11-‘11,
I
AUDITION/LC EVALUATION Of VARIABLES AND MATERIALS
IN THE RECOVERY OF WET FIBER MATS FROM
COMPRESSIVE DEFORMATION
April 1942
RESTRICTED
CLASSIFIED DOCUMENT
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the National Defense of the United States wit
meaning of the Espionage Act, USC 50:3
transmission or the revelation of '
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i
to I y law.
Information so classifie
b
only to perI
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cm who of necessity must be informed
4
ET ; CH LA I:3 0 RA 1 - 0
Y
aR, A RY
No. 1295
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison, Wisconsin
In Cooperation with the University of Wisconsin
tm e-6
ADDITIONAL EVALUATION 0: VARIABLES AND MATERIALS IN THE
RECOVERY OP WET _FIBER MATS PROM COMPRESSIVE DEFORMATION
3y
C. O. SEBORG, Assistant Chemist
And
F, A. SIMMOADS, Associate Chemist
ABSTRACT
At constant temperature, the recovery values for wet fiber mats
from compressive deformation were little affected until the surface tension
of the suspensions was reduced to. about 60 dynes per centimeter, but further
reduction resulted in marked, though variable, effects. Irrespective of the
effect on the recovery value, a decreased surface tension always resulted in
a decreased shrinkage of the test mat upon drying in air. The surface
tension of ordinary pulp suspensions is the range where recovery values are
not affected.
At the same surface tension and temperature, different wetting
agents, although not at the same concentration, resulted in different recovery
values. This is taken to indicate adsorption of the wetting agent and its
influence on the recovery values by a change in the condition of the external
fiber surface.
At constant surface tension and variable temperature, no consistent
trends were found, recovery values for some pulps increasing with increasing
temperature, others decreasing, and some remaining unchanged.
As duration of compression was increased, the recovery of unbeaten
and slightly beaten pulps was reduced considerably and in about the same
degree, but the effect became progressively less with increased beating.
These increases in degree of plastic deformation were indicated by the results
of recovery determinations made on screen classified size fractions from a
beaten pulp and also from groundwood pulps to be due to increasing development
of "fines." The fact that groundwood pulps have lower recovery values than
sulfate and sulfite pulps is also due to the larger percentage of fines in
the sulfite pulps.
It was confirmed that sulfate pulps, as a class, are higher in
recovery than sulfite pulps.
R1295
-1-
INTRODUCTION
In a previous reportl the recovery from compressive deformation
of a bleached southern pine sulfate pulp was shown to have decreased 25
percent, apparently linearly, as the temperature of the wet mat was increased
over the range of 13 to 42° C. The surface tension of the water was not
controlled in this instance and, although the change in the value was relatively small, it was necessary to recognize that two variables were undergoing change simultaneously.
A study was made at the Forest Products Laboratory to determine if
the effect of these two variables could be isolated. Data were obtained on
both the influence of duration of compression and screen fractions on recovery
values. The results of these studies are here presented
APPARATUS AND PROCEDURE
The apparatus and procedure used ars essentially the same:as-previously doecribed.1 Improvements have been made, however, by providing means
for controlling the temperature and eliminating possible side components of
force during compression. The latter is achieved by transmitting pressure
from a lever through a piston to a ball bearing automatically centered in a
plunger in direct contact with the pulp mat. This apparatus is shown in
figure 1. The temperature control apparatus, diagrammed in figure 2, maintains the selected temperature of 25° O. within 4. 0.5° C. This degree of
accuracy holds over a range of 11° to 75° C., provided the water entering
the heater is at constant temperature. In operation, artesian water at a
temperature of 11° to 12° C., available throughout the year, was passed from
an adjustable constant level device through the heater and then to the compression apparatus. An Occasional slight adjustment of the constant level
apparatus offset the small variation in the temperature of the entering water.
Temperature control in the 11° to 75° C. range was accomplished by using
various sized orifices to regulate the rate of flow of water to the heater.
The stream of constant temperature water passed through a copper coil in a
hollow plunger of the compression apparatus and overflowed to a diked base,
thus keeping both sides of the mat at the desired temperature. Prior to
compression, the pulp mats were brought to the desired temperature by
conditioning in ,a constant temperature bath.
The weight of the wet mats prior to pressing was standardized at
50 grams, since this was found to improve repetitive accuracy. In the
earlier trials, the weight of the pulp samples on the moisture-free basis
was 6 grams. It was later found with the improved apparatus that a sample
weight of 4 grams could be used.
1Paper Trade J. 109(8):35-42. Aug. 24, 1939.
R1295
-2-
The surface tension of the effluent obtained when the mats were
formed was measured with a DuNoi3y interfacial tensiometer at a temperature
of 25° ± 2° C. The wetting agents "Aerosol OT" and "Nacconal NR" were used
to adjust the surface tension.
EFFECT OF DURATION OF COMPRESSION
As the duration of compression was increased, the recovery of the
unbeaten and slightly beaten pulp was reduced considerably and in approximately the same degree, but the effect became progressively less with
increased beating, as shown in figure 3. This trend is the same as that
reported previously1 on 12-gram samples (moisture-free basis) of unbeaten
and beaten bleached loblolly pine sulfate pulp.
In the present instance it was observed that recovery values, except
for the stuff lowest in freeness, continued to be reduced after the thickness
of the mat had reached a constant value.
Recovery determinations made on screen-classified sized fractions
from both beaten pulp and mechanical pulps indicated the increases in degree
of plastic deformation to be an immediate result of the development of fines.
Possibly the more slender fibrils and fibrilated fibers in the pulp were
distorted to a greater curvature without exceeding the elastic limit than
were the whole undamaged fibers in the unbeaten pulp. Therefore, probably
fewer f i ber s exceeded their elastic limit in the neaten pulp than in the
unbeaten pulps. Furthermore, such plastic flow as did occur in the beaten
pulp might not show its effect, because the recovery of the beaten pulp was
in the lotv, insensitive range of the determination.
RECOVERY OF SCREEN-CLASSIFIED SIZED FRACTIONS
Chemical Pulp:
In figure 4, the recovery value of the coarse fraction from a
beaten bleached softwood alpha pulp is compared with other samples comprising
the coarse fraction plus increasing percentages of a fine fraction passing
115-mesh and retained on 150-mesh, as well as with this fine fraction alone.
Increasing the percentage of fines decreased the recovery, the unit effect
being greatest with the first 25 percent added. The effect • of fines is
further emphasized by comparing the recovery values of the 115-to 150-mesh
and 24-meSh fractions and the whole pulp, which were 45, 79, and 55 percent,
respectively,
Groundwood
Pulpsf
Recovery values of fractions and also the whole pulps of several
groundwoods are given in figure 5, with the same influence of fines in
R-1295
-3-
evidence. In this instance, however, the finest fractions collected (between
115-and 150-mesh) were, for each pulp, still higher than (roughly twice) that
of the whole pulp. The fraction passing 150-mesh was not collected, but it
seems obvious that this is the fraction which is responsible for the final
reduction of the recovery of the whole pulp.
Of the five groundwoods, southern pine had the highest percentage
of fines Massing 150-mesh. The higher recovery value of this pulp, in spite
Of the larger amount of fines, is attributed to the fact that this groundwood
had a greater amount of gummerwood fibers than the other pulps. It has been
showna that summerwood fibers are markedly stiffer than springwood fibers,
and that fiber stiffness is a major factor influencing recovery.
When the opportunity occurs, the recovery of similar coarse fractions, before and after purification to various degrees, will be compared
with that of corresponding ones from chemical pulps.
RECOVERY OF UNBLEACHED SULFATE AND SULFITE
PULPS USING IMPROVED APPARATUS
The order of magnitude of recovery values of groundwood pulps as
determined with the improved apparatus is shown in figure 5. Similar data
for sulfate and sulfite pulps from the same species are Given in table 1.
These results confirm previous indications that sulfate pulps are higher
in recovery than sulfite pulps. It was of interest to note that the recovery
value of the southern pine groundwood was practically as high as the highest
value for the sulfite pulps listed.
EFFECT OF TEMPERATURE, SURFACE TENSION NOT CONTROLLED
The recovery of a bleached southern pine sulfate pulp had been
found previously to decrease 25 percent, apparently linearly, as the temperature was increased from 13° to 42° C. with no control of surface tension.
Additional data dealing with this relation for two unbleached pulps over the
temperature range of 0° to 42.5° C. are in figure 6. In this instance neither
the recovery nor the surface tension was markedly affected by changes in
temperature. Since the recovery of some pulps varies with temperature, this
variable must be controlled at all times. In those instances in which the
variation due to change in temperature was greater than the variation due to
repetitive determinations, it was found that temperature control within
2° C. was adequate.
It was observed that surface tension tended to decrease somewhat
during beating, as is indicated by the data in table 2.
Paper Trade J., 113(17):49-50 Oct. 23, 1941.
R-1295
-4-
EFFECT OF TEMPERATURE UPON ZECOVERY AT
REDUCED SURFACE TENSION
Occluded Foam:
When a pulp suspension at greatly reduced surface tension was
agitated prior to mat formation, a great deal of foam was formed and subsequently occluded in the mat. This resulted in extremely bulky mats probably
due to both the reduced contracting force of the water and the mechanical
resistance -of the foam.
It was necessary, therefore, to determine if the increased recovery
values observed at reduced surface tension were the result of the entrapped
air bubbles under pressure, since, as shown by the data in table 3, solid
fraction determinations on the wet mats revealed greater void volumes in-the
mats under pressure at reduced surface tension than in those at normal surface
tension. Deaerating the pulp suspensions in a vacuum prior to the forming of
the mat helped little because considerable foam was formed again when the
suspension was poured into the deckle box for mat formation. It was found,
however, that deaeration of the mats after formation under repeated vacuum
treatment removed the foam.
The average recovery values in table 4 of mats with and without
the presence of foam are in good agreement, showing the presence of foam
to be without effect upon the recovery values at reduced surface tension.
Temperature Effect at Reduced
Surface Tension:
The effect of temperature on recovery at reduced surface tension
is illustrated in figure 7. The recovery values of the unbeaten and beaten
sulfate pulp decreased with increase in temperature. This trend at reduced
surface tension is opposite to that of the same pulp at normal surface tension.
The influence of temperature on the sulfite pulp decreased to some extent as
the degree of beating was increased. In the case of the sulfate pulp, the
effect of temperature was not altered by beating.
Of interest is the fact that both the unbeaten and beaten sulfate
pulps showed higher recovery at reduced surface tension as compared to the
values at normal surface tension, whereas, in the case of the sulfite pulp,
the recovery of the unbeaten pulp was lower and that of the beaten pulp was
higher at reduced surface tension.
EFFECT OF SURFACE TENSION AT CONSTANT TEMRATURE
To determine the effect of surface tension, the pulp suspensions,
either with or without the wetting agent, were allowed to stand 16 hours
R-1295
-5-
before determining recovery. This procedure was adopted after erratic results
were obtained with suspensions that had stood only a short time after the
addition of the wetting agent.
The influence of surface tension on recovery of unbleached unbeaten,
and beaten Douglas-fir sulfate and sulfite pulps is shown in figures 8 and 9.
It is apparent upon inspection of the recovery values at reduced
surface tension, as adjusted with the two different wetting agents, that they
had an appreciable direct effect, probably by virtue of adsorption, on the
recovery characteristics of the unbeaten pulp. The direct effect, although
greatly minimized, seems to persist in the beaten pulps. It is, therefore,
not possible to draw from these data a simple relation, if one exists, between
recovery and surface tension as varied by the wetting agents used.
If, however, the recovery values at the lowest surface tension used
are compared with those at the normal surface tension as given in table 5,
it is seen that an appreciable increase in recovery did occur when the surface
tension was reduced to approximately 30 dynes per centimeter.
Surface Tension and Shrinkage:
After determining the recovery of Douglas-fir sulfite pulp and
stuffs, the mats were air dried at 65 percent relative humidity, the diameters
measured, and the shrinkage calculated as a percentage of the diameter of
the wet mat. The shrinkages at three different freeness values over a wide
range of surface tension are plotted in figure 10.'
Although the essentially linear decrease of shrinkage with decrease
in surface tension may have been due partly to adsorbed wetting agent blocking fiber surface available for bonds, the reduction in surface tension is
believed to be the major factor. For example, Campbell: a has shown by calculation that the surface and internal tensions of water evaporating from a fiber
structure are great enough to account for a compacting force in causing the
shrinkage of the structure.
Effect of Weight of Pulp in Mats
of Groundwood Pulps:
The recovery of groundwood pulps of different species and of different weights of pulp in the mats is shown An figure 11. The influence of the
amount of pulp in the mat is found to be the same with groundwoods as ,:rith
the chemical pulps previously reported. The curves for the southern pine and
birch are in a distinctly different category than those of the other groundwoods. The southern pine groundwood was markedly higher in strength than the
other pulps although the birch possessed no outstandingly different strength
properties as determined by the usual test methods.
-Paper Trade J., 95(8):29-33, Aug. 25, 1932.
R-1295
-6-
Consequently, sample weight of 4 grams on the moisture-free basis
has been selected as the standard weight for use with the improved apparatus.
CONCLUSIONS
Recovery of pulps and stuffs from compressive deformation was
affected by the duration of compression. The longer the mat was pressed,
the lower the recovery value, especially in the case of the unbeaten pulps,
indicating the effect 'of plasticity of the fibers.
Recovery values of chemical and mechanical pulps and stuffs which
had been classified as to size of fractions showed the large influence of the
fraction passing 150-mesh on the recovery of the whole pulp.
It was confirmed that sulfate pulps as a class are higher in
recovery than sulfite pulps, and both are higher than groundwood pulps.
Tho effect of temperature on recovery values is a complex one,
being influenced by such factors as surface tension, plasticity, and the
physical condition of the fiber surfaces. At constant surface tension and
variable temp erature there were no consistent trends, recovery values for
some pules increasing with increasing temperature, others decreasing, and
some remaining unchanged.
When the surface tension was varied at constant tem perature with
two different wetting agents, the latter were found to have a direct effect
on the recovery characteristics of the pulp itself. This indicates that it
will be extremely difficult to determine the exact effect of surface tension
on recovery. It was, however, possible to show an increase in recovery at a
sufficiently reduced surface tension. Fortunately, the normal surface tension
of pulps and stuffs does not vary enough to necessitate control of surface
tension in the recovery determination. Beating was found to reduce surface
tension up to ? dynes per centimeter.
Tho shrinkage of mats of unbeaten and beaten pulps upon drying in
air decreased with decrease in surface tension, the effect becoming ;1-eater
as the degree of beating was increased. Adsorption of wetting agent blocking
off available surface for fiber-fiber bonds is recognized as a possible second
factor in reducing shrinkage.
As a result of the effect of the weight of pulp in mats of groundwood pulps on the determination (chemical pulps having been previously
covered), a sample weight of 4 grams on the moisture-free basis was selected
as standard.
R-1295
-7-
Table 1.--Recovery from compressive deformation
of sulfate and sulfite pulps
Species
Recovery
:Designation:
number : Unbleached : Unbleached
sulfite
sulfate :
Percent :
:
Red gum
Average
:
•.
Douglas-fir
A
•.
Average
Douglas-fir
:
3
.
Average
Jack pine
Average
Western white pine :
Average
1
-Sample weight 6 grams moisture-free
basis, normal surface tension.
R1295
100.0
101.5
103.0
98.5
100.8,
:
:
'.
:
:
64.4
64.8
64.6
64.8
64.6
58.1
62.0
64.9
65.0
62.5
93.0
95.0
96.4
100.0
96.1
76.0
73.0
74.5
77.3
77.5
74.6
Percent
:
:
:
:
49.8
51.8
55.2
54.3
:
52.8
92.5
90.4
92.5
92.0
91.9
50.0
50.8
49.8
51.3
50.5
69.6
70.0
68.6
68.2
69.1
56.6
56.3
55.7
55.7
56.1
Table 2. Surface tension values of unbeaten and beaten
Douglas-fir kraft and sulfite pulps
Pulp
Freeness
Surface Tension
S.-R,
cc.
Dynes Der cm.
Sulfate, unbeaten
860
71.3
Sulfate, beaten
710
69.2
Sulfite, unbeaten
885
71.2
Sulfite, beaten
816
68.4
Sulfite, beaten
500
67.0
Sulfite, beaten
300
64.0
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Table 4.--Comparison of recovery values of mats
with and without the p resence of foam
Recovery from compressive deformation, Percent
11
Sulfite=
Sulfate2 surface
2 surface::Normal surface :ReducedNormal surface :Reducedtension
tension
tension
tension
Normal: Deaer- : Mat : Deaer- ::Normal: Deaer- : Mat : Deaermat :ated mat :full of:ated mat:: mat :ated mat :full af:ated mat
: foam
• •
: foam :
•n•••n•••n•n••
69.6 : 74.5 : 151.2 : 139.2 :: 55.6 : 53.8 : 73.0 : 71.6
70.0 : 71.5
: 146.0 : 148.6 :: 56.3 : 52.6
: 70.8 : 68.0
68.6 : 71.8
: 141.0 : 150.0 :: 55.7 : 53.4 : 76.3 : 70.3
68.2 : 72.2
: 143.5 : 141.4 :: 55.7 : 54,0 : 69.8 : 72.0
: 144.0 : 149.5 ::
148.3 :
147.2 ::
: 59.3 :
: 71.7 :
150.5 : 138.4 ::
: 159.0 :
Am69.1 : 72.5 : 148.0 : 144.9 :: 56.1 : 53:4 : 71.8 : 70.5
Western white pine.
a Surface tension reduced to 28.5 dynes per
centimeter with "aerosol OT" wetting agent.
R1295
Table 5.--Oomoarison of average recovery values
at normal surface tension and at
approximatel y 30 dynes Der cm.
Percent change
Recovery at
Kind of : Pulp :Freeness:
S.-R. : surface tension : in recovery,
Douglas-: or
basis normal
fir pulp: stuff
value
: Normal :30 dynes:
: per cm.:
cc.
Sulfite : Pulp
885
Sulfate : Pulp
860
Sulfite : Stuff :
53
40
:
75
79
816
:
27
Sulfate : Stuff :
710
:
28
Sulfite : Stuff :
500
Sulfite : Stuff :
300
81295
:
:
- 13
:
+-5
31
+ 15
30
+
9.6 :
22
7.6 :
18
:
7
+129
+137
L.1
O
cZ
ti
ti
.1
,L,,I.
b.
n
NOTE. SAMPLE WEIGHT 6 GRAMS ON MOISTURE-FREE BASIS
11111
_1111h......mirmilli
ERR
-S.-R.
imunii
01....1.
II
im...........
_-_„imilm.......r-.--.......BEATE
BEATEN
0
._
._
S.-R.
FiREENESS 450cc.
I
40
50
nn
FREENESS 787cr
60
70
I
80
I.,
90
100
120
130
140
DURATION OF COMPRESS/ON (MINUTES)
FIG. 3
EFFECT OF DURATION OF COMPRESSION UPON THE RECOVERY
OF UNBLEACHED JACK PINE SULFITE PULP AND STUFFS.
80
Ct
kJ 75
A- RETAINED ON 54 MESH 0.7mm ON SIDE OF OPENING
B- PASSING 1/5 MESH BUT RETAINED ON 150 MESH
NOTE ' SAMPLE WEIGHT 4 GRAMS 01V MOISTURE-FREE BASIS
ti
70
CC
O
65
ri;")
CL.
k
60
t•J
55
cc
W
Lu 50
45 A 0
6 100
25
50
75
50
PERCENTAGE OF PULPS A AND B IN MAT
75
25
FIG. 4
Z U 40932 F
RECOVERY VALUES OF SCREEN-CLASSIFIED SIZED
FRACTIONS OF A BEATEN BLEACHED ALPHA PULP.
100 A
0 B
150
160
220
180
z
/60
cZi
(3-1 /40
120
&' 100
eifil.
Nom=
wrilm __........
Iwzmil
td,--, ... p..11111111
- NOTE.
SAMPLE WEIGHT 4
GRAMS, MO/STURE-FREE BASIS
--rilllit
sii.w...11._
PULP
LL.1
80
recco
..
zoo
-rail
1M
0175
PERCENT} 150-K151 1 SCREEN
PERCENT
.38
49
42
54
53
56
52
45
40
0.351
/50 /15
FuLp
o -COTTONWOOD
6,-BLACK WILLOW
• - SOUTHERN PINE
A- WHITE SPRUCE
n - CONWRCIAL SPRUCE
60
0.1
PEcovEw Of wHoLE AH001IT PASSING
0.700
SIZE OF MESH OPENING(mm)
80
42
24
MESH
FIG. 5
RECOVERY VALUES OF GROUNDWOOD PULPS AND SCREEN-CLASSIFIED SIZED FRACTIONS FROM THEM.
60
4-, 50
Q
•
•
• 566
7/0
n
—.1
•. sae
56.5
1----750
635
152.8
•,c 40
NOTE : SAMPLE WEIGHT 6 GRAMS ON MOISTURE-FREE BASIS
THE NUMERICAL VALUES AT EACH 6ROUP OF PO/NTS ON
CURVES REFER TO SURFACE TENSION IN DYNES PER CM.
k
L,-. 30
e 20
o
-.57,5
Ck /0
4.1
563
560
54.3
•
52.0
0 54.0
0 S6.0
n
53.0
530
0
20
30
TEMPERATUREX)
520
40
560
50
F16.6
RELATION OF TEMPERATURE AND RECOVERY OF UNBLEACHED DOUGLAS-FIR SULFITE AND
WESTERN HEMLOCK SULFATE PULPS AND STUFFS. (SURFACE TENSION NOT CONTROLLED)
Z M 40929 F
100
I
I
, LEGEND
UNBLEACHED DOUGLAS-FIR SULFITE
•- UNBEATEN, 5-R FREENESS &Mc
-
628ec
q -BEATEN, 3-H
381a.
• - BEATEN, 5-R
-
UNBLEACHED WESTERN HEMLOCK SULFATE
o - UNBEATEN, S -R FREENESS 860cc
5/0cc.
°
n - BEATEN ,S-R
1
NOTE SURFACE TENSION REDUCED' WITH.NACCONAL Nle
SAMPLE WEIGHT 6 GRAMS ON MOISTURE-FREE 84515
90
,•.1
!
Lk+ 80
3I4 ---_____
eaa
70 —,,........,—..—
------------
275
O
315
•
315 •
es
40
8 e7
4
a
;30
Z
k 20
4
Itl
n
IA
3A
an
an
an
71
TEMPERATURE CC)
F16.7
RELATION OF TEMPERATURE AND RECOVERY OF UNBLEACHED DOU6LAS-FIR SULFITE
AND WESTERN HEMLOCK PULPS AND STUFFS AT REDUCED SURFACE TENSION.
•
90
•
•
•
*ID
BO
A
a
•
o
o
••
•
A
4.1
Q..
70
UNBEATEN, S-R FREENESS 860fn
•
tz.
ti
60
•
LEGEND
Lu
A- NORMAL SURFACE TENSION
• SURFACE TENSION REDUCED WITH' NACCONAL NR •
TENSION REDUCED WITH 'AEROSOL OT'
SO
0 - SURFACE
NOTE : SAMPLE WEIGHT 6 GRAMS ON MOISTURE-FREE BASIS
t:t
40
z 30
O
VO
•
CC
CC
UNBEATEN, 5-R FREENESS 7 Occ.
e0
Ct
/0
0
80
70
Z M 40933
F
60
40
50
SURFACE TENSION (DYNES/CM)
30
F16. 8
RELATION OF SURFACE TENSION AND RECOVERY OF DOUGLAS-FIR
SULFATE PULP AND STUFFS AT CONSTANT TEMPERATURE.
HO
14:1
0 Ct
0
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,
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