Flammability of diene rubbers

Authors: Grażyna Janowska Agnieszka KucharskaJastrząbek Przemysław Rybiński Dorota Wesołek Iwona Wójcik

Publish Date: 2010/06/04

Volume: 102, Issue: 3, Pages: 1043-1049

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Abstract

This paper presents the results of testing the flammability and fire hazard of butadiene BR butadieneacrylonitrile NBR and butadiene styrene SBR rubbers with the use of oxygen index test ignition temperature measurement cone calorimetry and inverse liquid chromatography Toxicometric indices RTFH CO/CO2 WLC50SM and the concentration of polycyclic aromatic hydrocarbons PAH have been determined The results obtained have been interpreted from the point of view of the chemical constitution of the polymers testedPolymers and polymeric materials are now commonly used in all the fields of economy industry agriculture housing land sea and air transports In most cases polymers are flammable products There is a group of polymers such as polyolefines cellulose and others that undergo complete combustion in a medium that is poorer in oxygen than atmospheric air Only few polymers designed for special applications can be accepted as inflammable or flameretardant due to their chemical composition and molecular structure Generally speaking the flammability of polymers depends on the content of carbon and hydrogen in their macromolecule which ranges from over 85 of C and 14 of H to 0 of hydrogen eg in inflammable nitrozofluoric polymers The reduction in the flammability of polymeric materials and fire hazard resulting from their use consists in selecting properly the composition of polymeric blends which can be achieved by using appropriately selected flameretardant compounds and fillers or nanofillers surface modification of components or products Studies on the preparation of polymeric composites and nanocomposites that would be thermally stable and show limited flammability or selfextinguishing capability constitute now one of the more dynamically developed trends in material engineeringThe combustion process of solids can proceed according to the hetero or homophase mechanism depending on their structure The heterophase combustion consists in adsorbing oxygen on the material surface under combustion and flameless oxidation at the interface The combustion according to the homophase mechanism results from the reaction between the volatile products of thermal decomposition and oxygen with no interfacial surface between reagents 1 2 Generally in polymers their combustion proceeds according to an intermediate mechanism with visible features of homophase and heterophase combustionsThe combustion of elastomers is a complex process that depends on the chemical constitution and physical structure of macromolecules as well as on the chemical reactions and physical phenomena taking place in the sample under testing its boundary layer and flameThe diene rubbers used in our studies included cis14polybutadiene SKD II containing 87–93 of cis 14 mers made in Russia BR butadienestyrene rubber KER 1500 containing 235 of styrene from Synthos SA SBR and butadieneacrylonitrile rubber Perbunan 2255VP containing 22 of acrylonitrile from Lanxess NBRThe flammability of elastomers was determined by the method of oxygen index using an apparatus of our own construction 3 For flammability tests samples of dimensions 100 × 10 × 4 mm were prepared Using a constant rate of nitrogen flow amounting to 400 l/h the oxygen flow rate was selected so that a 50 mm sample length burned within time t = 180 s The sample top was ignited for 15 s by means of a gas burner supplied with a propane–butane mixture 4 5 6 The value of oxygen index OI was expressed in fractions on the basis of the oxygen volume fraction in the oxygen–nitrogen mixtureThe determinations of flammability in air were also performed measuring the combustion time of samples whose shape dimensions and location as well as ignition time were the same as those in the case of the oxygen index method 4 5 6 It was quite difficult to prepare shaped samples for flammability measurements due to their adhesion to the metal mold but this problem was solved by subjecting the elastomers tested to slight crosslinking by means of dicumyl oxide

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