Gaseous Ozone Resistance of Materials

Ozone has been widely used to sterilize containers and also working places. Gaseous and aqueous ozone are both used for sterilization. For pharmaceutical packaging, the common method is using gaseous ozone, so here we just discuss the resistance of the materials of pharmaceutical packaging (sprayers and bottles) to gaseous ozone.

Ozone kills microorganisms through oxidization. At the same time, oxidization can also damage the containers. However, the lucky thing is the concentration of ozone for sterilization is much lower than the concentration for materials resistance testing. The concentration of gaseous ozone used for sterilization is less than 100ppm, normally 10 to 20 ppm. The concentration of gaseous ozone for materials resistance testing is at least more than 1000 ppm (normally a few thousands of ppm). Therefore, the concentration of gaseous ozone during sterilizing can not damage the whole body of packaging’s material. At most, it just damages the surface with rarely detected level.

Below is the list of resistance of some materials to gaseous ozone. Only materials marked as D need be avoided in ozone sterilization.

• A = Excellent – no effect from ozone in normal operation
• B = Good – some oxidation from ozone, these materials can work with low ozone concentrations or short-term (less than 6-month) usage
• C = Fair – major effect from ozone oxidation, these materials should only be used for short-term applications or very low ozone levels
• D = Poor – severe oxidation from ozone will be noticed quickly.

Material	resistance level	remark
POM (Acetal)	C	strict pharmaceutical sprayers don’t use POM
Buna N (Nitrile)	D	some low quality sprayers use this rubber as gasket and O-ring
Butyl	A	the cap’s material of injection powder vial
HDPE	A-B	bottle materials
LDPE	B-C
PP	B-C
Silicone	A	very expensive gasket but very good performance
PET	n.a.	can not find the direct test result, but many sterilization lab experiments used PET as containers, and PET bottles are often be sterilized by ozone in industry. Therefore, PET is suitable for gaseous ozone sterilization.
PS	n.a.	can not find the direct test result, but ABS (also contain block of styrene) is B. Therefore, PS can be sterilized by gaseous ozone. In industry, sterilization of PS by gaseous ozone is also applied.
Stainless steel SUS304, SUS316	A-B	Used as spring. In some sprayers, also used as valve ball.
Aluminum	A-B	Used as the crimp on closure

Finally, the units of the concentration of gaseous ozone are summarized here for easy reference. Four general units include, % (Ozone Concentration in air by weight), g/m3, ppm, pphm.

100 g/m3 = 7.8%
1% = 12.8 g/m3
1% = 7,284 ppm = 728,400 pphm ( 1 ppm (per million) = 100 pphm (per hundred million))