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Radiation Resistance and Outgassing of PTFE/Fiberglass Laminates
Radiation resistance - the main effect radiation has on PTFE/fiberglass laminates
is on the mechanical properties. the molecular weight of the PTFE by breaking the
large molecules into small particles. This will increase the brittleness of the
laminate, while reducing the elongation, modulus, and tensile strength. In an
oxygen-free atmosphere, however,the effects of radiation are reduced. Oxygen is
necessary for some of the reactions to occur.
Irradiation will also affect the electrical properties of PTFE. Both the dielectric
constant and the dissipation factor will temporarily increase while the material
is being irradiated. This effect is less evident at the higher frequencies used in
microwave applications.
Most of the information compiled on radiation resistance is based on the dosage
encountered in the Van Allen radiation belt (10 rads/hour). At this rate, PTFE
will operate from 5-50 years. It is generally believed that the PTFE will survive
longer than many of the components.
Outgassing in vacuum - according to a NASA report dated August, 1980, PTFE/fiberglass
laminates have outstanding resistance to outgassing. Because of the high temperatures
necessary for the laminate manufacturing cycle, the volatiles (which would outgas)
are burned off. In tests performed according to ANSI/ASTM E-595-77, PTFE/fiberglass
laminates show a TML (total mass loss) of about 0.05%, and a CVCM (collected volatile
condensable materials) of 0.00%. For space applications, the maximum values allowed are
a TML of 1.0% and a CVCM of 0.10%. Laminates made from PTFE/fiberglass fall way below
this maximum limit.
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