Abstract
The spontaneous ignition behaviour of both uncontaminated and oil contaminated cotton fabric has been investigated by using differential thermal analysis (DTA) and evolved gas analysis (EGA) techniques. The temperature, at which the onset of spontaneous ignition T i occurs, was recorded as a function of the oxygen concentration of the flowing oxygen-nitrogen atmosphere to which the fabric materials wer exposed in the DTA furnace, when heated at different heating rates. The activation energy of pyrolysis E p was obtained according to a simple kinetic model derived by Horrocks et al, as follows In(Hr/T 1 2 )=- E p/R(1/Ti)+In A p -In( E p- E ox/R= where E ox is the activation energy of gaseous product oxidation. Plotting of 1/T i vs In [O 2 ] produces true linear regions which intersect at a certain oxygen concentration and have slopes equal to (E ox -E p )/m. Taking the minimum and maximum E p value, and estimating the slopes of the two regions, the value of the molar oxygen concentration m required for the oxidation can be estimated for both untreated and oil contaminated fabrics. The results showed that E p decreased as the oil content in the fabrics was increased. It is probable that the oxidation of the oils generates free radicals, which catalyse the pyrolysis reaction of the cellulose. The movement of the point of intersection of the 1/T i vs In [O 2 ] due to oil concentration increase, and may explain the observed decrease in E ox value with increasing oil concentration. The results also showed a simultaneous increase in the number of oxygen molecules required for combustion as the oil concentration increased, reflecting the sensitivity of the combustion mechanism to oxygen concentration. The evolved gas analysis measurements indicated a diminishing of the dehydration reaction when the fabric was contaminated with oil, therefore suggesting domination of the depolymerization route of reaction.
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