulps
i

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I
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4

Plot

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failure

load

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specimen

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2.5

g/m

handsheets

made

from

unbeaten

and

beaten

pulps

tooo 900 800

<NJ

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Figure

5

Plot

of

log

failure

load

against

specimen

length

for

5.0

g/m

handsheets

made

from

unbeaten

and

beaten

pulps

Table

1.

Short

Span

Breaking

Load

for

Unbeaten

Bleached

Kraft

Softwood

Pulp

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Table

2.

Short

Span

Breaking

Load

for

Bleached

Kraft

Softwood

Pulp

Beaten

for

5000

Revolutions

ina

Laboratory

Mill ii

IS) e o 0)

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Table

3.

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Span

Breaking

Load

for

Unbeaten

Bleached

Sulfite

Softwood

Pulp

i/i

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Table

4.

Short

Span

Breaking

Load

for

Bleached

Sulfite

Softwood

Pulp

Beaten

for

500

Revolutions

in

a

Laboratory

Mill

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ns <o C\J 00 CM co •si" o cd <a CO CO CO r— >d- 00 o r

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CM LO

CD oo CO CO r-~~ CO CO r-^ co CNJ I''. CO

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i

CD

sz -a

fT3 <T3 <D O CD

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(£x)
Table

5,

The

Coefficients

of

Correlation,

Slopes

and

y-Intercepts

for

the

Plots

O) o CO o 00 VO

+-> lo vo VO i—

fa VO VO cn un vo

O) coe

<d +J VO o CO CO

ra 1^ vo r— cn 1—

CL) cn VO cn VO JOe

=3 i

cn Q. o E

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<D cn VO CO cn CO CO

O) CO • 1 • 1 4-> •r— CM

4- E

r— >1 3 cn e r—

on LO CL) VO uri

C 00

O • -M oo cn cn o o> o CM (T3 cn VO CM CO

CD • i (/) • 1 JOe

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Q. o

Q.

«3

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H3 Q

(T3 Q e

CL)

n

_ 00 cn CO CL

oo cn r^. vo

-M r—

CM oc cn lo CO CO

rtJ c cn r— cn E cn C\J

O CD CO • 1 o i r— E

<u om

t; O

4J CO o CJ LO

CM <o CO vo r— 00 CM E CD cn r— CO cn r^ CO JO # i * i cn E o =3 . LT> LO Q. r“ O 3 e Q_

«3 CM E

+J E CD cn e— r— CO VO r-» 4- -*-> CO VO CO r— co

ca cn CO CO cn VO LO * e LO CD p 1 » 1 VO p CO cn CM

*r~ U_ E e CD

i— -M oo r— p— LO o CO

(T3 VO r— VO E CD cn cn CO *3- 3 JO i * t O E i J= ZD

II 00

oo E

01cn E

DO. cn E cn cn E cn cn O o O O

•r— 1 p* •*— i

+• 4-> +-> p 4-) +-> +J r> E ra VO CL e a vo CL

CD r— o O) CD 1— o <D

•r- CD 1 CJ •r- CD r— CJ CJ E X E CJ E X E

•r- E CD •i

— E CD 4- O CD +-> 4- O CD +-> 4- C_> Q. E 4- CJ Q. E

CD o i—

CDO

O 4- 1— | O M- ,

1 4J O 00 50 C_> O OO =o

NBS-114A (Rev. 9-7 s)

U.S..DEPT. OF COMM.

bibliographic data

SHEET

1. PUBLICATION OR REPORT NO.

4. TITLE AND SUBTITLE

Assessment of the Quality of Pulp Fibers by Short Span

Tensile Analysis

3. fecifstest* a Accession No.

5. Publication Date 9/19/79

!W' -"a'.Ml.f'l.

1

7. AUTHOR(S) , „ . . . Edmond L. Graminski and Keith Bomn

8. Performing Organ. Report No. NBSIR 79-1914

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

tO, Prc rk Unit No. 5630444

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, city, state, zip)

U. S. Department of Energy

Washington, D. C. 20545

13. Type of Report & Period Covered Progress Report

Oct. 1, 1977 - Sept. 30, 1978

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

IS. ABSTRACT (A 200-word or leea factual summary of most significant information. If document includes a significant bibliography

literature survey, mention it here.) . „ Fiber strength is air important factor tit paper strength,, but despite its

importance fiber strength is rarely assessed as it involves the tedious and

time consuming testing of single fibers- Tit the recycling of paper*

especially of the abundant lov* grades of waste paper* the question of fiber

qual i ty always arf ses. The i nabi T t ty. ta moni tor fi ber qual i ty of recycl ed

pulp, especially from- To** grade waste paper has Ted to- the practice of utr Vi nng-

/this pulp only for lo* grade papers regardless af the actual quality of the

pulp- fibers. Unfortunately* there is a limited demand for To» Papers.

Increased utfTiatfom af low grade waste paper could be enhanced if the fiber

quality of the recycled pulps could be monitored routinely. As the strength

of fibers is affected by defects that are randomly distrrouted among .and within

fibers it appeared a short span tensile test might provide a ^eans for assessing

fiber quality, lit short span tansiTe tasting of fibrous webs the Toad_*****

breaic declines as the span increases. The rate or^declinejs pa y

by the fiber length distribution. Since the probability of

in- fibers increases with increasing span lengths the rate ar d5lll J.JifS

strength with increasing span lengths should be a function of

Tj.

b#T

Jj -ag^its

for a specific fiber Tength distribution, aTT things being eb^a - of this investigation indicate that the rate of decline in wed with

increasing span length is indeed a function of fiber qua! i ty. rt appears that

the tast method could be used to monitor fiber qual ity routinely.

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

asperated by semicolons)

Fiber length distribution; fiber strength; interfiber bonding; recycled pulps;

short span tensile analysis; zero span tensile.

18. AVAILABILITY x§ Unlimited

CH For Official Distribution. Do Not Release to NTIS O Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003- CH Order From National Technical Information Service (NTIS), Springfield, V A. 22161

19. SECURITY CLASS 21. NO. OF

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