Flame retardancy, smoke suppression effect and mechanism of aryl phosphates in combination with magnesium hydroxide in polyamide 6

Abstract

The flammability, smoke emission behavior and mechanical properties of two oligomeric aryl phosphates [bisphenol A bis(diphenyl phosphate) (BDP) and resorcinol bis(diphenyl phosphate) (RDP)] combined with magnesium hydroxide (MH) in polyamide 6 (PA6) have been investigated. Combining 5 wt% BDP, 50 wt% MH imparts a limiting oxygen index (LOI) of 40.9% and UL94 V-0 rating to PA6, meanwhile the peak rate of smoke release (pRSR), total release of smoke (TSR) and Izod notched impact strength are 41%, 33% and 233% relative to the corresponding value of 55 wt% MH without BDP, respectively. Dynamic mechanical analysis (DMA) indicates that the improvement of toughness attributes to the enhanced compatibility between MH and PA6 by adding BDP. Furthermore, based on the comprehensive analysis of thermogravimetry (TG), cone calorimeter and SEM-EDX investigations, possible flame retardancy and smoke suppression mechanisms were revealed. Besides the fuel dilution and barrier effect of MH, the combination of MH and RDP shows an additional flame inhibition effect. The combination of MH and BDP results in a dominant condensed phase barrier effect which leads to obvious reduction on smoke emission and flammability.

Keywords

flame retardancy / smoke suppression / oligomeric aryl phosphate / magnesium hydroxide / polyamide 6

References

[1] Troitzsch J. Plastics Flammability Handbook, 2nd Ed[M], 1990 Munchen Hanser

[2] Lu S.Y., Hamerton I. Recent Developments in the Chemistry of Halogenfree Flame Retardant Polymers[J]. Prog. Polym. Sci., 2002, 27(8): 1 661-1 712.

[3] Levchik S. V., Bright D. A., Alessio G. R., . New Halogen-free Fire Retardant for Engineering Plastic Applications[J]. J. Vinyl. Addit. Technol., 2001, 7: 98-103.

[4] Weil E. D., Levchik S. V. Current Practice and Recent Commercial Developments in Flame Retardancy of Polyamides[J]. J. Fire Sci., 2004, 22: 251-264.

[5] Laoutid F., Bonnaud L., Alexandre M. New Prospects in Flame Retardant Polymer Materials: From Fundamentals to Nanocomposites[J]. Materials Sci. and Eng., R, 2009, 63: 100-125.

[6] Lyons J. W. Mechanisms of Fire Retardation with Phosphorus Compounds: Some Speculations[J]. J.Fire Flammability, 1970, 1: 302-315.

[7] Braun U., Balabanovich A. I., Schartel B., . Influence of the Oxidation State of Phosphorus on the Decomposition and Fire Behaviour of Flame-retarded Epoxy Resin Composites[J]. Polymer, 2006, 47: 8 495-8 508.

[8] Lewin M., Weil E. D. Horrocks A. R., Price D. Mechanism and Modes of Action in Flame Retardancy of Polymers. Fire Retardant Materials[M], 2001 Cambridge Woodhead Publishing

[9] Schartel B., Kunze R., Neubert D. Red Phosphorus-controlled Decomposition for Fire Retardant PA 66[J]. J. Appl. Polym. Sci., 2002, 83(10): 2 060-2 071.

[10] Braun U., Schartel B., Fichera M. A., . Flame Retardancy Mechanisms of Aluminium Phosphinate in Combination with Melamine Polyphosphate and Zinc Borate in Glass-fibre Reinforced Polyamide 6xxx6[J]. Polym. Degrad. and Stab., 2007, 92(8): 1 528-1 545.

[11] Pawlowski K. H., Schartel B. Flame Retardancy Mechanisms of Triphenyl Phosphate, Resorcinol Bis(Diphenyl Phosphate) and Bisphenol A Bis(Diphenyl Phosphate) in Polycarbonate/Acrylonitrile-Butadiene-Styrene Blends[J]. Polym. Int., 2007, 56: 1 404-1 414.

[12] Hornsby P. R., Watson C. L. A Study of the Mechanism of Flame Retardance and Smoke Suppression in Polymers Filled with Magnesium Hydroxide[J]. Polym. Degrad. and Stab., 1990, 30(1): 73-87.

[13] Marney D. C. O., Russell L. J., Wu D. Y., . The Suitability of Halloysite Nanotubes as a Fire Retardant for Nylon 6[J]. Polym. Degrad. and Stab., 2009, 93(10): 1 971-1 984.

[14] Li W. H., Yan D. Y. Synthesis and Characterization of Nylons Based on Hexadecane Diacid[J]. J. Appl. Polym. Sci., 2003, 88(10): 2 462-2 467.

[15] Manikandan-Nair K. C., Thomas S., Groeninckx G. Thermal and Dynamic Mechanical Analysis of Polystyrene Composites Reinforced with Short Sisal Fibres[J]. Composites Sci. and Tech., 2001, 61: 2 519-2 529.

[16] Xie M., Zhang Z. G., Gu Y. Z. A New Method to Characterize the Cure State of Epoxy Prepreg by Dynamic Mechanical Analysis[J]. Thermochimica Acta, 2009, 487: 8-17.

[17] Straka P., Náhunková J., Broová Z. Kinetics of Copyrolysis of Coal with Polyamide 6[J]. Journal of Analytical and Applied Pyrolysis, 2004, 71(1): 213-221.

[18] Pramoda K. P., Liu T. X., Liu Z. H., . Thermal Degradation Behavior of Polyamide 6/Clay Nanocomposites[J]. Polym. Degrad. and Stab., 2003, 81(1): 47-56.

[19] Hornsby P. R., Wang J., Rothon R. Thermal Decomposition Behaviour of Polyamide Fire-Retardant Compositions Containing Magnesium Hydroxide Filler[J]. Polym. Degrad. and Stab., 1996, 51(3): 235-249.

[20] Fei G. X., Liu Y., Wang Q. Synergistic Effects of Novolac-based Char Former with Magnesium Hydroxide in Flame Retardant Polyamide-6[J]. Polym. Degrad. and Stab., 2008, 93(7): 1 351-1 356.

[21] Martens R., Gentsch H., Freund F. Hydrogen Release During the Thermal Decomposition of Magnesium Hydroxide to Magnesium Oxide[J]. Journal of Catalysis, 1976, 44(3): 366-372.

[22] Pawlowski K. H., Schartel B. Flame Retardancy Mechanisms of Aryl Phosphates in Combination with Boehmite in Bisphenol A Polycarbonate/Acrylonitrile-Butadiene-Styrene Blends[J]. Polym. Degrad. and Stab., 2008, 93(1): 657-667.

[23] Bourbigot S., Duquesne S., Jama C. Polymer Nanocomposites: How to Reach Low Flammability[J]?. Macromolecular Symposia, 2006, 133: 180-190.

[24] Genovese A., Shanks R. A. Structural and Thermal Interpretation of the Synergy and Interactions Between the Fire Retardants Magnesium Hydroxide and Zinc Borate[J]. Polym. Degrad. and Stab., 2007, 92(1): 2-13.

[25] Li Z. Z., Qu B. J. Flammability Characterization and Synergistic Effects of Expandable Graphite with Magnesium Hydroxide in Halogen-free Flame-retardant EVA Blends[J]. Polym. Degrad. and Stab., 2003, 81(3): 401-408.

[26] Schartel B., Braun U. Fire Retardancy Mechanisms of Phosphorus in Thermoplastics[J]. Polym. Mater. Sci. Eng., 2004, 91: 152-153.