Abstract
AbstractAn apparatus for determination of regression (weight‐loss) rates before, at, and after ignition as a function of oxidant gas flow rates has been constructed and successfully operated with poly(methyl methacrylate). In addition, flame temperatures, gas evolution kinetics and composition can be ascertained. The apparatus allows a proper evaluation of diffusion processes and chemically controlled processes. The regression rate for PMMA is directly proportional to the air flow rate. At low air flow rates the process is diffusion controlled and the energy of activation is identical with the heat of vaporization of the monomer. There is a liquid monomer layer and on top of it a stagnant vapor layer having the equilibrium vapor pressure of the monomer. At higher flow rates the energy of activation increases steeply. The layers become thin and defective and eventually thermal depolymerization becomes rate determining. This depolymerization has an energy of activation between 30 to 40 kcal mol−1. Experiments have also been carried out in closed quartz tubes. Explosion limits, ignition lags and energies of activation have been determined. The latter were evaluated by the method of Semenoff.
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