DIFFERENCES AND SIMILARITIES IN THE THERMOOXIDATIVE DEGRADATION OF POLYAMIDE-46 AND POLYAMIDE-66

A comparison is made between the thermooxidative degradation of polyam ide 46 (PA46) and polyamide 66 (PA66), using oven ageing, oxygen uptak e and viscosity measurements on the two polymers. Model experiments we re used to determine the degradation mechanism of PA46. Although on a chemical basis it is expected that PA46 would be less stable than PA66 , the opposite is found. The time until the tensile strength becomes 5 0% of its initial value is twice as long for unstabilized PA46 compare d with PA66 at 145 degrees C. It is shown that the degradation of PA46 is a surface phenomenon and thus oxygen diffusion limited. PA46 is mo re stable than PA66 due to its lower oxygen permeability, probably cau sed by its higher crystallinity and density of the amorphous phase.