Archive of SID

Iranian Polymer Journal 13 (3), 2004, 219-224 The Comparison Between Synergistic Effect of Sb2O3 and Al(OH)3 on the Flame- retardancy of HIPS in the Presence of Tetrabromobisphenol-A

Ali-Reza Mahdavian*1, Jalil Morshedian2, and Mahdieh Rezaie2

(1) Department of Polymer Science; (2) Department of Plastics Iran Polymer and Petrochemical Institute, P.O. Box: 14965/115 Tehran, I.R. Iran

Received 23 May 2003; accepted 13 January 2004 ABSTRACT

rominated flame-retardants are one of the common and efficient groups in produc- ing flame retardant plastics, such as high impact polystyrene. trioxide is Boften used as a synergistic agent for halogenated flame-retardants. tri- hydrate (ATH), also is a primitive additive for making flame retardant plastics but no report exists on synergistic effect of this compound in presence of brominated flame-retardant. In this research, the synergistic effect of Sb2O3 and ATH, in presence of tetrabromo- bisphenol-A as a flame-retardant agent has been compared. Limited indexes (LOI) of the compounded samples were measured by flammability tests. Also thermal gravimetry analysis (TGA) and scanning electron microscopy (SEM) were applied in order to study the thermal behaviour and morphology of the samples, respectively.

Key Words: flame-retardancy; HIPS; tetrabromobisphenol-A; limiting oxygen index; synergistic effect.


Fire is an important part of combus- fuel, an oxidant and energy (the fire tion. The combustion of polymers is triangle). The mechanism of physi- a multi-stage process involving of cal and chemical processes during many mutually associated chemical combustion of polymers has been and physical processes. From chem- described in several reports [1-5]. ical aspects, combustion is an In recent years, polymers-clay (*) To whom correspondence should be addressed. E-mail: [email protected] exothermic reaction that requires a nanocomposites have attracted spe- ArchiveThe Comparison of SID Between Synergistic Effect of ... Mahdavian A.R. et al.

cial attention in the scope of flame retardancy. The ly used for numerous applications such as in particular main advantage of these composites is improvement of buildings, transportation and electrical applications. In thermal resistance and flammability behaviours of cor- many of these, fire safety regulation rules must be con- responding polymers, nevertheless physical and sidered and so flame-retardants have to be used to mechanical properties of the polymer must not be improve the ignition resistance of polymers [13] due to changed markedly [6-9]. some disadvantages of Sb2O3 like discoloration, high Brominated flame-retardants continue to offer high cost, increasing smoke and afterglow. In this research performance and cost efficiency for plastic compounds. we have compared the synergistic effect of antimony From this group of flame-retardants, tetrabromo- trioxide and aluminium trihydroxide in the presence of bisphenal-A (TBBA) has been widely used and its tetrabromobisphenole-A in the flame-retardancy of application in polystyrene and other plastic compounds HIPS. The synergism mechanism of has been investigated before [10-12]. has been known [14,15], but according to our knowl- In order to consider resistance standards of poly- edge, there is no specific study about the synergistic meric materials against combustion, one should add effect of aluminium trihydrate in presence of brominat- large amounts of halogen inhibitors. Their content in ed flame-retardants in the literature. the polymeric materials may be as high as 40% by weight. Such a large proportion of non-polymer com- ponent normally has bad effects on physical and pro- EXPERIMENTAL cessing properties of polymers like reducing or elimi- nation of its transparency, changing its colour, acceler- Materials ating degradation under conditions of use and often High impact polystyrene (HIPS) obtained from Iranian raising the cost of end-product [13]. It is, therefore, Petrochemical Industries (Tabriz Petrochemical Co.) necessary to reduce the content of flame-retardants and was used in this research work. Tetrabromobisphenol- ensure optimum physical and mechanical properties A (TBBA) as the halogenated flame-retardant was and processing of the obtained plastics. obtained from Fluka Chemical Co. Antimony trioxide Antimony trioxide (Sb2O3) shows no particular (Sb2O3) and Aluminium trihydrate (ATH) were pur- flame-retardant effect on its own. However, it produces chased from Merck Chemical Co. and used without fur- a marked synergistic effect with halogen-containing ther purification. compounds. The most important reaction takes place in the gas and as a result it has effects on the radi- Equipments cal chain mechanism. Antimony trioxide reacts with the Mixing of samples was performed with 60 cc Haake halogen chloride produced during degradation of the internal mixer with banbury rotors (HBI- System 90). halogenated flame-retardant and forms antimony The bulk of compounds were compression moulded in trichloride and various antimony oxychlorides, which order to prepare sample sheets. act as radical interceptors like HCl or HBr in the poly- Limiting oxygen index (LOI) measurements were meric [12]. carried out by using of FTA flammability unit, Stanton Inorganic metal make up more than Redcroft. Vertical burning test was applied for evalua- 50% of the mass of all flame-retardants sold world- tion of LOI in accordance with ASTM D2863, with 10* wide. Depending on the type of polymeric material and 7*0.2 cm specimen dimensions. its end-use, a flame retardant filler is added in amount Thermal gravimetric analyses (TGA) were per- of 5-65% by weight specifically in the case of alumini- formed with a PL instrument and a heating rate of um trihydrate (ATH) [Al(OH)3]. ATH starts to break- 10°C/min in the region of 25-600°C. The sample down in the temperature range from 180°C to 200°C, weight was 5-10 mg in each run. converting to aluminium taking place in an The morphological studies were carried out by endothermic reaction with release of water vapor. The using scanning electron microscopy (SEM, Stereoscan advantages and disadvantages of Sb2O3 and ATH have 360, Cambridge Instrument). Each sample was evacu- been reported exceedingly before [12]. ated, flushed with argon gas, evacuated again and coat- High impact modified polystyrene (HIPS) is wide- ed with powdered gold for SEM analysis.

220 Iranian Polymer Journal / Volume 13 Number 3 (2004) ArchiveMahdavian of SID A.R. et al. The Comparison Between Synergistic Effect of ...

Table 1. Formulation of samples with Sb2O3 and ATH as the 25 synergist. 20 HIPS TBBA Sb2O3 ATH Sample No. 15 (wt %) (wt %) (wt %) (wt %) S0 85.0 15.0 0.0 - 10

( ) Sb2O3 S1 84.0 15.0 1.0 - 5 ( ) ATH S2 82.0 15.0 3.0 - 0 S3 80.5 15.0 4.5 - 0 1 2 3 4 5 6 Weight percent A0 85.0 15.0 - 0.0 Figure 1. Limiting oxygen index amounts for samples con- A1 84.0 15.0 - 1.0 taining different weight percent of Sb2O3 & ATH. A2 82.0 15.0 - 3.0 A3 80.0 15.0 - 5.0 weight percent of a synergists, there is a slight increase in LOI amount in both cases. The flame-retardancy for Sample Preparation in the Presence of Sb2O3 as a samples containing Sb2O3 is more than those contain- Synergist ing ATH. This could be concluded from the greater HIPS, TBBA and Sb2O3 were mixed in a Haake inter- amount of the obtained LOIs given in Table 2. nal mixer with different amount of Sb2O3 at 170°C It was observed that the LOI amount will (Table 1). The rotor speed was set at 60 rpm and the increase about 20.5% in comparison with the blank residence time was 4 min. The obtained bulk com- sample [without any Sb2O3 (sample S0 in Table 2)] pounds were compression moulded at 190°C under 160 by addition of 4.5% Sb2O3. This increase for ATH bar pressure to form the corresponding sheets with was about 7.7%. 10*7*0.2 cm dimensions. Antimony oxide is a known synergistic agent and several mechanisms have been proposed due to its Samples Preparation in the Presence of ATH as a effect in the presence of halogenated flame-retardants Synergist [14,16-18]. One of its most common mechanisms was The procedure in these experiments were similar to the introduced before [11]. previous one (samples containing Sb2O3), except that According to the above mechanism, antimony ATH was used instead of Sb2O3. The reagent’s quanti- oxide is changed to antimony oxychloride in the pres- ties are listed in Table 1. ence of halides that is the effective interme- diate. This intermediate produces SbCl3 through the RESULTS AND DISCUSSION Table 2. The LOI values of samples containing Sb2O3 and Here we have performed simple mixing of HIPS, ATH. Sample NO. LOI(%) TBBA and the synergist (Sb2O3 or ATH) by using a Haake internal mixer at 170°C during 4 min residence S0 19.5 time. Then the obtained products were compression S1 21.5 moulded at 190°C and 160 bar to produce sheets, which S2 22.0 were used for some identification tests. S3 23.5 Flammability Studies A0 19.5 The variation of limiting oxygen index (LOI) quantities A1 20.0 versus weight percent of synergists (ATH and Sb O ) 2 3 A2 20.7 in each compound has been plotted in Figure 1 (Table 2). These results show that by increasing the A3 21.0

Iranian Polymer Journal / Volume 13 Number 3 (2004)www.SID.ir221 ArchiveThe Comparison of SID Between Synergistic Effect of ... Mahdavian A.R. et al.

chain reactions, which is a gas product and it is exclud- ed from the system. 120 ATH has a different mechanism. It has been proved 100

that it plays the role of a flame-retardant by itself via an 80 5% 1% endothermic and thermal degradation process [11,12]. 0% 60 3% The product of this degradation (i.e., Al2O3) on the substrate acts as an insulating protective layer together 40 with the charring product. 20 Consequently, antimony oxide enters the flame- 0 retardancy mechanism in the presence of a halogenated 0 100 200 300 400 500 600 700 compound as a synergist during chain reaction mecha- Temperature (oC) nism. However, according to the known mechanisms for ATH, it does not need any halogenated compound. Figure 2. TGA Thermograms of samples with different weight Therefore, large amounts of ATH are required in order percent of ATH. to obtain optimum and somewhat efficient flame-retar- dancy effect (up to 65% by weight). thermal degradation is about the same and does not Here, we observed that ATH also could have syner- change with varying the amount of synergist gistic effect in the presence TBBA according to the remarkably. Also the weight percent residue of increase in LOI amount of the corresponding com- samples after heating up to 600°C in the air atmos- pound. This means that it could have another degrada- phere were determined by TGA and the obtained tion mechanism plus to its previously known and con- data was plotted versus weight percent of synergist ventional proved one. This would be explained as (Figure 4). Samples containing ATH are thermally below (Scheme I). stable after heating process. But those including ∆ Sb2O3 have less or at most equal thermal stability Al(OH) + HBr AlOBr + 2H O 3 ∆ 2 relative to the primary compound. This could be 5AlOBr Al O Br + AlBr ∆ 4 5 2 3 because of some chemical reactions originating 4Al O Br 5Al O Br + AlBr 4 5 2 ∆ 3 4 3 from the antimony oxide, which cause its easier and 3Al3O4Br 4Al2O3 + AlBr3 faster thermal degradation. Of course, after the crit- ical amount of Sb2O3 (i.e., 1% by weight), this Scheme I effect is diminished and the residual weight percent increases as usual. It is notable that the above mechanism is similar to the However, the temperature relating to 10% weight proposed mechanism by Pitts et al. for antimony oxide loss is almost identical for each sample containing ATH [18]. Accordingly, the observed synergistic behaviour of ATH in the presence of TBBA would be explainable. 120

But at the same conditions it could not effectively act 100 as antimony oxide. This may be due to the more sus- 80 ceptibility and reactivity of Sb2O3 to contribute in the chain reactions than ATH. 60 1% 40 4.5% 3% Thermal Properties 20 0% In order to study thermal properties of samples, 0 TGA thermograms of the samples containing ATH 0 100 200 300 400 500 600 700 o (Figure 2) and also antimony oxide (Figure 3) as Temperature ( C) the synergist with different weight percents have Figure 3. TGA Thermograms of samples with different weight

been shown here. It could be concluded that their percent of Sb2O3.

222 Iranian Polymer Journal / Volume 13 Number 3 (2004) ArchiveMahdavian of SID A.R. et al. The Comparison Between Synergistic Effect of ...

mal properties of their corresponding compounds. 5

4 Morphological Studies 3 Figures 7 and 8 show the SEM of samples with ATH 2 and Sb2O3, respectively. With attention to melting ( ) Sb2O3 (%wt) point of TBBA (178-180°C) and processing tempera- 1 ( ) ATH (%wt) ture, it is clear that mixing of this material, is melt-melt 0 0 1 2 3 4 5 6 mixing and HIPS/TBBA form a continuous phase. Amount of synergist (wt%) Therefore, as shown in SEM micrographs, ATH and Sb2O3 are dispersed phase in TBBA/HIPS continuous Figure 4. Weight percent residue of samples at 600°C ver- phase. Although the amounts of synergistic agents are sus the amount of synergy. not too much, SEM micrographs show good dispersion and distribution during mixing process. The reason (Figure 5). Except for the sample containing 4.5% could be related to less surface activity of these fillers. Sb2O3, this trend could also be observed (Figure 5). Good dispersion, distribution and mixing of the syner- 10% Weight loss will occur at higher temperature in gistic agents in TBBA/HIPS are very important in this sample than the others. Similar behaviours were flame conditions in order to make fast cooling and found for the temperatures at which 90% weight loss flame-retardancy of the system homogeneously. would occur with different amounts of the synergist (Figure 6). This means that ATH and Sb2O3, as synergists in this research work, have the same effects on the ther-



300 200

( ) Sb2O3 100 ( ) ATH 0 0 1 2 3 4 Weight percent Figure 7. SEM Micrograph of the sample containing 5% ATH. Figure 5. Temperatures for 10% weight loss versus the amount of synergist.





( ) Sb2O3 400 ( ) ATH

380 0 1 3 5 Weight percent

Figure 6. Temperatures for 90% weight loss versus the Figure 8. SEM Micrograph of the sample containing 4.5%

amount of synergist. Sb2O3.

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CONCLUSION 8. Zilg C., Dietsch F., Hoffmann B., and Mulhaupt R., Nanofillers based upon organophilic layered silicates, In this research the effect of two components, Macromolecule, 169, 65-77 (2001). antimony trioxide and aluminium trihydrate, for creation 9. Morgan A.B., Gilman J.W., Harris R and Jackson CL., of synergism effect in flame-retardant high impact poly- Flammability of polystyrene-clay nanocomposites, ACS styrene with tetrabromobisphenol-A was studied and Polym. Mat. Sci. Eng., 83, 53-54 (2000). also compared. The obtained results from thermal analy- 10. Yang C.P., Sheen B.S., Effect of tetrabromobisphenol- A sis and limiting oxygen index measurements show that diallyl ether on the flame-retardancy of high impact poly- ATH like Sb2O3 has synergistic effect in the presence of styrene., J. Appl., Polym. Sci., 37, 3185-3194 (1989). TBBA. But its effect is less and the optimum amount of 11. Muller H. and Gachter R., (Eds.), Plastics Additives this component should be more than Sb2O3. Thermal Handbook, Hanser, Ch. 12, (1990). stability of samples containing ATH is improved in com- 12. Dufto P.W., Fire: Additives and Materials, RAPRA Tech- parison with samples containing Sb2O3. Morphological nology Ltd., Ch. 4, (1995). studies reveal that each of the above two mineral com- 13. Radloff B., Spiess H.W., Books J.T., and Dowling K.C., ponents has good dispersion and distribution in Interaction between polybrominated flame retardants and HIPS/TBBA system through the mixing process. high impact polystyrene, J. Appl. Polym. Sci., 60, 715-720 (1996). 14. Karak N. and Maiti S., Antimony polymers: III. Flame ACKNOWLEDGEMENTS retardant behaviour of chloroprene and natural rubber vul- canizates with antimony polymer. J. Appl. Polym. Sci., 98, Authors wish to thank Iran Polymer and Petrochemical 927-935 (1998). Institute for financial support of this work, Grant No. 15. Boryniec S. and Przygocki W., Polymer combustion 803P416. process: flame retardants of polymeric materials. Int. Polym. Sci. Technol., 27, 83-93 (2000). 16. Siddhamalli S.K. and Lee W.W., Injection moldable FR- REFERENCES HIPS formulation based on blends of chlorinated wax and non- diphenyl oxide-brominated flame retardant in con- 1. Pal G. and Macskasy H., Plastics: their behavior in fires, juction with metal oxide metal sulphide synergists, J. Elsevier, Ch. 2, (1991). Vinyl & Additive Technol., 4, 117-125 (1998). 2. Fire F.L., Combustibility of Plastics, New York, Van Nos- 17. Lewin M., Synergism and in flame retardancy trand Reinhold, Ch.7, (1991). of polymers, Polym. Advan. Technol., 12, 215-222 (2001). 3. Asseva R.M. and Zaikov G.E., Fabrikant T, Ed., Combus- 18. Starnes W.H., Kamg Y.A., and Payne B., Interaction of tion of Polymer Materials, Hanser, 347-351 (1981). antimony oxide with a chlorinated organic fire retardant in 4. Lewin M., Atlas S.M., and Pearce E.M. (Ed.), Flame- nylon 6.6., ACS Polymeric Materials, Fall Meeting, 83. retardant polymeric materials, 2, New York, Plenum, Aug. 94-95 (2000). 194-197 (1978). 5. Edenbaum J., (Ed.), Plastics and Modifiers Handbooks, New York, Van Nostrand Reinhold, 1034-1050 (1991). 6. Zhu J., Start P., Mauritz K.A., and Wilkie C.A., - methoxide modified clays and their polystyrene nanocom- posites, J. Polym. Sci., Part A: Polym. Chem., 40, 1498- 1503 (2002). 7. Zilg C., Thomann R., Baumert M., Finter J., and Milhaupt R., Organic/ inorganic hybride materials and nano com- posites based upon layered silicates modified with cyclic amidines. Macromol. Rapid Commun., 21, 1214-1219 (2000).

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