Influence of cenospheric fillers on the thermal properties, ceramisation and flammability of nitrile rubber composites

In this paper, the influence of cenospheric fillers of different particle sizes on the thermal properties and flammability of butadiene-acrylonitrile rubber is presented. A part of fly ash cenospheres was coated with an iron and iron (III) oxide layer. A series of examinations were conducted, these took the forms of: thermal analysis; oxygen index analysis; cone calorimeter measurements; SEM; AFM. These examinations enabled the explanation of iron-based combustion inhibition processes in terms of catalysis of char formation and elastomer cross-linking. Cenospheres itself without additional coatings or fillers provide high surface for polymer chain adsorption, and hence degradation of composite is reduced. Additionally, the results of the investigation on the effectiveness of cenospheric filler usage for ceramisation are discussed. It is proven that the durable ceramic structure is formed owing to the addition of cenospheres in the presence of an inorganic flux. Thus, replacement of silica by lightweight cenospheres is possible. Cenospheres with an iron coating and in the presence of wollastonite and an inorganic flux allow obtaining the NBR composites which are non-flammable in the air atmosphere; furthermore, the ceramic layer formed during the composite combustion has advantageous mechanical properties.