Langmuir-Type Model for Anomalous Moisture Diffusion In Composite Resins

Abstract

Considerable evidence has recently been presented for anomalous mois ture diffusion in epoxy matrix composites. In an earlier paper we noted that there is no a priori reason why moisture should obey simple diffusion theory rather than Kirkwood's (linear) generalization of the Boltzmann transport equation. With the intent of keeping the analytical aspects of the moisture diffusion problem as simple as possible, we here present a slightly generalized but linear model which involves sources and sinks of diffusing water molecules. With respect to diffusive characteristics, our model is related to the simplest form of neutron transport theory. With respect to bound and unbound particles it is similar to the Langmuir theory of ad sorption isotherms, although we here assume bulk absorption in the resin with no implication that surfaces are involved. An approximation to our exact solution of the coupled linear differential equations is used to fit mildly anomalous moisture uptake curves for 5208 resin exposed to several rclative humidities for two years. The fact that the same parameters give equally good fits to the data at all humidities suggests that the absorption anomaly does not result from nonlinear (e.g. concentration-dependent) effects.

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References

T. Alfrey , E.F. Gurnee and W.G. Lloyd , "Diffusion in Glassy Polymers," J. Polymer Science: Part C, (1966), p. 249.

C.D. Shirrell , "Diffusion of Water Vapor in Graphite/Epoxy Composites" Paper presented at the ASTM Symposium on Environmental Effects on Advanced Composite Materials held in Dayton, Ohio on September 29-30, 1977.

T.M. Whitney and C.E. Browning , "Some Anomalies Associated with Moisture Diffusion in Epoxy Matrix Composite Materials," Paper presented at the ASTM Symposium on Environmental Effects on Advanced Composite Materials held in Dayton, Ohio on September 29-30, 1977 .

H.T. Hann and R.Y. Kim , "Swelling of Composite Laminates," Paper presented at the ASTM Symposium on Environmental Effects on Advanced Composite Materials held in Dayton, Ohio on September 29-30, 1977.

R. Delasi and J.B. Whiteside , "Effect of Moisture on Epoxy Resins and Composites," Paper presented at the ASTM Symposium on Environmental Effects on Advanced Composite Materials held in Dayton, Ohio on Sepgember 29-30, 1977.

C.E. Browning , "The Mechanisms of Elevated Temperature Property Losses in High Performance Structural Epoxy Resin Matrix Materials After Exposures to High Humidity Environments ," AFML-TR-76-153, Air Force Materials Laboratory Wright-Patterson Air Force Base, Ohio, March 1977 .

E L. McKague, J. E. Halkias and J.D. Reynolds , "Moisture in Composites: The Effect of Supersonic Service on Diffusion ," J. Composite Materials, Vol. 9 (1975), p. 2.

G. J. van Amerongen , "Diffusion in Elastomers," Rubber Chemistry and Technology, Vol. 37 (1964), p. 1065.

R. Meredith in Rheology, F. R. Eirich , Ed., Vol. 2, Chapter 7, Academic Press Inc., New York, 1958.

10.

H.G. Carter and K.G. Kibler , "Rapid Moisture-Characterization of Composites and Possible Screening Applications," J. Composite Materials , Vol. 10 (1976), p. 355.

11.

J.O. Hirschfelder , C.F. Curtiss , R.B. Bird , and E.L. Spotz , "The Kinetic Theory of Gases," Thermodynamics and Physics of Matter, F. D. Rossini , Ed., Princeton University Press (1955), p. 192.

12.

H.G. Carter , "Moisture Absorption in Epoxy-Type Structures ," Paper presented at the AIAA North Texas Mini-Symposium at the University of Texas at Arlington, February 21, 1976.

13.

M.E. Gurtin , "Continuum Theory of Fracture," Mechanics of Composites Review, 25-27 October 1977, Dayton, Ohio , p. 85.

14.

S. Glasstone , Textbook of Physical Chemistry, 2nd Ed., Chapters XIII and XIV, D. Van Nostrand Co., Inc., New York, 1946.

15.

A.M. Weinberg and E.P. Wigner , The Physical Theory of Neutron Chain Reactors, Chapter VIII, The University of Chicago Press, 1958.

16.

E.L. McKague , J.D. Reynolds and T.E. Halkias , "Moisture Absorption, Swelling and Glass Transition Relationships for Epoxy Resin," J. Applied Polymer Science, in press, 1977.