Thermal decomposition of natural polystyrene, recycled plastics, low density polyethylene, acrylonitrile butadiene styrene, polyenterophthalate of ethylene, and polypropylene has been carried out. Both isothermal and dynamic experiments at different heating rates have been performed in a thermobalance with the objective of determining the kinetic parameters. Also, a first set of experiments, performed in a cylindrical stainless-steel atmospheric pressure reactor, was designed to evaluate the products of the pyrolysis process. The effects of N-2 flow rate (200-300 cm(3) min(-1)), initial mass fed to the reactor (1575 mg), temperature (415-490 degrees C), and heating rate (5-30 K min(-1)) were studied. By application of a first order kinetic model, the activation energy for every plastic has been determined. The values of activation energy in isothermic and dynamic regimen are the following: natural polystyrene: 136, and 168 to 286 kJ/mol. Recycled plastic: 250, and 150 to 290 kJ/mol. Low density polyethylene: 285, and 220 to 259 kJ/mol. Acrylonitrile butadiene styrene: 118, and 104 to 251 kJ/mol. Polyenterophthalate of ethylene: 161, and 117 to 255 kJ/mol. Polypropylene: 169, and 153 to 265 kJ/mol. (C) 2008 Elsevier B.V. All rights reserved.