Mechanical properties of polymeric packaging films after radiation sterilization

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Title: Mechanical properties of polymeric packaging films after radiation sterilization
Author: Pungthong, Viriya
Abstract: The use of radiation as a sterilization process is increasing. The well-developed technology of the radiation sterilization as applied to medical devices has assured the food industry that the process is reliable. Due to the food industry's possibility of widespread use, it is especially crucial that an appropriate packaging material be chosen so that its integrity is maintained after irradiation. This is because the commercial food packaging process carries products through more rigorous paths and channels than medical supplies. Many polymers used in the medical field show various degrees of degradation after radiation exposure, which can be determined either by visual or physical measurement. This paper studies the mechanical properties of polymeric films after irradiation doses of less than 10.0 Mrads and the extent to which this process causes film degradation. In this study, two mechanical properties will be measured: tensile strength and percentage elongation at break. Eight polymeric films commonly used in the food packaging industry are selected as the material samples. These materials will be irradiated with doses of 2.5, 5.0, 7.0, and 10.0 Mrads to determine cause-effect and dose related effect. Data collected for tensile strength and percentage elongation at break for each sample of one type of film before and after irradiation is analyzed and compared with data collected for other samples. Two primary purposes in undertaking this analysis are (1) to determine if the type of film significantly changes or degrades after irradiation, and (2) to study the relationship between the changes in mechanical properties of each film and the radiation doses of 0.0, 2.5, 5.0, 7.0, and 10.0 Mrads. In the analysis at 0.05 level of significance, polyethylene film (TD-transverse direction) is the only film which did not significantly change in either tensile strength or percentage elongation at break. The polyester/polyethylene film (MD-machine direction) significantly changed in percentage elongation at break although not in tensile strength. The rest of the film samples -PP, OPP, PETG, Polyester/PE(TD), polyester-MYLAR, PE(MD), PE/Nylon and PS film- exhibited significant changes in both mechanical properties after irradiation with doses of 2.5, 5.0, 7.0, and 10.0 Mrads. In the analysis of the degree of relationship between mechanical properties of each film and radiation doses of less than 10.0 Mrads [0.0 (non-irradiated), 2.5, 5.0, 7.0, andlO.O Mrads] found in this study can be catagorized into three types: the dose-dependent, the dose-independent, and the weak correlation. Among three film samples which exhibited the "dose-dependent" relationship, only oriented polypropylene(OPP) film was found to have the correlation between mechanical properties (both tensile strength and percentage elongation at break) and radiation doses; both mechanical properties decreased as the dose increased. Polypropylene (PP) was determined to exhibit the same correlation but only between tensile strength and radiation dose. For polyethylene (machine direction only), this correlation was found only for percentage elongation at break and radiation dose. The rest of the film samples were found to have no correlation between either mechanical property and radiation doses such as that indicated above. They are either "dose-independent" or exhibit a weak relationship between the two variables. For example, the polyester-MYLAR film exhibited obvious "dose-independent" characteristics since both mechanical properties increased significantly from 0.0 to 5.0 Mrads and then decreased at 7.0 Mrads. The films which obviously showed a very weak relationship between the mechanical properties and the radiation doses are two films which exhibited no change in mechanical properties after irradiation in the first study [PE(TD-tensile & percentage elongation) and polyester/PE (MD- percentage elongation)]. The films which exhibited a somewhat weak relationship between the two variables are PS (MD&TD- tensile & percentage elongation) and PE (MD-tensile). These last two films also showed a very small change in the mechanical properties after irradiation although not as small as the films irradiated in the first study.
Record URI: http://hdl.handle.net/1850/11179
Date: 1990

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