Thermal oxidation kinetics for a poly(bismaleimide)

Abstract

Abstract The thermal oxidation of poly(bismaleimide) of the F655‐2 type, supplied by Hexcel‐Genin, was studied by isothermal gravimetry at 180, 210, and 240°C and various oxygen pressures ranging from 0 to 1.2 bar. Comparison of various sample thicknesses and visible microscopy observations on bulk aged samples shows that the whole oxidized layer has a depth of about 75 μm at 240°C, 138 μm at 210°C, and 229 μm at 180°C. An attempt was made to build a kinetic model to predict this depth. It is based on a differential equation in which O 2 diffusion and its consumption rate, r(C), are coupled, C being the O 2 concentration. Its resolution needs two sets of experiments: the first one to determine the O 2 diffusivity and solubility in the polymer, and the second one to determine r(C). The mathematical form of r(C) is derived from a mechanistic scheme of radical chain oxidation in which initiation is mainly due to POOH decomposition. This expression contains two kinetic parameters, α and β, the values of which are determined from the experimental curves of mass loss rate against O 2 pressure (in the stationary state). The theoretical predictions, at each temperature under consideration, are in excellent agreement with experimental results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3418–3430, 2001