WHEATON 2015 Lab Catalog

WHEATON

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Steam Autoclave (Cont.)

If empty ware becomes distorted due to autoclave sterilization, it may be due to:

■

High stresses molded into the ware during manufacture

■

Unusual hot spots in the autoclave

■

Use of the wrong plastic

Tests should always be run on plastic ware to determine suitability for a given sterilization

method.

Autoclaving Filled, Sealed Ware

Autoclave sterilization of filled, sealed ware, is also known as “Terminal Sterilization”.

Many companies prefer terminal sterilization IF their product can withstand the rigors.

Autoclave temperature must be minimally 121°C (250°F). Of the common plastics,

polypropylene (PP) and polycarbonate (PC) have enough heat resistance to be autoclaved.

Also, there is a grade of a new transparent plastic material identified as a cyclic olefin

copolymer (COC) that is capable of withstanding steam autoclave sterilization. However,

autoclaving filled, sealed plastic ware is tricky. Temperature and pressure in the autoclave

must be controlled and balanced with temperature and pressure being generated in

the filled, sealed ware during autoclave heat up AND cool down. If not, ware could be

crushed or ballooned. Special autoclaves are sold to enable this temperature / pressure

balancing act.

If filled, sealed containers become distorted during autoclave sterilization. This may be

due to:

■

Improper balancing of temperature / pressure upon heating or cooling

■

High stresses molded into ware at the time of manufacture

■

Unusual hot spots within the autoclave chamber

■

Use of the wrong plastic

Tests should always be run on plastic ware to determine suitability for a given

sterilization method.

Autoclaving Closures

Polypropylene (PP) closures should be capable of withstanding steam autoclave

sterilization. However, autoclaving may cause blooming of additives in PP. PP homopolymer

is more heat resistant than PP copolymer. Linerless closures (closures with specially

molded-in sealing features) may or may not be acceptable for autoclaving dependent on

many factors (e.g. as application torque, autoclave conditions, closure design, etc.) If a

closure is lined, the liner and the adhesive used to affix the liner inside the closure must

also be considered. Lastly, PP closures applied to containers present a special case.

Closures are designed with tolerances that cause interference between the closure and

container. This interference results in stress. Since all thermoplastics become softer as

temperature increases, stress may be relieved or closure dimensions may change upon

autoclaving. This can result in closure torque reduction or seal loss.

If closures distort or a torque retention problem results, it may be due to:

■

High stresses molded into ware at the time of manufacture

■

Unusual hot spots within the autoclave chamber

■

Use of the wrong plastic

Due to moisture absorption, pulp liners are NOT anticipated to be acceptable for

autoclaving.Tests should always be run on plastic ware and liner / adhesive combinations

to determine suitability for a given sterilization method.

Radiation

Ware is exposed to ionizing radiation that knocks electrons off atoms it contacts. Ionizing

radiation is lethal to microorganisms because of its destructive effect upon the contents

of living cells. There are two common sources of ionizing radiation used for sterilization:

■

Cobalt 60 (gamma radiation) OR

■

Electron beam or E-beam (high energy electrons)

The amount of radiation from either Cobalt 60 or electron beam is measured in

MegaRads (MRads) or KiloGrays (KGy). One MegaRad equals ten KiloGrays. Because

gamma sterilization and E-beam both use radiation, packaging materials react similarly

in both systems.

Cobalt 60 Gamma Radiation

A gamma radiation sterilization facility consists of a thick walled concrete maze in a room

built around a well filled with water. In the well are a number of pencil-sized steel rods

impregnated with radioactive Cobalt. Articles to be sterilized are placed on conveyors

that bring them through the concrete maze into the room where the radioactive rods

are located. The number of rods raised from the well and the exposure time controls

the degree of exposure. After exposure, ware is conveyed from the room via the maze.

A radiation dose sufficient to kill bacteria and spores is about 2.5 MRads. To minimize

costs plus attain sterilization, bioburden is determined then the minimum dosage plus a

safety factor is selected.

Gamma radiation has high penetrating power (about 50 cm or close to 20 inches of the

same unit-density material). Thus, many parts can be packed together for sterilization. In

this instance, the dosage reaching the center of ware multi-packs is validated. Slightly

higher doses occur at the outside edges of multi-packs.

Usually, empty packaging components are sterilized via gamma radiation. Since effects

of radiation are cumulative, twice the normal dose is sometimes examined to insure

minimal problems.

Listed below are thermoplastic materials that are recognized as capable of being

gamma radiation sterilized, although tests should always be run on plastic ware to

determine suitability for a given sterilization method:

■

Low Density Polyethylene

■

Linear Low Density Polyethylene

■

High Density Polyethylene (those containing phosphite stabilizers

may yellow)

■

Polyethylene Terephthalate

■

Polystyrene

■

Polycarbonate

■

Nylon

■

Cyclic Olefin Copolymers (a newly emerging group of polymers)

■

Polyethylene Naphthalate (a newly emerging group of polymers)

Problems can occur when gamma radiation sterilizing polyvinyl chloride (PVC) or

fluoropolymers (PTFE, etc.).

Important Note About Polypropylene Gamma

Radiation Sterilization

Normal PP grades yellow noticeably and exhibit long term embrittlement when sterilized

via gamma radiation techniques. Special radiation resistant PP grades, having special

stabilizers, are available for radiation sterilization. Also, if ware is to be colored, then the

concentrate carrier should be a radiation resistant grade of PP. PP copolymers are more

radiation resistant than PP homopolymers. Tests should always be run on plastic ware to

determine suitability for a given sterilization method.

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Technical Data, Plastic