Sterilization-Irradiation

Sterilization is an important process that involves a major market for the use of plastics in packaging. The most common methods of sterilization are those using heat, steam 

Sterilization is an important process that involves a major market for the use of plastics in packaging. The most common methods of sterilization are those using heat, steam (autoclaving), radiation, and gas (EtO—ethylene oxide) (see Tables 4-5 and 4-6). Unfortunately, each of these methods has its limitations. There are, however, plastics that do meet performance requirements based on the various different processes, including radiation. 

Lx)ses 40% of its tensile strength, crumbles at higher doses Loses elongation properties rapidly, tensile strength remains Serious deterioration Deterioration beginning Loses its elasticity 

Threshold mechanical damage becomes weak and brittle Little effect 

Loses 25% mechanical properties electrical properties unaffected 

Resistivity temporarily changed, but few other effects noted 

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RADIATION PRESERVATION OF FOOD (COLD STERILIZATION IRRADIATION RAD APPERTIZATION RADICIDATION RADURIZA-TION) ... 

Irradiation. Although no irradiation systems for pasteurization have been approved by the U.S. Food and Dmg Administration, milk can be pasteurized or sterilized by P tays produced by an electron accelerator or y-rays produced by cobalt-60. Bacteria and enzymes in milk are more resistant to irradiation than higher life forms. For pasteurization, 5000—7500 Gy (500,000—750,000 tad) are requited, and for inactivating enzymes at least 20,000 Gy (2,000,000 rad). Much lower radiation, about 70 Gy (7000 tad), causes an off-flavor. A combination of heat treatment and irradiation may prove to be the most acceptable approach. 

The objective in packaging cool sterilized products is to maintain the product under aseptic conditions, to sterilize the container and its Hd, and to place the product into the container and seal it without contamination. Contamination of the head space between the product and closure is avoided by the use of superheated steam, maintaining a high internal pressure, spraying the container surface with a bactericide such as chlorine, irradiation with a bactericidal lamp, or filling the space with an inert sterile gas such as nitrogen. 

Polybutene can be cross-linked by irradiation at ambient temperature with y-rays or high energy electrons in the absence of air. The performance of articles manufactured from polybutene is only slightly affected by ionizing radiation at doses below 30 kGy (3 Mrad) (26). PMP is also relatively stable to P-and y-radiation employed in the sterilization of medical suppHes (27). 

Tinplate Containers for Packaging Irradiation-Sterilized Foods... 

At first, the program which investigated the packaging of irradiation-- processed foods, concentrated on the most advanced type of container, the tinplate can. It had performed successfully for a century as a container for thermoprocessed foods. However, as a container for the irradiation-processed foods, its physical, chemical, and protective characteristics had to be evaluated, including the effects of radiation on enamels and end-sealing compounds. This container was satisfactory for packaging foods that were irradiation sterilized while unfrozen (1, 2). 

A performance test of cans of irradiation-sterilized meat products (3). 

The metallurgical experiments showed that the beta-alpha transition of the tin coating did not occur at irradiation doses of 3-5 Mrad and 6-7.5 Mrad at 5, —30, and —90°C and that the tensile properties, impact ductility, peel strength of soldered lap joints, and microstructure of commercial tinplate and solder were not affected by the irradiation conditions that are used in the sterilization of meat products. 

The production test showed that the epoxy phenolic enamel was the preferred enamel for coating tinplate containers used in packaging irradiation-sterilized ham and beef. The preferred end-sealing compound for the same application was the blend of cured and uncured isobutylene-isoprene copolymer. 

Macerated femora from modern marten Martes martes, an omnivorous mustelid) were cut into pieces, sterilized by irradiation at 25kgy (kilograys)... 

While the minimum irradiation dose (MID) to achieve a 10" probability of sterility assurance may be calculated by Eq. (2) ... 

Such sterilization procedures (see also Chapter 20) may include heat treatment, filtration, irradiation, recrystallization flxm a bactericidal solvent such as an aleohol, or for dry products where eompatible, ethylene oxide gas. If the raw material is only a minor constituent and the final product is adequately preserved either by lack of chemically... 

In the case of injectables and ophthalmic preparations which are manufactured aseptically but do not receive a sterilization treatment in their final container the packaging has to be sterilized. Dry heat at 170°C is often used for vials and ampoules. Containers and closures may also be sterilized by moist heat, chemicals and irradiation, but consideration for the destruction or removal of bacterial pyrogens may be necessary. 

Recent sterilizer developments have led to the use of dry-heat sterilizing tunnels where heat transfer is achieved by infra-red irradiation or by forced convection in filtered laminar airflow tunnels. Items to be sterilized are placed on a conveyer belt and pass through a high-temperature zone (250 - 300 + °C) over a period of several minutes. 

The optimum wavelength for UV sterilization is around 260 nm. A suitable source for UV light in this region is a mercury lamp giving peak emission levels at 254 nm. These sources are generally wall- or ceiling-mounted for air disinfection, or fixed to vessels for water treatment. Operators present in an irradiated room should wear appropriate protective clothing and eye shields. 

Sandoli RL, WC Ghiorse, EL Madsen (1996) Regulation of microbial phenanthrene mineralization in sediment samples by sorbent-sorbate contact time, inocula and gamma irradiation-induced sterilization artifacts. Environ Toxicol Chem 15 1901-1907. 

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