Oxidation of polyethylene in closed mixing chamber

Abstract

The degradation of commercial LDPE was studied under dynamic conditions which simulate the processing. Dynamic oxidation above 140°C is similar to static oxidation under low oxygen pressure both having strong diffusion control. Fragmentation and crosslinking (mainly CC bonds) compete in the process. The hydroperoxides predominate at the beginning of the mixing. Their quantity rapidly decreases while that of oxo groups increases and becomes predominant. Below 140°C, the conditions are resembling to static oxidation performed under higher oxygen pressure but the process is still somewhat diffusion controlled. The change in the molecular mass is not considerable in the process. The hydroperoxides predominate among the functional groups formed. Their ratio is constant during mixing. The effect of mechanical stress is not considerable. An increase in the mixing speed resulted in an increase in the rate of the processes studied above. The higher the total amount of oxygen incorporated in the PE, the smaller is the remaining oxidative stability.