The thermoanalytical method offers a convenient means for testing a starting material before the end application. Differences in the kinetic parameters between neat and irradiated nylon 66 samples were estimated in the temperature range of 25degreesC-800degreesC by thermogravimetric analysis (TGA) and in the range of 25degreesC-300degreesC by differential scanning calorimetry (DSC). Under nitrogen flux the average activation energy for decomposition was in the range of 12.2-26.9 kcal/mol for the neat sample and 15.7-33.1 kcal/mol for the irradiated sample (250 h). Activation energy is affected by the process of bond breaking at the C-N bonds, which is the rate-determining step of the decomposition in nylon 66. (C) 2003 Wiley Periodicals, Inc.