City Research Online

Abstract

The main purpose of the present work was to discover and investigate the action of additives which, when incorporated into simple polyolefins (principally polypropylene), have both flame-retardant and photostabilising properties; and in this connection, particular attention has been paid to metal chelates, especially those containing transition metals.

The Introduction first reviews the combustion of organic polymers and its prevention. Accounts are included of factors affecting polymer flammability, of general principles of flame-retardance and of effects of metal compounds on polymer combustion. Finally, previous work on the photodegradation and photo-oxidation of simple polyolefins is described. A review is given too of the principal types of compound used as photostabilisers for organic polymers in general and particular attention is paid to the use of metal compounds as inhibitors of polymer photo-oxidation.

In the Experimental Section, the techniques used to incorporate the various additives into the polymers are first outlined. There follows a description of the limiting oxygen index method used to measure and compare the flammability of polymer samples and of the apparatus and procedure used to determine their smoke-producing tendency. An account is given of the computer method used to fit polynomial functions to the flammability data and to plot these in the form of triangular diagrams. The sophisticated experimental set-up for making thermoanalytical measurements on the polymer samples is then described. Finally an account is given of the procedures used to investigate the effects of the various additives on the photo-oxidation of polypropylene. Polymer films containing metal chelates were irradiated with u.v. light in air and the rate of oxidation was followed by means of their infra-red spectra. Ultra-violet absorption, fluorescence spectra and chemical tests were also used to elucidate the mechanism.

The Results Section first outlines some work involving polystyrene. However few of the additive systems investigated had useful flame-retardant effects on this polymer. More detailed studies were then carried out with polypropylene, where some four metal chelates viz: zinc(II) acetyl acetonate, tin(IV) bis acetyl acetonate dichloride, bis hydroxohexa benzoato tris iron(III) benzoate and ferrocene, when used in conjunction with an organic chlorine compound (Cereclor 70), raised the limiting oxygen index to about 30. Measurement of the rate of photo-oxidation of polypropylene films containing also the various metal chelates showed that certain compounds, viz. N,N'-bis salicylidene ethylenediamine zinc(II), zinc(II) acetyl acetonate and tin(IV) bis acetyl acetonate dichloride, had a sizeable photostabilising effect. The results are also presented of detailed studies of the thermoanalytical behaviour of polypropylene samples containing the more promising metal chelates, with and without Cereclor.

In the Discussion, attempts are made to account for the flame - retardant and photostabilising properties of certain of the metal chelates. Useful information regarding their flame retardant action is provided by the thermoanalytical results which show that they all function mainly in the condensed phase. Studies of the effect of benzophenone on the photochemical behaviour of polypropylene show that the polymer does not undergo oxidation by a triplet mechanism so that the metal chelates cannot act as triplet quenchers. Finally some likely alternative modes of photostabilising action of the chelates are discussed.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science Q Science > QD Chemistry T Technology > TP Chemical technology

Export

Downloads