Thermal Oxidation Kinetics for a Poly(bismaleimide)

摘要

The thermal oxidation of poly(bismaleimide) of the F7655-2 type, suppliedby Hexcel-Genin, was studied by isothermal gravimetry at 180, 210, and 240 deg 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 #mu#m at 240 deg C, 138 #mu#m at 210 deg C, and 229 #mu#m at 180 deg C. An attempt was made to 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 adn solubility in the polymer,a dn teh 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, #alpha# and #beta#, 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.