Source: UNITED STATES DEPARTMENT OF AGRICULTURE BULLETIN NO. 404: HEMP HURDS AS PAPER-MAKING MATERIAL
Authors: Lyster H. Dewey, Botanist in Charge of Fiber-Plant Investigations, and Jason L. Merrill, Paper-Plant Chemist, Paper-Plant Investigations.
Pages: This is an excerpt of the entire report. ". . ." indicates that text is omitted.
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.
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.
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 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 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 an 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.
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. 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 braes, 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.
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 where the machines have been used during the last two or three years, increase the total to more than 7,700 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.
BAILING 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 bout 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 boards, 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 BAILING.
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 forest 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.
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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.
. . .
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.
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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. 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.
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 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.
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In the tests described in this bulletin, the Department of Agriculture employed a rotary digester of its own design, 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.
OPERATIONS INVOLVED IN A TEST
A complete test on hurds comprises seven distinct operations,
Sieving,
Cooking,
Determination of yield,
Washing,
Bleaching,
Furnishing, and
Beating.
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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.
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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.
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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.
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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 degrees C. for five hours, or a total time of seven hours.
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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 leaching, and 11.4 per cent of bleach is a satisfactory figure, although a little high.
As to beating costs, 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.
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The most important point derived from this calculation is in regard to areas required for a sustained supply, which are in the ration of 4 to 1. Every tract of 10,000 acres which is devoted to hemp raising year by year is equivalent to a sustained pulp-producing capacity of 40,500 acres of average pulp-wood lands. In other words, in order to secure additional raw material for the production of 25 tons of fiber per day there exists the possibility of utilizing the agricultural waste already produced on 10,000 acres of hemp lands instead of securing, holding, reforesting, and protecting 40,500 acres of pulp-wood land.
The annual growth per acre, although decidedly in favor of hurds, has little bearing on the project, because the utilization of the hurds is subordinate to the raising of hemp, and the paper manufacturer probably could afford to use only hurds resulting from the hemp industry.
PHYSICAL TESTS OF THE PAPERS PRODUCED.
Samples of paper produced in the seven tests were submitted to the Leather and Paper Laboratory of the Bureau of Chemistry. The report of that bureau on its tests is given in Table III.
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CONCLUSIONS.
There appears to be little doubt that under the present system of forest use and consumption the present supply can not withstand the demands placed upon it. By the time improved methods of forestry have established an equilibrium between production and consumption, the price of pulp wood may be such that a knowledge of other available raw materials may be imperative.
Semicommercial paper-making tests were conducted, therefore, on hemp hurds, in cooperation with a paper manufacturer. After several trials, under conditions of treatment and manufacture which are regarded as favorable in comparison with those used with pulp wood, paper was produced which received very favorable comment both from investigators and from the trade and which according to official tests would be classed as a No. 1 machine-finish printing paper.
PUBLICATIONS OF UNITED STATES DEPARTMENT OF AGRICULTURE RELATING TO MATERIALS FOR PAPER MAKING.
AVAILABLE FOR FREE DISTRIBUTION BY THE DEPARTMENT.
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Utilization of American Flax Straw in the Paper and Fiber-Board Industry. Department Bulletin 322.
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