SULFATE PULPING CE PCNDERCSA PINE THINNINGS October 1951 U.S. DEPOSITORY opjinni iHalUUI No. uRtSTi If , ihDADV MAKI LI UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison 5, Wisconsin In Cooperation with the University of Wisconsin SULFATE PULPING OP PONDEROSA PINE THINNINGS BY J. STANLEY MAPTIN, Chemical Engineer Forest Products Laboratory., — Forest Service U. S. Department of agriculture Introduction Pcnderosa pine ( Pinus ponderosa ) wood obtained in thinning operations on a stand near Blanc hard in western Idaho was experimentally pulped by the sulfate process to determine its pulping characteristics. In such thinning operations, some trees are cut to give better spacing to the remaining trees, and some trees of poor form and vigor are removed to improve the quality of the stand. If satis- factory pulps could be produced from the pine thinnings ; . a use would be provided for the wood cut in such forest-management practices. Test Material and Pulping Procedures The test material consisted of 83 bolts, each h feet in length, and was repre- sentative of wood obtained by a combination of thinning operations at the crown and lower levels of the tree. It was obtained from a small stand of pure pcnderosa pine containing trees 20 to kO years old, h to 10 inches in diameter at breast height, and 15 to 30 feet in height. Pure stands of lodgepole pine occurred in the general area. The physical characteristics of the ponderosa pine= are given in the following tabulation, which lists average values obtained on representative transverse sections, approximately 1 inch thick: Specific gravity O.kO Density pounds per cubic foot 2^.0 Diameter inches 4.9 Age years Z> 6. Eate of growth rings per inch 14.Q Eeartwood, oj volume percent 1.9 Bark, by volume do... 20.9 bar!:, by weighs (dry basis) do... 19*9 —Maintained at Madison, "/is., in cooperation with the University of Wisconsin. 2 ~Pinus ponderosa . Shipment No. 2Qlk. i Report No. EI909 -1- Agri culture -Madison The density of the ponderosa pine, 25 pounds per cubic foot (based on weight of moisture -free wood and volume of green wood), was within the range of common northern coniferous pulpwoods, such as jack pine, Douglas-fir, western hemlock, Pacific silver fir, and lodgepole pine. If it is satisfactory as a pulpwood, the ponderosa pine might be expected to compete in the same market as these woods. The ponderosa pine resembled jack pine, a wood used extensively in the Lake States pulping industry, closely enough in chemical composition to indicate similar sulfate -pulping characteristics for both species. It has a slightly lower lignin content and a little higher solubility in alcohol -benzene and in ether than jack pine (table 1). Various ratios of pulping chemical to wood were used to produce sulfate semi- chemical, kraft, and bleaching sulfate pulps. The pulping digestions were made in a spherical, rotary autoclave, which was indirectly heated by steam and had a capacity of 0.5 cubic foot. Semichemical pulps were flberized in an attrition mill having an 8-inch, single rotating disk, and yields and strength properties of the flberized pulps were determined. Results and Discussion In the semichemical pulping series, an increase in the amount of chemicals (calculated as sodium oxide) from J ,Q to 11.7 percent of the weight of moisture- free wood caused a normal decrease in pulp yield from 73 to 5", L percent, a decrease in chemical consumption, an increase in the density of the black liquor, and progressively higher strength properties of the semichemical pulps (tables 2, 3). The pulps cooked with less than 11.7 percent of chemicals were very dark in color, as measured by brightness values, and were similar in bright- ness to high-yield pulps from softwood species. In the digestion in which the smallest amount of chemicals was used, cooking was stopped when the maximum temperature was reached, thereby making the total cooking time one -half that of the other digestions. The result was a higher pulp yield of 75 percent and lower strength properties, except for tearing strength, which showed no change. While all the sulfate semichemical pulps appeared to have more than adequate strength for corrugating board, the ponderosa pine sulfate pulp produced in a yield of 5^ percent also appeared to have sufficient strength for use in liner board of high quality. The pulping of ponderosa pine by conditions suitable for producing a kraft-type pulp (15.7; 15 »6, and 17.6 percent of sodium oxide) showed that the lowest quantity of chemicals was sufficient to produce the maximum yield of screened pulp, a low yield of screening rejects, and the highest pulp strength (tables 2, 3) . The yields of screening rejects obtained for the kraft digestions were lower than those normally obtained from jack pine and many softwood species, which indicated very favorable pulping characteristics for ponderosa pine by the sulfate process. Ponderosa pine kraft pulps were higher in bursting strength and lower in tearing strength (table 3) than southern pine pulps. The bursting strength of ponderosa pine kraft pulps was considerably lower than that of spruce and balsam kraft pulps. The kraft pulps from ponderosa pine were quite similar in strength to those from jack pine and appear to be suited for use in the same Report No. E1909 -2- types of papers, such as wrapping and kraft specialties , as the jack pine kraft pulps . Ponderosa pine vas readily cooked to produce a bleaching sulfate pulp that was sufficiently low in lignin content and permanganate numbers and sufficiently high in brightness after a one-stage bleach test to indicate satisfactory bleaah ing qualities with a normal quantity of chlorine (table 2). The additional amounts of chemicals used for producing the bleaching pulps over those required for the kraft- type pulps caused a normel reduction in pulp yield and in pulp strength and an improvement in the chemical purity of the pulps. Conclusions Except for the lower chemical requirements and the lover yields of screening re- jects in production of ponderosa pine kraft pulps , ponderosa pine was, in general, very similar in sulfate -pulping characteristics and in the strength of the pulps produced to jack pine, a pulpwood of accepted satisfactory quality. 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