Lyster H. Dewey and Jason L. Merrill - Hemp Hurds as Paper Making Material
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Lyster H. Dewey and Jason L. Merrill >> Hemp Hurds as Paper Making Material
UNITED STATES DEPARTMENT OF AGRICULTURE
=BULLETIN No. 404=
Contribution from the Bureau of Plant Industry WM. A. TAYLOR, Chief
[Illustration: USDA crests flanking bulletin banner]
Washington, D.C.
PROFESSIONAL PAPER
October 14, 1916
HEMP HURDS AS PAPER-MAKING MATERIAL.
By LYSTER H. DEWEY, _Botanist in Charge of Fiber-Plant Investigations_,
and JASON L. MERRILL, _Paper-Plant Chemist, Paper-Plant Investigations_.
=CONTENTS.=
Page.
The production and handling of hemp hurds,
by Lyster H. Dewey:
What hemp hurds are 1
Pith, wood, and fiber 2
Character of hurds affected by retting 2
Proportion of hurds to fiber and yield per acre 3
Hurds available from machine-broken hemp 3
Present uses of hemp hurds 4
Present supplies of hurds available 5
Baling for shipment 5
Cost of baling 5
Summary 6
The manufacture of paper from hemp hurds,
by Jason L. Merrill:
Introduction 7
Factors justifying an investigation of hemp hurds 8
Character of the material 11
Character of the tests 12
Operations involved in a test 13
Description of tests 16
Comparison of the tests and commercial practice 21
Physical tests of the papers produced 24
Conclusions 25
In preparing the report on the manufacture of paper from hemp hurds it
became evident that a short discussion of the agricultural aspects of
this material should be included in the publication. Such an article was
prepared, therefore, and the two reports are here presented together.
[NOTE.--This bulletin should be useful to all persons who are interested
in the economic phases of paper making, especially to print and book
paper manufacturers. It also should be of interest to scientific
investigators and chemists.]
=THE PRODUCTION AND HANDLING OF HEMP HURDS.=
By LYSTER H. DEWEY, _Botanist in Charge of Fiber-Plant Investigations_.
=WHAT HEMP HURDS ARE.=
The woody inner portion of the hemp stalk, broken into pieces and
separated from the fiber in the processes of breaking and scutching, is
called hemp hurds. These hurds correspond to shives in flax, but are
much coarser and are usually softer in texture.
The hemp stalk grown in a broadcast crop for fiber production is from
one-eighth to three-eighths of an inch in diameter and from 4 to 10 feet
tall. The stalk is hollow, with a cylindrical woody shell, thick near
the base, where the stalk is nearly solid, and thinner above, where the
hollow is relatively wider.
In the process of breaking, the woody cylinder inside of the
fiber-bearing bark is broken into pieces one-half of an inch to 3 inches
long and usually split into numerous segments. The thicker lower
sections are split less than the thin-shelled upper ones, and they are
often left quite solid.
=PITH, WOOD, AND FIBER.=
The inner surface of the hurds usually bears a layer of pith, consisting
of thin-walled cells nearly spherical or angular, but not elongated.
They are more or less crushed and torn. They are probably of little
value for paper, but they constitute less than 1 per cent of the weight
of the hurds. The principal weight and bulk consist of slender elongated
woody cells. The outer surface is covered with fine secondary fibers
composed of slender elongated cells, tougher than those of the wood but
finer and shorter than those of the hemp fiber of commerce. No method
has been devised thus far which completely separates from the hurds all
of the long fiber. From 5 to 15 per cent of the weight of the hurds
consists of hemp fiber, in strands from 3 inches to 8 feet in length.
Some fragments of the bark, made up of short cubical cells, usually dark
in color, cling to the strands of fiber.
=CHARACTER OF HURDS AFFECTED BY RETTING.=
Nearly all of the hemp in the United States is dew retted. The stalks
are spread on the ground in swaths as grain is laid by the cradle. The
action of the weather, dew, and rain, aided by bacteria, dissolves and
washes out the green coloring matter (chlorophyll) and most of the gums,
leaving only the fibrous bark and the wood. The plants in this process
lose about 60 per cent of their green weight, or about 40 per cent of
their air-dry weight.
The stalks are sometimes set up in shocks to cure before retting, and
after retting they are set up in shocks to dry. Each time the stalks are
handled they are chucked down on the ground to keep the butts even. In
these operations sand and clay are often driven up into the hollow at
the base of the stalks, and this dirt, which often clings tenaciously,
may constitute all objectionable feature in the use of hemp hurds for
paper stock.
In Italy and in most localities in Russia and Austria-Hungary where hemp
is extensively cultivated, it is retted in water, but water retting has
never been practiced in the United States except to a limited extent
before the middle of the last century. Hurds from water-retted hemp are
cleaner and softer than those from dew-retted hemp.
The fiber is sometimes broken from dry hemp stalks without retting. The
hurds thus produced contain a small percentage of soluble gums, chiefly
of the pectose series. Comparatively little hemp is prepared in this
manner in America.
Process retting by means of weak solutions of chemicals or oils in hot
water is practiced to a limited extent. The hurds from these processes
may contain traces of the chemicals or oils and also soluble gums in
greater degree than those of the dew-retted or water-retted hemp.
=PROPORTION OF HURDS TO FIBER AND YIELD PER ACRE.=
[Illustration: FIG. 1.--Hemp-breaking machine. The stalks are fed
sidewise in a continuous layer 2 to 3 inches thick, turning out about
4,000 pounds of clean fiber per day and five times as much hurds.]
The yield of hemp fiber varies from 400 to 2,500 pounds per acre,
averaging 1,000 pounds under favorable conditions. The weight of hurds
is about five times that of the fiber, or somewhat greater from hemp
grown on peaty soils. A yield of 2-1/2 tons of hurds per acre may be taken
as a fair average.
=HURDS AVAILABLE FROM MACHINE-BROKEN HEMP.=
Hemp hurds are available only from hemp which is broken by machines,
when the hurds may be collected in quantity in one place (figs. 1 and
2). Most of the hemp in Kentucky is still broken by hand brakes. These
small brakes are moved from shock to shock, so that the hurds are
scattered all over the field in small piles of less than 50 pounds each,
and it is the common practice to set fire to them as soon as the brake
is moved. It would be difficult to collect them at a cost which would
permit their use for paper stock.
Where machine brakes are used, the hemp stalks are brought to the
machine as grain is brought to a thrashing machine, and the hurds
accumulate in large piles, being blown from the machine by wind
stackers.
Machine brakes are used in Wisconsin, Indiana, Ohio, and California, but
to only a limited extent in Kentucky. Five different kinds of machine
brakes are now in actual use in this country, and still others are used
in Europe. All of the best hemp in Italy, commanding the highest market
price paid for any hemp, is broken by machines. The better machine
brakes now in use in this country prepare the fiber better and much more
rapidly than the hand brakes, and they will undoubtedly be used in all
localities where hemp raising is introduced as a new industry. They may
also be used in Kentucky when their cost is reduced to more reasonable
rates, so that they may compete with the hand brake. Hemp-breaking
machines are being improved and their use is increasing. The
hemp-growing industry can increase in this country only as machine
brakes are developed to prepare the fiber. A profitable use for the
hurds will add an incentive to the use of the machine brake.
[Illustration: FIG. 2.--Machine brake and hemp hurds. Hemp hurds from
machine brakes quickly accumulate in large piles.]
=PRESENT USES OF HEMP HURDS.=
Hemp hurds are used to a limited extent for barnyard litter and stable
bedding, as a substitute for sawdust in packing ice, and, in rare
instances, for fuel. They are not regarded as having a commercial value
for any of these uses, though they are doubtless worth at least $1 per
ton on the farm when used for stable bedding. They are a waste product,
without value for other purposes which might compete with their use for
paper stock.
=PRESENT SUPPLIES OF HURDS AVAILABLE.=
During the last season, 1915, about 1,500 acres of hemp have been
harvested outside of Kentucky and in regions where machine brakes are
used. Estimating the yield of hurds at 2-1/2 tons per acre, this should
give a total quantity of about 3,750 tons. Large quantities of hemp from
the crop of 1914, which are still unbroken in these areas, and large
piles of hurds undisturbed where the machines have been used during the
last two or three years, increase the total to more than 7,000 tons.
Hemp is now grown outside of Kentucky in the vicinity of McGuffey, east
of Lima, Ohio; around Nappanee, Elkhart County, and near Pierceton, in
Kosciusko County, Ind.; about Waupun and Brandon, Wis.; and at Rio Vista
and Stockton, Cal.
In Kentucky, hemp is grown in most of the counties within a radius of 50
miles of Lexington. No accurate statistics of the acreage are collected,
but the crop harvested in 1915 is estimated at 7,000 acres. A machine
brake will probably be used in Bourbon County and also in Clark County,
but most of the hemp in Kentucky will be broken on hand brakes.
=BALING FOR SHIPMENT.=
The hurds will have to be baled to facilitate handling in transportation
and to economize storage space at the paper mills. The bales will need
to be covered with burlap or some material to keep them from shaking
out. They may be baled in the same presses that are used for baling hemp
fiber, but care must be exercised to avoid breaking the press, for the
hurds are more resistant than hemp fiber. A bale of hemp 2 by 3 by 4
feet weighs about 500 pounds. A bale of hurds of the same size will
weigh about one-third less, or approximately six bales per ton.
Rough hemp fiber as it is shipped from the farm is not covered;
therefore, the covering material must be purchased especially for the
hurds. A piece of burlap about 36 by 48 inches placed on either side of
the bale will be sufficient, but these pieces, weighing about 3 pounds
each, cost about 40 cents a pair. Baling rope, in addition to jute
covering, will cost at least 5 cents per bale, making the total cost of
covering and ties $2.70 or more per ton. Possibly chip-board, costing
about $33 per ton, or not more than 5 cents for the two pieces for each
bale, may be used in place of burlap. Chip-board, burlap, and also rope
ties may all be used for paper stock. Burlap covers might be returned,
to be used repeatedly until worn out, but chip-board could not be used
more than once.
=COST OF BALING.=
If burlap covers are used the cost of baling, including covering, ties,
use of baling press, power, and labor will amount to at least 60 cents
per bale, or about $3.75 per ton. If chip-board can be used the cost may
be reduced to about $2 per ton. The cost of hauling and loading on the
cars will vary from $1 to $3 per ton, depending upon the distance and
the roads. The farmer must therefore receive from $4 to $6 per ton for
the hurds, baled, on board cars at his home station.
=SUMMARY.=
Hemp hurds are the woody inner portion of the hemp stalk, broken into
pieces in removing the fiber.
They are not used at present for any purpose that would compete with
their use for paper.
Hurds are available only from machine-broken hemp, for the cost of
collecting them from the hand brakes would be too great.
About 7,000 tons are now available in restricted localities in Ohio,
Indiana, Wisconsin, and California.
The quantity is likely to increase as the use of machine brakes
increases.
The hurds may be baled in hemp-fiber presses, with partial burlap covers
like those on cotton bales, or possibly chip-board covers.
It is estimated that the farmers may deliver the bales on board cars
profitably at $4 to $6 per ton.
THE MANUFACTURE OF PAPER FROM HEMP HURDS.
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 role 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. x75. 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.
