Ignition of poly(methyl methacrylate) slabs using a small flame

When exposed to a lean hydrogen-oxygen flat flame, slabs of poly(methyl methacrylate) ignited to flaming combustion after a delay, the length of which depended on the gas temperature and the separation between the slab and the igniting flame. The delay obeyed an Arrhenius-type expression, giving an activation energy of 96 plus or minus 8 kJ mol[-1 1]. By the end of the delay the surface of the sample was pitted if the delay was long and almost unchanged if the delay was short. The rates of flame development measured immediately after the ignition were proportional to the ignition delay, the proportionality constant varying with the separation between slab and flame. These rates decreased as temperature increased; the slope of the linear Arrhenius plots was independent of slab-flame separation. During the delay, carbon dioxide was formed within the boundary layer and a blue preignition glow was visible at its outer edge. These data were explained by a model in which ignition delay is governed by the induction period of gas-phase reactions in or near the boundary layer. Models in which delay is governed by the time taken to heat the polymer to a critical ignition temperature did not satisfactorily explain the data.Lorsqu'on expose \ue0 la flamme plate et allong\ue9e d'un m\ue9lange oxyg\ue8ne-hydrog\ue8ne des plaques de poly (m\ue9thacrylate de methyle), elles s'enflamment apr\ue8s un laps de temps qui d\ue9pend de la temp\ue9rature du gaz et de leur distance de la flamme. Le laps de temps peut s'exprimer par une loi du type Arrhenius donnant une \ue9nergie d'activation de 96 + ou - 8 KJ. mole[-1]. A la fin de l'essai la surface de l'\ue9chantillon \ue9tait piqu\ue9e, si le d\ue9lai d'inflammation \ue9tait long, et presque identique si le d\ue9lai \ue9tait court. La propagation des flammes mesur\ue9e imm\ue9diatement apr\ue8s l'inflammation \ue9tait proportionnelle au d\ue9lai d'inflammation, la constante de proportionnalit\ue9 variant selon la distance s\ue9parant la plaquette de la flamme. Ces valeurs diminuaient au fur et \ue0 mesure que la temp\ue9rature augmentait; la pente des courbes d\ue9duites de l'\ue9quation d'Arrhenius \ue9tait ind\ue9pendante de la distance entre la plaquette et la flamme. Avant l'inflammation, de l'anhydride carbonique se formait \ue0 l'int\ue9rieur de la plaquette et une lueur bleue de pr\ue9-inflammation \ue9tait visible sur l'ext\ue9rieur des bords. Ces observations s'expliquent \ue0 l'aide d'un mod\ue8le dans lequel le d\ue9lai d'inflammation d\ue9pend de la p\ue9riode d'induction des r\ue9actions en phase gazeuse dans les couches ext\ue9rieures ou \ue0 proximit\ue9 de celles-ci. Les mod\ue8les o\uf9 le d\ue9lai d'inflammation d\ue9pend du temps de r\ue9chauffement du polym\ue8re jusqu'\ue0 une temp\ue9rature critique d'inflammation ne correspondaient pas suffisamment aux observations.Peer reviewed: YesNRC publication: Ye