BLEACHING GROUNIDWOCI) PULPS
WITH IHYPOCIILOPITES
February 1949
INFORMATION REVIEWED
AND REAFFIRMED
March 1956
No. 81736
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison 5, Wisconsin
In Cooperation with the University of Wisconsin
BLEACHING GROUNDWOOD PULPS WITH HYPOCHLORITES-l'a
BY
RALPH M. KINGSBURY, Chemist
FORREST A. SIMMONDS, Chemist
and
EARLE S. LEWIS, Physical Science Aid
Forest Products Laboratory, 2 Forest Service
U. S. Department of Agriculture
am, .,n• .10
Summary
Bleaching experiments were made at the Forest Products Laboratory on
groundwood pulps from 13 hardwoods, 6 softwoods, and also a mixture of 6
hardwoods alone and in a mixture with Eastern white pine, as occur
naturally on Northeast farm wood lots. The results show that calcium
hypochlorite is a satisfactory bleaching agent for the hardwood pulps, but
probably is not satisfactory for the softwood pulp. In general, the brightness of the hardwood pulps, individually and in mixtures, was increased to
the range of 70 to 79 percent with 10 percent available chlorine. Upon
exposure to carbon arc light, the recession in brightness ranged from 4 to
11 points, Bleached pulp yields were 98 to 100 percent of the unbleached
pulp. The only consistent effect of the bleaching on drainage and strength
properties was an increase in tensile strength.
In order to get a good bleaching effect with hypochlorite, its tendency to
react very rapidly with groundwood pulp must be retarded considerably,
especially at the start of the reaction. This was done by use of low density, low temperature, and a high alkalinity, with the latter being the
most critical of the three. The lime requirement for control of alkalinity
ranged from 3 to 6 percent, including the free lime in the bleaching liquor.
Substitution of sodium silicate for a part of the lime in the bleaching of
-Presented at TAPPI Mechanical Pulping Conference, Poland Spring House,
Poland Spring, Maine, Sept. 27-29, 1948.
?The results included in this report are taken in part from an investigation
undertaken with funds furnished under the Research & Marketing Act,
-Maintained at Madison 5, Wis., in cooperation with the University of
Wisconsin.
Report No, R1736
some pulps further improved brightness up to 5 points. Final addition of
sulfurous acid, or equivalent, to the stock had a similar effect. Although
the hue of hypochlorite-bleached pulps was in the yellow range, in the case
of hardwood pulps, it is believed to be light enough to be generally
satisfactory.
Experimental results indicated that pulps from mixtures of hardwoods can be
bleached satisfactorily with hypochlorite and that the brightness of the
mixtures will be proportional to that obtainable on pulps from the individual
woods. Although the Eastern white pine pulp did not respond satisfactorily
to hypochlorite, a 50-50 mixture of it and the mixed hardwood pulp was
bleached to about 70 brightness with 10 percent available chlorine.
Essentially the same result was obtained, however, by blending bleached
mixed hardwood pulp with unbleached pine pulp. This procedure would be
the more economical of the two.
Introduction
The use of local supplies of pulpwood is advantageous not only to the pulp
manufacturer but also to any farmers of those regions owning stands of
timber. However, supplies of wood available on farm wood lots within easy
reach of the mills, are, in many instances, of poor quality or not the
kinds ordinarily used. If it can be shown how to produce satisfactory pulp
from these species and from mixtures of them as they occur, the marketability
of farm-lot wood will be increased. For example, these woods can be used to
a greater extent for the production of groundwood pulps when practical ways
of bleaching the pulps become available. The purpose of this work was to
develop bleaching procedures suitable for groundwood pulps made from a
variety of individual woods and from mixed species. The mixed species used
was representative of certain stands on farm woodlots in the Northeast,
The requirements for a process for bleaching groundwood pulps are that its
chemical cost will be low, that it will effect an appreciable increase in
brightness that will not recede too rapidly, that it will not develop a
strong yellow hue, and, finally, that it will cause only a small loss in
weight of pulp by chemical action. It appears that no one bleaching process
meets these requirements for all goundwood pulps. The most promising agents
for the commercial bleaching of groundwood pulps are hydrosulfites, peroxides,
and hYpochlorites (1, 4, 6, 7).
Important Factors in the Use of Hypochloritez
The rate of reaction between calcium or sodium hypochlorite and groundwood
with 10 percent available chlorine is normally extremely rapid, For
satisfactory result in any instance, the density, temperature, and alkalinity
must be adjusted so that the rate of reaction will be definitely retarded at
the start. It appears, however, that the alkalinity is the most critical of
the three variables. In general, density should not exceed 6 percent, and
Report No. 81736
no apparent .benefit was observed for lower values. Temperature does not
need to exceed 30° C., and alkalinity should be equivalent initially to the
PH range of 11 to 12 and : at the end of the reaction, to not less than pH 8.
Examples of the influence of alkalinity and of the use of sodium silicate in
the buffer system are given in a previous publication (4). Depending on the
pulp, the use of sodium silicate as a part of the buffer system will give a
somewhat better brightness than otherwise. It further appears that the reaction should be stopped a little short of complete chlorine consumption in
order to realize the maximum brightness. The addition of sulfur dioxide at
the end of the reaction is usually beneficial to brightness, but it does not
improve its stability.
Effects of Bleaching
Brightness
The brightness of the hardwood pulps reported . on here was increased from 8 to
23 points with calcium hypochlorite at the level of 10 percent available
chlorine. It is shown in table.1 that those increases resulted in brightness
values of 70 to 79 percent for the bleached pulps. In some instances, with,
for example, the sugar maple and sweetgum pulps, sodium hypochlorite gave from
4 to 8 points higher brightness values than calcium hypochlorite. In general,
however, calcium hypochlorite gave higher brightness values for the hardwood
ground pulps than did sodium perioxide under the conditions used.
Pulps made from two different lots each of quaking aspen, paper birch,
yellow-poplar, and sugar maple woods were studied to note possible variations
within species. Although little difference was observed between the lots of
aspen and paper birch, the results obtained for the yellow-poplar and sugar
maple pulps indicate that variation within some species is to be expected.
The experience with the two lots of yellow-poplar was especially interesting.
The fresh pulp from lot II in its natural condition did not respond to hypochlorite nor to sodium peroxide. When the pulp was extracted with alcohol,
however, either before or after treatment with 10 percent chlorine as
calcium hypochlorite, a brightness increase of 7 points resulted. The
alcohol removed a yellow-colored material. After a portion of the unextracted pulp at about 25 percent density had been in storage about 50 days
at 5° C., it did not respond to hypochlorite, but another portion at the
same density after storage at room temperature during the same period did
respond to the extent of 11 points in brightness.
No difficulty was experienced in bleaching a pulp from a mixture of hardwoods
comprising 29 percent each of red maple and paper birch, 16 percent each
sugar maple and yellow birch, and 5 percent each of white ash and American
beech by weight. On a volume basis, the percentage values were essentially
the same as on the weight basis because of the similarity of the specific
gravities. The optimum conditions for calcium hypochlorite bleaching were
the same as for the other hardwood pulps. Uhen a brightness value was
calculated for the mixture on the basis of direct proportionality from the
experimental brightness values for the bleached pulps from the individual
Report Not 4.736
woods, the calculated value agreed with the value determined experimentally.
Although pulps from two of the component woods, white ash and American beech,
contained numerous shives that were not bleached satisfactorily, there was no
evidence of unbleached shives in the bleached pulp from the mixture.
The brightness values obtained for the softwood mechanical pulps indicate
that, as a class, they do not respond well to hypochlorites. Of five softwood pulps, only a white spruce pul p reached a brightness value possibly of
practical significance when treated with 10 percent available chlorine as
calcium hypochlorite. With sodium hy pochlorite equivalent to 10 percent
chlorine, a southern yellow pine pulp reached only 63 brightness, with the
increase being 8.5 points. The Eastern white pine pulp required 15 percent
chlorine as calcium hypochlorite for a brightness approaching 70, and even
then the bleached pulp was quite yellow in hue.
The use of silicate in conjunction with lime as the buffer system with calcium
hypochlorite gave no improvement in the brightness of the Eastern white pine
pulp. The use of sodium hypochlorite or extractions with hot water, sodium
hydroxide, or hydrochloric acid had little effect. Extraction with alcohol,
however, removed a yellow material; and when the extracted pulp was treated
with 10 percent chlorine as calcium hypochlorite and this was followed with a
final treatment with sulfurous acid, a brightness increase of 4.2 points resulted. At the present time, hypochlorites show little promise as practicable
agents for bleaching softwood mechanical pulps.
stability of Brightness
Relative stability of the brightness of the mechanical pulps after bleaching
with hypochlorites is compared to that of those bleached with sodium peroxide
by the recession values given in table 2. The values were obtained by
exposure of test sheets to single-arc carbon arc light. Because of differences in exposure time, all pairs of pulps are not directly comparable, but
it appears that the greater proportion of recession effected by carbon arc
light occurs at the end of 1 hour (5). The data show that the brightness
of pulps after bleaching with hypochlorite was less stable than after
bleaching with sodium peroxide, The hardwood Pulps bleached with hypochlorite, including the mixed hardwood pulp, retained, however, 50 to 80
percent of the original brightness increase. Owing to a generally higher
initial brightness than that of the peroxide-bleached pulps, they were at
least as bright as the latter after both had been subjected to exposure.
I
Hue
Because of the hue of mechanical pulps, either bleached or unbleached, the
brightness value alone is inadequate to characterize appearance. Consequently, the appearance of the pulps dealt with in this report is given in
terms of brightness, dominant wave length, and purity (2), as shown in table
1. It was previously suggested (4) that a yellowness value (3) might be a
sufficient supplementary value for a numerical comparison of the appearance
of bleached groundwood pulps. Further experience, however, indicates that
Report No. 81736
-4-
the usefulness of the yellowness value is limited, apparently because
bleached groundwood pulps are too far removed from the degree of whiteness
for which the yellowness value was originally intended to be used, The
amber, green, and blue filters used in the tristimulus measurements had maximum transmission values of approximately 590, 555, and 156 millimicrons.
The range of dominant wave length for all pulps, both bleached and unbleached,
was from 562 millimicrons for the hypochlorite-bleached white spruce pulp to
about 582 millimicrons for the unbleached yellow birch and sugar maple pulps.
The range for green is considered to be 500 to 570 millimicrons, and that for
yellow, 570 to 590 millimicrons (2). On that basis, the experimental pulps
were all essentially yellow in hue. If 580 millimicrons are taken arbitrarily as yellow, the indication is that bleaching with hypochlorites consistently gives hues slightly toward the green, or lower, wave length. With
sodium peroxide the trend toward the green is, in general, the same, but
the effect is slightly less, In general, the purity of hue resulting from
hypochlorite bleaching appeared to be about the same as that resulting from
bleaching with sodium peroxide, The high purity values of the bleached
yellow-poplar II (table 1), Western hemlock, and the Eastern white pine
pulps after bleaching with 10 percent available chlorine accords well with
their strong yellow appearance.
Yield
The yield values given in table 1, determined without loss of fiber, show
that losses in weight due to the chemical action of calcium hypochlorite
averaged 0.9 percent, with a maximum of 2.7 percent. Those results appear
very favorable in comparison to those obtained with sodium peroxide.
Freeness and Strength
All of the experimental pulp were not made under grinding conditions for
optimum freeness and strength. Consequently, the effect of bleaching on
those properties is expressed as a percentage change in table 3.
A decrease in freeness was obtained more frequently than an increase, with
the changes ranging from a negligible to an appreciable amount. Although
the percentage values for changes in bursting strength were large because
the bases for calculation were all small, they represent only small actual
changes in points. The same was true of the changes in tearing strength.
Since there was no definite trend toward higher or lower values, it is
apparent that there was no significant effect of bleaching on bursting and
tearing strengths.
There was a definite trend toward relatively large increases in tensile
strength as a result of hypochlorite bleaching, although the tensile
strength of the southern yellow pine and American beech pulps was decreased
about 80 pounds per square inch, With those two pulps excluded, the average
increase in tensile strength was 365 pounds per square inch, the maximum
being 972 pounds per square inch, As previously reported (4), a somewhat
Report No, 81736
-.5-
smaller increase in tensile strength can be expected when bleaching with
sodium peroxide.
Hardwood and Softwood Mixtures
The possibilities of processing mixtures of hardwoods and softwoods are of
interest to manufacturers l of groundwood papers. Results are given in table
4 of hypochlorite-bleaching experiments on stocks composed of mixtures of an
Eastern white pine groundwood with one made from a mixture of hardwoods.
The failure of the Eastern white pine pulp to respond to a treatment of 10
percent available chlorine as hypochlorite, except for improvement in
tensile strength, was discussed above. When mixtures of the pine and mixed
hardwood pulps were treated with 10 percent available chlorine as calcium
hypochlorite, the brightness was increased in proportion to .the amount of
'iardwood pulp in the mixture. This is shorn by the fact that the experimental values can be calculated almost exactly on a direct proportionality
basis from the brightness values of the unbleached pine pulp and of the
bleached mixed hardwood pulp. The indication is that when the mixture of
the unbleached pine and mixed hardwood pulp was treated with hypochlorite,
the effective rates at which chlorine was consumed by the two pulps were
equal despite the large difference in the reaction times when the pulps
were bleached separately.
In the preparation of a mixed pulp in the brightness range of 65 to 73 from
Eastern white pine and mixed hardwoods of the composition dealt with here,
less chlorine would be required by mixing unbleached pine pulp with hypochlorite-bleached hardwood pulp than by bleaching the mixture with hypochlorite.
Report No, 81736
-6-
Literature Cited
(1)
Andrews, I. H. Zinc Hydrosulfite Treatment of Groundwood. Pulp &
Paper Magazine of Canada 46(9)679-81,, Aug. 1945. Pulp cc Paper
Industry 19(8)58, 60, Aug. 1945.
(2)
Hardy, Arthur C. and staff. Handbook of Colorimetry. The Technology
Press, Cambridge, Mass. 1936.
(3)
Hunter, Richard S. Photoelectric Tristimulus Colorimetry with Three
Filters. Natl.Bureau of Standards Circ. C429, July 30, 1942.
(4)
Kingsbury, R. M. Simonds, F. A., and Lewis, E. S. Observations on
Bleaching Groundwood Pulps, Paper Trade Jour. 126(24)49-59,
June 10, 1948. Pulp & Paper Magazine of Canada, Oct. 1948.
(5)
Lewis, Harry F., Reineck,, Edward A., and Fronmuller„ Douglas. The
Fading of Groundwood by Light. Paper Trade Jour. 120(8)44-48,
Aug. 23, 1945.
(6)
McEwen, Robert L. High Density of Mechanical Pulp with Hydrogen
Peroxide. Paper Trade Jour. 122(17), Apr. 25, 1946.
(7)
Reichert, J. S. Sodium Peroxide Bleaching of Mechanical Pulps.
Paper Trade Jour. 118(11)45-52, Mar. 16, 1944.
Report No. 81736
-7-
Table 1.--Influence et hvpochlorites and sodium peroxide on appearance and yield of mechanical pulp.
Specie,
1
_
:Yield of
purity
:Bleaching agent -: Stock :Temper-: Alkalinity :Duration : brightness-2
:Dominant wave length:
:bleat.hqd
:
:
or
•
:density: ature : .1 : Lind :Amount :
:Initial: Final:treatment:Unbleathed:Bleached:Unbleached:Bleached :Unbleached:Bleaohed: pulp4
: pulp
.•
:
I
t
i
: pulp
pulp
pulp
: null, :
pulp
:
•
:
•
:
:
:Peroent:Percent: .0: : pa
:
:
:
2ff
:
:
:Hr. :Min.: Percent : Percent: Mmu.
:
:
:
: Mau.
: Percent : pervlal:fIrclulk
Hardw o od.
98.8
:
74.1 : 10.7 : 8.6 : 1 1
53,5 :
100.0
, 10.
10.4: 9.0 r 2 2
72
53.5
98.8
: 10.9 : 10.0 :
: 4 :
.6 *
97.5
: 10.3: 9.2 , 2 : 3 :
61.3
.
:
657
. '
Water tupelo
TaLF:5 1}2
1
0
2
99.3
: 11.3 : 8.2
1 ,
:
66.0 :
73.9 100.0
2
•
66.0 :
76.6 ' 10.5 : 9.2 : 2 2 1 :
12 ' '40
98.8
Yellow-poplar I lia3 F2.g 11, 21 10
6 : 37
: 11.1 : 8.9 1 1 :
:
72.0 : 61.0
2
12 : 41
•
: 10.3 : 8.5 1 4 1
61.0 •
70.3 •
99.0
Yellow - poplar .//tc:011, 2
: 16.1 10
6 : 37 - : 11.7 : 8.3 : 1 ;
: li
: 576.5 :-. 10.5
:
k
--3.0 : 578.2
,1.3
10.5
: 13. 6 2
12 I 40
: 10.3 : 9.2 2 1
577.5 :
61.3 : ‘ 60.5 578.2
;;_11:FO 112:
: ,11.4 : 10.0 :
6 : '34
: 576.5 :
1
Eastern 0
13.5
: 4 :•
9. 9 :
:
52.z : 271.2 : 580.4
12 1 42
: 10.7 : 9.7 : 1 :
13.5
1 10.2 2 19947.3
: 577.2 :
qu r,Itznaloped. I ;
:
66.7 : 580.4
52.2 :
g:f0S1)2 2f2
99.2
10
: 11.2 : 8.5
.
:
I
:
.
63.4
:
. •
75.7
: 10.5
: 8.7 : 2 1
'
97.9
97
2
1 6 : a
63.4 :
77.0 7.9 : .. 9.9
:
Quaking aspen IIIICI:fgal)2;' 10
: -573.5 :
6 : 27 . 1 11.0 : 8.4 : 2 : 3 :
.5
76.0 : 576 .5,
63.5 :
6.0 '
:
12 1 40
9.9
: 10.3 : 8.5 : 2 : 4 :
63.5 2: _76.9: 576.5 : 577.0 :
-: 10 .5 : 8 .9 :
Paper birth I
TX61)2; 102-
6 : 36
11.3 ' 275.0 •
59.0
2 4 :
98.
12 1 41
12.018.8:2:51.560279.0:5743.84.3
10.2 : 8.5 2 2 :
59.0 :
75.6
:
:
8.3
Paper birch II ; g :F g L) 2 : 102
6 : 30
:
.3 ...
:
53.8
i
liv.
11 gm
t 5.79.5 :
28 2 42
14.3
: 3 1
10.3 : 8.8 :
:
88:77 •
56.3
:
; 241? g 61) 2 ; 102
8.7 :
: 575.0 :
12.0
99.7
Yellow birth
11.9 : 8.4 1 2 : 4 :
: 10.5 :
12.0
28 : Z?
10.3 2 9.0 2
: 580.0 :
98.6
: 2 I
53.8
._6.9 : 581.2
:
6.0 15.7
; 1=61) 2 : 102
6 :
: 36
I 2 z
: 570.0 :
3.1.0 :581.3
266.0
Sugar maple I
10.1 :
6,4 :
Ma0C1, : 10
15.7
6 : 35 1 11.4 1 9.2 :
1 4 :
113..8 :
2 575.3 :
71.3 1 581.3
9.1
:
:Na0C12 I 10
6
:
15.7.
11.2: 9.0 : 1 :
49.5 :
4 576.7 I
74.2 : 581.3
96.2
12 ; ?i5
4
15.7
: 12.4 :
:
11e,,0,•
2
'; 10.5 : 7.3 : 1 :
2
1 580.0 1
49:5 1255.0 1 581.3
97,3
7.6 :
:
,
: 577.1 1 12.0
Sugar maple' II 180081)2 1 10 6
1 12.3 ! 8.6 : 2 :
178.6 : 581.2
57.9
6.0 :
99.8
:
I
12.0
12 ; 41
71.4: 581.2
1
: 577.5 :
10.3 : 9.1 : 1 :
57.9 :
2
1842 0 21
: 574.4 :
12.0
:
7.6 :
98.9
:
I 4 :
2
28 1 42
I 10,4 : 9.3 :
57.9 : ,73.9 : 581.2
sil. 1120 2
99.3
10.(001)21 10
6 1 30
: 12.0 : 8.3 2 1 : 4 :
: 575.0 :
10.5
Red maple
.
57.6 1 278.9 1 580.0
28 1 39
: 10.6 9.2 :
10.5
1
: 577.8 1
2 .3, :99. 4
: 4 t
72.6: 580.0
57.6
11.3
: 10.0 2
99.8
:104:Fggli2
6 : 31 :: 11
Ash, white
.7 10
: 8.0
1 : 1 :
57 .2 ; 274.8 : 577.3
: 571.4 :
1/.3
:
9.0
28 43
: 572.4 1
: 10.2 : 9.3
99.1
2 57.2 ‘70.6 : 577.3
teag
13.5
6 : 30
: 576.0 :
: 11.3 : 101.0
: 11.5 : 8.0 : 1 : 4 :
American beech
49:1 : a72.0 : 580.4
1)2: 102
99.4
: 12.1 :
578.2 :
13.5
2
28 : 40
: 10.3 : 9.8 :
: 30 :
49.1 : ,62.0 580.4
3 : 30 1 11.6 : 8.3 : 2 I 15 :
Mixed hardwooder081) 2 ; 10
54.5 : 277.2: 580.9 : 576.0 1 12.0 I 9.1 : 99.0
12.0
:
9.9 : 99.2
28 1 42
: 10.4 : 10.1 :
: 25 ,
54.5 •
• 576.5 •
70.9 : 580.9
•
2
' 842 0 2
Sweetgum :os(o0112: 10
2
Black tupelo
:101.:0 11,2;
1
0
:
6 : 35
12 1
40 .
6 : 36
12 2 41
6 : 35
Softwoods
Eastern white
Pine
zCs.COC1)2: 10
,c.(0C1121 15
2
2
iMe.202
Southern - yellow :Ca(0C1) 2 : 15
01.001
: 10
pine
:11.,02
t0e2COC1/2: 152
Tack pine
IN,21
20
2
10 02( 00 2! 10
White .prate
:0222.(0C1 2 1 15
!
2
Western bowie,*
a(001) 2 . 10
zNa0C1
: 10
2
1. 842°2
!
6 : 31
6 : 30
28 1
10 :
10 :
12 :
10 :
12 :
6 :
41
36
36
42
36
45
25
6 : 25
12 : 40
6 : 37
4 : 27
12 : 40
: 11.2: 9.9 1
: 33
: 11.4 : 10.1 : 1 : 37 :
63.5 • i23.4 : 578.5
9.6 : 578.5
63.5 :
: 15 : g2,..3 ;
: 10.7 : 10.2 :
2:g ! 578.5
: 11.3 : 10.9 : 1 : 55 :
: 11.4 , : 9.1 : 1 : 50 •
63.o •
54.5 :
: 10.3 1 9.1 : 3 : 0 1
65.5 54.5 :
: 11.3 1 10.2 :
: 20 :
57.1 :
60.6 : 10.3: 9.1 : 4 , 0 : 57.161.7 •
: 40 :
1 11.1: 9.6 :
61.4 : 467.9 : 11.2 : 7.9 : 2 : 0 :
61.4 : 274.0 61.4 :
70.9 : 10.4 : 9.6 : 1 : 30 i
2 10 :
: 10.3 : 9.6 :
48.9 : ,45.0 : 580.0
: 12.8 : 12.6 :
: 30 :
48.9 : 254.7 : 580.0
: 10.2: 9.9 : 1 1 0 1
52.2 : 580.0
48.9 :
1
: 577.8 :
: 576.5 :
: 576.0 :
: 14.3 : 11.4 :
9.9 :
:
12.0
12.0
12.0
100.6
• 11.7 : 100.0
577.0
: 40 :
15.4:
1 11.1 : 100.0
20.4 :
98.8
98".8
15.4
I 580.0 :
99.4
99.5
99.o
97.6
97.5
99.3
96.7
15.4
! 15.8 !
98.2
[
1Percentage
values refer to weight of available chlorine, sodium peroxide, or other chemicals and are based on unbleached pulp. The calcium
hypoohlorite solution contained 0.3 to 0.7 percent free alkali as hydroxide and required 1 to 6 percent additional lime for adjusting
initial pH. The sodium hypoohlorite contained 3.6 percent free alkali as hydroxide and required up to 2 percent additional caustic for
adjusting initial pH. The peroxide bleaching solution contained 2 percent sodium peroxide, 5 percent sodium silicate, 0.05 percent
magnesium sulfate, and up to 1.5 percent sulfuric &old to adjust initial pH.
2Measured on air-dry teat sheets. Except as noted, test sheets of the hypochlorite-bleached pulps were formed at pH 7.5 from pulp washed
with tap water of pH 7.5. In the case of peroxide-bleached pulps a final adjustment of pH to 5 was made with eulfurous acid and the
test sheets were formed at pH 5 from unwashed pulp.
IBased on unbleached pulp.
-This sample of pulp was freshly made. When bleached after 53 days . storage at room temperature the brightness obtained was 71.5 percent.
IA final adjustment of pH to 5 was made with sulfurous acid and test sheets were formed at pH 5.0 from unwashed pulp.
Two percent sodium meta silicate was added to the bleach mixture.
2Twenty-nine percent each of red maple and paper birch, 16 percent each of sugar maple and yellow birch, and 5 percent each of American
beech and white ash on • weight basis and essentially the same by volume.
K
79943
P
Table 2.--Recession of brightness of bleached groundwood .ulps upon exposure
to carbon arc light
Pulp
:
•
Bleaching
agent'
:
Paper birch I
Paper birch II
:
:
!
Yellow birch
2
Sugar maple I
Ca(0C1) 2
Na2 02
Ca(0C1)
Na202
Ca(0C1) 2
Na2 02
Red maple
•
White ash
:
American beech
.
•
Mixed hardwood
Eastern white pine
White spruce
:
:
2
:
•
:
•
16.0
16.6
22.6
19.8
19.7
13.1
:
:
:
:
2
:
:
:
2
:
1
1
1
1
:
:
:
Points
7.9
8.6
9.9
7.7
4.2
3.3
:
8.7
5.5
:
2
:
4.5
Ca(0C1) 2
Na 2 0_ 2
Ca(0C1)
Na2 02
ca(oc1) 2
Na2 02
:
20.7
:
1
:
10.6
16.0
:
1
:
,
22.4
Ca(0C1) 2
2 02
Ca(0C1) 2
Ns
_.2 0
_2
Ca(0C1) 2
Na 2 02
--Ca(OC1) 2
Na2 o2
'Ca(0C1)2
5-Ca(0C1)
2
!
13.4
22,9
12.9
22.7
:
_
_.
Eastern cottonwood
:
Hours
24.7
Na
•
.•
1
:
:
:
Sugar maple II
:
Points
:
:
-Na0Cl
:
:
:
: Duration : Recession
: Brightness
of
: increase when :
: exposure-2 ::
bleached
:
Na2°2
'
:
:
:
:
1
:
1
1
21.3
15.0
:
:
:
1
1
1
:
:
:
:
:
:
14.5
2
:
6.1
1
1
2
2
2
21.0
6.5
12.6
9.5
•.
:
5.3
9.1
5.8
1
1
2
16.4
4.5
:
:
2
:
:
:
:
:
6.8
5:5
6.4
4.3
7.6
5.2
8,7
4.7
12.1
2.4
13.1
18.3
11.5
-The amount of hypochlorite was 10 percent expressed as available chlorine,
except in the two instances footnoted, and the amount of sodium peroxide
was 2 percent.
?Single-arc, carbon arc light.
-Two percent of sodium metasilicate was added to the bleach mixture.
4
-Twenty-nine
percent each of red maple and paper birch, 16 percent each of
sugar maple and yellow birch, and 5 percent each of white ash and American
beech on the weight basis.
-Fifteen
percent available chlorine.
Report No. 81736
Table 3.--Change in freeness and strength resulting from bleaching groundwood pulps with hypochlorites.
Pulp
: Bleaching :
: agent
:
:
:Bursting:Tearing :Tensile
Freeness
:
:strength:strength:strength
:
:
:Canadian:Shopper-:
:
:
:standard: Riegler:
••nn•
-----r-:
:Percent :Percent :Percent
------- :Percent : Percent
Sweetgum
: Ca(0C1) 2
: Na0C1
Black tupelo I
: Ca(0C1) 2
: Na0C1
Black tupelo II
: Ca(0C1) 2
: Na0C1
Water tupelo
: Ca(0C1) 2
Yellow,Toplar I
: Ca(OC1) 2
Quaking aspen I
: Ca(0C1) 2
Quaking aspen II : Ca(0C1) 2
Sugar maple I
: ?Na0C1
Red maple
: Ca(0C1) 2
White ash
: Ca(0C1) 2
American beech
: ,Ca(0C1) 2
Mixed hardwood
: Ca(0C1) 2
: 3
Eastern white pine : -Ca(0C1) 2
Southern pine
t
:
27
36
:
:
:
:
:
-24
:
-4
:
-6
3
:
'
-34
20
:
:
33
'
:
-19
;
110
:
:
-17
1
45
:
-1
:
:
1
: -11
: -23
: -16
: -19
: 27
:
-4
:
:
-35
: -20
/
-3
6
: 4.12
;
14
: -1
:
:
5
Ca(0C1) 2 :
4a(oc1) 2 ;
-24
-3
:
:
:
-10
:
:
-13
..6 :
:
-11
:
:
:
-8
-14
20
22
75
42
67
0
33
25
:
80
95
:
:
:
:
:
:
294
260
1i2
:
52
:
:
132
35
55
19
:
-17
:
0
:
:
11
-25
:
70
:
0
11
107
:
-15
198
;
22
•
-83
,
'
5
22
-4
6
-12
25
;
:
!
:
2
6
-3
85
94
35
38
3
;
:
57
:
0
-2
-8
:
::
:
-8
4
42
-12
11
:
-The amount of hypochlorite, except as noted, was 10 percent expressed as
available chlorine.
?Two percent sodium metasilicate was added to the bleach mixture.
-Fifteen percent available chlorine.
Report No. 81736
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