Polyolefins are finding increased usage in medical applications because of their inertness and excellent chemical resistance. Some of the medical products are expected to be sterilized by either of the two processes : *Autoclaving; where the material is expected to withstand temperatures of more than 121 degree C for at least 20-30 minutes or
Gamma irradiation; generally gamma irradiation involves dosage of about 50kGy.

For the products that are autoclaved, Polypropylene(PP), because of higher heat deflection temperatures, is more suitable than Polyethylenes. Among Polypropylenes, homopolymer grades have the highest heat deflection and are therefore more suitable compared to copolymers. On the other hand, PP, because of its tertiary Methyl group, is less resistant to high-energy gamma irradiation. Polythylenes, particularly HDPE and LDPE are thus more suitable. When PP is exposed to gamma irradiation it develops a yellowish colour and also tends to become brittle. Resistance can be enhanced by incorporation of Ethylene groups in PP. In fact, both random PP copolymer and impact copolymer provide better gamma resistance compared to homopolymer. PP copolymers alone are not able to provide sufficient resistance to gamma irradiation and are formulated with special additives for improvement of �resistance. PP is required to be stabilized with antioxidants at higher levels to prevent chain scission.

>Generally antioxidants are based on hindered Phenols. These Phenols develop yellowish colour when exposed to the Gamma irradiation. These hindered Phenols should therefore not be used. Instead, HALS and Phosphites/Phosphonites should be used to improve the Gamma irradiation resistance. While monomeric HALS may be suitable, polymeric HALS with FDA approval perform better and should be used to improve the performance of PP. To further enhance resistance, a blend with PE or advanced Polyolefins like Metallocene based PE with higher content of Octene comonomer should be considered. Higher molecular weight of the advanced Polyolefins would provide better resistance. However, typically, material with 1 MFR at about 5-20% levels can enhance the gamma irradiation resistance. Some of the leading suppliers of PP like Borealis supply PP grades for the Gamma irradiation sterilization techniques.

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