Publication restrictions have been removed. This report is one of a series issued in cooperation with the Army Air Forces and the Bureau of Aeronautics under the supervision of the Aeronautical Board

Forest Products Laboratory (U.S.)

Keller, Eugene L.

McGovern, John Neilson, 1908-

Undetermined

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SUIFITIE PULP FOP PAPPieLaminates From Pulps intade FromShort and Standard LengthElacIR Spruce ChipsAugust 1943RESTRICTEDThis document contains classified inforiathe National Defense of the Uni	 themeaning of the Espionage A	 , . 'and 32. Itstransmission or the reve	 of	 contents in anymanner to arm unlit	 skin is prohibited by lass,information w	 be imparted only to per-sons in t.	 d naval Services of the 'UnitedStat •	 civilian officers_ and employees ofovernment who have a legitimate interestud to United States Citizens of known loyally _discretion Oho of necessity must be informedthereof.CLASSIFIED DOCUMENTThis Report is One of a SeriesIssued in Cooperation with theARMY AIR FORCESand thePUREAU OF AERONAUTICSUnder the Supervision of theAERONAUTICAL BOARDNo. 1590UNITED STATES I DEPARTMENT OF AGRICULTUREC/itFREST SERVICEORESD- PRODUCTS LABORATORYMadison, WisconsinIn Cooperation with the University of WisconsinSULFITE PULP FOR PAPREG:LAMINATES FROM PULPS MADE FROM SHORT AND STANDARD LENGTHBLACK SPRUCE CHIPS1ByE. L. KELLER, Junior ChemistandJOHN N. MC GOVERN, Associate TechnologistI= MN, =0 =IPSUMMARYSulfite pulp from short (0-inch) black spruce chips was found tohave essentially the same chlorine demand as like-prepared pulp from stand-ard length (5/8-inch) chips. The pulp from the short chips, however, wasconservatively estimated to have an average fiber length 20 percent shorterthan that of the normal pulp, and test sheets and impregnating papers fromit had 15 to 20 peroent lower bursting and tensile strengths and 25 percentlower tearing strengths than sheets and papers from the pulp from the stand-'and length chips,' Papreg made from base paper composed of "short chip" pulp,on the other hand, had closely similar strength' properties in tension andflexure to those of papreg from the normal pulp, but had compressive strengths10 percent lower, Slight processing of both types of pulp caused a slightlowering of papreg strength properties.INTRODUCTIONThe effect on the properties of papreg of changes in sulfite fibercharacteristics resulting from variations in species, pulping conditions,and particularly, extent of pulp delignification was discussed in previousreports..a, .1 Another fiber characteristic which affects paper propertiesand may affect papreg properties is fiber length. The general impressionof the relation between fiber length and plastic strength seems to be thatthe longer the fiber the stronger the plastic. Prior to this study, however,there appears to be no definite information available on this relation.1This mimeograph is one of a series of progress reports prepared by theForest Products Laboratory to further the Nation's war effort. Resultshere reported are preliminary and may be revised as additional databecome available.?Forest Products Laboratory Mimeograph 1393. Restricted.-Forest Products Laboratory Mimeograph 1399. Restricted.Mimeo. No. 1596	 -1-The average length of fibers in sulfite pulp from any one speciescan be varied by using chips of different lengths in the direction of thegrain. In experiments with western hemlock heartwOod, 4 a considerablevariation in average fiber length was achieved by varying chip length from1/8 to 1-1/e inches. Presuming the reduction in fiber length by the chip- .ping process was shown by values for average length of cut plus uncut fibers,the average length of fibers in pulp from normal 5/8-inch chips was approxi-mately 1.4 times that of fibers in pulp from 1/4-inch chips. Thus the aver-age fiber length in the pulp from short chips was nearly 30 percent lessthan that in normal pulp. The pulp from short chips had a preponderance offibers below 2 mu in length, whereas the normal pulp showed an even distri-bution of fibers over the fiber length range up to 5 mm.The relations between - fiber length and sheet properties have alsobeen investigated. Recently, Clark,E using a fiber measurement procedurehe had developed previously,s found that the following relations apparentlyheld:Bursting strength = K2 d LTensile strength	 K3 d 12•5Tearing strength .= K4 L1'5A1where d is the density of the test sheets, L is a weighted average fiberlength determined by the method described, 6- and K2 , K3 , and K4 are constantswhen other factors are constant.The purpose of this report is to present data showing the effect offiber length on the properties of two similarly prepared sulfite pulps withdifferent average fiber lengths, the effect on the properties of the impreg-nating paper and, particularly, the effect on laminated paper plastics madefrom the two types of pulp. The two average fiber lengths were obtained by.using normal (5/8-inch) and short (1/4-inch) chips of black spruce. Thedigestion conditions used *ere developed previously?. as suitable for produc-ing pulp satisfactory for conversion to papreg.EXPERIMENTAL PROCEDURESThe black spruce (Picea mariana) pulpwood (shipment P-1700) used forthese experiments was cut in the Algoma District, Ontario, Canada. Itsproperties, normal for the species, are given in a previous report.? Thelogs were converted into chips 5/8 inch long in the fiber direction, that is,standard length, and into chips 1/4 inch long, called short chips, Two simi-lar digestions of each length of chips were made in an alloy-lined rotarydigester of 13 cubic feet capacity equipped with a steam jacket.McGovern, J. N. and Chidester, G. H. Paper Trade Journal 98(18): 41-46(May 3, 1934).lark, James d'A. Paper Trade Journal 116(1): 31-38 (Jan. 7, 1943).Clark, James d'A. Paper Trade Journal 115(26): 36-42 (Dec. 24, 1942).Mimeo. No. 1596.	 -2-The digestion conditions were as follows: The chip charge, equivalentto 112 pounds of moisture-free wood, was steamed 0.5 hour before chargingwith 65 gallons of sulfite cooking acid having a concentration of 6.0 percenttotal sulfur dioxide with 1.2 percent'combined sulfur dioxide. The tempera-ture was raised to 110° C. in 2 hours, held at this temperature for 2 hoursmore, raised to 130° C. in 2 hours additional, and finally held at this maxi-mum temperature for 4 hours; the total digestion time was thus 10 hours. Thepulp was discharged by blowing, at 50 pounds per square inch pressure. Themaximum pressure employed during the digestion was 80 pounds per square inch.The pulps were screened through 8-cut screen plates and their chemicaland physical properties were determined on representative samples according toForest Products Laboratory standard test methods. The combined pulps fromeach of the two sets of duplicate digestions were divided into two portionsfor running over the paper machine, one without further processing and oneafter receiving processing for 5 minutes in a beater of 50 pounds capacitywith the roll on the bedplate. The paper machine was controlled to producepaper having a directional tensile strength ratio of more than two, a reamweight of nearly 30 pounds, and a caliper less than 3 mils.The papers were impregnated with uncured phenolic resin, dried, paral-lel laminated, and molded under a pressure of 250 pounds per square inch at325° F. The laminated paper plastics, after"48 hours conditioning, weretested for strength and stiffness in tension; flexure ,4 and compression.Specific gravity and water absorption were determined.DISCUSSION OF RESULTSPulping Experiments Although fiber measurements were not made in these experiments, thereduction in average fiber length resulting from using short spruce chipscan be estimated from the data on western hemlock. 4 Since the two specieshave approximately the same average length of fiber in the wood itself, aconservative value of 20 percent can be set for the reduction in fiber lengthwhen using 1/4-inch instead of 5/8-inch black spruce chips. The spruce pulpfrom the short chips, like the corresponding hemlock pulp, would also probablyhave a preponderance of fibers in lengths below 2 mm., whereas the standardpulp fibers would be normally distributed over the range of fiber length.The rate of delignification of the short and standard length sprucechips under similar sulfite pulping conditions appeared to be nearly equal,since the chlorine demands and chemical characteristics of the pulps of thetwo types were the same within the limits of experimental error (table 1).?Tests on the plastics were made according to Federal Specifications forPlastics, Organic: General Specifications (Methods of tests) L-P-406,Dec. 9, 1942.Mimeo. No, 1596	 -3-Table 1.--Chemical composition of sulfite pulps from standardand short length black spruce chips ∎Pulp analysisConstituentDigestion numberChlorine demand (percent)Lignin (percent)Total cellulose (percent)Alpha cellulose (percent)Total pentosans (percent)Standard	 Shortchips	 chips	( 5005 )	( 20)40210 ''5006'	7.5	7.1.	1 405	 1.45	93.1	 94.276,,66.077.96.08.91% NaCH solubility (percent) :	 8,7The strength properties of test sheets made from pulp samplesobtained at regular test beater intervals were plotted against correspond-ing sheet density values. Strength values were then taken from the curvesat densities of 0.70, 0.75 and 0.90 grams per cc. to furnish the datagiven in table 2. Comparison of the strength properties of test sheetshaving the same density show the pulps from the short chips to be signifi-cantly weaker than the normal pUlps. The losses amounted to approximately15 percent in bursting strength, 20 percent in tensile strength and 25 percentin tearing strength in the density range of 0.70 to 0.75 grams per cc.inwhich the pulps would probably be used. At a density of 0.90 grams per cc.the losses were not quite so high for bursting and tearing strengths.If a 20 percent reduction in average fiber length is assumed toresult from shortening the chip length, theoretical ratios between thestrength values for normal and short-fibered pulps can be estimated accord-ing to the relations obtained by Clark. These are given in table 2 also.The ratios calculated in this manner showed fairly good agreement with theexperimental ratios for the property of tearing strength in the densityrange of 0.70 to 0.90 grams per cc. for bursting strengths in the densityrange of 0.70 to 0.75 grams per cc. and for tensile strength at a densityof 0.90 grams per cc. The theoretical ratio was higher than the experi-mental ratio for bursting strength at a density of 0.90 grams per cc. andlower for tensile strengths in the density range of 0,70 to 0.75 grams percc.Mimeo. No. 1596	 -4-Paper Properties All of the impregnating papers made from both types of spruce pulp,both unprocessed and slightly processed, were satisfactory in regard todensity, thickness, ream weight, absorbency (porosity), and tensile strength,for conversion into high-strength laminated plastics (table 3). The slightprocessing treatment given both types of pulp resulted in very small increasesin bursting and tensile strengths and no appreciable change in tearingstrength. The differences between the strength properties of the two pulpswere also evident in the papers. The impregnating papers from the short-fibered pulp were lower in bursting strength by approximately 20 percent, intearing strength somewhat over 20 percent, and in tensile strength about 15percent when compared with the papers from the normal pulp. The ratios ofthese strength properties in the normal pulp to those in the other pulp werein good agreement with the theoretical ratios estimated for a reduction inaverage fiber length of 20 percent,Papreg Properties Application of Forest Products Laboratory standard resin impregnatingand drying procedures to the various papers resulted in impregnated paperswith practically the same contents of resin and volatile matter (table 4).These contents were considered satisfactory for subsequent laminating intoplastics. All the plastics produced as described had tensile strengths whichexceeded the usual minimum requirements for papreg of 35,000 pounds per squareinch for ultimate strength, and 3,000,000 pounds per square inch for modulusof elasticity.Although both the pulp test sheets and papers made from the two typesof pulp reflected differences attributable to the lengths and distributionof their fibers, the laminated plastics molded from the impregnated papersmade from the short-fibered pulps had closely similar values for ultimatestrength and stiffness in tension and flexure to those"from the normal pulps(table 4). The laminates from the short-fibered pulps, however, were 10 per-cent lower in ultimate compressive strength and had a somewhat lower waterabsorbency than those from the normal. It appeared, from the limited numberof experiments made that the strength properties of the laminated plasticwere independent of a relatively large change in the length of the fibersin the base papers, except possibly for a small effect on compressivestrength. The papreg containing slightly processed pulp had slightly lowerstrength properties than the corresponding papreg containing unprocessedpulp.Mimeo. No. 1596.coNcimplom,Sulfite pulp from short, 1A--inch chips of black spruces had anestimated- SG perceftt-loWer average fiber length than a similarly prepared'pulp from standard, 5/6 inch ,chips. , Although this relatively Iatuhde-parture ftomvriortal fiber length' had an adverse effect on pulp and imprep=nesting paper ttrength properties, it caused only a slightly lowered com-pressivestrength An the papteg from the short. ,ftberedpulp. The tensileand flexural propettlea!of the papreg from the two types of pulp wereclosely similar.'Mimeo. 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Sulfite pulp for papreg : laminates from pulps made from short and standard length black spruce chips

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Sulfite pulp for papreg : laminates from pulps made from short and standard length black spruce chips

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