Cross-Linking & Chain Scission
Modifying the molecular structure of many polymers
enhances their physical characteristics, such as resistance to heat
and abrasion. Applied Sterilisation Technologies
(AST) employ Electron Beam and Gamma irradiation
which are well-established technologies for initiating these
changes at the molecular level in polymers. The absorption of
the radiation energy can lead to either cross-linking or chain
scission of the macro-molecular chains; Electron Beam
accelerators frequently carry this out, although Gamma radiation is
used in some instances.
The chemical structure and morphology of the polymer plays an
important role with regards to its tendency to degrade or to
cross-link. For some polymers, the aim is to change
thermoplastic materials into thermosets. The molecules in the
thermoplastic materials tend to slip and slide over one another
fairly freely. As temperatures rise, these uncross-linked
materials soften and finally melt. When they are
cross-linked, molecular movement is impeded and the material
becomes more stable against heat.
The principal types of polymeric product that benefit from
treatment by irradiation are as follows:
- Cable jacket materials
- Wire insulation
- Heatshrink and other types of tubing
- Components to be used in high temperature applications, e.g.
electrical switchgear parts
- Moulded components requiring chemical or temperature
resistance
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