By JASON L. MERRILL, _Paper-Plant Chemist, Paper-Plant Investigations_.
=INTRODUCTION.=
The purpose of this paper is to report upon preliminary tests which were
conducted to determine the paper-making value of hemp hurds, a crop
waste of the hemp-fiber industry.
The search for plant materials capable of being utilized in paper
manufacture is a comparatively recent but world-wide activity which has
for its object the husbanding of present sources of paper-stock supply
by the substitution of new materials for some of those which are rapidly
becoming less plentiful and more costly.
The abstract idea of utilizing that which is at present a waste can play
no important rôle in such activities, the successful commercial outcome
of which must be based on the three fundamental factors--market or
demand for product, satisfactory raw material, and cost.
Since hemp hurds are to be treated in this report as a raw material for
the manufacture of book and printing papers, the qualities, supply,
probable future, and cost of the material will be considered in
comparison with wood, with which it must compete. There seems to be
little doubt that the present wood supply can not withstand indefinitely
the demands placed upon it, and with increased scarcity economy in the
use of wood will become imperative. This effect is already apparent in
many wood-using industries, and although the paper industry consumes
only about 3 per cent of the total forest cut, it is probable that it
will be affected through this economy. Our forests are being cut three
times as fast as they grow, and as wood becomes more expensive proper
growing and reforesting will receive more attention. Thus, naturally, a
balance will be established between production and consumption, but as
this condition approaches its limiting values the price of wood may rise
to such levels that there will be a demand for other raw materials.
The use of waste paper in conjunction with chemical wood pulp has
increased to enormous proportions, and it is probable that the increase
will continue. Although it is a cheaper raw material than wood, it is
reasonable to suppose that as the wood supply decreases and the price of
wood pulp advances, the price of waste paper will advance somewhat
proportionately.
In view of these conditions it is advisable to investigate the
paper-making value of the more promising plant materials before a
critical situation arises. To be of substantial value the investigations
should include not only a determination of the quality and quantity of
pulp and paper which the material is capable of producing, but should
embrace a consideration of such relevant factors as agricultural
conditions, farm practice, assembling conditions, transportation, and
probable future supply.
Certain cultivated plants seem particularly promising, because in the
harvesting of the regular crop that portion which might be utilized for
paper manufacture necessarily is either wholly or partially assembled.
To this class of plants belong corn, broom corn, sorghum, sugar cane,
bagasse, flax, hemp, and the cereal straws.[1]
[Footnote 1: For descriptions of investigations of some of these crops,
see the list of publications at the end of this bulletin.]
It is generally conceded that the employment of different raw materials
would probably yield products of a somewhat different quality than those
now prevailing in the markets, but the qualities of papers and the
public demands are so diversified and numerous that this possible
objection should not be serious. Ten years ago sulphite manufacturers
would not accept consignments of spruce logs if they contained over 5
per cent of fir, while to-day many manufacturers tolerate 50 per cent.
Rope papers are found to contain not only jute, but when this raw
material is not plentiful, chemical pulp of various kinds. "Linen paper"
is often no more than a trade term. Not long ago printing papers were
made entirely from chemical wood pulp, but to-day if it is desired to
secure paper which is free from ground wood the specifications must so
stipulate. Writing papers, formerly made entirely from rags, now are
likely to contain either chemical or even ground-wood pulp unless the
specifications prohibit it. Without doubt, many paper manufacturers have
maintained certain papers up to a fixed standard for a long series of
years, but it is equally true that competition has lowered the standard
of a great many papers, some of which had acquired a distinctive
recognition. The employment of plant fibers will not necessarily lower
the present quality of papers, but if their employment does result in
products whose qualities are somewhat different from our so-called
standard papers it does not necessarily follow that such papers will not
find a ready market.
=FACTORS JUSTIFYING AN INVESTIGATION OF HEMP HURDS.=
Hemp hurds form a crop waste, in that they necessarily are produced in
the raising and preparation of hemp fiber, and their present use and
value are comparatively insignificant.
The assembling of the hurds may be effected with economy, since the area
in which hemp is handled with the use of machine brakes is restricted.
Although it must be stated that the present annual supply would not be
sufficient to justify the installation of a pulp mill nor would its
transportation to existing mills appear feasible, it is expected that
the available annual tonnage, especially in certain general sections,
will increase, due to the increased use of the machine brake. The
present tonnage per annum is approximately as follows: In the region of
Ohio and Indiana, 2,500 tons; in the Wisconsin section, 1,000 tons; in
the California region, 1,400 tons.
In years of adverse weather conditions there are often large areas of
hemp which are not harvested on account of its poor quality; there are
also large areas of cut hemp which become overretted, due to inclement
weather. It has been suggested by some of the hemp raisers that this
large amount of material might be utilized as a paper stock. In these
cases the cost of the whole material would probably be somewhat higher
than that of the hurds, because either all or part of the cost of
harvesting and the total cost of breaking would have to be borne by the
paper maker. Moreover, the quality of this material would be so very
irregular and the supply so uncertain that it probably would not appeal
to the paper manufacturer.
Without doubt, hemp will continue to be one of the staple agricultural
crops of the United States. The wholesale destruction of the supply by
fire, as frequently happens in the case of wood, is precluded by the
very nature of the hemp-raising industry. Since only one year's growth
can be harvested annually the supply is not endangered by the pernicious
practice of overcropping, which has contributed so much to the present
high and increasing cost of pulp wood. The permanency of the supply of
hemp hurds thus seems assured.
The favorable location geographically of the hemp regions in relation to
the pulp and paper industry is a factor of considerable importance. The
Kentucky region is not at present in a position to supply hurds, as
machine methods have not been adopted there to any appreciable degree.
The Ohio and Indiana region, which at present has the greatest annual
tonnage, with the prospect of an increase, is situated south of the
Wisconsin and Michigan wood-pulp producing region and at a distance from
the eastern wood-pulp producing regions; therefore, it is in a favorable
position to compete in the large Ohio and Indiana markets. Since, as
will be shown, the hurd pulp acts far more like soda poplar stock than
sulphite stock, competition would be strongest from the eastern mills;
in fact, the hurd stock might very possibly meet with favor as a
book-stock furnish in the Michigan and Wisconsin paper mills, which are
within the sulphite fiber-producing region. Because of its very close
proximity to paper mills, this latter possibility applies with far
greater force to the Wisconsin hemp region, where a considerable
extension of the hemp industry is anticipated.
[Illustration: FIG. 3.--A representative sample of hemp hurds, natural
size, showing hemp fiber and pieces of wood tissue.]
=CHARACTER OF THE MATERIAL.=
As received from Pierceton, Ind., the hurds consisted of a mixture of
tangled hemp bast fibers and pieces of broken wood of the hemp stalk.
(Fig. 3.) No reliable data were secured as to the proportion of bast
fiber in the total shipment of 4 tons, although two hand separations of
small representative samples gave results averaging 8 per cent. The
chemical character of the material was such and the quantity was so
small that any appreciable variation of the proportion should not affect
materially the treating processes finally adopted, yet its presence in
varying proportions undoubtedly would modify to some extent the quality
of the resulting paper product. Since the length of the ultimate bast
fiber averages about 22 mm. and the length of the ultimate hemp wood
fiber averages 0.7 mm., it is natural to assume that the bast fiber
would tend to increase the strength of paper produced from the hurds.
(Fig. 4.)
[Illustration: FIG. 4.--Fiber derived from the woody portion of the
hurds. ×75. From a microphotograph.]
The broken pieces of wood contained in the hurds varied in length from
mere particles which were somewhat finer than sawdust to pieces about
3-1/2 inches long, exceptional pieces being found which measured 6
inches in length. The majority of the long pieces were between 2 and 3
inches in length. In thickness the pieces ranged from one-eighth of an
inch, in case they were derived from the base of the hemp stalks, to
about one sixty-fourth of an inch in those pieces which were derived
from the top and branches of the stalks. In cross section the pieces
often were found to be a quarter or half of the rounded rectangular
woody shell of the stalk, although there appeared to be no regularity in
this respect.
From the pulp-maker's standpoint the great irregularity in thickness,
length, and mass of the woody pieces militates decidedly against economy
in pulp production. The smaller pieces reduce by chemical treatment
sooner than the larger fragments and are thereby overtreated, which
results in a lower yield of cellulose fiber and a product composed of
undertreated and overtreated fibers, the production and use of which are
not satisfactory or economical. It probably would be found more
satisfactory, therefore, to screen or sort the hurds and treat the
various sizes separately and differently.
Associated with the hurds was a small quantity of chaff and dirt,
composed chiefly of sand, soil, particles of hemp leaves and flowers,
and other extraneous matter. The sand and soil were present because of
the practice of placing the stalks in shocks in the field, the butts of
the stalks being in contact with the soil. It is a simple matter,
however, to remove the chaff and dirt by sieving, and this practice was
followed in most of the paper tests conducted with this material.
=CHARACTER OF THE TESTS.=
Because of the similarity of hemp hurds to other materials which have
been tested by the Office of Paper-Plant Investigations, semicommercial
tests were conducted in cooperation with a paper manufacturer without
preliminary laboratory tests. Laboratory pulp and paper tests are
regarded only as a preliminary to semicommercial tests and therefore are
not employed unless the material in question presents new features which
should receive investigation before larger sized tests are undertaken.
The advantages of cooperative mill tests are many, among which may be
mentioned the counsel and advice of the mill management and employees,
the services of specialized and skilled labor, facilities for comparing
the processes and the results of tests with commercial processes and
results, and the use of commercial or semicommercial types and sizes of
machinery. Tests conducted in this manner and on this scale are of a
different quality than is possible in those conducted in a laboratory,
and the results are susceptible of commercial interpretation with a fair
degree of reliability. It is found, in general, that the cost of
securing such equipment and service for a complete and comprehensive
test does not exceed $500, while the installation of an equally
satisfactory equipment alone would cost at least $50,000 and in many
cases very much more. Tests conducted in this manner constitute a direct
demonstration to the manufacturer, and the results obtained are found to
carry more weight when presented to other manufacturers for
consideration.
It is well known that the method of conducting tests necessarily varies
with the size of the test. In the matter of yield determination, for
example, laboratory tests may be on such a small scale that the weighing
and sampling of the resulting cellulose fibers may be conducted by means
of chemical laboratory apparatus and analytical balance, while in tests
involving a matter of 5 to 10 pounds of material larger and different
types of equipment are necessary. When the tests are so increased in
size as to employ 300 or 400 pounds, still other types of equipment are
necessary for the treatment of the material and for a determination of
the yield of fiber. In tests involving tons of material the equipment
involves the use of machines. Accuracy in degree of control and in
results will vary materially with the size of the test. As the size of
the test increases, certain factors will vary in a beneficial manner,
while others will vary in a detrimental manner, so it is a question for
each investigator to decide, after taking all factors into
consideration, as to the size of test which will give the most
satisfactory results. In work of this nature it is found, on the whole,
that better results are obtained in large tests, although the control of
the factors and the determination of the yield of fiber are more
difficult than in smaller tests.
In the tests described in this bulletin, the Department of Agriculture
employed a rotary digester of its own design,[2] comprising a shell 5
feet 5 inches in length by 4 feet in diameter, capable of holding about
300 pounds of air-dry hurds. It is believed that a test of this size is
large enough to give satisfactory results and that the results are
susceptible of commercial interpretation, while at the same time they
are sufficiently small for complete control and to afford fiber-yield
figures which are both accurate and reliable. Two such rotary charges
gave enough fiber for one complete paper-making test.
[Footnote 2: For a description of this rotary digester, see Brand, C.
J., and Merrill, J. L., Zacaton as a paper-making material, U. S. Dept.
Agr. Bul. 309, p. 28, 1915.]
=OPERATIONS INVOLVED IN A TEST.=
A complete test on hurds comprises seven distinct operations, and the
method will be described, operation by operation, in the order in which
they were conducted.
_Sieving._--The hurds for the first test were not sieved to remove sand
and dirt, but the resulting paper was so dirty that sieving was
practiced in all subsequent tests. The hurds were raked along a
horizontal galvanized-iron screen, 15 feet long and 3 feet wide, with
11-1/2 meshes per linear inch, the screen being agitated by hand from
below. Various amounts of dirt and chaff could be removed, depending on
the degree of action, but it was found that if much more than 3 per cent
of the material was removed it consisted chiefly of fine pieces of wood
with practically no additional sand or dirt; in most of the tests,
therefore, the material was screened so as to remove approximately 3 per
cent. It became apparent that a finer screen would probably serve as
well and effect a saving of small but good hurds.
_Cooking._--Cooking is the technical term for the operation by which
fibrous raw materials are reduced to a residue of cellulose pulp by
means of chemical treatment. In these tests about 300 pounds of hurds
were charged into the rotary with the addition of a caustic-soda
solution, such as is regularly employed in pulp mills and which tested
an average of 109.5 grams of caustic soda per liter, or 0.916 pound per
gallon, and averaged 85 per cent causticity. Sufficient caustic solution
was added to furnish 25 or 30 per cent of actual caustic soda,
calculated on the bone-dry weight of hurds in the charge. After closing
the rotary head, it was started rotating at the rate of one-half
revolution per minute, and in about five minutes steam at 120 pounds per
square inch was admitted at such a rate that the charge was heated in
one hour to 170° C., which is the theoretical equivalent of 100 pounds
of steam pressure per square inch. It was found, however, that when the
temperature reached 170° C. the pressure was usually 115 or 120 pounds
instead of 100 pounds, due to air and gases inclosed in the rotary. At
this point the rotary was stopped and steam and air relieved until the
pressure dropped to 100 pounds, or a solid steam pressure. The
temperature was maintained at this point for the number of hours
required to reduce the hurds, which was found to be about five, after
which the rotary was stopped and steam relieved until the pressure was
reduced to zero, when the head was removed and the stock was emptied
into a tank underneath, measuring 5-1/2 by 6 by 2 feet deep, where it
was drained and washed. Samples of waste soda solution or "black
liquor," which were taken from some of the "cooks" for analysis, were
drawn while the stock was being thus emptied into the drainer.
_Determination of yield._--For determining the yield of cellulose fiber
the stock in the drain tank was washed with water until free from waste
soda solution, when, by means of a vacuum pump communicating with the
space between the bottom and the false perforated bottom, the water was
sucked from the stock, leaving the fiber with a very uniform moisture
content throughout its entire mass and in a condition suitable for
removing, sampling, and weighing for a yield determination. Tests have
shown that it is possible to sample and calculate the yield of bone-dry
fiber within 0.05 per cent of the actual amount.
It has been found that stocks from different materials vary greatly in
their ability to mat in the drain tank, thereby enabling a good vacuum
to be obtained, some stocks permitting a 25-inch vacuum to be obtained,
while others will not permit more than 5 inches. For this reason the
moisture content of the stock will vary from 65 to 85 per cent.
_Washing and bleaching._--Washing and bleaching were performed for the
purpose of bleaching the brown-colored cooked stock to a white product,
since it was regarded as highly probable that the fiber would be
suitable for book-paper manufacture. The colored stock was charged into
a 400-pound beating and washing engine of regular construction and
washed about one hour, the cylinder washer being covered with 60-mesh
wire cloth in order to remove fine loose dirt and chemical residues. The
washer was then raised, the stock heated by steam to about 40° C., and a
solution of commercial bleaching powder was added in the quantity judged
to be necessary, after which the stock was pumped to a large wooden
tank, to remain and bleach over night. If the stock was bleached
sufficiently white it was drained and washed from bleach residues, and
if not more bleach was added until a good color was obtained. The
bleaching powder used was estimated to contain 35 per cent of available
chlorin, as this is the commercial practice, and the amount required was
calculated to the bone-dry weight of the unbleached stock. More bleach
is required for undercooked stock than for stock which is properly
cooked or overcooked; therefore, the percentage of bleach required is an
indication of the quality of the cooked stock. Since bleaching is
usually more expensive than cooking, it is desirable to cook to such a
degree that the consumption of bleach will be held within certain
limits, depending on the raw materials used and the quality of paper to
be produced. In these tests it was desirable so to cook the hurds that
the consumption of bleach would not be over about 10 per cent of the
fiber.
_Furnishing._--Furnishing is the operation of charging the beating
engine with the desired kind or kinds of fiber in the proper proportion
and amount and the adding of such loading and sizing agents as may be
necessary. As shown in the record of results, the furnish in these tests
consisted of hurd stock alone and of various proportions of hurds,
sulphite fiber, and soda fiber. The percentages to be given in the
record of the furnishes refer to the percentage of the total fiber
furnish, and this likewise applies to the loading and sizing agents. In
case sulphite or soda fiber was used, the commercial product in the dry
state was charged into the beating engine and disintegrated, after which
the hurd stock was added in the wet condition.
_Beating._--Beating is that operation concerning which the paper makers
often say "there is where the paper is really made," and although the
statement may not be literally true it contains a great deal of truth.
It is the operation whereby the fibers are separated from each other,
reduced to the proper lengths, and put in such a physical or chemical
condition that they felt properly and form into a satisfactory sheet. It
is probable that the quality of the sheet depends more upon the proper
beater action than upon any other single operation. The action consists
in drawing a water suspension of the fiber between two sets of rather
blunt knives, one set being located in the bottom of a circulating
trough and the other set on the periphery of a roll revolving just above
the former set of knives. It is during this operation that the loading
and sizing agents are incorporated and the whole furnish is tinted
either to produce a satisfactory white or the desired color.
The term "paper making," as used in this publication, means the
operation of forming the finished sheet of paper from stock which has
been furnished and prepared in the beater. In these tests a 30-inch
Fourdrinier machine of regular construction was used, a machine which
often is used for the production of paper for filling regular commercial
orders. The machine is designed to cause the water suspension of fibers
to flow on to a traveling wire cloth, whereby the water drains away.
More water is removed by passing the wet sheet through a series of press
rolls, after which the sheet is dried on steam-heated drums and passed
through polished iron rolls, which impart a finish to the sheet. A
Jordan refining machine was employed in conjunction with the machine to
improve further the quality of the fiber, and a pulp screen was used in
order to remove coarse and extraneous materials from the fiber.
=DESCRIPTION OF TESTS.=
The nature of each complete paper test and the dependence of each
operation on the others were such that it does not seem advisable to
submit the results of the seven tests in tabular form. The numerous
cooks, however, which furnished the pulp for the paper tests are
presented in Table I in all essential detail.
TABLE I.--Data on cooking hemp hurds.
------+-----------+------------+----------+--------------------+-----------
| | | | |
| | | | Cooking | Yield of
| Caustic |Strength of | | | bone-dry
| soda used |caustic soda|Causticity+--------+-----------+ fiber
Cook |(percentage| (grams per | of soda | | |(percentage
No. |of bone-dry| liter). | solution.| Time |Temperature|of bone-dry
| hurds). | | |(hours).| (°C.) | unsieved
| | | | | | hurds).
------+-----------+------------+----------+--------+-----------+-----------
293 | 20.6| 100 | 75.3| 3| 166|
294 | 21 | 100 | 75.3| 3| 166|
295 | 21.6| 100 | 75.3| 3| 166|
296 | 20.3| 100 | 75.3| 3| 166|
301 | 21.9| 100 | 82.5| 4| 166| [3]
302 | 24.4| 100 | 82.5| 4| 166|
303 | 24.2| 100 | 84.3| 4| 166| 44.1
304 | 25 | 100 | 84.3| 4| 170| 39.5
305 | 25 | 100 | 84.3| 5| 170| 39.4
306 | 27.8| 107.5| 84.3| 4| 166| 36.5
307 | 26.7| 107 | 84.4| 5| 170| 38.1
308 | 26 | 107 | 84.4| 5| 170|\_ 37.3
309 | 27.3| 107 | 84.4| 5| 170|/
310 | 27.1| 107 | 84.4| 6| 170| 37.0
311 | 27.2| 107 | 84.4| 6| 170| 36.8
312 | 28.3| 116.5| 85.5| 5| 170| 35.9
313 | 29.1| 113.1| 84.9| 5| 170|\_ 35.2
314 | 29.1| 109 | 83.9| 5| 170|/
315 | 29.4| 109 | 83.9| 5| 170| 34.9
316 | 30 | 109.5| 84.9| 5| 170| 37.2
317 | 29.6| 109.5| 84.9| 5| 170| 37.0
318 | 29.6| 107 | 84.8| 5| 170| 37.7
319 | 29.4| 107.5| 84.2| 5| 170|\_ 35.4
320 | 29.3| 107.5| 84.2| 5| 170|/
------+-----------+------------+----------+--------+-----------+-----------
[Footnote 3: Stock not used; dirty.]
Discussion of the various cooks will be given in connection with the
descriptions of those paper tests in which the stocks from the cooks
were used, since a stock and its cooking condition can be judged
adequately only after it has been put through the various processes and
into the finished sheet of paper.
The first test consisted in making four separate cooks, Nos. 293, 294,
295, and 296, of approximately 300 pounds each, dividing the total stock
into two parts and making two separate paper tests. The first test was
made primarily in order to learn some of the qualities and
characteristics of the stock and to get the machinery equipment adjusted
properly. The yield of fiber was not determined in this preliminary
test, since the knowledge of it was not essential at this stage of the
work. The cooked stock which was emptied into the drainer to be washed
free from black liquor was composed largely of whole pieces of hurds,
but only slight pressure between the fingers was required to crush the
pieces. In the case of wood, this condition ordinarily would indicate
undercooking, but might not in the case of hurds. Further observation on
the action of the cooked stock during subsequent processes was necessary
in order to judge of its quality or the suitability of the cooking
conditions. The total cooked stock, about 500 pounds, was divided into
two portions of 200 and 300 pounds, respectively, and work was continued
on them separately. The 200-pound test, designated as run No. 135, was
put into a 350-pound washing engine, washed one hour, and given a total
light brush of 2-1/4 hours. The washing removed a great amount of dirt,
but the engine did not reduce the hurd stock as much as was desired.
After heating the stock in the beater to 40° C., it was bleached with
bleaching-powder solution, 94 gallons at 0.418 pound bleach per gallon,
equivalent to 19.7 per cent of the fiber. This percentage of bleach is
regarded as too high for stock intended for book-paper manufacture, and
subsequent cooks therefore were given harder treatment in order to
reduce this figure. After draining and washing free from bleach
residues, the stock was furnished in the beater with 13 per cent of
clay, 1 per cent of resin size, and 2.5 per cent of alum, was tinted
blue, given one hour's light brush, and pumped to the stock chest. When
running it on the paper machine, the Jordan refiner seemed to have
little effect in reducing shives of undertreated wood, which indicated
further the necessity of harder cooking. The furnish acted well on the
paper machine at 70 feet per minute, but appeared somewhat too "free" on
the wire. The paper produced from this test is of very low quality, due
to the improper preparation of the stock, lack of sufficient bleach, the
use of too small an amount of blue tinting, and the presence of an
excessive amount of dirt, sand, and shives. The excessive amount of dirt
and sand suggested the sieving of the hurds before cooking, and this was
performed in all subsequent cooks.
The finish of the sheet is very poor, due to the fact that the calender
stack was composed of very light rolls which did not have a satisfactory
surface, yet the stack is known to be able to produce better finishes if
the proper stock is employed.
Run No. 136 was made on the 300-pound portion of stock from cooks Nos.
293, 294, 295, and 296, and in essentially the same manner as run No.
135. The stock was washed one hour, but given a brush of three hours,
and this brush was harder than in run No. 135. Bleach to the extent of
19.8 per cent of the fiber was used, assisted by 1 pint of oil of
vitriol, and the resulting color was an improvement over that of run No.
135. After adding 13.5 per cent of clay and sizing with 1.1 per cent of
resin size, the furnish was given one-half hour's light brush, tinted,
and run on the machine, which was set at 70 feet per minute. This stock
acted better on the wire and gave no trouble on the machine, but it
still seemed to be impossible to reduce the wood shives by manipulation
of the Jordan refiner. The resulting sheet is an improvement over that
produced by No. 135, but is far from satisfactory.
Run No. 138 was made from hurds which, as in all subsequent tests, were
sieved on a 11-1/2-mesh wire screen until practically all the loose dirt
and sand was removed, which operation caused a loss averaging 3 per cent
of the hurds. Stock from cooks Nos. 302 and 303 was used for this run
and the increased amount of caustic soda and the increase in the time of
cooking gave a stock of better appearance than those of preceding tests.
The stock, amounting to 231 pounds dry weight, was washed and at the
same time given a light brush for one hour only, after which it was
bleached with 17 per cent of bleach without the addition of acid. Since
the preceding paper appeared somewhat weak and had a low tearing
quality, it was decided to use a furnish of 15.7 per cent bleached
sulphite and 84.3 per cent bleached hemp-hurd stock. After loading with
13.1 per cent of clay and sizing with 1.1 per cent of resin size, the
furnish was given a medium brush for one hour, tinted, and run on to the
machine at 70 feet per minute. The stock gave no trouble on the machine,
but it was impossible to judge the effect of the Jordan refiner, because
through an oversight the machine chest had not been cleaned since
previous use on an unbleached yucca material. It is believed, however,
that sheet No. 138 shows improvement in the preparation of the hurd
pulp.
Run No. 139 was made from stock of cooks Nos. 304 and 305, in which
still more caustic soda was employed and the time and temperature of
cooking were increased, giving a yield of total fiber of 40.7 per cent
of the sieved or 39.4 per cent of the unsieved hurds. The cooked stock
still seemed to be undertreated, but it must be remembered that in
working with any new raw material it is impossible to know in advance
how the properly treated material should appear. A washing of one hour
was given while the roll was lowered from a light to a medium brush,
after which the stock was bleached with 17.1 per cent of bleach without
the aid of acid. Since sulphite stock improved the previous paper, this
bleached stock was used in a furnish of 16.6 per cent sulphite and 83.4
per cent hurds, loaded with 16.7 per cent clay, sized with 1.4 per cent
resin size, given a medium brush of two hours, tinted, and run on to the
machine at 70 feet per minute. The Jordan refiner seemed to have little
effect in reducing shives and was therefore left "just off." No trouble
was experienced with the stock on the machine, and the sheet is an
improvement over previous samples.
Run No. 140 was made from cooks Nos. 306 and 307, in which more caustic
soda was employed than in any previous cooks and at a higher
concentration, the fiber yields of which averaged 37.3 per cent of the
unsieved hurds. Not much improvement was apparent in the cooked stock,
in spite of the increased severity of cooking. The stock was washed and
given a medium brush for one hour, bleached with 11.9 per cent of
bleach, assisted with one-half pint of oil of vitriol, and made into a
furnish of 14.9 per cent sulphite and 85.1 per cent of the hurd stock.
After loading with 14.7 per cent of clay and sizing with 1.28 per cent
of resin size, the furnish was given two hours' medium brush, tinted,
and run on to the paper machine at 70 feet per minute. Again the Jordan
refiner did not seem to reduce the wood shives sufficiently, and it was
left "just off." No trouble which could be attributed to the stock was
experienced on the paper machine. The color of the resulting paper is
due to the use of too little blue in tinting and probably in some
measure to the use of too low a percentage of bleach.
Run No. 141 was made from the stock of cooks Nos. 308 and 309 in
practically the same manner as run No. 140. The stock was washed and
brushed one hour, bleached (the record of the amount of bleach was
lost), made into a furnish of 14.7 per cent of sulphite and 85.3 per
cent of hurd stock, loaded with 14.9 per cent of clay, sized with 1.26
per cent of resin size, given one hour at a medium brush, tinted, and
run on to the machine. The Jordan refiner was able to reduce the wood
shives to a somewhat greater degree than in previous runs and was held
at a medium brush. The stock acted well on the machine and produced a
sheet of better quality than any preceding, with the exception of the
color, which was due to using too small a quantity of blue.
Among the cooks made for run No. 142 are Nos. 312 and 313, in which the
concentration of the caustic soda was raised to 113 and 116 grams per
liter and the percentage employed was also increased. In spite of these
increases the stock from these two cooks did not show any appreciable
improvement when dumped from the rotary. Stock from cooks Nos. 310, 311,
and 312 was given a medium brush and washing of one hour, bleached with
10.95 per cent of bleach, made into a furnish consisting of 15.2 per
cent of sulphite and 84.8 per cent of hurd stock, loaded with 15.2 per
cent of clay, sized with 1.28 per cent of resin size, given a medium
brush for one hour, tinted, and pumped to the stock chest. Stock from
cooks Nos. 313 and 314 was treated in exactly the same manner, except
that 11.4 per cent of bleach was used. It was pumped to the stock chest
and mixed with the furnished stock from cooks Nos. 310, 311, and 312. A
medium Jordan brush was given the stock and it acted well on the paper
machine, which was speeded to 75 feet per minute. There seems to be a
tendency in the hurd stock to crush a little at the "dandy roll," and
although the marks are not removed by the calender stack which was
employed in those tests it was found that one "nip" on the
supercalenders renders them practically imperceptible and it is believed
that the proper size and weight of calender stack would entirely remove
these marks. All of the papers produced up to this point are somewhat
lacking in the bulk desired in a book paper; therefore, in the two
following runs soda-poplar stock was included in the furnishes.
In run No. 143 stock from cooks Nos. 315 and 316 was given a medium
brush and washing for one hour and was medium brushed for one hour more,
bleached with 11.3 per cent of bleach assisted with one-half pint of oil
of vitriol, made into a furnish of 16.5 per cent of sulphite, 22.3 per
cent of soda poplar, and 61.2 per cent of hurd stock, loaded with 22 per
cent of clay, sized with 1.38 per cent of resin size, given a hard brush
for one hour, tinted very strongly, and pumped to the stock chest. This
stock was beaten to a greater extent than in previous runs. The stock
was run on the paper machine at a speed of 75 feet per minute, using a
medium Jordan brush, and no trouble whatsoever was experienced. Not over
2 pounds of "broke" was produced during the whole run, and that was in
the "threading" of the machine. The color of the sheet is entirely
satisfactory for many uses. The wood shives apparently were reduced to a
satisfactory degree. Experienced paper makers commented very favorably
on the running of this furnish and the quality of the paper produced.
Run No. 144 was intended as a duplicate of run No. 143. Stock from cooks
Nos. 317 and 318 was given a medium brush and washing for one hour and a
further medium brush of one hour, bleached with 11.4 per cent of bleach,
and made into a furnish composed of 15.5 per cent of sulphite, 23.5 per
cent of soda poplar, and 61 per cent of hurd stock, loaded with 21.4 per
cent of clay, sized with 1.17 per cent of resin size, hard brushed for
one hour, tinted by the expert colorer of the company, and pumped to the
stock chest. Stock from cooks Nos. 319 and 320 was treated in exactly
the same manner except that the stock was bleached with 12.1 per cent of
bleach and pumped to the stock chest to mix with the former furnish. The
stock acted very well on the machine, which was speeded to 75 feet per
minute, with the Jordan refiner set at a medium brush. The sheet is as
good, if not better, than that of run No. 143, and it is also a good
illustration of the extent to which proper tinting will enhance the
general appearance of a paper. The poor appearance of the samples of
previous runs is due largely to lack of proper tinting. Various degrees
of whiteness, however, are demanded by the trade.
=COMPARISON OF THE TESTS AND COMMERCIAL PRACTICE.=
In work of this nature and on this scale it is practically impossible to
arrive at a cost figure which would be susceptible of commercial
interpretation, and in this preliminary publication nothing will be
attempted beyond a comparison of the process used with the hurds with
that process commercially applied to poplar wood. The process last used
with the hurds should not be regarded as final, satisfactory, or most
suitable, as it has been shown that progress was being made up to the
conclusion of the work.
In comparing the method of using hurds with the method of handling
poplar wood, a difference is apparent on the delivery of raw material at
the mill. Ordinarily, poplar is received at the mill in the form of logs
about 4 feet in length, which may be stored in piles in the open. Hurds
very likely would be received baled, and it would seem advisable to
store them under cover for the following reasons: (_a_) Baled hurds
would probably absorb and retain more water during wet weather than logs
of wood, thereby causing excessive dilution of the caustic liquor; (_b_)
prolonged excessive dampness might create heating and deterioration
unless the hemp were properly retted; (_c_) wet hurds could not be
sieved free from sand and chaff. Should further work show that the first
two reasons need not be taken into consideration, the third objection
might be overcome by sieving the hurds before baling. Even then, it is
probable that baled hurds stored in the open would accumulate and retain
considerable dirt from factory chimneys, locomotives, and wind. Checked
pulp wood exposed in the open invariably suffers from these causes.
In the preparation of the raw material for the digesters there is
likewise considerable difference between hurds and poplar wood. The
former apparently requires only a moderate sieving to remove sand and
chaff, which operation doubtless would require only a small amount of
labor and the installation of some simple machinery of low power
consumption. In preparing poplar for digestion, the 4-foot logs are
chipped by a heavy, comparatively expensive chipper of high power
consumption, after which the chips are sorted by sieving, the large
pieces being rechipped. There would be a noteworthy difference in the
installation, operating, and depreciation costs of the two equipments,
and this difference would counterbalance to a considerable extent the
difference in cost of raw material storage.
It is possible that in the use of the chip loft more care would have to
be exercised in using hurds because of the tendency of the bast fiber to
cause lodgments, but this should not be considered a serious difficulty.
The weight of hurds which are capable of being charged into a rotary is
a decidedly unfavorable factor. The weight of a cubic foot of hurds
varies somewhat with the proportion of bast fiber, but averages about
5.4 pounds, which, compared with a cubic foot of poplar chips at 8.93
pounds, represents a digester charge of 60.5 per cent of the weight of
a poplar-wood charge, or, in terms of fiber capacity, the hurds charge
would yield 38.6 per cent as much fiber as the wood charge. The hurds
upon being baled for transportation may be broken and crushed to such a
degree that the weight of the charge may be increased, and it might be
found possible to increase the charge weight by steaming or by the
employment of tamping devices. This small weight of charge constitutes
one of the most serious objections to the use of hurds in paper
manufacture.
In those tests in which the most satisfactory results were obtained, the
cooking conditions were 29.5 per cent of caustic soda at a concentration
of 107 grams per liter and a causticity of 84.0 per cent acting at a
temperature of 170° C. for five hours, or a total time of seven hours.
The steam condensation in the rotary used for these tests was abnormally
high, due to the fact that the steam supply pipe was uncovered for a
considerable distance and the rotary was entirely uncovered. It is
believed, therefore, that a larger amount of caustic was necessary than
would otherwise have been the case. This belief is strengthened by the
quality of the waste liquor from one of the later cooks, which gave on
analysis 16.85 grams per liter of free caustic soda and showed a
causticity of 27.75 per cent. These data show that only 67.3 per cent of
the total caustic employed was actually consumed in the cooking
operation, which percentage is lower than obtains in practice. The stock
from this cook was bleached with 11.5 per cent of bleach. But even as
the figures stand, the comparison with poplar cooking practice is as
follows: 29.5 per cent caustic soda used as against 22 to 25 per cent;
107 grams per liter as against 100 to 110; 84 per cent causticity is
little different than obtains in practice; 170° C. is about commercial
practice; five hours at pressure as against four to six hours; seven
hours' total time as against possibly six to eight hours; 11.5 per cent
bleach as against 8 to 10 per cent. Thus, it is evident that the cooking
conditions employed were slightly more severe and expensive than those
in commercial use with poplar wood.
The yield of total fiber obtained from the hurds may be placed at 35 per
cent of bone-dry fiber calculated on the bone-dry weight of hurds used,
or 33.1 per cent of air-dry fiber calculated on air-dry hurds. The yield
of bleached fiber was not determined in this preliminary work, but may
be safely estimated as 30 per cent, which is low when compared with a
yield of about 47 per cent of bone-dry bleached fiber from bone-dry
poplar wood. It is believed quite possible that satisfactory cooking
conditions may be found which will give a higher yield than was obtained
during these tests. The stock should be classed as easy bleaching, and
11.4 per cent of bleach is a satisfactory figure, although a little
high.
As to beating cost, in the last two and most satisfactory tests the
total washing and beating time was three hours, which may be about an
hour more than ordinarily is used in making papers of this grade,
although the practice varies to a considerable extent.
In regard to furnish, there is such a diversity of practice that it is
difficult to make a comparison, but if the hurd stock can be produced as
cheaply as soda-poplar stock, the furnish used in these last two tests
should be regarded as satisfactory to the book and printing paper
manufacturer.
The finish of the paper was not all that might be desired, but that was
due almost entirely to the calender stack available for the work, which
was composed of nine light rolls, many of which were about 6 inches in
diameter and which had not been reground for some time. From a small
test on a large calender stack it was readily shown that the paper
produced is capable of taking a satisfactory finish.
This comparison, satisfactory in many respects, develops two factors
which are decidedly unfavorable to hemp hurds, namely, raw-material
storage and digester capacity, and they must be taken into full account
in considering the paper-making value of this material, although it
should be recognized that investigation may result in the material
improvement of these conditions. Moreover, it is not at all improbable
that further investigation would develop more satisfactory treating
conditions and more suitable furnish compositions, and the belief in
this possibility is strengthened by the fact that material progress was
being made at the conclusion of this preliminary work.
Calculations on the raw material and acreage for a permanent supply for
a pulp mill producing 25 tons of fiber a day for 300 days per annum, or
7,500 tons per annum, give the comparison between hurds and wood shown
in Table II.