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with anions and cations, respectively, to the left and right gelatin solutions are chilled to about 10" C., the turbidity of pH = 4.7. The assumption carries with it the idea that is intensified but diminishes again with rise in temperature. gelatin may be purified or de-ashed only a t pH = 4.7, when Thus the solubility of the precipitate is a function of the temit is not in combination with either ion. To test this widely perature. accepted theory, specimen E, extracted from originally acidAt relatively high concentrations of isoelectric gelatin, the conditioned stock, having its isoelectric point at approxi- turbid effect is greatly diminished even in the cold and again mately pH = 8, was de-ashed by the method of Loeb. The when the concentration is too low, so that the turbidity effect ash was reduced from an original content of 0.76 to 0.04 per is also a function of the concentration. cent, the whole operation being conducted a t pH not greater A number of measurements were made (Figure 7) and it than 4.5 a t any time. This position corresponds to the first was found that maximum turbidity is in the region of a 1 jelly-consistency maximum of this class of gelatin and pre- per cent solution of isoelectric gelatin in water (with very sumably in the condition of its greatest combining power weak or low-grade gelatin the concentration necessary may with anions. After drying, the pH changed to 4.7, some of reach 1.5 per cent). The most logical explanation for these the acetic acid being evolved in the process. This de-ashed effects appears to be that a t concentrations greater than 1 gelatin shows a second maximum a t pH = 9. From the per cent the gelatin acts as a protective colloid, inhibiting turbidity maxima the isoelectric point remains a t approxi- precipitation a t the isoelectric point, while a t concentrations mately pH = 8. The original characteristics are unchanged less than 1 per cent the solubility in water diminishes the and obviously gelatin may be de-ashed without reference to relative volume of the precipitates. Accordingly, at approxiits isoelectric point. mately 1 per cent concentration water a t 10' C. may be conThe suggestion has been made that gelatin may not be in sidered as saturated with respect to isoelectric gelatin. The chemical combination with electrolytes and the above experi- measurements were made optically, through a depth of 15 ment appears to lend support to the adsorption theory.13 mm. as in the other turbidity experiments. TURBIDITY CHARACTERISTICS-Anumber of determinations were made to study the behavior of the substance reAcknowledgment sponsible for the turbid effect. In solution a t normal temperature this phenomenon is known as the Tyndall effect Grateful acknowledgment is made to S. E. Sheppard for and is due to selective absorption of blue light observable a very fine specimen of ash-free gelatin, to A. W. Thomas when a beam of white light is passed through a weak gelatin for checking some of the pH measurements, and to the Atsolution and viewed a t right angles to incidence. When the lantic Gelatine Company for choice specimens of raw materials and the use of its laboratory equipment. 11 09. c k , pp. 232 and 327.
Cellulose from Cornstalks'" H. A. Webber DEPARIMBNT OF CHEMICAL ENGINEBRING, IOWASIAIB COLLBGB, AXES, IOWA
HE idea of utilizing cornstalks as a source of cellulose in the United States is almost one hundred years old. On August 13, 1838, Homer Holland was granted United States Patent 878 for a process for "Preparing the Lignia or Fibrous Portion of Corn Husks, etc., by digestion in a solution of alkali carbonate causticized with lime." Since that time and up through the year 1927 more than two dozen other United States patents have been granted for making pulp from cornstalks.
T
Quantity of Cornstalks Produced
It is small wonder that the idea of making pulp from stalks occurred to so many, when one considers the vast amount of cornstalks available each year in this country. It is estimated that 175 million tons of cornstalks are produced each year in the United States. The methods used in arriving at this figure may be of interest to those not acquainted with the problem. It may be said that there is no general agreement as to the yield of cornstalks per acre. The data obtained from various sources show considerable variation in 1 Presented by 0. R. Sweeney before the Division of Cellulose Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928. 2 The results which this paper so briefly summarizes have been obtained by the joint codperation during the last few years of the United States Bureau of Standards, the Engineering Experiment Station, and the Agricultural Engineering and Chemical Engineering Departments of Iowa State College. A bulletin giving in detail the work done thus far is being issued by the Engineering Experiment Station, Iowa State College, and copies will soon be avnilable to those interested.
amount, as they have been determined for several varieties of corn grown under widely different conditions of soil and climate. L. K. Arnold, of the Engineering Experiment Station, Iowa State College, has made an extensive study of the yield data extant in the literature. Some reported results were discarded, as it was not always possible to determine whether they represented silage corn, corn fodder, or stover grown for grain. "Stover" is the agricultural term for that part of the corn plant which remains after the corn is husked, and includes the stalk proper, the leaves, tassels, and husks, but does not include the roots. The data considered, therefore, represent only the amounts of mature cornstalks (stover) available after the husking season. The data gathered for this study were tabulated in three groupings. The first group comprised data from nine corngrowing states showing actual ratios of the stover to the grain yields. The second group contained data from twelve state universities and agricultural experiment stations and four private investigators, showing stover yields in tons per acre. The third group included data from six state colleges and agricultural experiment stations, giving the average weight of mature stalks, and data obtained from four investigations, representing nearly two hundred fields of corn, giving the number of stalks per acre. An average of 9000 stalks to the acre with a bone-dry weight of 262 grams (0.576 pound) per stalk was obtained in the third grouping. A summary of the average yields of cornstalks (stover) obtained by these three methods is given in Table I.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
March, 1929 Table I-Yields
of Bone-Dry Stalks per Acre
Calculated from ratio stalks grain
Stover (by direct weighing)
Calculated from number and weight of stalks Field dried average (10 per cent moisture)
Tons 1.35 2.10 2.56 Av. 2.00 2.2
271
based on an average yield of 1.5 tons per acre and for factories operating 300 days a year. The amount of forest land necessary for the continuous operation of a 50-ton per day paper plant varies with the locality and kind of wood, but is estimated a t 100 square mile^.^
The average by the three methods is practically the same Cost of Hauling and Harvesting as the average of the reports in group 2. A yield of 2 tons The following are the average hauls based on the usual of bone-dry stalks per acre can be expected under average conditions in the Corn Belt states. I n 1925 the total acreage road system of Iowa, in which the roads run a t right angles to in the United States was 101,631,000 acres. Of this, 86,339,000 each other one mile apart in each direction. The cost of acres were harvested as grain. With a yield of 2 tons per hauling is calculated a t 20 cents per ton mile. acre, this would give a total of 172,678,000 tons of stalks for cost Size of Plant Av. Haul the United States. Tons Miles $1.12 5.58 50 If the stalks are harvested before the corn is mature, it is 1.39 6.93 75 1.58 believed that 2 tons per acre is a reasonable figure. If the 7.92 100 corn is husked in the field Some idea of the cost of and the stalks are harvested harvesting can be realized over a considerable period The rapid growth of the cellulose industries, together from the following data: of time, the losses due to with the increasing scarcity of suitable woods, has wind whippage and other (1) Cost, per ton, of cutcreated a lively interest in other possible sources of ting stalks: causes would decrease the cellulosic raw material. This article summarizes the yield to 1.5 tons per acre. If By hand $1.68 results of studies made on cornstalks to ascertain if With sled harvester 1.40 the stalks stand for a long the cellulose obtainable from this source is satisfactory With corn binder 1.90 With c o n shocker 1.59 period in the field with the enough, both in quality and quantity, to make it a Cost of baling 1.66 cattle eating the leaves, the profitable source of raw material. The results indicate yield will be about 1.25 tons (2) Cost of harvesting that in the Corn Belt states stalks are sufficiently conper acre. Even if the stalks based on experimental work centrated so that they can be economically gathered by the Agricultural Engineerare entirely trampled down, and converted into pulp, etc. Chemical analyses show ing Department, Iowa State they can readily be gathered. that about 35 per cent of the stalk is cellulose. AlCollege, is given as $3.12 per This has been demonstrated ton. though stalks are bulkier than wood, they are more by the Agricultural Engi(3) Cost data for harvesteasily delignified. The cellulose obtained from stalks ing 10,000 tons of cornstalks neering Department, Iowa has properties which indicate that it should be a satisat Tilton, Ill., are given by S t a t e College. However, factory source for many materials. Rommel.4 The average cost the stalks are dirtier and not was $8.00 per ton for an averso desirable as those harage 15-mile haul. This figuie was total over-all cost, vested while standing. The region in the Middle West known as the Corn Belt is including the price paid to the farmers. beyond question the largest producer of corn in the world. Structure of Corn Plant There are only two or three other regions where corn is grown to any appreciable extent. One is in Argentine, another is Although there are numerous varieties, there exists only one in the valley of the Danube River. botanical species of corn, eea maize. The mature plant consists of stems, roots, leaves, husks, and ears. The ears conCornstalk Yield over Small Areas sist of the grain arranged upon the cob. The stem is covered Cornstalks are rather bulky and there has been some on the outside with a hard, flinty rind or shell called the question as to the cost of transporting them and also as to cortex. The inner portion consists of a soft pith traversed the availability of sufficient stalks over a small area. Con- longitudinally by numerous fibro-vascular bundles, arranged sideration of the following data will show that a small area will with the smaller ones thickly placed near the outer edge and furnish ample supply for an ordinary pulp mill. the large ones, less abundant, towards the center. The outer covering of the stalk is made up of long, thick-walled, slender Table 11-Annual Yield of Cornstalks over Various Areas cells or sclerenchyma fibers. The fibro-vascular bundles are 60% OF LANDIN CORN ONE-THIRD OF LANDIN CORN made up of long fibers and vessels or tubes. The pith cells Paper Paper RADIUS are short, broad, and without much strength. At intervals Stalks &$& Wall board Stalks Wall board of 8 to 10 inches along the stalk the fibro-vascular bundles yield) yield) send out branches to the leaves, thus forming by the branchTons per Tons per Sq. f l . per Miles Tons per Tons per Sg.f f . fie? ing and rejoining of bundles dense, enlarged portions known day day day day day day as nodes. These nodes make up about 26 per cent of the 150 50 401,900 5 27 223,000 SO 217 72 578,700 40 321,400 6 121 stalk proper or about 6 per cent of the entire plant. The 384 128 1,028,800 8 71 577,500 214 602 201 shell, not including the nodes, is about 54 per cent and the 1,607,800 10 893,000 335 112 pith, 20 per cent, of the stalk. However, because of the I n Iowa the acreage planted to corn varies in different light, porous nature of the pith, the percentage by volume is parts of the state from 8 to 60 per cent of the total. One- much greater. third of all the land is planted to corn each year. Table I1 The stalk has the apparent disadvantage of not being so gives the yield of cornstalks together with the corresponding uniform as wood. However, part of the uniformity of wood yields of paper pulp and wall board over various radii. These is obtained only by discarding portions of the tree such as are calculated for both the state average of one-third of the branches, bark, and leaves. The stalk is less dense, thus land in corn and for the better sections of the state where 60 8 Kellogg, “Pulp and Pulpwood in North America,” p. 199, McGrawper cent of the land is in corn. I n either case the haul to Hill Book Co., 1923. factories centrally located would be small. All figures are 4 Rommel, IND. END. CHBM.,20, 716 (1928). ~
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requiring more storage space, but it is also more readily cut or broken up into suitable sizes for cooking and beating.
VOl. 21, No. 3
I n several of the pentosan analyses the furfural phloroglucide was extracted with alcohol, acting on the suggestion that the alcohol-soluble portion represented the phloroChemical Composition of Cornstalks glucinol precipitants coming from the oxycellulose and An average of several chemical analyses made by different methyl pentosans. No appreciable difference in weight of investigators on mature cornstalks indicates that the stalks precipitate was obtained. This procedure is a debated consist of 33 to 35 per cent cellulose, 30 to 35 per cent lignin, question, but if it is reliable it indicates that most of the and 27 to 29 per cent hemicelluloses of which the greater part furfural does come from xylan present as such in the tissue. is apparently pentosan bodies. Furfural can be determined quantitatively in the presence The chemical uniformity of the three physically distinct of 12 per cent hydrochloric acid by means of thiobarbituric parts of the stalk is shown in the following analyses (Table 111) acid, but this reagent also combines the methyl furfural and by Peterson and Hixon : so this substance and furfural would be determined together. Some efforts were made to determine furfural colorimetrically, Table 111-Comparison of Compositions of Cortex, Vascular Bundles, a n d P i t h of the Cornstalks using aniline acetate or aniline hydrochloride as an indicator. OUTERSHELLVASCULAR TOTAL No success was had, however, as the furfural obtained by the OR CORTEX BUNDLES CORNSTALK distillation, when working in very dilute solution, imparted Per cent Per cent Per cent Pe? cent a yellow color to the indicator solution, whereas the standard Pentosan 25.9 26.4 27.7 27.6 furfural solution gave the well-known pink coloration, making Lignin 33.5 35.2 32.0 34.3 Cellulose pulp 55.9 50.2 50.1 52.6 i t impossible to match colors. At present the method of Pentosans in pulp 16.6 13.1 12.2 14.2 Cellulose (by diff.) 39.3 37.1 determining furfural by precipitation of the hydrazone with 37.9 38.4 phenylhydrazine is being tested. Until some method of LIGNIN-The cornstalks run very high in both lignin and determining pentosans directly is found it will probably be pentosans and they are usually classified as pentocelluloses. impossible to determine what percentage of xylan as such The lignins isolated by the Klason method, using 72 per cent occurs in the stalk. sulfuric acid, run much higher than those isolated by the TOTAL CELLULOSE-The cellulose fraction of the cornstalk Willstatter method, using fuming hydrochloric acid. The represents about 35 per cent of the stalk. Analyses of total lignin fraction obtained by the Klason method amounts to cellulose run much higher and various investigators have 31 to 35 per cent of the stalk, while the lignins isolated by the obtained values between 45 and 50 per cent of the stalk. The Willstatter method represent about 26 per cent of the stalk. total cellulose determinations were made using the Cross and The lignins in stalks probably belong to the same class of Bevan chlorination method. An average of 45.03 per cent compounds as the wood lignins, although there are no reasons total cellulose was obtained by the author, using the apparaa priori for believing them to be identical. Peterson and tus recommended by Dore.7 The determinations were Hixon6 determined the methoxy (CH,O) content of the lignin made on cornstalks gathered in March after standing in the isolated and obtained the high value of 14 per cent, which is field all winter. They were ground to pass an SO-mesh very close to the value RitterB obtained for mesquite (14.05) Tyler standard sieve. The samples were previously extracted and incense cedar (14.51) and intermediate between his values with alcohol-benzene mixture. No extraction with 1 per for western yellow pine (13.13) and western white pine (15.10). cent sodium hydroxide was made previous to the chlorination, The stalk lignins isolated by Peterson and Hixon were ob- as it has been stated that in the case of woods this treatment tained as a light brown, amorphous powder, which when lowers the yield of total cellulose. suspended in water softened a t 60" C. to a sticky, resinous oil It was found that five 5-minute chlorinations with a modwhich on cooling quickly set to a brittle, easily powdered erate stream of chlorine (40 to 50 bubbles per minute) were mass. The fraction contained only a trace of pentosans necessary before a residue was obtained which when digested and consisted almost entirely of lignins and moisture (22 per with 2 per cent sodium sulfite solution gave no pinkish coloracent). The same investigators failed to isolate any pectin tion. This total cellulose residue, when corrected for or pectic acid from the stalk. An attempt was then made to pentosans (8.15 per cent) and ash (1.39 per cent), yielded a determine galactose on the assumption that any pectin present fraction amounting to 35.49 per cent of the stalk, and this would yield mucic acid on oxidation. Mucic acid was ob- was considered to be true cellulose. Peterson and Hixon5 tained in such small amounts that no definite identification isolated cellulose from stalks by the Cross and Bevan method was possible. It seems plausible to assume, then, that pectin and obtained a 45.5 per cent yield. When this fraction was is either absent or present in very minute quantities. corrected for its ash, lignin, and pentosan content, it amounted PENToSAN-It has been known for a long time that corn- to 35.4 per cent of the stalk. From the analytical work done cobs are very high in furfural-yielding substance and, since on stalks using the chlorination process for isolating the stalks are so similar chemically to cobs, the high pentosan cellulose, it seems probable that with stalks, the same as with content is to be expected. It is generally agreed that the woods, it is impossible to obtain a pentosan-free cellulose pentosan present in stalks and cobs is xylan, but it has not in this manner. Possibly on repeated treatment with chlorine yet been determined just what percentage of the furfural the pentosans would be eliminated, but only a t the expense obtained by acid hydrolysis comes from xylan occurring as of some cellulose, the extent of which loss is not known a t such in the stalk and what part is due to other furfural- present. At any rate, other methods seem more feasible for yielding substances. The pentosan contents were all de- securing a pentosan-free cellulose from the stalks. termined by distillation with 12 per cent hydrochloric acid, Schweitzer reports the crude fiber content of the stem to followed by precipitation of the furfural with phloroglucinol, be 34.75 per cent, of the leaves to be 24.42, of the husks to and then calculating back with the aid of Krober's tables. be 33.87, and of the whole plant to be 28.29 per cent. As is well known, degraded celluloses, such as oxycellulose ALPHA-CELLuLosE-The foregoing analyses would indicate and other constituents present in the tissue, are capable of that the cellulose content of the stalks is somewhere near 35 yielding furfural or products such as methyl furfural which per cent. If stalks are to be used as one source of cellulose will yield phloroglucinol precipitates. for the rayon industry, it would seem necessary to know the 6 Peterson and Hixon, unpublished data, Department of Chemistry, alpha-cellulose content. By alpha-cellulose is meant that Iowa State College. 0
Ritter, IND. END. CHEM.,16, 1264 (1923).
7
Dore, J. IND. ENG.CHEM.,12, 264 (1920)
March, 1929
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2 73
fraction of the cellulose which is not soluble in 17.5 per cent water. Then the residues were placed in a beaker with 500 sodium hydroxide or will withstand the mercerizing process. cc. of water and boiled 3 hours. After being filtered, the pulps It must be admitted that not a great deal is known of the were washed again with hot water, dilute acetic acid, and true nature of cornstalk cellulose. Are we justified in assum- hot water. Then they were dried a t 105" C. and weighed. ing that the cellulose fraction obtained after deducting the Each residue was then treated with 25 cc. of 17.5 per cent ash, lignin, and pentosan from Cross and Bevan cellulose sodium hydroxide for 2 hours and purified in the same manner represents normal or cotton type cellulose, as Heuser and as before. The results are given in Table IV. others claim for wood cellulose, or shall we adopt the view of An inspection of the results obtained in many caustic cooks Cross and Bevan that the nature of the cellulose depends on carried out for the preparation of paper pulps, in which the its source? If we take the first viewpoint, it is logical to pressure was varied from 25 to 150 pounds, the caustic-tom u m e that if any of the 35 per cent cellulose fraction is stalk ratio varied from 5 t o 40 per cent, and the concentration soluble in strong caustic solution, the soluble portion is present of the caustic solution from 1 to 10 per cent, brought out the as cellulosedegraded and made less resistant during the process following facts: The effect of pressure decreases as the of isolation. According to the second viewpoint, the alkali- pressure increases; the effect of increasing caustic concensoluble portion of the cellulose fraction may be a true cellulose tration is fairly uniform a t all pressures investigated and is or celluloses, but because of different configurations be less a much more important variable than increasing pressure; resistant to strong alkali than other types which are also increasing the cooking time from 2 to 6 hours has but little effect. The stalks show an increasing resistance to destrucpresent. Schorgers states that the method of determining alpha- tion when 60 per cent by weight has been lost and this becomes cellulose with 17.5 per cent sodium hydroxide is too severe quite pronounced when 65 to 70 per cent has been lost. for wood celluloses and recommends digestion with 2 per cent Evidently a t this stage the normal cellulose is being slowly boiling sodium hydroxide solution. Some Cross and Bevan attacked, and this would indicate that the stalks contain cellulose was treated with 17.5 per cent sodium hydroxide 30 to 35 per cent of a quite resistant cellulose. solution, in the standard procedure for determining alphaPeterson and Hixon5 arrived at an average value of 36 per cellulose. The residue amounted to 56.14 per cent of the cent cellulose as the result of analyses made by several original pulp. This residue was then treated with 72 per cent methods. Phillips'o carried out a fractional extraction of sulfuric acid, in which it dissolved entirely, though in time the lignin from corncobs, which should be very similar chemically solution darkened and then turned black. The alpha-cellu- to cornstalks, using sodium hydroxide solutions, and oblose in this solution was then determined by the volumetric tained a lignin-free residue amounting to 35 per cent of the method of Bray and A n d r e w ~ . ~The results of this analysis moisture-free cobs. in terms of the Cross and Bevan pulp gave alpha-cellulose The Cornstalk Products Company, Inc., operating a t 53.34 per cent. The difference (56.14 - 53.34) consisted of Tilton, Ill., reports pulp yields of 38 to 40 per cent using 10 1.39 per cent ash as determined on another sample, and 2 per cent sodium hydroxide cooks a t 20 pounds gage pressure. per cent lignin, which probably gave the black coloration to The alpha-cellulose content averages 70 per cent and from 4 the sulfuric acid solution. It has been noticed, however, that tons of this pulp a &ton yield of 90 per cent alpha-cellulose is even purified cotton solution turns black after several hours' obtained. These figures give 33 per cent yield of 90 per cent standing. The beta- and gamma-celluloses in the alkaline alpha-cellulose from the original stalks. filtrate were determined by the Bray and Andrews method Commercial Developments and the results were as follows: beta-cellulose 26.33 per cent, gamma-cellulose 16.57 per cent. On multiplying the percentThe foregoing statements indicate that the alpha-cellulose age of Cross and Bevan cellulose by that of alpha-cellulose content of the stalks is approximately 30 to 35 per cent. present in this pulp, a value of 24.2 per cent alpha-cellulose This pulp is suitable for rayon, nitrocellulose, and similar for the entire stalk was obtained. products, but it has been determined that higher yields of pulp suitable for making cheaper grades of paper can be Table IV-Alkali-Insoluble Cellulose in Cornstalks obtained by less drastic treatment of the stalks. The pulps CONCENTRATION OF SOLUTION in these higher yields still retain an appreciable percentage of 2%' 5%," 15%a 17.5%b 40%b pentosans and lignins. It is hoped that the commercial utilization of cornstalk Gram Gram Gram Gram Gram Gram cellulose will develop along each of two distinct lines. The Weight of residue 0.3916 0.4005 0.3910 0.3505 0.4055 0.3650 Following treatment of first residues with 17.5% NaOH first includes those applications which can utilize the entire Weight of residue 0.3380 0.3455 0.3360 0.3305 0.3730 0,3400 Less lignin 0.0235 0.0605 0.0605 0.0485 0.0349 0.028 stalk as crude fiber. Under this heading would come wall Less ash 0.006 0.0105 0.006 0.0046 0.008 _-0.0075 --- - -_ --board, artificial lumber, box board, cornstalk flour, and Weight of cellulose 0.3070 0.2800 0.2650 0.2760 0.3336 0.3060 similar articles. The other development would be the use Cellulose yield (cor. for9% moistwe) 34.50% 31.10% 29.45% 30.65% 37.10% 34 00% of cornstalk cellulose purified from incrustants and properly prepared to serve as raw material for paper, rayon, nitroBoiled 2 hours under reflux. b Treated 2 hours in cold. cellulose, cardboard, and similar products. WALL BOARD, Em-Considerable research has been A series of experiments was made to determine how much alkali-insoluble cellulose is present in cornstalks. One-gram carried on during the last few years in the Chemical Engineersamples of cornstalk powder passing 60-mesh screen were ing Department a t Iowa State College, in conjunction with treated with sodium hydroxide solutions of various concen- the United States Bureau of Standards, on the development trations, as shown in Table IV. Each solution, however, held of a satisfactory wall board from the entire stalk. This the same amount of solid caustic and the ratio of solid sodium work will not be discussed in detail here, but a few of the hydroxide to stalks in each case was 5:l. After this treatment results obtained thus far may be interesting. It has been the pulp residues were purified by washing with 4 per cent found that by preparing a mechanical pulp from the entire hydroxide, hot water, dilute acetic acid, and again with hot stalk as much as 90 per cent of the original stalk will appear in the finished wall board. The general procedure is to shred I Schorger, "Chemistry of Cellulose and Wood," p. 540, McGraw-Hill the stalks and then beat them to proper size in a Hollander Book Co.. 1926. 9
Bray and Andrews, IND.
ENG.CHEM.,15, 377 (1923).
10
Phillips, J. Am. Chem. Soc., 50, 1986 (1928).
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machine, adding a sizing material during this operation. The pulp is then pumped to an Oliver continuous vacuum filter, where the board is formed. From the Oliver, the board passes through a Downington press roll and then through a Coe roller drier. The board issuing from the drier is cut and trimmed, and in appearance and properties closely resembles many of the wall boards now on the market. No bleach is used during the process, so the board is light brown in color. It has been determined that the manner of shredding the stalk and the preparation of the fiber previous to feeding it to the beater is probably the most important step in the entire process, as upon this step depends to a great extent both the yield and the physical structure of the fiber. Inasmuch as cornstalks are made up of three physically distinct parts, the process of reduction to beater-feed size with maximum yield and proper physical condition of all three parts has required a great deal of experimental work. Many different types of reduction machines have been tried, including corn shredders, swing hammer mills, and ensilage cutters. Swing hammer mills seem to give good reduction. At present tests are being conducted on rod mills, as it is hoped that these, besides giving good reduction, will also make it possible to eliminate the Holland beater. The stalks have been reduced in both the wet and dry state. Wet reduction seems to give a better fiber and causes less loss from dusting. The action of the beater is to hydrate the fibers and draw the pith out into a fibrous condition. Reduction of the pulp in the beater is not carried nearly so far as in the production of paper stock. It is desirable to have the fibers relatively coarse and long so as to interlace on the Oliver filter and produce the thick, fibrous mat essential for good insulation board. PAPER 8TocK-h the production of paper stock from cornstalks, it was recognized many years ago that the physical differences in the stalk components might have an adverse effect on the paper, and on June 27,1899, George R. Sherwood was granted U. S. Patent 627,882 on a machine for removing the pith from stalks. He was granted U. S. Patent 720,850, February 17, 1903, for a process for making parchment-like paper from the pith, and he also made paper from the more fibrous portions of the stalk. The pith of the stalk, being composed of short, square cells, but loosely held together, is very easily reduced to pulp, either by beating or by treatment with chemicals. This pith produces a brittle, parchment-like paper, while the outer fibers produce a soft, fibrous paper. Several of the early investigators tried cooking the pith and fibers apart and then running the pulps together to form paper, as it was known that the pith required less chemicals and digestion than the more resistant fibers. I n general, the experimental work done in this laboratory on the production of a pulp suitable for paper-making has been devoted to efforts to use the entire cellulose content of the stalks. Instead of separating the pith from the fibrous portions of the stalk, efforts were made to secure a satisfactory physical condition of the pith so that the pith pulp, together with the fiber pulp, would work up into good paper. The reason for making these attempts was to secure an increased yield of pulp, as the pith makes up about 20 per cent of the stalk by weight and a much larger percentage by volume. Besides the increased yield, the cost of preparing the stalk pulp would also be decreased if i t was found unnecessary to remove the pith. The pith cellulose seems to be quite as resistant to chemical action as the fiber cellulose as regards degradation and solubility, but owing to its much greater ease of reduction by digestion and beating, the pith cellulose is liable to be in an almost colloidal state before the fibrous portions are properly purified. The pith, when in this condition, washes through
Vol. 21, No. 3
the screen and is lost in the wash water. The experimental work has been concerned to a great extent, therefore, with developing methods whereby the pith can be preserved for the pulp in proper physical condition and a t the same time the fibrous portions will be satisfactorily purified. The goal has been to draw out the pith in fibrous form instead of disintegrating it. Preparation of Cellulose
The methods of preparing the cellulose from stalks have, in general, been those methods used in the delignification of woods and straw modified to meet conditions. The general methods of preparation have been the use of alkali cooks, sulfite cooks, sulfate cooks; removal of the incrustants with chlorine, bromine, dilute nitric acid, and reduction to mechanical pulp by grinding. Most of the experimental work has been done on alkali cooks, using sodium hydroxide, but lime cooks, mixtures of soda ash and caustic, lime and caustic, soda ash alone, and even sodium silicate cooks have been made. The stalks are first shredded in a swing hammer mill, corn shredder, or ensilage cutter, and then charged into the cooker after dusting. Cooks have been made both with live steam and with jacketed kettles, but usually live steam is used. As is quite evident, the yields depend on a number of variables, such as strength of alkali, duration of cook, temperature of cook, degree of beating, and other conditions. The kind of paper desired will define the conditions but in general the aim has been to secure the greatest yield of easily bleached pulp that would produce a satisfactory paper. Samples of the papers made by the various cooks were tested for tensile strength with a Scott machine, for bursting strength with a Mullen machine, and for folding endurance with an M. I. T. type Olsen machine. After being cooked the stalks are beaten, then screened through regular bronze paper screens with slotted openings 0.03 cm. (0.012 inch) in width, and fitted with pulsating diaphragms to prevent clogging. From the screens the pulp is carried to the dewatering screens, then it is bleached with chloride of lime or chlorine and washed. If the pulp is to be made into a sized paper, it is then sized with rosin soap and aluminum sulfate, a filler being added if required. The pulp is next sent to the stuff chest and then to the sheet-forming machine and the drier. Many of the finished papers were left unsized, but they acquire a glaze and take up writing and printing inks without running or blotting as if a sizing material were present. This property is thought to be due to the pentosan constituents of the pulp. The results obtained so far substantiate those of earlier investigators in that the fibrous outer shell used alone makes the strongest paper; the pith used alone gives a translucent parchment-like paper, while paper varying between these two extremes is obtained when the entire stalk is used. The pulp made from the fiber requires less bleach than that from the pith, although the fiber is more colored in the raw state. The leaves and husks produce the weakest paper. When the entire stalk is used, a good paper can be produced if the cook is relatively short (11/* to 2 hours) and the beating is not too severe, as in this case the entire pith is not reduced t o a colloidal condition, but some of it is drawn out into fibrous forms which interweave with the more resistant fibers. A summary of the results obtained so far using various cooks is given in Table V. Optimum conditions as far as determined and average yields only are included. The sodium hydroxide cooks give the best results when everything is considered, although the pulps made with the halogens require less bleach. I n general, the bleach consumption of the sodium hydroxide cooks amounts to 20 per cent of the weight of the dry pulp and there is a loss of about
INDUSTRIAL AND ENGIiVEERIhlG CHEMISTRY
March, 1929
10 per cent of the pulp during the bleaching process or about 3 to 3.5 per cent of the original weight of stalk, giving an overall yield of good paper-grade pulp amounting to 30 to 32 per cent of the original weight of stalks with an alpha-cellulose content of 70 to 75 per cent. Table V-Cellulose CHSYICALS
USED
275
The sodium hydroxide, soda, Kraft, and halogen processes make pulps suitable for magazines, books, and writing paper. The lime-soda and sulfite processes give a weaker paper, suitable perhaps for toilet paper and similar grades, while the lime pulp seems suitable for box board and other articles, where an unbleached pulp can be used.
Yields w i t h Various Cooks
$~~~~~ Tm8 PRG&ASRE
YIELD OF
ALPHACELLULOSE
PULP
I N PULP
Per cent Hours Lbs./sq. i n . Per cent Per cent Sodium hydroxide 10 to I5 2 50 t o 7 5 35 70 t o 7 5 Sodium Kraft hydroxide 9 5 50 43 t o 4 8 60 Sodium sulfide 1 Sodium carbonate 15 50 33 70 5 Magnesium chloride 4 to 5 35 Unsatisfactory pulps Sodium hydroxide Sodium sulfate 25 50 Unsatisfactory pulps 5 10 1 Sodium hydroxide 5 38 65 50 Lime 51 Sodium silicate Up t o 70 4 50 No pulping effect 10 I Sodium carbonate Sodium hydroxide sulfite 50 40 65 Sodium (sulfiteJ 1 Sodium silicate 34 Poor results 312' 30 Sodium hydroxide Sodium carbonate ~ : ~ ] 3 t o 1 6 25 Poor results Sodium sulfide Lime 30 40 65 t o 7 0 6:7d?5 Sulfur 20 4 50 80 Pulp hard to Lime bleach D e Vain's procedure as spedfied in patents 33 65 t o 7 0 Pomilio'sl(gaseous chlorine) procedure as speafied in patents 30 60 t o 6 5 Z/S None 28to30 60 Bromine water (saturated)
i
'8 1
5"t '21
1
Conclusion The experimental work done in this laboratory and elsewhere indicates that cornstalks are more easily reduced to cellulose than are woods. On the other hand, cornstalks are more bulky, give a lower yield of cellulose, and the pulp requires slightly more bleach. At the present time the production of wall board from stalks offers the most attractive outlet, and a factory for the manufacture of wall board from stalks will soon start operations in Dubuque, Iowa. Another promising field is the manufacture of cellulose for rayon and paper pulp, and the progress of the factory a t Tilton, Ill., is being observed with great interest. I n the near future it is believed that, owing to the increasing cost of wood pulp for paper-making, this industry will offer a large outlet for cornstalk cellulose. Still another field is the manufacture of nitrocellulose from cornstalk pulp. It has been determined that both bleached and unbleached pulps nitrate readily and satisfactorily with a high degree of stability. Important statistics on the economics of harvesting will be available within a year or two.
Cellulose from Cereal Straws' Sidney D. Wells PAP8R MILL LABORATORIES, INC., QUINCY,ILL.
Cereal straws constitute a n enormous source for cellulose which is readily gathered and capable of purification by very mild processes. Caustic soda in dilute solution will remove more than half the incrusting substances a t room temperature and more than 70 per cent a t 100" C. Higher temperatures are even more effective. Sodium carbonate has considerable action a t 100' C. and a t higher temperatures is a very effective agent, especially in the presence of sulfur compounds of a reducing nature. Milk of lime is the most commonly used agent in technical operations, but it is useful only where the purity of the pulp is of minor importance or where it is to be further purified with chlorine. Chlorine is a n effective agent used alternatively with 1 per cent caustic soda, and yields of 55 per cent of white fiber may be obtained. Yields
of 66 per cent may be obtained by cooking with sodium carbonate and sulfur and bleaching with calcium hypochlorite in several steps. Yields of 43 per cent of pentosan, lignin, and ash-free cellulose, comparable with alpha cellulose from cotton or wood pulp, may be obtained by alternate chlorine and caustic soda treatments. Xylan may be extracted from straw with caustic soda to the extent of almost 15 per cent. Another 9 per cent of furfural-yielding components remains which can be largely removed after chlorination by further extraction with caustic soda. The spent cooking liquors from digestion with sodium carbonate and sulfur are capable of hydrolysis and fermentation with the production of lactic acid, acetic acid, and other valuable products in promising quantities.
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T
HE straw from the cultivation of cereals is one of the largest potential sources for cellulose. Under this classification is usually included the straw of wheat (triticum), rye (secali), oats (avena), and barley (hordeurn). Rice straw is not usually included in general discussions of the subject, although enormous quantities are produced and it lends itself readily to the production of cellulose. The results of studies of the cellulose of the cereal straws have usually been reported on the whole material. Straw, however, is a mixed product, being composed of cells of widely different characteristics and functions. There are Presented before the Division of Cellulose Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14. 1928.
variations in the cell structure not only of separate portions of the stem but also of the leaf sheaf and the various elements of the head, such as the chaff, consisting largely of the glumes and palets, dwarf cells, etc. The stem is made of widely different structures, of which the internode with a welldeveloped fistula is most characteristic. There are also the nodes and false nodes or motile organs and the rachis from the head, which give considerable trouble to the paper maker as well as to the student endeavoring to obtain typical samples. A cross section of the stem shows on the outside the epidermis, made up of thin and broad cells with serrated edges which dovetail into each other and form a compact shell. Below these we have the chlorenchyma spaces, which give color to the plant and take an active part in the con-
