Ammonium Pentaborate: an Intumescent Flame Retardant for Thermoplastic Polyurethanes

Abstract

Ammonium pentaborate (APB) is shown to be an effective intumescent, char- forming additive for thermoplastic polyurethanes (TPU). As little as 5 to 10 parts of APB, added to a flame retarded TPU, provides a 7 to 10-fold improve ment in burn-through resistance. The APB/TPU char is characterized by its glassy, multicellular structure which provides virtually instantaneous thermal protection to heat-sensitive substrates and is able to resist thermo-oxidative degradation.

In contrast to its behavior in polyurethanes, APB is found to be somewhat less effective as an intumescent additive for several non-urethane polymers such as natural rubber, polyester resin, polyamide and polyvinyl chloride. A mechanism is proposed to account for the unique nature of the APB/TPU system. It is suggested that, via a series of chemical reactions, APB redirects the thermal decomposition of the polyurethane thereby producing less volatiles and increased char.

Get full access to this article

View all access options for this article.

References

Vandersall, H.L. , J. Fire and Flammability , 2, p. 97 (1971).

Naitove, M. H., ed., Plastics Technology, 28, p. 69 ( July 1982).

Naitove, M. H., ed., Plastics Technology, p. 37 (May 1981).

Myers, R.E. and Licursi, E. , J. Fire Sciences, submitted for publication .

Heylin, M., ed., Chem. Eng. News, 62, p. 36 (February 1984).

Kroenke, W.J. , J. Materials Science , in press (1986).

Vol'fkovich, S.I. , Zuzzer, E.E. and Remen, R.E. , Bull. Akad. Sci. U.S.S.R. Klasse Sci. Khim ., 571 (1946); Chem. Abs., 43, 7781h (1948).

Chambers, W.E. , Internal Report, BFGoodrich R&D Center Report, unpublished (July 1980).

Kroenke, W.J. , J. Appl. Polym. Sci ., 26, p. 1167 (1981).

10.

Kay, M. , Price, A.F. and Lavery, I. , J. Fire Retard. Chem., 6, p. 69 (1979 ) and references contained therein.

11.

Barnett, J. C., Fr. Pat. 1,462,604 (1966 to Monsanto Co.); J. C. Barnett, U.S. Pat. 3,423,343 (1969 to Monsanto Co.).

12.

Fabris, H.J. and Sommer, J.G. , "Flame Retardation of Natural and Synthetic Rubbers," Flame Retardancy of Polymer Materials, Vol. 2, pp. 135-199, Marcel Dekker, Inc., New York (1973 ).

13.

Schollenberger, C.S. and Stewart, F.D. , "Thermoplastic Urethane Structure and Ultraviolet Stability," Advances in Urethane Science and Technology , Vol. 2, pp. 71-108 (1973).

14.

Hewitt, L.E. , Soc. Plastics Eng. Proceedings, SPE 38th Annual Technical Conference , pp. 497-499 (May 1980).

15.

Grassie, N. and Zulfiquar, M. , "The Effect of the Fire Retardant, Ammonium Polyphosphate, on the Thermal Degradation of a Polyurethane," Developments in Polymer Stabilization, Vol. 1, pp. 197-217 (1979).

16.

Brotherton, R.J. , "Boric Acid Esters," Kirk-Othmer Encylcopedia of Chemical Technology, Vol. 4, 3rd ed., pp. 111-123, John Wiley & Sons, New York (1978 ).

17.

Aries, R.S. , U.S. Pat. 2,931,831 (1960); Aries, R. S., U.S. Pat. 2,945,841 ( 1960).

18.

Erdey, L. , Gal, S. and Liptay, G. , Talanta, 11, p. 913 (1964).

19.

Grassie, N. and Mackerron, D.H. , "Synthesis and Degradation of Polyurethanes Containing Phosphorus—Part III," Polymer Degradation and Stability, Vol. 5, pp. 89-103 (1983).

20.

Dickens, E.D. , Jr. , "ILS Sheet: A Decorative Sheet for Reducing the Flame Spread of Flammable Substrates," Paper given at the 31st Annual Meeting of the Forest Product Research Society, Denver, Colo. (July 3-8, 1977).

21.

Dickens, E.D. , Jr. and Smith, G.F. , "New Low Smoke Thermoplastics to Meet New Needs in the Marketplace," 8th International Conference on Fire Safety, p. 227 (January, 1983).