Radiation sterilisation

PE has considerable better radiation resistance than PP due to the absence of the tertiary carbon atom which initiates degradation of the material and loss of the mechanical properties. 

Irradiated PP has been used as a plant wrapping which gradually degrades in the soil. These wrappings are suitable for both manual and machine planting of forests and fields. 

PP can encounter radiation from various sources when used in the nuclear industry. Gamma radiation, used for medical sterilisation, is far more penetrating than beta, electron radiation or alpha radiation. The radiation dosage level harmful for PP is quite low. Hence, use of PP in the nuclear industry where high radiation occurs is not possible. Suitable resins for use in nuclear industry include phenolics, polystyrene, polyester, particular epoxies, silicone, etc. 

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Garrison, W.M. (1981). The radiation chemistry of amino acids, peptides and proteins in relation to the radiation sterilisation of high-protein foods. Radiat. Effects 54, 29-40. 

Following the favourable response of this committee, steps were taken to amend the existing UK legislation which permitted only the radiation sterilisation of foods for people whose immune response was compromised. New regulations came into force in early 1991 which permitted the irradiation of seven groups of foods under strictly controlled conditions (Anon., 1990a) (Table 1). 

RADIATION STERILISATION COMPATIBILITY OF MEDICAL PACKAGING MATERIALS... 

The various elements of the ISO standards for a validation programme of a radiation sterilisation process are shown in Fig. 6.11. 

Radiation sterilisation of microbial-laden water is a possible method of... 

Radiation sterilisation is used mainly for the sterilisation of heat sensitive materials and products. Many medicinal products and some packaging materials are radiation-sensitive, so this method is permissible only when the absence of deleterious effects on the product has been confirmed experimentally. Ultraviolet irradiation is not normally an acceptable method of sterilisation. 

Appropriate validation studies for radiation sterilisation should be conducted. (See also Contract Sterilisation.)... 

Chemical indicators are available for heat, ethylene oxide and radiation sterilisation, usually in the form of adhesive tapes or patches, colour spot cards, small tubes or sachets. They change colour as a result of chemical reaction brought about by the sterilisation process, but it is possible for the change to take place before the sterilising time has been completed, and hence, with the exception of plastic dosimeters used in radiation sterilisation, they are unsuitable as proof of sterilisation. 

Radiation-sensitive colour discs, not to be confused with plastic dosimeters, are used to differentiate between packages which have been subjected to irradiation and those which have not They are not indicators of successful sterilisation, and the monitoring of radiation sterilisation by calibrated plastic dosimeters is the only way of ensuring that the sterilising dose has been given. 

Radiation sterilisation is used mainly for sterilisation of heat sensitive materials and products. 

Sterilisation by means of ionising radiation of pharmaceutical preparations is not allowed in a number of countries. Many active substances and raw materials are decomposed by the doses required for sterilisation. Some polymers become brittle and glass may become discoloured. For these reasons there is only limited application for this sterilisation method for pharmaceutical preparations. Radiation sterilisation is however widely used in the medical device industry. 

Ionising radiation sterilisation an absorbed radiation dose of at least 25 kGy. This method leads to breaks in the DNA of micro-organisms and, in presence of water, the formation of free radicals. 

Gas sterilisation is performed with ethylene oxide or hydrogen peroxide gas. Sometimes peracetic acid is used, but this method is too specialised to mention here in detail. In the past (fi-om 1940) formaldehyde was used as well, but this method is rarely used anymore. Gas sterilisation is used for sterilisation of medical devices and of surfaces of pharmaceutical containers where the contents are too sensitive to the high temperature of steam sterilisation and/or cannot withstand radiation sterilisation. 

Silicone rubber is often used in medical devices as it offers good flexibility, a degree of softness (for face masks, etc.) and good resistance to both EtO and gamma radiation sterilisation processes. Silicone rubber can be bonded with the aid of a primer (see Section 10.6). 

As PE is a popular material for disposable medical devices, considerable effort has been applied to assess its response to radiation sterilisation. In experiments up to 75 and 200 kGy, it has been reported that most mechanical properties improve with radiation exposure. Slight discoloration due to phenolic-based antioxidants and particularly in combination with HAS was one detrimental aspect observed. Radiation resistance is measured by changes in properties. Bulk properties such as HDT and failure by yielding will be insensitive to surface degradation and will therefore imply high radiation resistance. Tensile properties are less sensitive to surface degradation than flexural ones. 

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