Heightening of radiation resistance of plastics for medical use

There are high pressure steam process, ethylene oxide gas process and Co-60 gamma ray irradiation for the sterilization of medical appliances. At present, ethylene oxide gas process is the main method, but there are the problems of residual gas and the unsterilized parts in the appliances of complex shapes. Also the residual gas concentration in working environment is strictly regulated because of its toxicity, therefore, the change to Co-60 gamma ray or electron beam sterilization is considered. In this paper, the examination on the additives for improving the radiation resistance of the polypropylene and polyvinyl chloride used for medical appliances is reported. Polypropylene is used most as the material for medical appliances in Japan. Under the irradiation condition in the air, it causes decay at 2.5 Mrad, and the physical properties begin to lower. As the result of experiments, monoalkyl diphenyl ether has the effect of heightening the radiation resistance of polypropylene. Polyvinyl chloride is excellent in its workability, and is cheap, therefore, it is used for various medical appliances. However, it causes coloring by gamma ray sterilization. As the result of experiment, the addition of monoalkyl diphenyl ether suppressed the oxidation of polyvinyl chloride, therefore even after one year, the effect of its addition was observed. (K.I.)