3 LAOUriitiOfir
LiEitARY
SULFITE PULP FROM
LOVILANIU
FIR
June 1942
No. 11404
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison 5, Wisconsin
In Cooperation with the University of Wisconsin
SULFITE PULP FROM LOWLAND WHITE FIR
By
G. H. CHIDESTER, Engineer
and.
J. N. McGOVERN, Technologist
Forest Products Laboratoryy 1 Forest Service
U. S. Department of Agriculture
Abstract
Heartwood and sapwood portions separated from a lowland white fir
(Abies grandis) sample having a medium density and high total and alpha cellulose contents have been pulped by the sulfite process to produce pulps covering
a range of bleachability. The important results were: (1) an increase in
bleach requirement of the heartwood and sapwood pulps from 8 to 20 percent corresponded to a decrease in cooking time of 1.5 hours, an increase in yield of
1.5 percent, a decrease in total cellulose content of 3 percent, small increases
in lignin and pentosan contents and slight increases in bursting and tensile
strengths. The tearing strengths passed through a maximum in the bleach requirement range. The alpha cellulose content of the pulps did not vary with
the bleach requirement. (2) For pulps having the same bleach requirement those
from the sapwood were lower in yield by 1 percent, had slightly higher lignin
and total and alpha cellulose contents, and showed somewhat lower amounts of
material soluble in ether than the heartwood pulps© The sapwood pulps were
slightly lower in bursting and tensile strengths and somewhat higher in tearing strength. (3) In comparison with average spruce and western hemlock
sulfite pulps the lowland white fir pulps were produced in slightly higher
yields, had pulp strengths closely the same, and were appreciably higher in
total and alpha cellulose contents.
Introduction
Lowland white fir, a true fir growing in the western part of the
United States, is at present used in relatively small quantities, often mixed
with western hemlock, for sulfite pulp. The consumption of "white fir" pulpwood, including lowland white fir, reach 174,000 cords in 1935, of which
approximately two-thirds was pulped by the sulfite process.
1
Maintained at Madison, Wis., in cooperation with the University of Wisconsin.
-1-
Agriculture-Madison
Lowland white fir, or grand fir as it is also known, is generally considered to be readily reducible to a pulp of good quality by the sulfite process.
Experiments conducted by Sutermeister over 30 years ago (1) indicated that no
difficulty was encountered in cooking this wood to produce a pulp free from
shives and screenings and having qualities enabling its substitution for spruce
fiber. However, there is little information available regarding specific properties of sulfite pulps from this species. Therefore, digestions were made at
the Forest Products Laboratory to determine the yield and properties of lowland
white fir pulps having different degrees of pulping.
The digestions reported herein were made on heartwood and sapwood
samples which had been separated from the whole logs in order to obtain information on the pulping of these portions of the wood. In this connection
some work has been done on the sulfite pulping of the heartwood and sapwood of
other species. McGovern and Chidester (2) have reported on the sulfite pulping
of the heartwood and sapwood of western hemlock, a species with which lowland
white fir is usually associated. Their report also reviewed the work of other
investigators on the pulping of spruce heartwood and sapwood.
Experimental Part
The lowland white or grand fir (Abies grandis) used in these experiments
was obtained from Columbia County, Oregon, through the Pacific Northwest Forest
and Experiment Station. The wood had been cut in November, 1933, from a fairly
dense stand composed of 80 percent Douglas-fir, 15 percent western redcedar,
2.7 percent western hemlock, and 2.5 percent lowland white fir and was subjected
to sulfite pulping tests during the period of February to June, 1934. Pertinent
physical and chemical data on lowland white fir shipment No. 1409 are found in
table 1; these data were taken from a comprehensive evaluation (3). A number of
the white fir logs were separated into heartwood and sapwood and the separated
portion converted into 5/8-inch chips for the pulping experiments. The chips
were screened to remove knots and chunks before use. The heartwood and sapwood
chips differed some in their moisture contents and the moisture contents of the
chips also varied during the course cf the experiments. The moisture data for
the various digestions are included in table 2. The chip charge for each
digestion was approximately 90 pounds on a moisture-free basis.
The calcium base sulfite pulping liquor used for the pulping trials
was made up as usual by passing sulfur dioxide from a cylinder into milk of
lime. The concentration of the cooking liquor was approximately 5.5 percent
in total sulfur dioxide with 1.25 percent as combined sulfur dioxide. The acid
charge was 65 gallons. The liquor-wood ratio then varied from 67 to 86 gallons
per 100 pounds of moisture-free wood, depending on the chip moisture. The
liquor-wood ratios are found in table 2.
The digestions were made in an alloy-lined, tumbling digester equipped
with a steam jacket and having a capacity of 13 cubic feet. Indirect steam
only was used for heating.
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9RECON FORM PRODUCTS LABORATORY
LIBRARY
Upon completion of the digestion the contents of the digester were blown
into a blowpit and the pulp washed thoroughly with water. The pulp was then
screened on a flat diaphragm screen and lapped on a small wet machine.
Further digestion conditions were as follows:
Pressure: 75 pounds per square inch
Temperature schedule: 2 hours to 110° C.
4 hours 110 to
145° C.
Held at 145° C. to end of digestion.
The only digester condition varied was the time at the maximum temperature. That time was increased by intervals of 15 or 30 minutes after 2 hours
at the maximum temperature up to a total of 4 hours at the maximum temperature.
The pulp yield was determined from the moisture-free weights of the
lapped pulp and the chips. The pulps were subjected to chemical analyses and
pebble-mill processing for strength development. The bleach requirement of the
pulps was ascertained by the amount of standard bleach powder necessary to give
a blue reading of 83 as measured by the Ives photometer in a single stage hypochlorite method. The time required for penetration of calcium bisulfite into
the chips was determined by treating the chips with sulfite liquor for various
times at the penetration temperature. The extent of penetration was judged
by the application of a bromphenol blue to interior surfaces of the chips exposed by splitting them; a blue color indicated the presence of the bisuifite
while a yellow color indicated the presence of sulfurous acid. The minimum
time for penetration of the bisulfite into the innermost portions of the chips
was taken as the penetration time. In the present case the penetration temperature was 110° C. and the acid contained 5 percent total with 1.2 percent
combined sulfur dioxide.
DISCUSSION AND RESULTS
The Wood
The physical and chemical properties of lowland white fir given in
table 1 indicated that the fairly rapid-growth wood in this particular lot
had pulpwood qualities for the most part equal to those of eastern spruce
and western hemlock samples tested at the Laboratory. The density of the
fir of approximately 25 pounds per cubic foot was much the same as that for
average spruce and hemlock and its color was the same as spruce but lighter
than hemlock. The chemical analyses of the white fir showed it to be
higher in total and alpha cellulose and somewhat lower in lignin than
average white spruce or western hemlock samples. The fir also had less
pentosans and ether soluble material than the spruce, but the same as the
hemlock.
It is pointed out that western pulp mill operators have found lowland
white fir to be less dense than western hemlock. McGregor (5), for example,
states that white fir has a lower specific gravity than western hemlock and
Holzer (private communication) reports density figures of 22 pounds per cubic
_3_
foot for lowland white fir and 26 pounds for western hemlock. McGregor (5),
also reported a high cellulose content for the fir in comparison with
hemlock.
The tracheids in lowland white fir are generally considered to be
longer and coarser than spruce, although reported measurements vary consid-
erably. The tracheid length is most often taken as 3.2 millimeters.
Only alcohol-benzene and ether solubility values and color readings
were available to compare the heartwood and sapwood for the lowland, white
fir (table 1). The heartwood had typically higher solubility factors than
the sapwood. However, the solubility values were not excessive in the Case
of the heartwood. The heartwood was slightly darker than the sapwood.
Penetration
Employing an acid containing 5 percent total with 1.2 percent combined
sulfur dioxide at a temperature of 110° C. a time of 2-1/4 hours was required
to penetrate lowland white fir heartwood chips completely with calcium bisulfite and a time of 2 hours for the sapwood chips. Western hemlock heartwood
chips tested previously (4) with an acid containing 6 percent total with 1.25
percent combined sulfur dioxide at the same temperature required. 1-3/4 hours
for penetration of the bisulfite. Since increasing the sulfur dioxide concentration aids penetration, it would appear that the white fir needed only
something like one-fourth hour more for penetration than the hemlock. Therefore, the same precautions taken with spruce and western hemlock to insure
thorough penetration should suffice for the sulfite pulping of lowland white
fir. On this basis the pulping experiments were made with a temperature
schedule calling for a 2 hour rise to 110° C. The mall amount of screenings
of 0.5 percent or less experienced in the digestions indicated that this
penetration time was ample.
Pulping
With the exception of the time at maximum temperature which was
varied to produce different degrees of pulping, the same conditions were
used in all digestions of both heartwood and sapwood. In making comparisons, however, it was necessary to make allowances for more rapid cooking
resulting from unavoidable drying of the chips as explained later.
Effect of Moisture Content
The digestions carried out in the later stages of the experimental
series of pulping with white fir heartwood and sapwood were made with chips
considerably drier than those used for the digestions performed at the
beginning. For purposes of comparison chips with moisture contents below
25 percent were termed "dry chips" and those having moisture contents above
D1404
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this figure were termed "wet chips" The data in table 2 showed that a good
comparison of wet and dry chips was available for both the heartwood and sapwood pulping. The digestions in question were numbers 3619 (wet chips) and
3626 (dry chips) for the heartwood and numbers 3620 (wet chips) and 3625 (dry
chips) for the sapwood.
The principal effect of the dry chips was the half hour shorter cooking
time needed to achieve the same degree of pulping. The dry heartwood chips
(number 3626) required 8 hours in comparison with 8.5 hours for the wet chips
(number 3619), to give pulps requiring approximately 20 percent bleach. The
dry sapwood chips (number 3625) required 8-3/4 hours whereas the wet chips
(number 3620) required 9-1/4 hours for approximately 11 percent bleach.
No appreciable differences were evident in the yield, chemical composition, or strength properties of the pulps from the dry and wet chips from
either the heartwood or sapwood.
When the pulp yields and properties were plotted against the time of
pulping, as described in the discussion of degree of pulping, the proper
allowances were made for the time of pulping to offset the effect of differences in the moisture content of the chips.
Degree of Pulping
When the time of pulping was increased by 15 or 30 minute intervals
from 2 hours at the maximum temperature (8 hours total time) to 4 hours (10
hours total time), a series of pulps varying in their degree of pulping resulted. As the time was increased, the bleach requirements of the pulps were
lowered and certain changes in pulp yields and properties were produced. The
pulping results and properties of the pulps given in table 2 are arranged in
order of increasing time of pulping for the heartwood and sapwood digestions,
respectively. While the trends resulting from the changes in the primary
variable of pulping time can be traced roughly from the data in table 2, a
clearer picture was obtained by noting the changes in terms of the bleach
requirements of the pulps. To enable this interpretation it was necessary to
convert the various relations from the basis of pulping time to the basis of
pulp bleach requirement. The conversion was carried out by first plotting
the pulp bleach requirements as well as yields and pulp properties against
the respective cooking times for both the heartwood and sapwood digestions,
making certain allowances, as explained in the foregoing for chip moisture
differences. The times needed to achieve specified bleach requirements of
8, 12, 16, and 20 percent were taken from the bleachability-time curves.
The pulp yields and properties at these rectified cooking times were then
noted on the curves obtained by plotting the respective pulp properties
against cooking time and these figures finally plotted against the specified
bleach requirement values of 8, 12, 16, and 20 percent. The resultant
curves are depicted in figure 1. The preliminary curves are not presented
in this report.
The curves in figure 1, showed clearly the effect, of the degree of
pulping on the yield and properties of the heartwood and sapwood pulps.
Under the pulping conditions employed the effects for an overall increase
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in bleach requirement from 8 to 20 percent were briefly a decrease in cooking
time of 1.5 hours, an increase in pulp yield of 1-5 percent, a decrease in the
total cellulose content of the pulps of 3 percent, increases in the lignin and
pentosan contents of approximately 1 percent, an increase in bursting strength
of about 0.1 point per pound and in tensile strength of 7,000 pounds per square
inch. The tearing strengths of the two types of pulps appeared to pass
through a maximum at bleach requirement values in the range of 12 to 16 percent.
The alpha-cellulose contents of the pulps showed no variation with
bleach requirement. The changes noted above were small but indicate the nature
of the relation of the bleach requirement to the properties of the pulps.
Comparison of Heartwood and Sa wood Pulps
The curves in figure 1 also afforded a comparison between the lowland
white fir heartwood and sapwood pulps, indicating that certain small differences existed between the heartwood and sapwood of the particular wood samples
employed for the digestions. For low bleachability values of 12 percent or
under the sapwood pulps required about 15 minutes longer cooking to attain the
same bleachability as the heartwood pulps. For equal bleachability values between 16 and 20 percent the cooking times were closely the same for the heartwood and sapwood. The slightly longer cooking time required by the sapwood
to attain the same bleach requirement as the heartwood in the lower bleach
requirement range is not in accordance with observations on other species
where the reverse was true.
The sapwood yielded about 1 percent less pulp with a slightly higher
lignin content than the heartwood for pulps having the same bleach requirement, but the sapwood pulps were higher by 0.5 percent in total and alpha
cellulose. The pentosan values for both types of pulps were virtually the
same. The yields of total and alpha cellulose, as determined by multiplying
the pulp yield by the percentage of each constituent in the pulp, were approximately 1 percent lower for the sapwood than for the heartwood. The lower
pulp yield and the lower cellulose yield from the sapwood in comparison with
the heartwood is again contrary to reported experiences with western hemlock
and white spruce (2). The material soluble in alcohol-benzene and in ether
as given in table 2 was only slightly higher for the heartwood in comparison
with the sapwood pulps.
The heartwood and sapwood pulps also differed in certain respects in
their strength properties. The heartwood pulps had bursting strengths
averaging 0.05 point higher and tensile strengths about 5,000 pounds per
square inch higher than the sapwood pulps, while the latter had 0.4 gram
higher tearing strengths. These strength trends checked those already
reported for western hemlock (2).
In general, the differences in yields and properties of pulps from
the heartwood and sapwood were small and pulps from the whole wood should
possess qualities between those reported for the heartwood and sapwood
separately.
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Yield and. Quality of Lowland White Fir Sulfite Pulp
The results from the foregoing experiments show that lowland white fir
is readily pulped by the sulfite process, yielding pulps having bleach requirements covering a wide range and that the strength and chemical properties
of the pulps vary normally with degree of pulping. An outstanding characteristic of the lowland white fir pulps is their high total and alpha cellulose
and low pentosans contents, a characteristic favoring their outlet as pulps
for chemical derivatives after suitable purification.
Comparable yield and pulp strength values are given in table 3 for
western hemlock, white spruce, and lowland white fir. The hemlock and spruce
data are averages based on some 20 digestions for each species made under a
variety of conditions. These data showed that the white fir yields were
higher than the others and that the white fir pulps had strength properties on
a par with the others. Because of its generally accepted low density white
fir might be expected (5) to yield less pulp per digester than the others.
Literature Cited
(1)
Sutermesiter, E.
Project 74. U.S.D.A. Forest Service,
Washington, D. C. (Dec. 1909)
(2)
McGovern, J. N. and Chidester, G. H.
Paper Trade Jour. 107 (1)i-):34-36, (Oct. 6, 1938)
(3)
Pew, J. C. and Schafer, E. R.
Project L-168-7, Problem D-146. Forest Products
Laboratory Mimeographed Report. (Nov. 18, 193)4-)
(4)
Hrubesky, C. E. and Chidester, G. H.
Paper Trade Jour. 98 (7):77-80, (Feb. 15, 193)-i-)
(5)
McGregor, G. H., Kelly, W. N., and Heuer, H. R.
Tech. Assoc. Papers 20, 143, (1937)
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Table 1.--Properties of lowland white fir pulpwood
Physical properties
25.3 pounds
54 years
43 percent
9.9 rings
Density (oven-dry weight per cubic foot green volume) Age Heartwood Rate of growth (average per inch) Color (percent white from Ives parts blue) Heartwood ................. . Sapwood. . .. .
42 percent
percent
46
Chemical analyses
Whole wood
Cellulose Alpha cellulose Lignin Totalpentosans ...................... Solubility in:
Hot 1 percent sodium hydroxide Hot water
Alcohol benzene Ether 63.0 percent
45.9 percent
27.0 percent
8.9 percent
10.3 percent
2.3 percent
2.6 percent
.9 percent
Heartwood
4.1 percent
1.2 percent
Solubility in alcohol benzene Solubility in ether Sapwood
Solubility in alcohol benzene .....
Solubility in ether 1.5 percent
.3 percent
4
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Table 3.--Yields and strengths of various sulfite pulps bleaching in the
TILEL2112L222LI2EPent
•nnn•••n•n•n••••n170........
Species
Yield :
Pebble mill strength tests.1
: Bursting strength : Tearing strength
: after 80 minutes : after 20 minutes
•
. Percent : Point per pound
per ream
: Grams per pound
per ream
•
Western hemlock
0.98
2.5
White spruce
1.00
2.1
.97
2.4
Lowland white
fir
1
– 25 x 40 - 500 ream
D14o4
•