Sterilization and Radiation Resistance

Different POs respond differendy to radiation treatments. PEs (particularly LDPE) can withstand higher total doses of radiation than PPs and many other polymers. A PE s strength and impart properties may even increase from the crosslinking mechanism initiated by the radiation. By contrast, homopolymer PP must be sufficiently stabilized to prevent chain-sdssion and losses in tensile properties, if it is to be used in aitides such as syringes. Fortunately, POs, which are more often used for disposable, one-time-use items, often only need to withstand one or two irradiation treatments during their short lifetimes [3-4, 16-2, 16-3, 16-4, 16-5]. 

Various factors have been proposed as increasing the impact of gamma radiation, X-ray, or e-beam treatments on PO products  

EtO gas sterilization has declined in use because of its overall toxicity to operators, and polymers reactivity wdth (and surface adsorption of) the EtO gas. Testing has shown negative property changes in POs from EtO treatments. For example, repeated treatments have produced a 50% reduction in HOPE tensile modulus, lower dart-impact resistance, and lower ultimate tensile elongation. In similar testing vvdth PP, tensile yield modulus was reduced by 78% after only two EtO exposures [16-3], 

Other kinds of heat-based sterilization are used in food apphcations. For instancy retortable packaging is typically exposed to 120°C for 30 minutes or more in retort sterilization treatments that cook the food inside the package Used for hotels, restaurants, and the military, retortable pouches are made from multilayer films combining layers of POs and other polymers (see Case 16.1) [16-6]. 

As mentioned above extra stabilization is needed in some POs, particularly PP, to prevent induced oxidation and aging from sterilization treatments. Radiation-stabilized materials require a carefiil mix of primary and secondary antioxidants for optimum stabilization. However, given the multiple factors affecting sterilization degradation and the compoimds specialized nature, suppliers often conceal their stabilization formulations as proprietary information. 

---

Sterilization and radiation resistance 16 Growing use of POs in medical applications, radiation-intensive sterilization treatments Better antioxidants and stabilization against radiation... 

---