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The formation of antimony oxychloride in flame retardant mixtures and its influence on flame retardant efficiency
Polymer Degradation and Stability I 1 (1985) 205-210
The Formation of Antimony Oxychloride in Flame Retardant Mixtures and its Influence on Flame Retardant Efficiency V. V. Bogdanova, S. S. Fedeev, A. I. Lesnikovich, I. A. Klimovtsova & V. V. Sviridov Institute of Physico-Chemical Problems, Byelorussian University, Minsk, 220080 USSR (Received: 11 April, 1984) ABSTRACT Interaction of Sb20 3 with HCl vapour and chlorine-containing organic .flame retardants in the presence and absence of polymers (polypropylene, polyethylene) has been studied at 473-773 K. It has been shown that SbOCl isformed in thermally degrading mixtures in the condensed phase. The influence of SbOCl .formation on flame retardant efficiency is discussed.
INTRODUCTION The clarification of the nature of the primary processes which take place during the burning of polymer/flame-retardant compositions is of p a r a m o u n t importance for the proper choice of new flame retardant additives, as well as for improving the efficiency of those already in use. Recent results 1'2 do not agree with the reaction scheme suggested by Pitts, 3 according to which SbOCI is an intermediate in the formation of SbC13. During our investigations of the systems discussed in references 1 and 2 we obtained data which confirm the inaccuracy of Pitts' scheme 3 which suggests that SbCI 3 is formed only by SbOC1 thermolysis. We have established that the intermediate product, which was not reported in references 1 and 2, is formed by pyrolysis and that the flame retardant 2o5 Polymer Degradation and Stability 0141-3910/85/$03.30 ~', Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain
206
v . v . Bogdanova et al.
efficiency depends on the nature of the products formed in the pre-flame zone of the condensed phase. We have investigated the products formed on heating antimony oxide with chlorine-containing flame retardants in the presence and absence of polymers, as well as the products of reaction of Sb20 3 with gaseous hydrogen chloride at various temperatures (473-773 K) and times. The temperature range is chosen on the basis of previous investigations which have shown that Sb2 03 begins to react with halogen-containing additives at temperatures exceeding 473 K 4 and that the burning polyolefin surface temperature is about 773 K. 5 In addition, the effect of heat on SbOC1, produced by SbCI 3 hydrolysis, 6 was investigated.
EXPERIMENTAL Materials Two crystal modifications of antimony oxide were used: cubic (senarmontite) and orthorhombic (valentinite) (Fig. l(a)). SbC13, trademark P.A., was used to produce antimony oxychloride. Chlorinated paraffin (CP) C27H31C125and Diels-Alder adduct (B-l) C15H6C112were used as halogen-containing flame retardants (FR). Polyolefin (PO) compositions were based on high pressure polyethylene (PE) and polypropylene (PP). Procedure Mixtures of Sb203 + FR in the weight ratio 1:1 and mixtures of Sb203 + FR + PO in the ratio 1:1:1 (300 mg) were heated in a tubular oven which had been preheated to the desired temperature. Thermal degradations were carried out from 1 to 10 min. Interaction of Sb203 with HC1 vapour was investigated in the same oven through which gaseous HCI was passed over antimony oxide at a flow rate of 1.5-2 cm3/s. The flame extinguishing efficiency of flame retardants was estimated by the dependence of the self-burning times of polymer compositions on the flame retardant concentration.7 X-ray diffraction studies were made on X-ray diffractometer DRON-2 using CuK0t radiation.
Formation of antimony oxychloride in .[tame retardants
207
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20 Fig. 1. Diffractograms of SbzO3(a), SbOCl( l) (b), SbOCl(h)(c), the products of interaction of SbzO 3 + C P at 523K (d) and 773 K (e), the products of thermal degradation of polymer compositions at 673-773 K (f). Thermal degradation for d - f was carried out for 2 3 min., 0 , senarmontite: ×, valentinite, ~ , SbOCl(h), IS], Sb.
RESULTS AND DISCUSSION According to X-ray data, SbOCI(I), produced by SbCI 3 hydrolysis, is similar to the product prepared as in reference 8 (Fig. l(b)). However, SbOCl(h), formed by passing HC1 o v e r S b 2 0 3 , has a different crystal lattice (Fig. l(c)) and conforms to the crystal data given in reference 9. It is suggested that a high temperature modification of antimony oxychloride is formed when HC1 is passed o v e r S b 2 0 3. This suggestion was confirmed by heating SbOC1 obtained by SbC13 hydrolysis. X-ray analysis showed that, on heating, SbOCI(1) changed its structure to SbOCI(h), starting in
208
v . v . Bogdanova et al.
the temperature range 523 to 573 K. Increasing the heat treatment temperature resulted in only diffraction peaks of SbOCI(h) Experiments on the reaction of antimony oxide with gaseous HCI have shown that SbOCI formation starts at 523 K. With increasing temperature, the number and intensity of SbOCI peaks on the X-ray diffractogram increases. Starting at 623K, there is considerable volatilization of antimony in the form of SbC13. It was also found that SbC13 volatilized at even lower temperature if the reaction time was more than 2 min. It should be noted that antimony oxychloride in the form of SbOCl(h) was always found in the products of reaction of flame retardants, both in the presence and absence of polymer. Reaction of antimony oxide with CP and B-l, accompanied by antimony oxychloride formation, starts at 523 K and 673 K, respectively (Fig. l(d)). With increasing temperature and time of heat treatment, the number and intensity of Sb/O 3 diffraction peaks decreases and that of SbOCl(h) increases (Fig. l(e)). In the heat treatment of PE + CP + Sb20 3 and PP + CP + Sb20 3, which was carried out for 10min, SbOCI formation starts at 573K. However, in contrast to the mixture of flame retardants (CP + Sb203), at temperatures above 623K the intensity of SbOC! diffraction peaks decreased and, starting at 673 K, metallic antimony peaks appear on the diffractogram of the products. A typical example of a diffractogram of heat treatment products of the polymer composition at 673 773 K is shown in Fig. l(f). This phenomenon was previously described by the present authors. 4'5 On heating the polymer composition P E + B1 + Sb203, SbOC1 was not formed at any heat treatment temperature. Metallic antimony begins to appear at 573 K. On the other hand, SbOCI was formed in the heat treatment products of the mixture PP + B1 + Sb203 at 623 673 K. At higher temperatures metallic antimony again appears. X-ray diffractograms of drops formed during the burning of PO compositions with CP and PE composition with B-I clearly show diffraction peaks of metallic antimony, while in the products of burning of PP + B-1 compositions there are only weak Sb203 peaks. It is interesting to compare the flame retardant efficiency with the nature of the products formed in the condensed phase. The efficiency of CP + Sb203 (at 5~o) in PE and PP is similar, the efficiency of B1 + Sb20 3 in PP is lower: the mixture B-I + Sb203 in PE shows a flame retardant effect only at higher concentrations. 7
Formation of antimony oxychloride in flame retardants
209
Comparison of the experimental data shows that, in the less fire proof composition, SbOCI formation, as detected by X-ray analyses, does not take place. The phenomenon is not necessarily correlated with the flame resistance of the compositions but nevertheless our results indicate that flame retardant mixtures do undergo qualitatively and quantitatively different transformation in the pre-flame zone of the condensed phase and that these differences influence the FR efficiency. It seems that, in many cases, these differences explain the contradictory literature data mentioned above. It may be suggested that the more thermally resistant B-1 reacts with Sb203 within a temperature range characterized by direct SbC13 formation. Antimony chloride is reduced by polymer degradation products to metallic antimony which decreases the amount of SbCI 3 entering the burning zone, thus lowering the flame retardant efficiency. With the intermediate formation of SbOCI, reduction takes place only in the high temperature zone after the reaction: SbOC1 + 2HCI --~ SbC13 + H / O which decreases the loss of SbCI z associated with the reduction of SbCI 3 to Sb. It is to be noted that, in general, the formation of Sb from SbC13 should not be considered to be a flame retardant efficiency reducing process. It may have a positive influence on their efficiency through polymer degradation termination reactions. It should be emphasized that flame retardant efficiency is determined by the degree of transformation of antimony compounds in various reactions: that is, by rates of individual reactions of the overall process. Thus, an understanding of the peculiarities of flame retardant action will be made possible only by a detailed kinetic analysis of the processes which occur in the system Sb203 A-flame retardant + polymer. REFERENCES 1. 2. 3. 4.
J. Simon, T. Kantor, T. Kozma and E. Pungor, J. Therm. Anal., 25, 57 (1982). L. Costa, J. Camino and L. Trossarelli, Poly. Deg. andStab., 5, 267 (1983). J. Pitts, J. Fire and Flammability, 3, 51 (1972). S. S. Fedeev, V. V, Bogdanova, A. F. Surtaev, A. I. Lesnikovich, V. D. Rumyantsev and V. V. Sviridov, Doklady Akademii Nauk BSSR, 27, 56 (1983). 5. S. S. Fedeev, A. I. Lesnikovich, V. V. Bogdanova, V. D. Rumyantsev and N. Z. Mayorova, Vysocomolekulyarnye soedinen(va, B, 25, 150 (1983).
210
V.V. Bogdanova et
al.
6. G. Brauer, Handbook of preparative inorganic chemistry, Acadmic Press, New York (1965). 7. S. S. Fedeev, V. V. Bogdanova, A. I. Lesnikovich, N. Z. Mayorova and V. D. Rumyantsev, Chimicheskaya Fizika, 8, 1113 (1983). 8. Maja Edstrand, Arkiv. Kemi, 6, 82 (1953). 9. L. I. Mirkin, Spravochnik po rentgenostructurnomu analizu monokristallov, M. (1961), p. 539.
The Formation of Antimony Oxychloride in Flame Retardant Mixtures and its Influence on Flame Retardant Efficiency V. V. Bogdanova, S. S. Fedeev, A. I. Lesnikovich, I. A. Klimovtsova & V. V. Sviridov Institute of Physico-Chemical Problems, Byelorussian University, Minsk, 220080 USSR (Received: 11 April, 1984) ABSTRACT Interaction of Sb20 3 with HCl vapour and chlorine-containing organic .flame retardants in the presence and absence of polymers (polypropylene, polyethylene) has been studied at 473-773 K. It has been shown that SbOCl isformed in thermally degrading mixtures in the condensed phase. The influence of SbOCl .formation on flame retardant efficiency is discussed.
INTRODUCTION The clarification of the nature of the primary processes which take place during the burning of polymer/flame-retardant compositions is of p a r a m o u n t importance for the proper choice of new flame retardant additives, as well as for improving the efficiency of those already in use. Recent results 1'2 do not agree with the reaction scheme suggested by Pitts, 3 according to which SbOCI is an intermediate in the formation of SbC13. During our investigations of the systems discussed in references 1 and 2 we obtained data which confirm the inaccuracy of Pitts' scheme 3 which suggests that SbCI 3 is formed only by SbOC1 thermolysis. We have established that the intermediate product, which was not reported in references 1 and 2, is formed by pyrolysis and that the flame retardant 2o5 Polymer Degradation and Stability 0141-3910/85/$03.30 ~', Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain
206
v . v . Bogdanova et al.
efficiency depends on the nature of the products formed in the pre-flame zone of the condensed phase. We have investigated the products formed on heating antimony oxide with chlorine-containing flame retardants in the presence and absence of polymers, as well as the products of reaction of Sb20 3 with gaseous hydrogen chloride at various temperatures (473-773 K) and times. The temperature range is chosen on the basis of previous investigations which have shown that Sb2 03 begins to react with halogen-containing additives at temperatures exceeding 473 K 4 and that the burning polyolefin surface temperature is about 773 K. 5 In addition, the effect of heat on SbOC1, produced by SbCI 3 hydrolysis, 6 was investigated.
EXPERIMENTAL Materials Two crystal modifications of antimony oxide were used: cubic (senarmontite) and orthorhombic (valentinite) (Fig. l(a)). SbC13, trademark P.A., was used to produce antimony oxychloride. Chlorinated paraffin (CP) C27H31C125and Diels-Alder adduct (B-l) C15H6C112were used as halogen-containing flame retardants (FR). Polyolefin (PO) compositions were based on high pressure polyethylene (PE) and polypropylene (PP). Procedure Mixtures of Sb203 + FR in the weight ratio 1:1 and mixtures of Sb203 + FR + PO in the ratio 1:1:1 (300 mg) were heated in a tubular oven which had been preheated to the desired temperature. Thermal degradations were carried out from 1 to 10 min. Interaction of Sb203 with HC1 vapour was investigated in the same oven through which gaseous HCI was passed over antimony oxide at a flow rate of 1.5-2 cm3/s. The flame extinguishing efficiency of flame retardants was estimated by the dependence of the self-burning times of polymer compositions on the flame retardant concentration.7 X-ray diffraction studies were made on X-ray diffractometer DRON-2 using CuK0t radiation.
Formation of antimony oxychloride in .[tame retardants
207
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20 Fig. 1. Diffractograms of SbzO3(a), SbOCl( l) (b), SbOCl(h)(c), the products of interaction of SbzO 3 + C P at 523K (d) and 773 K (e), the products of thermal degradation of polymer compositions at 673-773 K (f). Thermal degradation for d - f was carried out for 2 3 min., 0 , senarmontite: ×, valentinite, ~ , SbOCl(h), IS], Sb.
RESULTS AND DISCUSSION According to X-ray data, SbOCI(I), produced by SbCI 3 hydrolysis, is similar to the product prepared as in reference 8 (Fig. l(b)). However, SbOCl(h), formed by passing HC1 o v e r S b 2 0 3 , has a different crystal lattice (Fig. l(c)) and conforms to the crystal data given in reference 9. It is suggested that a high temperature modification of antimony oxychloride is formed when HC1 is passed o v e r S b 2 0 3. This suggestion was confirmed by heating SbOC1 obtained by SbC13 hydrolysis. X-ray analysis showed that, on heating, SbOCI(1) changed its structure to SbOCI(h), starting in
208
v . v . Bogdanova et al.
the temperature range 523 to 573 K. Increasing the heat treatment temperature resulted in only diffraction peaks of SbOCI(h) Experiments on the reaction of antimony oxide with gaseous HCI have shown that SbOCI formation starts at 523 K. With increasing temperature, the number and intensity of SbOCI peaks on the X-ray diffractogram increases. Starting at 623K, there is considerable volatilization of antimony in the form of SbC13. It was also found that SbC13 volatilized at even lower temperature if the reaction time was more than 2 min. It should be noted that antimony oxychloride in the form of SbOCl(h) was always found in the products of reaction of flame retardants, both in the presence and absence of polymer. Reaction of antimony oxide with CP and B-l, accompanied by antimony oxychloride formation, starts at 523 K and 673 K, respectively (Fig. l(d)). With increasing temperature and time of heat treatment, the number and intensity of Sb/O 3 diffraction peaks decreases and that of SbOCl(h) increases (Fig. l(e)). In the heat treatment of PE + CP + Sb20 3 and PP + CP + Sb20 3, which was carried out for 10min, SbOCI formation starts at 573K. However, in contrast to the mixture of flame retardants (CP + Sb203), at temperatures above 623K the intensity of SbOC! diffraction peaks decreased and, starting at 673 K, metallic antimony peaks appear on the diffractogram of the products. A typical example of a diffractogram of heat treatment products of the polymer composition at 673 773 K is shown in Fig. l(f). This phenomenon was previously described by the present authors. 4'5 On heating the polymer composition P E + B1 + Sb203, SbOC1 was not formed at any heat treatment temperature. Metallic antimony begins to appear at 573 K. On the other hand, SbOCI was formed in the heat treatment products of the mixture PP + B1 + Sb203 at 623 673 K. At higher temperatures metallic antimony again appears. X-ray diffractograms of drops formed during the burning of PO compositions with CP and PE composition with B-I clearly show diffraction peaks of metallic antimony, while in the products of burning of PP + B-1 compositions there are only weak Sb203 peaks. It is interesting to compare the flame retardant efficiency with the nature of the products formed in the condensed phase. The efficiency of CP + Sb203 (at 5~o) in PE and PP is similar, the efficiency of B1 + Sb20 3 in PP is lower: the mixture B-I + Sb203 in PE shows a flame retardant effect only at higher concentrations. 7
Formation of antimony oxychloride in flame retardants
209
Comparison of the experimental data shows that, in the less fire proof composition, SbOCI formation, as detected by X-ray analyses, does not take place. The phenomenon is not necessarily correlated with the flame resistance of the compositions but nevertheless our results indicate that flame retardant mixtures do undergo qualitatively and quantitatively different transformation in the pre-flame zone of the condensed phase and that these differences influence the FR efficiency. It seems that, in many cases, these differences explain the contradictory literature data mentioned above. It may be suggested that the more thermally resistant B-1 reacts with Sb203 within a temperature range characterized by direct SbC13 formation. Antimony chloride is reduced by polymer degradation products to metallic antimony which decreases the amount of SbCI 3 entering the burning zone, thus lowering the flame retardant efficiency. With the intermediate formation of SbOCI, reduction takes place only in the high temperature zone after the reaction: SbOC1 + 2HCI --~ SbC13 + H / O which decreases the loss of SbCI z associated with the reduction of SbCI 3 to Sb. It is to be noted that, in general, the formation of Sb from SbC13 should not be considered to be a flame retardant efficiency reducing process. It may have a positive influence on their efficiency through polymer degradation termination reactions. It should be emphasized that flame retardant efficiency is determined by the degree of transformation of antimony compounds in various reactions: that is, by rates of individual reactions of the overall process. Thus, an understanding of the peculiarities of flame retardant action will be made possible only by a detailed kinetic analysis of the processes which occur in the system Sb203 A-flame retardant + polymer. REFERENCES 1. 2. 3. 4.
J. Simon, T. Kantor, T. Kozma and E. Pungor, J. Therm. Anal., 25, 57 (1982). L. Costa, J. Camino and L. Trossarelli, Poly. Deg. andStab., 5, 267 (1983). J. Pitts, J. Fire and Flammability, 3, 51 (1972). S. S. Fedeev, V. V, Bogdanova, A. F. Surtaev, A. I. Lesnikovich, V. D. Rumyantsev and V. V. Sviridov, Doklady Akademii Nauk BSSR, 27, 56 (1983). 5. S. S. Fedeev, A. I. Lesnikovich, V. V. Bogdanova, V. D. Rumyantsev and N. Z. Mayorova, Vysocomolekulyarnye soedinen(va, B, 25, 150 (1983).
210
V.V. Bogdanova et
al.
6. G. Brauer, Handbook of preparative inorganic chemistry, Acadmic Press, New York (1965). 7. S. S. Fedeev, V. V. Bogdanova, A. I. Lesnikovich, N. Z. Mayorova and V. D. Rumyantsev, Chimicheskaya Fizika, 8, 1113 (1983). 8. Maja Edstrand, Arkiv. Kemi, 6, 82 (1953). 9. L. I. Mirkin, Spravochnik po rentgenostructurnomu analizu monokristallov, M. (1961), p. 539.