The influence of polypropylene fibers on the thermal degradation of epoxy composites was investigated with thermogravimetric analysis. Three composites with 5, 10, or 15 wt % polypropylene fibers were prepared with epoxy as a matrix material. The polypropylene fibers, used as reinforcing materials, retarded the thermal decomposition, and increasing the weight percentage of the fiber material increased the thermal stability to a certain extent. Of the three composites, the 10 wt % polypropylene fiber/epoxy resin composite showed very good thermal stability, which was indicated by the increase in the resin decomposition temperature from 280 degrees C for the 5 wt % polypropylene fiber/ epoxy resin composite to 375 degrees C for the 10 wt % polypropylene fiber/epoxy resin composite. The Horowitz-Metzger method was used to calculate the activation energies, and the results were tabulated. A morphological analysis was carried out with scanning electron microscopy to evaluate the dispersion of the fibers in the epoxy matrix. (c) 2007 Wiley Periodicals, Inc.