Microorganisms on components should be killed through sterilization in order to ensure the safe use of medical products for patients. Therefore, polymer parts are treated particularly with gamma radiation, ethylene oxide, or superheated steam; such treatment may result in a modified structure or the degradation of the polymer. The present paper shall demonstrate how the mechanical properties of tension bars and welded samples of polypropylene and polycarbonate change during the sterilization procedure. The resulting changes in the structure and the degradation respectively will be analyzed by Fourier transform infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) and structural property relationships shall be derived. The conducted analyses showed that the changes in the mechanical properties depend on the sample, the sterilization procedure, and the corresponding polymer; and that those changes must be considered when designing the respective products. (C) 2016 Society of Plastics Engineers