Hemp Hurds as Paper-Making Material Part 2

_Furnis.h.i.+ng._--Furnis.h.i.+ng 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 pa.s.sing the wet sheet through a series of press rolls, after which the sheet is dried on steam-heated drums and pa.s.sed 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 coa.r.s.e 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 was.h.i.+ng engine, washed one hour, and given a total light brush of 2-1/4 hours. The was.h.i.+ng 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 was.h.i.+ng 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 s.h.i.+ves 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 s.h.i.+ves. 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, a.s.sisted 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 s.h.i.+ves 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 was.h.i.+ng 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 s.h.i.+ves 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, a.s.sisted 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 s.h.i.+ves 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 s.h.i.+ves 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 quant.i.ty 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 was.h.i.+ng 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 was.h.i.+ng for one hour and was medium brushed for one hour more, bleached with 11.3 per cent of bleach a.s.sisted 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 s.h.i.+ves 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 was.h.i.+ng 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 ill.u.s.tration 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 acc.u.mulate 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 const.i.tutes 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 a.n.a.lysis 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 cla.s.sed 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 was.h.i.+ng 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.

TABLE II.--_Comparison between wood and hemp hurds._

-----------+-------------+--------------+-----------+-------------------- | | | | Acres required for | | | | sustained supply.

| | | |---------+---------- | | Raw material | Annual | | Material. | Pulp yield. | required per | growth | For | For 1 ton | | year. | per acre. | 25-ton | of fiber | | | | mill. | per year.

-----------+-------------+--------------+-----------+---------+---------- Wood | Two cords | 15,000 cords | 0.37 cord | 40,500 | 5.4 | yield 1 ton | | (about | | | of fiber. | | 0.55 ton).| | | | | | | Hemp hurds | One ton | 25,000 tons | 2.5 tons | 10,000 | 1.33 | yields 600 | | | | | pounds | | | | | of fiber. | | | | -----------+-------------+--------------+-----------+---------+----------

The most important point derived from this calculation is in regard to areas required for a sustained supply, which are in the ratio 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.

TABLE III.--_Report of the Leather and Paper Laboratory of the Bureau of Chemistry on papers manufactured from hemp hurds._