SAMPE Journal - May/June 2023 - 10

FEATURE / PHTHALONITRILE (PN) RESINS
PEEKTM
-Based High-Char Resins: Key to Novel
Properties
Although such a wide array of useful properties
exist for PN resins/polymers, several important
roadblocks have precluded their implementation
in many perfectly suited engineering systems.
Economic and efficient manufacturing has stood
as the biggest challenge that these materials face.
In 2005 and subsequent improved processable
version
resin systems (e.g. PEEKTM-Based19,24
in 2014, NRL developed oligomeric
) with their
chemical precursors cost decreased significantly
over the past decade. Coupling with our simple
reaction chemistry, producing near quantitative
yields without purification, these systems can
now compete with other decades old resins for
economy of scale that other resin systems currently
enjoy. (Figure 2) These PEEKTM
-Based systems exist
as low melting solids that are indefinitely stable
under ambient conditions. They have the ability
of being processable at moderate temperatures
(125-175°C) (250-350°F), allowing them to produce
void free composites with ease. While PN is within
its neat powder stage, it melts between (75-125°C)
150-250°F and cures at temperatures above 300°F.
Depending on the starting bisphenol, initial
viscosities at 150°C (300°F), range from 1000-2000
cPs (10-20 pa.s). Moreover, as the polymer resin is
heated above 700°C (1300°F), these PNs char but
retains a very high carbon yield of over 65-75%.
Interestingly,
this polymer has also become a
replacement carbon source and key functional
ingredient in a novel polymer-derived ceramic
process developed at the NRL. The process
currently uses a more expensive all carbon resin
(1,2,4,5-tetraphenylethylnyl-benzene25
, but PN has
been found to be a cost effective alternative. Despite
the PN containing both oxygen and nitrogen, the
majority of these species are removed by thermal
heating to 1000°C (1800°F), before conversion to
ceramic components.
NRL's PN resins are easily processed into voidfree
composite components by a variety of methods,
due to its inherent addition cure chemistry.
Although these resins were originally designed
for a vacuum infusion process, tradition prepreg
consolidation via hot pressing or autoclave have
been proven as value added options for processing
at moderate temperatures. Figure 3 outlines a
generic autoclave process for the Bis A PEEKTM
PN that was applied to T650 carbon fabric after
being prestaged (B-staged). The staging process
increases the initial viscosity of the neat material
to 10,000-30,000 cP (10-30 pa.s.) at 175°C (350°F),
to acclimate the resin for this methodology. The
10 | SAMPE JOURNAL | MAY JUNE 2023
Figure 2. Schematic of the PEEKTM
-based synthesis process and the three
unique resin systems derived from bisphenol A, resorcinol and bisphenol
A6F.
B-staged PN/Carbon fabric composite is heated
to 125°C (250°F) under full vacuum for an hour, to
remove trapped solvents and water. Afterwards, the
vacuum is removed and the composite is heated
above 175°C (350°F), for consolidation. Subsequent
heating to around 250°C (450°F) is necessary to
adequately cure the thermoset, as a means to avoid
damaging the composite during the debulking
step. Depending on the resin that is used, these
times and temperatures can vary slightly. We
suggest running rheology on all
resin batches
before attempting composite manufacturing.
Figure 3. Example of an autoclave process for our PEEKTM
systems.
-based resins
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SAMPE Journal - May/June 2023

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