Polyimide-Foam/Aerogel Composites
for Thermal Insulation

Composites of specific types of polymer
foams and aerogel particles or blankets
have been proposed to obtain thermal
insulation performance superior to those
of the neat polyimide foams.

These composites have potential to also
provide enhanced properties for vibration
dampening or acoustic attenuation.

The specific type of polymer foam is
denoted "TEEK-H," signifying a series,
denoted "H," within a family of polyimide
foams that were developed at NASA's
Langley Research Center and are
collectively denoted "TEEK" (an acronym
of the inventors' names).

The specific types of aerogels include
Nanogel® aerogel particles from Cabot
Corporation in Billerica, MA. and of
Spaceloft® aerogel blanket from Aspen
Aerogels in Northborough, MA.

The composites are inherently flame-retardant
and exceptionally thermally stable.

Because of thermal cycling, aging, and
weathering most polymer foams do not perform
well at cryogenic temperatures and will
undergo further cracking over time.

The TEEK polyimides are among the few
exceptions to this pattern, and the proposed
composites are intended to have all the
desirable properties of TEEK-H foams, plus
improved thermal performance along with
enhanced vibration or acoustic-attenuation
performance.

A composite panel as proposed would be
fabricated by adding an appropriate amount
of TEEK friable balloons into a mold to
form a bottom layer. A piece of flexible
aerogel blanket material, cut to the desired
size and shape, would then be placed on
the bottom TEEK layer and sandwiched
between another top layer of polyimide friable
balloons so that the aerogel blanket would
become completely encased in an outer layer
of TEEK friable balloons. Optionally, the
process could be further repeated to produce
multiple aerogel-blanket layers interspersed
with and encased by TEEK friable balloons.

The sandwiching of aerogel bulk-fill particles
would follow the same methodology or could
be mixed directly with friable balloons up
to 40% weight loading of the aerogel particles
to friable balloons. After sandwiching or
mixing of the polymide and aerogel components,
the mold, without a top cover, would be
placed in a convection furnace and heated at
a temperature of 250 °C for one hour.

Then the top cover would be placed on the mold
and the temperature increased to about 320 °C
for between 1 and 3 hours for full imidization
of the polyimide component.

The resulting composite should have all the
desirable properties of TEEK, and its effective
thermal conductivity should be less than that
of an approximately equally dense panel made
of TEEK foam only. The heat transfer reduction
is directly proportional to % loading of the
aerogel component. The excellent structural
integrity of the foam material is maintained
in the composite formulations.

~ Full Article @Nasa Tech Briefs