Degradation with Ionising Radiation

IR spectroscopy was used to follow the ageing processes of two types of epoxy resins. Resin samples were exposed to ionising radiation and the effects at the molecular level were determined. Aromatic amine cured resins were oidy slightly affected by the radiation, but those cured by alkyl diamines were more sensitive and thus absorbed more water molecules (41). 

The effect of radiation dose and the hydrolysis conditions on the chemical structure of electron irradiated PTFE was studied. Irradiation produced acid fluoride (COF) groups and, under ambient conditions, these hydrolysed with atmospheric humidity to form free and associated carboxylic acid (COOH) groups. The concentrations of these groups were different in the near-surface and bulk regions. The formation of carboxylic groups in different states of association depended on the hydrolysis conditions (146). 

IR spectroscopic analysis showed that the treatment of PAN films and fibres by gamma-irradiation led to cleavage of the polymer chains forming carbonyl-containing functional groups, the composition of which depended on the treatment conditions (330). 

---

The energy associated with UV light is in competence with the chemical bond energies associated with any two atoms [104]. Hence, UV radiation often has the potential for retention of the properties of monomers and polymers while the other surface grafting techniques, which use ionisation radiation, cause damage to the substrate polymer due to excessive degradation. 

For non-aqueous liquids, semisolids and dry powders 2 h sterilisation at 160 °C in dry heat is preferred. Where it is not possible to carry out terminal sterilisation by heat due to formulation instability, a decision should be taken to utilise an alternative method of terminal sterilisation, filtration and/or aseptic processing. It is recognised that new terminal sterilisation processes other than those described in the pharmacopoeia may be developed to provide sterility assurance levels equivalent to present official methods and such processes, when properly validated, may offer alternative approaches. If necessary, a different time-temperature combination may be applied to obtain an SAL of 10 . If too much degradation occurs in dry heat, ionising radiation or gas sterilisation can be applied. If these methods are not suitable either, sterilising membrane filtration and validated aseptic processing, sometimes robotised or with barrier system technology are considered as a last resort. 

Anthocyanins are unstable when exposed to visible, ultraviolet or ionising radiation. Decomposition takes place mainly as photooxidation. Anthocyanins substituted at C-5 hydroxyl group, which are fluorescent compounds, are more sensitive to photochemical degradation in comparison with C-5 unsubstituted anthocyanins. 

High levels of magnetic flux and trapped solar radiation. This environment may degrade a composite quite quickly, with the polymer cross-linking embrittlement occurring as a consequence of the high ionisation... 

---