Poly(tetrafluoroethylene) (PTFE) scraps were recovered as a filler material for low-density polyethylene (LDPE) after they were degraded by Co-60 gamma-rays under atmospheric conditions to make small-size powder. The powder PTFE, which was called secondary PTFE (2 degrees-PTFE), was melt mixed with LDPE and then extruded to obtain 200 mu m films. The mechanical and thermal properties and also the morphology of the fractured surface of these 2 degrees-PTFE-filled LDPE were studied. It was found that the addition of 2 degrees-PTFE resulted in thermofilm property of LDPE but it slightly decreased the thermal oxidative temperature of LDPE. The tensile strength and ultimate elongation of LDPE were found to decrease with the addition of 2 degrees-PTFE. However, when it is compared to the addition of virgin PTFE into LDPE, 2 degrees-PTFE shows better mechanical properties due to the presence of oxy groups which are capable of interacting with the main matrix. A further improvement in mechanical properties was achieved by silane coupling agent treatment of 2 degrees-PTFE. Silane coupling agents were found to enhance the interfacial adhesion between 2 degrees-PTFE and LDPE. The study on the fractured surfaces by scanning electron microscope revealed this adhesion between these two polymers. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 866-876, 1999.