Gamma Radiation Effects on Polymers : Part 2
Benzene ring Structures
- The benzene ring acts as a electron bank loaning and accepting electrons
- Polymers with benzene rings include PS, PET, PU, PC and PSU
- Polystyrene is stable
Amorphous Polymers
- Highly amorphous materials (non crystalline) are generally resistant to radiation since the chain structure is capable of great ductility and they can tolerate many scissions without breaking up
Polyamides (Nylons)
- Nylons especially aromatics 12, 11, 6/12, 6/10 are highly resistant to irradiation
- Nylon 6 is least radiation resistant
Butyl Rubber
- Natural rubber survives irradiation very well but butyl rubber crosslinks to become stiffer, loses elongation and turns friable and powdery
- For this reason butylene -containing polymers such as ABS and PBT loses impact strength on irradiation
Stress Cracking
- A polymer under stress is attacked more by radiation than unstressed material is.
- Scissioning and oxidation effects are concentrated in the stressed zones
- Therefore plastic parts must have reproducible molded-in stresses
Key Messages
- Aromatic polymers (e.g. with benzene rings) are more stables than aliphatic chains
- Look at ratio of scissioning to crosslinking
- Most natural PP and PTFE are unstable with irradiation
Survey Exposure
- If it is difficult to predict how a polymer system will resist irradiation (e.g. by accelerated ageing) then the use of an exaggerated dosing at 100 kGy should highlight problems and marginal materials
If you are unsure if your material will hold up to this sterilization technique, please visit the TriStar Plastics Corp. website for contact information.
Tags: exposure, Gamma radiation, sterilization, sterilization effects, Surface treatment
