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

October 14, 1916 Washington, D.C.
PROFESSIONAL PAPER: 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.

  • What hemp hurds are
  • Pith, wood, and fiber
  • Character of hurds affected by retting
  • Proportion of hurds to fiber and yield per acre
  • Hurds available from machine-broken hemp
  • Present uses of hemp hurds
  • Present supplies of hurds available
  • Baling for shipment
  • Cost of baling
  • Summary

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 -3- 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.

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 2½ tons of hurds per acre may be taken as a fair average.

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.

Figure 1
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.

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 -4- 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.

Machine brake and hemp hurds.
Hemp hurds from machine brakes quickly accumulate in
large piles.

Figure 2
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 2½ 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 -6- 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.

 

Continue to the second half of the paper: The Manufacture of Paper From Hemp Hurds