Simplified Modeling of the Dynamic Gel Time and/or the Dynamic Gel Temperature for a Thermosetting Resin or Composite

Abstract

The simple analytical model developed in this study has been found to give a successful engineering estimate of when gel will occur during the cure cycle of a thermosetting resin. This simple analytical model provides a quick result that appears to be equivalent to similar results obtained with much more complicated computer programs. The replacement of the Arrhenius activation energy with the reaction release energy in the relationship between the isothermal temperature and the time to reach gel significantly contributed to the simple analytical solution that was able to be developed in this study.

Resins used in both autoclave processing and Vacuum Assisted Resin Transfer Molding (VARTM) processing were evaluated in this study. It was found that the calculated Dynamic Gel Temperatures were much higher and the calculated Dynamic Gel Times were much longer for the autoclave resins than for the VARTM resins at the same heating rate. The VARTM resins also appeared to be more exothermic on a relative scale than the autoclave resins.

Several multiple step cure cycles were evaluated for two Hercules resins. In general the agreement between the measured and calculated Dynamic Gel Temperatures was very good. In addition, two cure cycles for Hexcel F-263 composites were calculated and autoclave evaluated for dynamic gel time and the resulting mechanical properties. For Cure Cycle I the autoclave pressure was not applied until after dynamic gel had been reached. For Cure Cycle II the dynamic gel was achieved after the pressure was introduced into the autoclave. The short beam shear strength Cure Cycle I was nearly one-half the strength of the composite generated with Cure Cycle II. In addition, the void content of the composite for Cure Cycle I was approximately four times higher than the composite for Cure Cycle II.

This study has clearly shown that if the time-temperature history of a cure cycle is known, then the dynamic gel analysis developed in this study should be able to predict when a particular resin formulation will gel. The importance of the correct prediction of when the gel time occurs in a cure cycle was also clearly shown.

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References

1. Loos, Alfred C. and Springer, George (March 1983). Curing of Epoxy Matrix Composites , Journal of Composite Materials, 17: 135-169 .

2. Lee, W.I., Loos, A.C. and Springer, G.S. (1982). Heat of Reaction, Degree of Cure, and Viscosity of Hercules 3501-6 Resin , Journal of Composite Materials, 16 (nov): 510-520 .

3. Springer, G.S. (1982). Resin Flow During the Cure of Fiber Reinforced Composites , Journal of Composite Materials, 16(Sept): 400-410 .

4. LeGrand, Marc and Bellenger, Veroique (1998). The Cure Optimization of Carbon/Epoxy Prepregs , Composites Science and Technology, 58: 639-644 .

5. Hojjati, Mehdi and Hoa, Suong V. (1995). Model Laws for Curing of Thermosetting Composites , Journal of Composite Materials, 29(13): 1741-1761 .

6. Flory, Paul J. (1969). Molecular Weight Distributions in Nonlinear Polymer and the Theory of Gelation, In: Principles of Polymer Chemistry, Chapter 9, pp. 347-398, Comell University Press, Ithaca, N.Y. Copyright 1953, seventh printing 1969.

7. Juska, T.D., Dexter, H.B. and Seeman, W.H. (1998). Int. SAMPE Symp Exhib, 43: 33 .

8. Sudduth, Richard D., Loving, David A., Loving Jerry and Sargent, Randy. (1999). Resin Transfer Molding Involving Center Injection Using a New Production-Oriented Process for Composites: VIMP , In: ICCE/6 Conference Proceedings, pp. 513-514 , Orlando, Florida, (Sponsored by College of Engineering at the University of New Orleans) June 27-July 3 (1999).

9. Cook, W.D., Lau, M., Mehrabi, M., Dean, K. and Zipper, M. (Jan 2001). Control of Gel Time and Exotherm Behavior During Cure of Unsaturated Polyester Resins , Polymer International, 50(1): 129-134 .

10.

10. Vilas, J.L., Laza, J.M., Garay, M.T., Rodriguez, M. and Leon, L.M. (January 2001). Unsaturated Polyester Resins Cure: Kinetic, Rheologic and Mechanical-Dynamical Analysis. I. Cure Kinetics by DSC and TSR., Journal of Applied Polymer Science, 79(3): 447-457 .

11.

11. Yang, H. and Lee, L.J. (February 2001). Comparison of Unsaturated Polyester and Vinylester Resins in Low Temperature Polymerization , J. Appl. Polym. Sci., 79(7): 1230-1242 .

12.

12. Malkin, A. Ya., Kulichikhin, S.G., Kerber, M.L., Gorbunova, I. Yu. and Murashova, E.A., (August 1997). Rheokinetics of Curing of Epoxy Resins Near the Glass Transition , Polymer Engineering and Science, 37(8): 1322-1330 .

13.

13. Adam, M., Delsanti, M., Durand, D. (1985). Mechanical Measurements in the Reaction Bath During the Polycondensation Reaction, Near the Gelation Threshold , Macromolecules, 18: 2285-2290 .

14.

14. Adam, M., Delsanti, M., Durand, D., Hild, G. and Munch, J.P., (1981). Mechanical Properties Near the Gelation Threshold, Comparison with Classical and 3D Percolation Theories , Pure & Appl. Chem., 53: 1489-1494 .

15.

15. Sudduth, Richard D., Posey, Kenneth T., Wyatt, Tracy and Wyatt, Tison. (2000). Measurement of Polymerization Reaction Conversion Using DSC, Gel Time and Reaction Voltage as Measured Using Identical Electrodes, PittCon 2000, New Orleans, Louisiana , March 12-17.

16.

16. Sudduth, Richard D. (1985). A Simplified Analytical Approach to Calculate the Dynamic Gel Temperature , 30th National SAMPE Symposium and Exhibition, pp. 649-659 , March 19-21.

17.

17. Boll, D.J. and Hoffman, R.E. (April 1984). The Use of Dynamic Gel Temperature to Develop Cure Cycles , In: Proceedings 29th National SAMPE Symposium and Exhibition, pp. 1411-1421 . Reno, Nevada.

18.

18. Buyny Bob, Private Communication, Hexcel Corporation.

19.

19. Yokota, Michael J. (July/August 1978). In-Process Controlled Curing of Resin Matrix Composites , SAMPE Journal, 14(4): 11-17 .

20.

20. Ghiorse, S.R. (January 1993). Effect of Void Content on the Mechanical Properties of Carbon/Epoxy Laminates , SAMPE Quarterly, 24(2): 54-59 .

21.

21. Judd, N.C.W. and Wright, W.W. (January/February 1978). Voids and Their Effects on the Mechanical Properties of Composites - An Appraisal , SAMPE Journal, 14(1): 10-14 .

22.

22. Boey, F.Y.C. (1990). Reducing the Void Content and its Variability in Polymeric Fibre Reinforced Composite Test Specimens Using a Vacuum Injection Moulding Process , Polymer Testing, 9: 363-377 .

23.

23. Sudduth, R.D. (1995). A Generalized Model to Predict the Effect of Voids on Modulus in Ceramics , Journal of Materials Science, 30: 4451-4462 .