U . TS U7 65 FORESTE COU.C6E Of AA6IUCW.T BULLETIN OF ram No. 72 Contribution from the Forest Service, Henry S. Graves, Forester. May 29, 1914. SUITABILITY OF LONGLEAF PINE FOR PAPER PULP. By HENRY E. SURFACE, Chemical Engineer in Forest Products, and ROBERT E. COOPER, Chemist in Forest Products. SOUTHERN PINES FOR KRAFT PULP. The southern pines have not, until within the last few years, been considered suitable for paper pulp. Their resinous nature is the chief drawback in most processes of paper making. The recent development in Europe, especially in Sweden and Norway, of the sulphate process, however, and the superior quality of the product made from resinous woods has turned attention to longleaf and other southern pines as a possible source of pulp in this country. These pines have long, thick-walled fibers, and also high specific gravities, implying large yields per cord, and therefore seem particu- larly adapted for the manufacture, at low cost, of strong wrapping papers. The waste wood from the lumber industry in the South sug- gests a source of cheap raw material. While the sulphate process can be used in the manufacture of bleaching pulps, its principal product is an undercooked, nonbleach- ing, brown pulp known as "kraft" pulp, the term, a German one, signifying strength. True to its name, this pulp produces a remark- ably strong paper, very resistant to wear. Kraft papers, which may be made by the soda as well as by the sulphate process, are especially adapted for wrapping purposes. Wrapping papers stand third among the paper products of the United States, being exceeded in amount and value only by news and book papers. In 1909 the production of wrapping papers of all kinds aggregated 764,000 short tons, with a value of $42,296,000. 1 The value of wrapping papers imported in 1912 was $846, 500. 2 Complete 1 Tariff Board Report, Pulp and News Print Paper Industry, 1911, p. 21. Senate Doc. 31, 62d Cong., 1st sess. 2 Bureau of Foreign and Domestic Commerce, Monthly Summary of Commerce and Finance for Decem- ber, 1912, p. 744. 24542 14 1 477615 2 BULLETIN 72, U.^S. DEPARTMfcfrT* OF AGRICULTURE. ' statistics for recent importations 6*f kraftTpap*e*r are not available, but in 1908, three years after its introduction into the United States, the imports amounted to between 10,000 and 12,000 tons. 1 In 1912 the imports of unbleached sulphate pulp from Sweden alone were approximately 21,600 short tons, and from Norway 8,400 short tons. 2 Manila wrapping papers, including the better imitation manilas, have generally been considered the strongest and best wearing, but the light-weight kraft papers give the same service as manilas almost twice as heavy. Although strong, light-weight wrapping papers are made in this country from sulphite pulps, the imported kraft papers and papers made from imported kraft pulps have proved too formidable competitors for even the best wholly-domestic product of this kind. The immediate success and largely increasing use of kraft products has brought on the market imitations, colored to resemble the gen- uine, made from strong sulphite pulp or from such pulp together with ground, steamed-wood pulp. Although some of them are quite strong in the light weights, they are not equal to the genuine in other ways. The opportunity for developing an increased domestic output of kraft products from native woods is apparent. The above-mentioned conditions led the Forest Service to conduct a series of tests at the Forest Products Laboratory, maintained in cooperation with the University of Wisconsin, Madison, Wis., in order (1 ) to determine the suitability of the southern pines for paper pulps ; (2) to ascertain the effects of varying cooking conditions in the sul- phate process of pulp making; (3) to compare the sulphate process with the soda process. Only longleaf pine has so far been used in the tests, of which this bulletin gives the results under such preliminary analyses as have been made at this time. LUMBER WASTE AVAILABLE FOR PULP MAKING. The total stand of longleaf pine (privately owned) was estimated by the Bureau of Corporations in 1910 at 232 billion feet board measure, while for all southern pines the amount was placed at 384 billion feet. The lumber cut from these pines in 1910 amounted to 14 billion feet. The sawed lumber represents approximately one- half the volume of the log as it comes to the mill. Bark and saw- dust, which are valueless for paper making, constitute a large pro- portion of the waste, but it is safe to say that 20 per cent of the volume of the log, exclusive of the bark, is lost in slabs, edgings, and trimmings. Tops and defective logs left in the woods and small logs which at present are converted into lumber with little or no profit would furnish a supply of raw material for pulp making even greater than that derived from the mill waste. 1 Pulp and Paper Investigation Hearings, 1909, Vol. V, p. 3041. House Doc. 1502, 60th Cong., 2d sess. 2 From estimates made by the Swedish Wood Pulp Association in 1913 and furnished the Forest Service by Mr, M, Giatzler, New York City. SUITABILITY OF LONGLEAF PINE FOR PAPER PULP. 3 The waste wood mentioned is not as a rule the clean, clear material to which pulp mills have been accustomed. But when the soda and sulphate processes are employed, the presence of knots, pitch pockets and streaks, and remnants of decayed wood and bark are not very objectionable. The expense of handling and preparing slabs and other irregular sizes and shapes, however, is greater than for round pulp- wood, so the initial cost of such material must be low enough to offset the extra cost incident to its use. PULP MAKING PROCESSES APPLICABLE TO LONGLEAF PINE. Four or five mills are at present using southern pine mill waste for the manufacture of wrapping paper and similar products, three of which employ the sulphate process. . Several other sulphate mills are either projected or in course of construction. Because of the resinous nature of the wood the preparation of paper pulp from long- leaf pine is confined to the soda and sulphate processes, unless special extraction treatments are employed preliminary to cooking. The soda process consists in digesting suitably prepared wood with caustic soda (NaOH) solution. The cooking results in dissolving the lignin and resin constituents of the wood, and separating the individual fibers from one another. The action depends partly upon the direct solvent and saponifying power of the caustic soda, and partly upon the hydrolysis of the wood in the presence of water at high temperatures, forming organic acid products which unite with the alkali present. Cellulose, of which the fibers are chiefly composed, withstands the cooking action, except under very severe treatment. The spent cooking liquor, or " black liquor," is separated from the pulp fibers and evaporated; the residue is calcined in a furnace, and the soda compounds are recovered as " black ash/' an impure sodium carbonate (Na 2 CO 3 ) . This ash is dissolved in water, and the solution is causticized with freshly burned lime; the resulting caustic soda is again used in cooking. The losses of soda occurring in the operations are made up by adding fresh soda ash (commercial sodium carbonate) previous to causticizing. The sulphate process is similar to the soda process, except that sodium sulphide (Na 2 S) is employed as a cooking chemical in addi- tion to the caustic soda. The sodium sulphide is derived from sodium sulphate (Na 2 S0 4 ), which is added during the recovery operations to make up for the losses, and it is from this chemical that the process derives its name. The sodium sulphate is mixed with the black ash and subjected to a high temperature in a "smelter"; this treatment reduces it to sodium sulphide, although the reaction is not complete. The " smelt," containing sodium carbonate, sodium sulphide, and unreduced sodium sulphate, is dissolved in water and the solution is causticized, as in the soda process, with lime, which has, however, 4 BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. little action on the sulphide and the sulphate. During cooking the organic acids produced react with the sodium sulphide 1 as well as with the caustic soda, so that in calcining both chemicals are recovered as sodium carbonate. If desired, soda ash may be added to the smelt solution before causticizing in order to increase the proportion of caustic soda in the cooking liquors. Some mills have also found it advantageous to mix with the causticized cooking liquors some of the black liquors diverted from the recovery operations. The soda and sulphate processes can be applied to extracted or steam-distilled chips from which rosin and turpentine have been removed. Turpentine can also be obtained from resinous chips during the cooking operations by condensing the " relief" from the top of the digester. However, the turpentine is very impure, and in the case of the sulphate process contains organic sulphur compounds from which it is separated with great difficulty. EXPERIMENTAL METHODS. KINDS OF TESTS. The tests made by the Forest Service were of two classes : (1 ) Auto- clave tests and (2) semicommercial tests. The autoclave tests com- prised several series of cooks made to determine the effects of varying the cooking conditions of the sulphate process. The semicommer- cial tests include cooks made by the soda as well as by the sulphate process. The semicommercial sulphate cooks employed such cook- ing conditions as the autoclave tests indicated would give good results, while the tests using the soda process were made with cooking conditions that would give results comparable to those obtained from the sulphate cooks. Because the semicommercial tests show in a more direct manner the possibilities of preparing paper pulp from longleaf pine, they will be discussed before the autoclave tests. WOOD USED. The test material consisted of longleaf pine (Pinus palustris Mill.) from two localities, Perry County, Miss, (shipment L-3), and Tangi- pahoa Parish, La. (shipment L-176). A portion of the former, con- sisting of edgings containing approximately equal amounts of sap- wood and heartwood, was used for cooks 176-1, 2, and 3 of the semi- commercial soda tests (Table 3), and another similar portion of the same shipment was used for cooks 1 to 65, inclusive, of the autoclave tests. The average bone-dry weight of the wood used in these auto- clave tests was 30.4 pounds per cubic foot green volume; the maxi- mum and minimum values were 36.4 and 26.6 pounds, respectively. The wood was fairly free from resin. The remaining cooks employed 1 In this reaction volatile organic sulphur compounds having extremely disagreeable odors are produced. Unless these odors are eliminated, or held in check by proper means, sulphate pulp mills are highly objec- tionable except in sparsely populated regions. SUITABILITY OF LONGLEAF PINE FOR PAPER PULP. 5 two butt logs (15 and 22 inches diameter) of the Louisiana wood, including all of the sapwood and heartwood. These logs were quite resinous, but were free from knots. They had an average bone-dry weight of 35.5 pounds per cubic foot green volume. The maximum and minimum weights were 40.1 and 32.3 pounds, respectively, for the various determinations. The material was prepared for cooking by removing the bark and sawing the pieces across the grain into sections five-eighths inch thick, which were then split into chips about three-sixteenths to one-fourth inch by 2 to 6 inches across the grain. The chips were screened to remove sawdust, and each lot was thoroughly mixed so as to be uniform throughout. APPARATUS. The semicommercial cooks were made in a vertical, stationary digester * consisting of a cast-steel cylindrical shell with top and bot- tom cones, with a capacity of about 62 gallons. The digester was fitted at the top with a " relief" or vent pipe, a pressure gauge, and a thermometer; and at the side with a gauge glass for noting the height of the liquor. The bottom was arranged for " blowing" the contents after cooking. Heat was furnished partly by passing steam directly into the digester at the bottom and partly by two steam coils placed inside the bottom cone. The pressure and temperature were regulated by admitting either more or less steam into the diges- ter and by relieving any excess pressure by means of the top vent. The autoclave cooks were made in a horizontal rotary autoclave with a capacity of about 2 gallons. This vessel was made of a 6-inch steel pipe with blank flange ends, fitted with trunnions, to one of which was attached a pressure gauge. A screw-joint handhole opening in the side provided for charging. Heat was furnished by Bunsen-burner flames underneath the autoclave, and the pressures were regulated by increasing or decreasing the heat. The autoclave was not relieved during cooking, and no observations of tempera- tures were made. The cooked pulps were not blown, as in the case of the semicommercial tests, but the cooking vessel was quickly cooled and the contents poured out. PROCEDURE IN TESTING. The liquor charges for the sulphate cooks were prepared by mixing caustic soda and sodium sulphide solutions of known composition, as determined by previous analyses, together with water and dry sodium sulphate. The amounts of each constituent were taken in such proportions that when the whole mixture was charged, with the chips, 1 The apparatus used in the semicommercial cooks is practically the same as,that fully illustrated and described in U. S. Department of Agriculture Bulletin No. 80, "Effects of Varying Certain Cooking Con- ditions in the Productions of Soda Pulp from Aspen,'' by Henry E. Surface, 1914. 6 BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. into the digester or autoclave, the amounts of each chemical per pound of chips (bone-dry basis) was in the desired proportion, and the concentration of chemicals in the digester liquor (including the water in the chips) was of the desired degree. For soda cooks the procedure was similar, except that caustic soda was the only chemical to be taken into consideration. The general procedure in conducting the tests was as follows: The chips to be used for a cook were sampled and weighed. By means of the sample the amount of moisture in the chips and the equivalent bone-dry weight of the charge were determined. The chips, together with the cooking liquors, were then charged into the auto- clave or digester, and the vessel closed. After a cook was completed the crude pulp obtained was washed thoroughly, pressed to remove water, shredded, weighed, and sampled for determining its equivalent bone-dry weight. The pulp was then mixed with water and treated in a Hollander-style beating engine 1 with the roll barely touching the bedplate (light brush) until the soft chips in the pulp had become disintegrated into fibers and the wet fibers had a smooth, slippery feel. The beater roll was then pressed hard down on the bedplate (stiff brush), and the beating operation continued until the pulp was suitable for making wrapping paper, as determined by its "feel." The beaten pulp was then screened through the slots (0.012 inch width) of a diaphragm pulp screen. In all cases the screenings obtained were so small in amount that they were dis- regarded in the yield calculations. The semicommercial pulps were run over a Pusey and Jones 15-inch Fourdrinier paper machine into rolls of dry paper, while the autoclave pulps were made up into sheets on a small hand mold. The papers thus produced contained the experimental pulps alone, without the addition of any other materials. DETERMINATION OF YIELDS AND PROPERTIES. The yield of pulp (bone-dry basis) is usually expressed as a per- centage of the bone-dry weight of the chip charge, both weights being determined as explained above. When yields per cord are given they are based on a "solid cord" containing 100 cubic feet of clear wood (green volume) having a bone-dry weight of 35.5 pounds per cubic foot; 2 or 3,550 pounds per cord. The strengths of the papers from the semicommercial pulps were determined by means of a Mullen paper tester, five "pop tests" being made on double thicknesses of each paper. The value is expressed as a "strength ratio," which is the average of the five test values in pounds per square inch divided by the average sheet thicknesses 1 A 25-pound Emerson beater was used for the semicommercial tests and a 1-pound Noble and Wood beater for tiie autoclave tests. Both makes were equipped with steel fly bars and steel bedplate bars. 2 This was the average bone-dry weight of the two butt logs of long leaf pine from Louisiana, the material used in the tests for which yields per cord are given. SUITABILITY OF LOKGLEAF PINE FOR PAPER PULP. 7 in ten-thousandths of an inch, and also as a "strength factor/' which is the average of the five pop tests divided by the weight per ream of 500 sheets of paper, each measuring 24 by 36 inches. The relative resistance of the papers to wear was determined by crumpling the sheets in the hand, and all other properties mentioned, except strength, were determined by feel or by observation without the aid of instruments. DEFINITIONS OF TERMS USED. While the significance of most of the terms used in recording the test data (Tables 1 to 10, inclusive) is either self-evident or sufficiently clear in view of the previous discussion, there are several which may require explanation. Water in chips. The amount of moisture is expressed in per- centage of water, based on the calculated bone-dry weight of the chips. All sodium compounds as Na 2 0. This is the sum of the sodium oxide (Na 2 O) equivalents of the amounts of the several constituents entering into the chemical charge. "Total Na 2 O" has an analagous significance in the soda process. Sulphidity. The sulphidity of the liquor charge is the percentage ratio of the Na 2 O equivalent of the amount of sodium sulphide (Na 2 S) used to the amount of all sodium compounds present expressed as Na 2 O. Causticity. This has a similar significance with respect to the amount of caustic soda (NaOH) used. Initial volume of digester liquors. The digester liquors include the water in the liquor charge, together with the water in the chips and the water condensed from the steam passed into the digester during cooking. This condensation, of course, does not enter into the calcu- lation of the initial volume. Apparent condensation. The apparent condensation is the differ- ence between the calculated yiitial volume of the digester liquors and the observed volume, as read from a water gauge, at the end of the cook. It roughly represents the amount of steam condensing in the digester during cooking, but does not take into account the volume of the pulp and the differences in temperature of the initial and final liquors, nor the steam and liquid lost during relief. SEMICOMMERCIAL TESTS. SULPHATE PROCESS. The object of the semicommercial sulphate cooks was to secure the best quality of pulp with the highest possible yield. The severity of cooking employed depends largely upon the use for which the pulps are intended. If bleaching or easy bleaching pulps, such as are used in book and other white papers, are desired, more severe cooking 8 BULLETIN 72, U. S. DEPARTMENT OP AGRICULTURE. treatments are necessary than if the pulps are to be used in natural- color wrapping papers. The present experiments apply more espe- cially to the latter, for which the important properties are strength, toughness, and resistance to wear. The terms mild, medium, and severe cooking, and undercooked, well-cooked, and overcooked pulps used in the following discussion are significant only with respect to the object of the tests. MILD COOKING TREATMENTS. The less severe the cooking of a wood the larger will be the yield of crude pulp. However, there is a point at which the pulp will begin to lose its valuable properties for making wrapping papers. For cook 71 the digesting conditions were outlined to give a much undercooked pulp (see Table 1), but the treatment given the wood was even less severe than is indicated by the recorded data, since a portion of the digester liquor was lost through leakage soon after the cook had been started. The crude unbeaten pulp from this cook was full of soft chips, which, while hard enough to resist the action of a stream of water under pressure, could easily be picked apart with the fingers. The paper made from the beaten pulp had a strength factor of 0.50, was moderately tough, and had fair wearing properties. As a wrap- ping paper it would be considered of medium grade. The yield, 61.2 per cent, or 2,172 pounds per solid cord, was very high, considering the quality of pulp obtained. Pulps produced under less severe cooking conditions had higher yields (see autoclave tests, pp. 14-24), but the quality was not so good, as evidenced by brittleness, lack of strength, and poor wearing properties. TABLE 1. Record of semicommerdal tests using the sulphate process. Liquor charge. Initial volume of di- Weight Initial concentrations. gester Cook otchips charged Water I'M liquors per No. (bone- dry basis.) in chips. NaOH. NasCOs. Na 2 S. S0 2 com- pounds Na 2 SO 4 . All sodium com- Caus- ticity. Sul- phid- ity. pound of chips (bone- as pounds dry Na 2 S0 3 . as Na 2 O. basis). Grams Grams Grams Grams Grams Grams 171 Pounds. 38.62 Perct. 34.6 per liter. 26.5 per liter. 1.4 per liter. 13.2 per liter. per liter 13.2 per liter. 38.5 Per ct. 53.3 Per ct. 27.3 Gallons. 0.679 77 38.61 34.7 44.6 2.7 22.3 2.9 22.1 64.9 53.2 27.3 .538 81 23.97 22.7 60.4 3.2 30.0 4.0 30.0 87.6 53.4 27.2 .300 85 23.97 22.7 36.0 1.9 18.0 2.4 18.0 52.3 53.3 27.3 .500 92 23.97 22.6 48.0 2.4 30.0 4.0 30.0 77.5 48.0 30.8 .300 98 23.97 22.6 28.8 1.4 14.4 1.9 14.4 41.8 53.3 27.4 .500 113 25.38 18.2 34.2 1.9 17.1 2.2 18.5 50.4 52.6 27.0 .700 138 25.38 18.2 59.9 3.0 30.0 3.9 30.0 87.0 53.4 . 27.4 .400 141 25.38 18.2 60.0 3.3 15.0 2.1 30.0 74.4 62.4 16.0 .400 146 25.38 18.2 26.5 1.4 13.2 1.8 13.2 38.5 53.3 27.3 .680 147 26 67 12.5 26.5 1.2 13.2 1.8 13.2 38.4 53.4 27.4 .680 148 26.67 12.5 26.5 1.2 13.2 1.8 13.2 38.4 53.4 27.4 .680 1 A portion of the digester liquor was lost, due to leaks during the early stages of cooking. SUITABILITY OF LONGLEAF PINE FOR PAPER PUtP. 9 TABLE 1. Record of semicommercial tests using the sulphate process Continued. Chemicals charged per 100 pounds of chips (bone-dry basis). Duration of cooking. Cook No. NaOH. Na 2 S. S0 2 com- pounds as NaaSOs. Na 2 S0 4 . All sodium com- pounds as Na 2 0. Total. At zero gauge pres- sure. At maxi- mum gauge pres- sure. Maximum cooking temperature. Pounds. Pounds. Pounds. Pounds. Pounds. Pounds. Hours. Hours. Hours. F C 171 15.0 0.8 7.5 .0 7.5 21.8 3.0 0.1 2.8 331 166 77 20.0 1.2 10.0 .3 9.9 29.1 3.0 .2 2.3 331 166 81 15.1 .8 7.5 .0 7.5 21.9 3.0 .1 2.5 331 166 85 15.0 .8 7.5 .0 7.5 21.8 3.0 .1 2.5 331 166 92 12.0 .6 7.5 .0 7.5 19.4 3.0 .25 2.5 331 166 98 12.0 .6 6.0 .8 6.0 17.4 5.0 .1 4.3 331 166 113 20.0 1.1 10.0 1.3 10.8 29.4 3.0 .25 1.0 331 166 138 20.0 1.0 10.0 1.3 10.0 29.0 3.0 .1 2.8 331 166 141 20.0 1.1 5.0 .7 10.0 24.8 3.0 .1 2.5 331 166 146 15.0 .8 7.5 1.0 7.5 21.8 3.0 .2 2.3 338 170 147 15.0 .7 7.5 1.0 7.5 21.8 3.5 .3 . 2.8 338 170 148 15.0 .7 7.5 1.0 7.5 21.8 3.5 .2 3.0 338 170 Digester pres- Steam Appar- Duration of beater sures per square ent con- treatment. inch. pres- sure densa- Tj Cook No. per square inch at di- gester inlet. tion per pound ofchips (bone- dry basis). Yield of crude pulp (bone-dry basis). Total. At light brush. At stiff brush. Strength ratio ofpaper. Strength factor ofpaper. weight of papers tested. Maxi- mum gauge. Blow- ing. Lbs. per solid Pounds. Pounds. Pounds. Gallons. Per cord. Hours. Hours. Hours. Pounds. 171 90 40 105 10.20 61.2- 2,172 3.5 1.5 2.0 0.60 0.50 76 77 90 40 105 .50 15.3 1,609 3.5 2.0 1.5 1.15 .91 31 81 90 50 103 .58 47.9 1,700 5.0 2.5 2.5 1.08 .93 44 85 90 50 108 52.0 1,846 7.0 3.0 4.0 .91 .87 38 92 90 40 110 ""."49" 48.8 1,733 6.5 2.5 4.0 .86 .70 28 98 90 40 108 .50 51.8 1,839 4.5 1.0 3.5 .60 .56 28 113 90 40 100-95 .32 48.6 1,725 6.0 2.0 4.0 .70 .59 37 138 90 40 110 46. 1 1,637 141 90 40 108 44.2 1,569 8.5 4.5 4.0 1.02 .86 36 146 100 40 105 54.9 1.949 9.0 4.0 5.0 .72 .68 45 147 100 40 115 .41 49.1 1,743 6.5 4.0 2.5 .92 .71 37 148 100 40 115 .63 48.4 1,718 8.5 4.0 4.5 1.02 .77 33