Aromatic Organic Phosphate Oligomers as Flame Retardants in Plastics

Chapter 4

Aromatic Organic Phosphate Oligomers as Flame Retardants in Plastics Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 12, 2017 | http://pubs.acs.org Publication Date: July 21, 1995 | doi: 10.1021/bk-1995-0599.ch004

Rudolph D. Deanin and Mohammad Ali Department of Plastics Engineering, University of Massachusetts, Lowell, MA 01854

Polyaryl phosphate oligomers were synthesized by transesterification of triphenyl phosphate with hydroquinone and with bisphenol A. These were used as flame-retardants, in comparison with three commercial controls: triphenyl phosphate, Dechlorane /antimony trioxide 3/1, and decabromo diphenyl oxide/antimony trioxide 2/1, at concentrations up to 30 parts per hundred of resin. In high-density polyethylene, the polyaryl phosphate oligomers increased oxygen index from 17 up to 29, while the commercial systems reached up to 35. In modified polyphenylene oxide, the polyaryl phosphate oligomers increased oxygen index from 24 up to 36, while the commercial systems reached up to 49. In polycarbonate, the polyaryl phosphate oligomers increased oxygen index from 26 up to 39, while the commercial systems reached up to 52. Whereas the commercial systems were more effective in increasing oxygen index, the polyaryl phosphate oligomers offered promise of lower opacity, smoke, toxicity, and corrosion. R

Wherever plastics are used in building and construction, electrical equipment, and transportation, flammability is a serious consideration, and it is common to add flameretardants to control it (7,2). Of the elements which reduce flammability, organic phosphorus is generally most effective, on a weight basis, followed by organic bromine + antimony oxide, organic chlorine + antimony oxide, and inorganic hydrates (3). In a fire, bromine, chlorine, and antimony produce problems of smoke, toxicity, and corrosion. Inorganic hydrates must be used in such large amounts that they lower strength properties. Organic phosphates do not cause any of these problems; thus they should be the most desirable class of flame-retardant additives. In addition, if they are designed to be soluble in the plymer, they should not reduce its transparency. The object of this study was to synthesize and evaluate aromatic organic phosphate oligomers as flame-retardant additives for plastics in electrical applications. Literature on preparation of polyaryl phosphate polymers generally tends toward difficult conditions and complex expensive structures (4-10). Most promising were a couple of vague references for transesterification of triaryl phosphates with aromatic diols (9,10). These were therefore adopted as the experimental starting point for the present study.

0097-6156/95/0599-0056$12.00/0 © 1995 American Chemical Society Nelson; Fire and Polymers II ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

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DEANIN & ALI

Aromatic Organic Phosphate Oligomers

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Model Reaction When triphenyl phosphate (P) is transesterified with aromatic diols (D), such as hydroquinone or bisphenol A, and phenol (M) is removed, the reaction can be modeled as follows: 2 M3P +1 D ->M2PDPM2

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 12, 2017 | http://pubs.acs.org Publication Date: July 21, 1995 | doi: 10.1021/bk-1995-0599.ch004

3 M3P + 2 D ->M2PDPDPM2 M 4 M3P + 3 D->M2PDPDPDPM2 + M2PDPDPM2 M L i

DPM2

and so on. Thus increasing stepwise should produce series from liquids to solids to infusible solids. This is assuming that all reactions produce a single homogeneous molecular weight. In practice, they would more likely produce a normal molecular weight distribution, so each sample would contain some smaller and some larger molecules as well. Synthesis In a 1-liter resin flask fitted with gas inlet, stirrer, thermometer, condenser, and electrical heating mantle, triphenyl phosphate and aromatic diol (hydroquinone or bisphenol A) were melted together in the presence of catalyst (0.18% MgCl2 for hydroquinone, 0.29% sodium phenate for bisphenol A). The flask was swept with dry nitrogen, heated gradually from 50 to 300°C with constant stirring to produce transesterification, vacuum was applied and maintained, and the phenol which evolved was distilled out and condensed in an ice bath. Yields of phenol were 95-99% of theoretical; lower molecular weights were more fluid and phenol removal was more complete. At the highest molecular weights, products were so viscous as to suggest some cross-linking, at least part of the broad MWD product. Bisphenol A gave whiteyellow products; whereas hydroquinone, suffering from easy quinoid formation, gave brown products. Results are summarized in Tables I and II. Table I. Reactions of Triphenyl Phosphate with Hydroquinone Mol Ratio Calculated Calculated Viscosity of Product TPP:HO Molecular Phosphorus Weight Content, % 1:0 326 9.5 Solid 2:1 574 10.8 Fluid 3:2 822 11.3 Fluid 4:3 1070 11.6 Fairly Viscous 5:4 1318 11.8 Viscous 6:5 1566 11.9 Viscous 7:6 1814 12.0 Highly Viscous 8:7 2062 12.0 Highly Viscous 9:8 2310 12.1 Very Highly Viscous 10:9 2558 12.1 Solid

Nelson; Fire and Polymers II ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


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FIRE AND POLYMERS II

Table II. Reactions of Triphenyl Phosphate with Bisphenol A Mol Ratio Viscosity of Product Calculated Calculated Molecular Phosphorus TPPrBPA Weight Content, % 1:0 326 9.5 Solid 2:1 692 9.0 Fluid 3:2 1058 8.8 Fluid 4:3 1424 8.7 Fairly Viscous 5:4 1790 8.7 Viscous 6:5 2156 8.6 Highly Viscous 7:6 2522 8.6 Highly Viscous 8:7 2888 8.6 Very Highly Viscous 9:8 3254 8.6 Almost Solid 10:9 3620 8.6 Solid Compounding and Testing Three commercial polymers typically used in electrical products were chosen for this study: HDPE: Dow 08054-N: MI 8, D 0.954 PPO: GE Noryl 731: GP, UL 94 HB PC: Mobay Makrolon 2658: GP, MI 12, UL 94 V-2 One hundred parts of each polymer was fused in a Brabender Banbury mixer and meltblended with 0,10,20, or 30 parts of each of 6 polyaryl phosphate oligomers made from 2 mois Triphenyl Phosphate +1 mol Hydroquinone 6 " +5 " |Q « » w _|_ g η η M

w

2 6 " 10 «

M

" " «

M

+1 " Bisphenol A +5 _|_ g « M M

»

or with each of 3 commercial control flame-retardants: 3 Occidental Dechlorane 1000 + 1 M&T Thermoguard S Sb2Q3 2 Decabromo Diphenyl Oxide + 1 M&T Thermoguard S Sb2Q3 Triphenyl Phosphate The lowest MW oligomers mixed poorly with the molten plastics, and caused brittleness (antiplasticization) in polycarbonate. The highest MW oligomers mixed well, and did not reduce transparency of the parent polymers. The commercial flameretardants were solid fillers which mixed well and gave opaque blends. Banbury blends were compression molded, cut into 1/4x1/8 inch samples, and tested for oxygen index according to ASTM D-2863. Results are summarized in Table III.


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DEANIN & ALI

Table III. Effects of Flame-Retardants on Oxygen Index of Commercial Plastics 10 Flame-Retardant PHR: 0 Dechlorane/Sb2Q3 3/1 17 26 DBDPO/Sb2Q3 2/1 17 27 TPP 17 20 TPP/BPA 2/1 17 20 6/5 17 23 10/9 17 26 17 20 ΤΡΡ/Ηα 2/1 6/5 17 22 10/9 17 24 24 38 Dechlorane/Sb2CB 3/1 DBDPO/Sb2Cg 2/1 24 40 TPP 24 26 TPP/BPA 6/5 24 28 10/9 24 32 TPP/HQ10/9 24 33 Dechlorane/Sb2Cfc 3/1 26 37 DBDPO/Sb2C3 2/1 26 42 TPP 26 29 TPP/BPA 6/5 26 32 10/9 26 37 TPP/HQ 6/5 26 33 10/9 26 34

Polymer HDPE



PPO

PC

59

20 28 30 22 21 25 28 22 24 26 39 44 28 29 33 35 39 47 33 33 38 35 36

30 33 35 23 22 27 29 23 26 29 42 49 30 30 34 36 45 52 36 35 39 36 39

Discussion In high-density polyethylene, synthetic polyaryl phosphates raised oxygen index from 17 up to 20-29, while commercial additives gave 20-35. In polyphenylene oxide, synthetic polyaryl phosphates raised oxygen index from 24 up to 28-36, while commercial additives gave 26-49. In polycarbonate, synthetic polyaryl phosphates raised oxygen index from 26 up to 32-39, while commercial additives gave 29-52. Increasing molecular weight of the polyaryl phosphates produced significant increase in flame-retardance. Use of hydroquinone and bisphenol A to synthesize the polyaryl phosphates produced about equivalent flame-retardance in polyethylene and polycarbonate, whereas hydroquinone phosphate was somewhat more effective than bisphenol phosphate in polyphenylene oxide. Halogen/antimony combinations were more effective on a weight basis, because they contained a higher percentage of the flame-retarding elements (Table IV). Table IV. Concentration of Flame-Retardant Elements in Additives Additives Elements Concentration Dechlorane/Sb203 3/1 CI, Sb 69.7% DBDPO/Sb2Q3 2/1 Br, Sb 83.6 TPP Ρ 9.5 TPP/BPA 2/1 Ρ 9.0 6/5 Ρ 8.6 10/9 Ρ 8.6 TPP/HQ 2/1 Ρ 10.8 6/5 Ρ 11.9 10/9 Ρ 12.1



60


Conversely, qualitative observations indicated the polyaryl phosphates produced much less smoke than the halogen/antimony systems. Instead of comparing flame-retardant additives at equal concentrations, it is interesting to compare flame-retardant elements at equal concentrations, by interpolating from the above experimental data (Table V, Figures 1-3). Generally phosphorus was most effective at equal concentration, followed by bromine and chlorine in that order, in agreement with many earlier studies. Surprisingly, molecular weight of the polyaryl phosphates correlated directly with effectiveness of phosphorus, even at equal phosphorus concentration; probably lower volatility kept the phosphorus in the polymer longer, permitting it to keep retarding the burning process. And bisphenol phosphate was generally somewhat more effective than hydroquinone phosphate at equal phosphorus concentration, probably for the same reason. Conclusions When polyaryl phosphate oligomers were added up to 30 PHR in commercial plastics, they increased oxygen index of high-density polyethylene from 17 up to 29, polyphenylene oxide from 24 up to 36, and polycarbonate from 26 up to 39. At equal loading of flame-retardant additive, commercial halogen/antimony flame-retardants gave higher oxygen index, but polyaryl phosphate oligomers offered promise of greater transparency and lower smoke, toxicity, and corrosion.

Table V. Effects of 2% of Flame-Retardant Elements on Commercial Plastics Oxygen Flame-Retardant Flame-Retardant Index Polymer Elements Additive HDPE Dechlorane/Sb2Q3 3/1 Cl+Sb 20 Br+Sb 20 DBDPO/Sb2Q3 2/1 TPP Ρ 22 TPP/BPA 2/1 Ρ 21 6/5 Ρ 26 10/9 Ρ 28 TPP/HQ 2/1 Ρ 22 6/5 Ρ 24 10/9 Ρ 25 PPO Cl+Sb 28 Dechlorane/Sb2Q3 3/1 DBDPO/Sb2Q3 2/1 Br+Sb 28 TPP Ρ 28 TPP/BPA 6/5 Ρ 29 10/9 Ρ 33 TPP/HQ 10/9 Ρ 35 PC Dechlorane/Sb2Q3 3/1 Cl+Sb 29 DBDPO/Sb2Q3 2/1 Br+Sb 30 TPP Ρ 33 TPP/BPA 6/5 Ρ 34 10/9 Ρ 39 TPP/HQ 6/5 Ρ 34 10/9 Ρ 35




DEANIN & ALI

Figure 1. Efficiency of Flame-Retardant Elements i n HDPE. Β i s BPA, Η i s HQ, Τ i s TPP.




T/H

0

1

2

C o n c e n t r a t i o n of FlameRetardant Elements, %

10/9

3

F i g u r e 2 . E f f i c i e n c y of Flame-Retardant Elements i n PPO. Β i s BPA, Η i s HQ, Τ i s TPP.




DEANIN & ALI

0

1

2

3

Concentration of FlameRetardant Elements, % Figure 3. Efficiency of Flame-Retardant Elements i n PC. Β i s BPA, Η i s HQ, Τ i s TPP.


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Literature Cited 1. Edenbaum, J. Plastics Additives and Modifiers Handbook; Van Nostrand Reinhold: New York, NY, 1992; Sect. X. 2. Troitzsch, H. J. In Plastics Additives Handbook; Gachter, R.; Muller, H., Eds.; Hanser: Munich, 1990, Ch. 12. 3. Lyons, J. W. The Chemistry and Uses of Fire Retardants; Wiley: New York, NY, 1970; pg. 23. 4. Weil, E. D. Encyc. Polym. Sci. Tech..; Vol. 11, pp. 96-126. 5. Cass, W. E. (GE). U. S. Pat. 2,616,873 (1952). 6. Zenftman, H.; McLean, A. (ICI). U. S. Pat. 2,636,876 (1953). 7. Helferich, B.; Schmidt, K. G. Chem. Ber. 1959, 92, 2051-6. 8. Stackman, R. W. Ind. Eng. Chem., Prod. Res. Dev. 1982, 21, 332-6. 9. Coover, H. W. Jr.; McConnell, R. L.; McCall, M. A. Ind. Eng. Chem. 1960, 52 (5), 409-11. 10. Cerini, V.; Nouvertne, W.; Freitag, D. (Bayer). U. S. Pat. 4,481,338 (1984). RECEIVED February 6, 1995


Aromatic Organic Phosphate Oligomers as Flame Retardants in Plastics

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