Ef KCT ON PAPREG CE SIX WATER-ALCOHOL RATIOS USED AS DILUENTS CE IMPREGNATING RESINS June 1943 RESTRICTED CLASSIFIED DOCUMENT document contains classified information |f£^@k National Defense of the United State|^Alfcj>g ung of the Espionage Act, USC SfcftfatkSpKgr Ita transmission or the revelation ^.WVnMn in any manner to an unauthorized ^rsSra|jp%nibited by law. Information so classinexkjraj^be wrparted only to per- sons in the nHlitar«*%Mw*fcal Services of the United Siatri, appr9pQaJe"^iv%nm officers and employees of the Fedeai «SwpAiEn t who have a legitimate interest the^j^]sn|ffl£»xJnited States Citizens of known loyalty ion who of necessity must be informed This Report is One cf a Scries Issued In Cooperation with the ARMY AIR FORCES and the BUREAU CF AERONAUTICS Under the Supervision of the AERONAUTICAL BOARD Nc. 13S7 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wiicontin EFFECT OH PAPREG OF SIX WA TER-ALCOHOL _RAT I OS USED AS DILU E NTS OF IMPREGNATING RESINS^ By G, E. MAC KIN, Associate Industrial Specialist R. J. SEIDL, Assistant Chemical Engineer and P. K. BAIRD, Senior Chemist Preliminary experiments, previously reported by the Forest Products Laboratory ,£ indicated that some properties of papreg£ were appreciably affected by impregnating the base paper with resin varnishes which had been diluted with a mixture of water and alcohol in place of alcohol alone. The water resistance was found to be considerably improved, but the Izod impact values were somewhat lowered. This report presents more conclusive data on the subject. Test Material The bas-- paper (M.R. 2047) used in these experiments was made on the Forest Products Laboratory experimental paper machine from a commercial Mitscherlich spruce sulfite pulp especially developed from Laboratory speci- fications for this purpose. The paper was impregnated with six water-alcohol (ethyl) solutions of phenol-formaldehyde resin, Bakelite No, BV-16303. The term "alcohol" used throughout this report refers to the commercial 95 percent grade. In each solution the resin solids content was 40 percent by weight, but the proportion of water in the water-alcohol diluent was varied from to 50 percent by volume in 10 percent steps. The resin content of the paper was held at 36 + 0*3 percent and the volatile content at 4.5 + 0.1 percent throughout the impregnation series. All plastic panels were parallel —This mimeograph is one of a series of progress reports issued by the Forest Products Laboratory to further the nation's war effort. Results here reported are preliminary and may be revised as additional data become available. 2 —High-strength Laminated Paper Plastics for Aircraft , Mime o. No. 1395, 'Revised April 1943 (restricted), 3 —The name "papreg," identifying the experimental high-strength laminated paper plastic developed by the Forest Products Laboratory, has been sent to the U. S. Patent Office for registration, Mimeo. No. 1387 _1_ I nated at 250 pounds f r uare inch for 12 minutes at 325° re prepared, conditioned, and tested for tension, compression, ber. . ct, total water absorption, and specific gravity d.eter- , accor to procedures set forth in "Fronosed Federal Specifications for Organio Plastics; General Specifications I .ods of Fhysical Terts)" July 7, 1£42. In addition to the standard total water absorption test, the face water absorption of the papreg was determined by a special test method- developed at the Laboratory and as yet unpublished. Since the edges of papreg as used in many applications, such as wl Lna or fuselage ^■irfaces, will be protected or sealed from moisture, it is believed that this type of test for water absorption is of particular value. Discussion of Results Water Absorption The decrease in the water absorption of papreg, which occurs with an increase in the water to alcohol ratio of the resin diluent, over the range studied, is shown for both test methods in table 1 and figure 1. The total water absorption of oa~ aa reduced from 4.7 percent when alcohol alone was used as the diluent to 1,4 percent when the resin was diluted with a half-and-half mixture of water and alcohol. The face v.-ator absorption 'was reduced from 6.3 mg. per square cm. to 2.6 mg. per square 01 . by the same procedure. This effect may be attributed to a greater pe - tration of resin into the fiber wall when a higher proportion of water is ore sent. Unpublished Laboratory data on wood and paper treated with water- soluble resin corroborates this explanation and indicates that such treatment actually reduces the equilibrium moisture content and thus produces a more permanent water-resistant material in addition to retarding the rate of water absorption as measured by the standard test method. The appearance of the plastic after exposure to water in the face absorption test is a visual measure of the effect of the various water- alcohol diluent mixtures of the impregnating rosin. T:. ; s i.- illustrated in figure 2. 4 . -e water absorption test.--A sample, 2-1/2 inches square, is cc: ned 24 hours at 50° C. and its weight determined. A 2-inch diameter brass cap with rubber -.-asher is then damned on the specimen. The cap is filled with distilled water through a small hole, the hole stopped, and the assembly placed in a desiccator for 24 hours at room temperature. The specimen is then removed from the cap, wiped dry, and >d.. The face water " I ion value is expressed as milligrams per square centimeter absor v en in 24 hours. H60 '"c. 1387 Specific Gravity As the water to alcohol ratio was increased, the specific gravity of the resulting pacreg decree sed slightly. This effect should be taken into consideration for strict comparison of the pap.reg strength data, but for practical purposes the strength data are directly comparable. Ultimate Tensile Strength The ultimate tensile strength of the plastic was affected but little by an increase of the water-alcohol ratio of the resin diluent for impregnation. Compared to the strength obtained from papreg made with a resin diluted with alcohol alone, a decrease in tensile strength of less than 7 percent occurred when a half-and-half water-alcohol mixture was used. Edgewise Compressive Strength The maximum edgewise compressive strength of the papreg was increased from about 23,000 pounds per square inch when alcohol alone was used as the resin diluent* to 27,200 pounds per square inch when a 50 percent mixture of water and alcohol was used. The rate of increase of the edgewise com- pressive strength was greatest in the range where the proportion of water to alcohol was from 30 to 40 percent. This is shown in figure 3. Modulus of Rupture The modulus of rupture of papreg was not greatly affected by changes in the solvent used in the resin impregnating mixture, although there was a trend toward lower bending values as the proportion of water was increased. Moduli of Elasticity The changes in moduli of elasticity in compression, bending, and tension were so small, with an increase in the amount of water added to the alcohol in the impregnating mixture, that they can be interpreted only as trends. Izod Imoact marked loss in the Izod impact resistance of the papreg occurred with an increase in the proportion of water to alcohol. Increasing the water-alcohol ratio from percent water to 50 percent water resulted in a decrease of the impact resistance of flatwise notched specimens from 5.5 to 3.3 foot pounds per inch of notch (table 1 and fig. 4). The impact resistance of edgewise notched specimens decreased from 0.79 to 0.51 foot pounds per inch of notch. 1'Iimeo. No. 1387 -3- Conclusions alcohol ratio. ti^Sta™^ J' affected fc y the use of various nation. 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