Burning of polymers

The Ohio State University (OSU) calorimeter (12) differs from the Cone calorimeter ia that it is a tme adiabatic instmment which measures heat released dufing burning of polymers by measurement of the temperature of the exhaust gases. This test has been adopted by the Federal Aeronautics Administration (FAA) to test total and peak heat release of materials used ia the iateriors of commercial aircraft. The other principal heat release test ia use is the Factory Mutual flammabiHty apparatus (13,14). Unlike the Cone or OSU calorimeters this test allows the measurement of flame spread as weU as heat release and smoke. A unique feature is that it uses oxygen concentrations higher than ambient to simulate back radiation from the flames of a large-scale fire. 

Figure 4 Combustion pathways illustrating the burning of polymers.

The authors deal at length with the various theories for the processes, leading to ignition and burning of polymers, as well as with the conditions leading to fire extinction after removal of the ignition source. 

T here has been surprisingly little fundamental work reported on the A chemistry of the process involved in the burning of polymers and its inhibition, despite the great technological and socio-economical importance of the subject. In our laboratories we have undertaken a funda-... 

To understand the burning of polymers better, the combustion region may be divided into five zones, as shown in Figure 5.1. The first zone is defined by the polymer layer where pyrolysis takes place due to heat produced in the flame, but very little oxidation takes place. Thermal oxidation takes place in the second superficial zone. In the third zone, which is a gaseous one, low-molecular-weight products formed in these two zones are mixed with heated air and are decomposed or oxidized by oxygen or by radicals coming out of the flame. 

The burning of polymers could be described simply as a kind of rapid, exothermic, oxygen-induced degradation. Somewhat like heat-induced processing... 

Scheme 12.19 The initial steps in the formation of carbon-rich molecules in burning of polymer...

The nature of smoke produced during the burning of polymers depends to a large extent on their chemical composition, pyrolysis conditions and oxidation processes. 

A simplified model of ignition and burning of polymers which docs not require one to work with partial differential equations has been proposed by Rychly [49]. It was applied to the combustion carried out in a mass loss cone calorimeter system [50]. A series of simulations of heat release rate curves was performed for polymers with intumescent additives [51]. The model was also used for the prediction of limiting oxygen index (LOI) [52],... 

Table 12.1 Relative resistance to burning of polymers of different chemical structures...

Due to the small thickness the usual concerns in bulk sample preparation such as nonuniform heating, burning of polymer and removal of gas products are not serious obstacles for thin film preparation. On the other hand, the quaUty of films and coatings is much more sensitive to the coating solution viscosity, stabiUty of metal complexes during gelation and to particle agglomeration upon heat treatment. 

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