Here is a little info on the topic. It is directed at the effect of radiation on plastic, but it is obvious that there could potentially be harmful affects to other chemicals as well. What is really interesting is that electron beams only penetrate to about 2 inches. So long as the gear is deeper than two inches inside the package, it shouldn't affect it. I think the idea is to treat mostly letters because people are much more cautious about opening an unknown package than they are envelopes. Anyway here it is:
Radiation: Radiation means exposing ware to be sterilized to an ionizing radiation source. Ionizing radiation knocks electrons off atoms it contacts. Ionizing radiation is lethal to micro-organisms because of its destructive effect upon the contents of living cells. There are two common sources of ionizing radiation used for sterilization:
Cobalt60 (gamma radiation) OR
Electron beam or E-beam (high energy electrons)
The amount of radiation from either Cobalt60 or electron beam is measured in MegaRads (MRads) or KiloGrays (KGy). One Megarad equals ten KiloGrays. Because E-beam and gamma sterilization both use radiation, packaging materials react similarly in both systems. Cobalt60 Gamma Radiation: A gamma radiation sterilization facility is expensive so this technique is usually performed by a contract sterilizer. The facility consists of a very thick walled concrete maze and room built around a well containing water. In the well are a number of pencil-sized steel rods, impregnated with Cobalt and made radioactive by exposure to an atomic reactor. The articles to be sterilized are placed on conveyors that bring them through the protective concrete maze into the room where the radioactive rods are located. The amount of radioactivity to cause sterilization is controlled by the number of rods raised from the well and the exposure time. After exposure, ware is conveyed from the room via the maze.
A radiation dose sufficient to kill bacteria and the most resistant spores is 2.5 MRads. But, to keep costs down and minimize radiation exposure, companies will determine bioburden then find the minimum dosage plus a safety factor to attain sterilization.
Gamma radiation has high penetrating power (about 50 cm or close to 20 inches of the same unit-density material). Because of this, a large number of small parts can be packed together for sterilization. In this instance, companies are sure to have the validated sterilization dosage reach the center of the ware multi-pack. This means that slightly higher dosages occur on the ware at the very outside edges of the ware multi-pack.
Usually, empty packaging components are sterilized via gamma radiation therefore, the effect of the dose on the plastic material used to make the ware is important. Companies may determine the effect of radiation on ware at the level used for sterilization. Since the effects of radiation exposure are cumulative, twice the normal sterilization dose is sometimes examined to be sure no problems will occur.
Typically, thermoplastic materials that can be gamma radiation sterilized without problems are:
Low Density Polyethylene
Linear Low Density Polyethylene
High Density Polyethylene (those containing phosphite stabilizers may yellow)
Polyethylene Terephthalate
Polystyrene
Polycarbonate
Nylon
Typically, thermoset and rubber materials that can be gamma radiation sterilized without problems are:
Phenol formaldehyde
Urea formaldehyde
Natural rubber
Nitrile rubber
Important Notes:
Special radiation resistant grades of polypropylene are needed for gamma sterilization. Polypropylene fares poorly upon radiation exposure. Normal PP grades yellow noticeably and exhibit long term embrittlement when sterilized via radiation techniques. Special radiation resistant PP grades, having special stabilizers, are available for radiation sterilization. Also, PP copolymers are more radiation resistant than PP homopolymers.
Problems can occur when gamma radiation sterilizing polyvinyl chloride (PVC) or fluoropolymers (Teflon, etc.)
Note: We do not anticipate problems when sterilizing ware via electron beam. But, we do not have experience with all conditions and criteria each customer judges ware to be acceptable. We will happily provide samples for exposure to the conditions of interest and your determination of ware meeting your performance criteria. The following guidelines should be considered for questions on gamma radiation sterilizing ware made from polypropylene:
A radiation grade of polypropylene should be used to manufacture ware that is to be exposed to gamma radiation. If polypropylene ware is made from a radiation resistant grade of polypropylene, we do not anticipate problems when sterilizing it in this manner. However, we do not have experience with conditions and criteria by which each customer judges ware to be acceptable. We will happily provide samples for exposure to the conditions of interest and your determination of this ware meeting your performance criteria.
Electron Beam (E-Beam Radiation
An E-beam radiation sterilization facility is expensive so this technique is usually performed by a contract sterilizer. The facility consists of a protective maze built around an E-beam generator. The E-beam generator delivers a high dose of electrons in a narrow beam at the items to be sterilized. After exposure, ware is conveyed from the room.
A radiation dose sufficient to kill bacteria and the most resistant spores is 2.5 MRads. But, to keep costs down and minimize radiation exposure, companies will determine bioburden then find the minimum dosage plus a safety factor to attain sterilization.
Electrons from the E-beam generator have limited penetrating power (a 10-MeV E-beam will penetrate only about 5 cm or 2 inches of a unit-density material). Because of this, only a small number of parts can be packed together for sterilization. When this is done, companies must be sure to have the validated sterilization dosage reach the center of the ware multi-pack. This means higher dosages occur on the ware at the very outside edges of the ware multi-pack.
Usually, empty packaging components are sterilized via E-beam therefore, the effect of the dose on the plastic material used to make the ware is important. Companies may determine the effect on ware at the level used for sterilization. Since the effects are cumulative, twice the normal sterilization dose is sometimes examined to be sure no problems will occur. Typically, thermoplastic materials that can be E-beam sterilized without problems are:
Low Density Polyethylene
Linear Low Density Polyethylene
High Density Polyethylene (those containing phosphite stabilizers may yellow)
Polyethylene Terephthalate
Polystyrene
Polycarbonate
Nylon
Typically, thermoset and rubber materials that can be E-beam sterilized without problems are:
Phenol formaldehyde
Urea formaldehyde
Natural rubber
Nitrile rubber
Important Notes:
Special radiation resistant grades of polypropylene are needed for E-beam sterilization. Polypropylene fares poorly upon E-beam exposure. Normal PP grades yellow noticeably and exhibit long term embrittlement. Special PP grades, having special stabilizers, are available for E-beam sterilization. Also, PP copolymers are more resistant than PP homopolymers.
Problems can occur when E-beam sterilizing polyvinyl chloride (PVC) or fluoropolymers (Teflon, etc.)
Note: We do not anticipate problems when sterilizing ware via electron beam. But, we do not have experience with all conditions and criteria each customer judges ware to be acceptable. We will happily provide samples for exposure to the conditions of interest and your determination of ware meeting your performance criteria.
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