PHYSICAL AND MECHANICAL PROPERTIES OF LIGNIN-FILLED LAMINATED PAPER PLASTICS

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1 PHYSICAL AND MECHANICAL PROPERTIES OF LIGNIN-FILLED LAMINATED PAPER PLASTICS August 1943 No UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin

2 PHYSICAL AND MECHANICAL PROPERTIES OF LIGNIN-FILLED LAMINATED PAPER PLASTIC 1 The properties of the lignin-filled laminated paper plastic given in this report were determined at the U. S. Forest Products Laboratory in cooperation with the Canadian Department of Munitions and Supply, the Howard Smith Paper Mills Ltd., Cornwall, Ont., and the Forest Products Laboratories, Ottawa, Canada. Description of Material The lignin used in this plastic was obtained from soda pulp mill spent liquor by a precipitation process. The lignin was added to kraft pulp and the mixture formed into a lignin-filled paper by usual procedures. The impregnated paper was laminated and molded into a plastic material. The pulp used in the base paper of the plastics reported here was a black spruce kraft pulp produced especially for laminating purposes at the U. S. Forest Products Laboratory. It differed from ordinary kraft pulp principally in its considerably higher strength properties. The lignin-impregnated paper was laminated at a pressure of 500 pounds per square inch and a temperature of 356 F. Panels 1/8 inch in thickness were pressed for 10 minutes, panels 1/2 inch in thickness for 20 minutes. The panels were cooled before removing then from the press. The laminating paper, like all paper made on a Fourdrinier paper machine, has, because of the major fiber orientation, higher strength in the machine direction (direction of forward movement of the paper machine) than in the cross direction. Hence, a laminated plastic of higher-strength is obtained when the machine direction of all sheets are laid parallel (parallel laminated). This higher strength, obviously, is only in the major fiber (grain) direction of the plastic. Lower, but more isotropic, properties are obtained when alternated sheets are laid with their machine directions perpendicular (cross laminated). Cross laminated material, however, is generally stronger than parallel-laminated material tested crosswise. Preparation and Testing of Specimens The specimens were cut, from 11-inch square panels of either approximately 1/8 inch or 1/2 inch thickness with high-speed steel tools, in a manner as to be practically free from tool marks or of over heating. The 1 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. Mimeo. No

3 preparation, conditioning, and testing of the specimens conformed to Federal Specifications for Organic Plastics (Methods of Tests) L-P-406, December 9, 1942, except the water absorption test which was according to the Proposed Specifications dated July 7, In referring to the application of loads in test, the definitions are used: following Flatwise: Load applied to the flat side of the plastic, that is, in a direction normal to the plane of the original panel. Edgewise: Load applied to the edge of the plastic, that is, in a direction parallel to the length (or width) of the original panel. Hence, on parallel-laminated panels, loads applied edgewise may be either parallel to the grain or perpendicular to the grain. Test Results The physical and mechanical properties of the lignin-filled paper laminate at normal temperature are given in table 1. Although based on a limited number of tests a comparsion of data with the properties of conventional phenolic laminates will show that this plastic apparently possesses equal or superior strength properties with the exception of edge compressive strength. Of special interest is its exceptionally high resistance to impact, which may be considered as a measure of toughness. The flatwise Izod impact strength values are from three to six times those of some fabric- and paper-base laminates. The range of the average values of ultimate tensile strength of parallel-laminated material tested in the grain direction of three variations of the plastic shown in table 1 is from 24,540 to 28,520 pounds per square inch, and the total range of test values is from 24,050 to 28,720 pounds per square inch. The range of the average values of modulus of rupture is from 25,470 to 27,860 pounds per square inch, and the total range of test values is from 25,400 to 28,170 pounds per square inch. The range of the average values for the three moduli of elasticity is from 1,909,000 to 2,513,000 pounds per square inch, and the total range of test values is from 1,868,000 to 2,874,000 pounds per square inch. The most marked difference between tests in the grain direction and across the grain direction of parallel-laminated material is shown in the tensile strength where the strength in the crosswise direction averages only about 32 percent of the strength in the lengthwise direction. The same comparison for the moduli of elasticity shows an average of about 39 percent, the modulus of rupture about 45 percent, and the edge compression about 85 percent. A comparison of cross-laminated material with parallellaminated material shows that some strength properties of the crosslaminated material are about equal to the average of the values for crosswise and parallelwise tests on parallel-laminated material. A notable Mimeo No

4 exception is the toughness as measured by both the Izod impact and the Forest Products Laboratory methods where the cross-laminated plastic has only about 60 percent of the average toughness of the parallel-laminated plastic. The specific gravity of the lignin-filled paper plastic is about The water absorption is about 5.5 percent with an increase in thickness of' about 4.3 percent in 24 hours on the 1/8-inch by 1-inch by 3-inch specimen. The effect of temperature on the lignin-filled paper plastic is given in table 2. Coosidering the parallel-laminated material, tested in the grain direction at 200 F., there was a loss in ultimate tensile strength of about 32 percent and a slight increase (about 4 percent) in modulus of elasticity, as compared to properties obtained at room temperature. Although lignin is a thermoplastic material, the loss in tensile strength of the laminated plastic at high temperature is no greater than that observed on certain phenolic paper laminates. An increase in tensile strength of about 6 percent was noted when the plastic was conditioned in dry ice prior to test. In general, the Izod impact strength of the ligninfilled paper plastic was lower at both high end low temperatures than that at room temperature, This is a characteristic of phenolic laminated paper plastics as well. Nevertheless, the impact strengths of the lignin-filled plastic at the extreme temperatures were higher than those of phenolic paper laminates at room temperature. Stress-strain curves representative of tho average elastic behavior of this material in tension are presented in figure 1. The end points indicated for each curve are arbitrary and do not represent the ultimate stresses and corresponding strains at failure. Application has been made by the cooperators for United States patents covering the preparation of lignin and its use for incorporation into paper for laminating purposes. It is expected that the use of such patents will be made available to others by the Secretary of Agriculture on a wartime license basis. Mimeo. No

5 Figure 1.--Stress-straincurves of lignin-filled, laminated-paper plastic tested in tension. Straight lines are extensions of the stress-strainrelationship established at loads less than the proportional limit. Z M F

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