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.