polyimide wire insulation, aging

[whitbeck]

The aging aircraft problems include damaged wire insulation. It seems that
polyimides (e.g. polyarylimides like kapton) are (were?) used and present
special problems if the insulation is damaged. Presumably this also includes
the aging damage from long term exposure to moisture, etc.

Anyone know of a source of information on the relative volume fractions of
different plastics used for wire insulation? That is, what fraction of the
market for wire insulation is filled by polyimides vs say PVC or PTFE?

For that matter any particular reason for selecting an imide or pvc or ptfe
insulation?

I raise these questions in the context of aging electronics which surely
must exist in other areas besides the aircraft industry.

Thanks

[Mark Thorson]

whitbeck wrote:

> For that matter any particular reason for selecting an imide or pvc or ptfe
> insulation?

PI has excellent mechanical properties at elevated temperature (say, 150C).
PTFE has lousy cut resistance. PI absorbs water like a sponge
(Kapton is about 4% water at saturation). PTFE has excellent
resistance to acids, alkalis, and solvents. PVC is cheap.