IKP and E2 function methods were used to study thermal stability of HDPE–HA nanocomposites synthesized by in situ ethylene polymerization at different volumes of solvent and temperatures. Thermal analysis was carried out at five different heating rates, b = 3, 5, 7, 10, and 13 C/min, under N2 atmosphere. Kinetics parameters calculated by IKP method presented a slight increase on activation energy when HA was incorporated in HDPE. A similar tendency was observed in the results obtained from the E2 function method, where the activation energy of the nanocomposites increased 100 kJ/mol with respect to unfilled polymer (420–460 kJ/mol). These results implied higher stability of HDPE due to HA incorporation. HDPE and HDPE–HA degradation mechanisms are represented by a set of functions, those with the highest probability were: nucleation and nucleus growth (S3) 23 %, reaction order (S5) 16 %, reaction in the interface (S6. S7, S8) 11–14 %, and potential law (S14, S17) 3 %.