4. Thermo-chemical-mechanical coupling: thermo-oxidation

Thermo-oxidation mainly affects organic polymers which, when held at high temperatures (from around 120°C, depending on the type of resin), undergo irreversible structural changes associated with their instability and interaction with atmospheric oxygen. Oxidation reaction rates depend on polymer "availability", oxygen concentration and temperature. They may exceed the diffusion rate of oxygen in the polymer. In this case, the oxidation process is diffusion-controlled. For polymers whose oxidation process is diffusion-controlled, if there are enough oxidizable sites, the thickness of the oxidized layer will remain constant, so the diffusion-reaction system is stationary. Observations by optical microscopy show the formation of a fairly thin oxidized layer (of the order of hundreds of micrometers) located near the surface exposed to the environment: the aging process takes place mainly in...