Study on discoloration mechanism of polyamide 6 during thermo-oxidative degradation

There is a great difference of opinion on the discoloration mechanism of polyamide in the course of thermo-oxidative degradation. To clarify the exact structure of the chromophore group produced in a polyamide during thermo-oxidation, hydrolysis of the yellow polyamide film after thermo-oxidation was carried out and a yellow substance with low molecular weight was separated from the hydrolysis products by preparative column chromatography and characterized by IR, FAB, MS, UV, (HNMR)-H-1 and (CNMR)-C-13. The structure of the chromophore group in the yellow substance was determined and the structure of the chromophore group in the oxidized polyamide 6 was also inferred. Based on the experimental results obtained, a never discoloration mechanism of polyamide is suggested. According to this mechanism, the discoloration of polyamide during thermo-oxidation was caused by the formation of chromophore alpha-ketoamide groups by oxidation of the methylene group adjacent to the carbonyl of the amide to a carbonyl group. (C) 1998 Elsevier Science Limited. All rights reserved.