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Abstract

Studies haye been made of the effects of a number of anhydrous metal oxides, hydrated metal oxides, mixed metal oxides and metal oxy-salts on the thermal decomposition of chlorinated wax in an attempt to predict those compounds which are most likely to be effective, synergistic flame retardants. It was hoped that the results, when coupled with mass spec— trometric data, would throw light on their possible mode of action. The flammability of high-density polyethylene and acrylonitrile-butadienestyrene, flame retarded by metal oxide-halogen systems, was then studied on the basis of an experimental design.

In the Introduction, the mechanisms of the thermal decomposition of polyethylene and acrylonitrile-butadiene-styrene are discussed. The different tests available for the evaluation of the flammability of various polymers have been described and the need for more stringent rules for the measurement of flammability is emphasised. The different modes of flame-retardant action are also reviewed and the use of and need for a simplexlattie experimental design are discussed.

In the Experimental Section the materials and procedures used are described and accounts are given of the construction and operation of the thermobalance, the polymer mill, the hydraulic press used for preparing polymer "candles", and the oxygen index apparatus.

The Results Section describes the experimental measurements made on the decomposition of a variety of metal oxides when heated alone, with polymers and with appropriate halogen compounds. The results show that thermogravimetric behaviour is at best only a qualitative indicator of any possible flame retardant activity. The results of the flammability measurements show that in general the oxygen index for samples containing polyethylene was easier to measure for samples containing acrylonitrilebutadiene- styrene, as the flames on top of polyethylene samples were generally clean and ablation of the candles did not occur. The samples containing acrylonitrile-butadiene-styrene generally burned with sooty flames, produced large amounts of char and had a tendency either to undergo ablation or periodically to shed char, thereby causing the flame to flare up.

In the Discussion Section, various possible modes of flame retardance for the systems studied are suggested. It can be seen that the introduction of other metal oxides as partial substitutes for antimony oxide does not, in general, improve the flame retardance. The decrease in flame retardance is smallest with iron(III)oxide, talc and aluminium oxide monohydrate. LIron(III)oxide acts predominantly by promoting char formation and by catalysing the decomposition of the halogen compound. Talc undergoes endothermic dehydration in the flame zone near the temperature of combustion of the polymer and hence smothers the flame. Aluminium oxide monohydrate appears to undergo dehydration as well as to inhibit combustion by acting as a filler. Evidence has also been obtained (for what is believed to be the first time) for some chemical interaction between anhydrous alumina and the halogen (particularly bromine) compounds in the polymers studied.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > Q Science (General) T Technology > T Technology (General)
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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