The pyrolysis of polyolefin wastes is one of the possible ways to obtain chemical feedstocks. In this work, the thermal degradation of low density polyethylene, (LDPE), which is a major product within plastics, was investigated in a semi-batch reactor system. First-order rate kinetics approach was chosen and reaction rate coefficients, k, and some thermodynamic quantities determined such as activation energy, reaction enthalpy, free activation enthalpy, and entropy of degradation of LDPE for different air flow rates. We found that the maximum value of some thermodynamic quantities, such as reaction rate coefficient is 0.0243 min(-1) at 600 mL min(-1) air now rate and the free activation enthalpy (Delta G(not equal)) is 148.66 kJ mol(-1) at 450 mL min(-1) air flow rate and the reaction enthalpy (Delta H(not equal)) is 57.65 J mol(-1) at 623 K temperature conditions. Moreover, we found that the oxidative degradation of LDPE is not spontaneous and has lower energy necessary (for degradation) than non-oxidative degradation processes. (C) 2008 Elsevier B.V. All rights reserved.