INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1950
841
The experimental values are shown in Figure 10 as a function of the temperature. At low temperatures, where E E , L . is a constant, W depends on the initial modulus only and increases with decreasing temperatures. As is to be expected on the basis of Figure 6, it is also approximately independent of the molecular weight. Above -20“ C., W appears t o be independent of the temperature. Evidently the effect of temperature on EO and E ; & , is about equal. In this range W depends on the molecular weight analogous to the variation of EO. Stress-Strain Properties of Filled Polyethylene. The techniques described above have also been found useful in the evaluation of filled polyethylene compounds. These studies are more completely described in another paper (2). The rwults may be summarized briefly in terms of the following conclusions: 1. The incorporation of fillers in polyethylene results in an increase in initial modulus. In some instances, the inclusion of 40% filler results in doubling the modulus. 2. The linear relation between SE L . and EO%L .-i.e., Equation 10-applies to filled compounds. 3. The addition of filler is analogous to a decrease in testing temperature. The degree of curvature, a,is increased and correspondingly the strain a t the elastic limit, E E . L . , is decreased becoming approximately independent of filler content above a concentration of 30%. The increase in initial modulus outweighs the effect of decreasing E E L , resulting in increased strew a t the elastic limit and increased strain energy. ACKNOWLEDGiMENT
Figure 9. Stress at Elastic Limit ( S E . L . )as Function of Temperature for Various Molecular Weight Polyethylenes
Above -30” C., L . increases with temperature because the stress-strain curves become flatter but it is still independent of molecular weight. It is in the higher temperature range that the dependence of stress, and therefore of modulus, on the molecular weight is most pronounced. ils mentioned before, the area under the stress-strain curve from 0 to e E . L . was also evaluated and referred to as W , the energy of strain. A value for W can also be obtained from Eque tiori 8 by integrating it between the limits of 0 and This gives:
The cooperation of Thomas Hazen in determining the low temperature tensile data is gratefully acknowledged. LlTERATURE CITED
(1) Aljrey, T., Jr., “Mechanical Behavior of High Polymers,” New York, Interscience Publishers, 1948. (2) Rostwick, R., and Carey, R. H., IND. ENQ.CHBIM., 42, 848 (1950). (3) Bridgman, P. W., privata communication. (4) Bryant, W. M. D., J. Polyner Sei., 2,547-84 (1947). ( 5 ) Clash, R. F., Jr., and Berg, R. M., Modern Plastics, 21, 119 (1944). (6) Dienes, G. J., and Dexter, F. D., IND.ENO.CHEM.,40, 2319 (1948). (7) Dienes, G. J., and Klemm, H. F., J. Applied Phys., 17, 458 (1946). (8) Maibauer, A. E.,and Myers, C. S., Trans. Electroehem. Soc., 90, 449 (1946). (9) Itamberg, W., and Osgood, W. It., Natl. AdvisoTy Cmm. Aeronaut., Tech. Note 902, (July 1943). (10) Seely, F. B.,“Resistance of Materials,” pp. 17-18, New York, John Wiley & Sons, Inc., 1935. (11) Trayer, G. W.,and March, H. W., Natl. Ad&wru Cornm. Aeronaut., Rept. 334 (1930). RECEIVEDOctober 7, 1949. Presented before the Division of Paint, Varnish, and Plastics Chemistry at the 116th Meeting of the AMERICAN CHEUICAL SOCIETY, Atlantic City, N. J.
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Los Angeles Smog Problem-Correction
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SIR: Attention is called to an omission in the references in my article “The Los Angeles Smog Problem” [IND.ENG.CHEM.,41, 2476-86 (1949)l. The hypothesis concerning the synergistic effect of fine oil droplets in causing eye irritation and their relationship to Los Angeles smog was suggested and tested in the laboratory by Lucien Dautrebande. The reference to his work will appear as: “Studies on Aerosols. IX. Enhancement of Irritating Effects of Various Substances on the Eye, Nose, and Throat by Particulate Matter and Liquid Aerosols in Connection with Pollution of the Atmosphere” [Arch. intern. pharmacocl2/namy?,82, 148 (1950)l.
PAUL L. MAGILL
TEMPERATURE, E O C
Figure 10. Strain-Energy, W , for Polyethylenes as Function of Temperature
AIR & WATERPOLLUTION LABORATORY STANFORD R E ~ E A R CINSTITUTE H STANFORD, CALIF.
