SAMPE Journal - January/February 2023 - 13

products are proprietary, but basic information is
listed on publicly available datasheets [18,19]. The
composition by weight of Frekote B-15 mold sealer
includes 1-5% silicone components (reaction
product of TMAS and PDMS) and 90-100% dibutyl
ether as the solvent. The composition by weight
of Frekote 710-NC release agent includes 1-5%
silicone components (reaction product of TMAS
and PDMS), 1-5% octane, 1-5% hydrocarbons (C710),
60-100% petroleum as the carrier, and 10-30%
dibutyl ether as the solvent. Polydimethylsiloxane
(PDMS) acts as the active silicone in both Frekote
mold sealer and release agent, which allows for
chemical compatibility between the two products,
high abhesion (i.e.,
low surface
and high chemical/thermal stability14
free energy),
. After the
release coating components are applied on tools,
most of the carrier and solvent evaporate, while
the silicones and hydrocarbons remain and form
micro-agglomerations on the lay-up surface
(Figure 1b,c).
The composite material used in this study
was Toray T800S/3900-2 UD prepreg with a resin
content of 35 % by weight20
. 3900-2 is a toughened
aerospace-grade epoxy resin, while T800S is an
intermediate modulus and high strength carbon
fiber. In addition to epoxy resin, the prepreg's
surface is partially covered with micro-spherical
thermoplastic tougheners. In recent decades, the
T800/3900-2 system has been used as a primary
structural material on major aircraft such as Boeing
787.
Method
The experimental method consisted of sequential
rounds of tool preparation, autoclave processing,
and tool inspection. First, two production tools
were prepared to have identical surface conditions
with equivalent amounts of release coating. These
tools were then used as mold surfaces throughout
twenty autoclave processing cycles of composite
parts. Throughout the processing campaign, one
tool was treated with one fresh layer of RA after
every three cycles, while no RA reapplications were
conducted on the other tool. This approach was
used to investigate the effects of RA reapplications
on aging. Then, after a pre-determined number
of autoclave processing cycles, a novel technique
was used to inspect the surfaces of both tools. Tool
inspections were performed after each autoclave
cycle for the first five cycles, then after every five
cycles through the remainder of the campaign.
Each inspection session consisted of using portable
analysis equipment to identify signs of aging and
contamination on the production tool surfaces. The
www. sampe.org
experimental campaign continued until significant
aging and contamination on the tool surface caused
evident declines in tool abhesion properties. The
overall goal of the procedure was to develop and
validate the novel inspection technology's ability
to identify and evaluate process- induced aging of
release coating and contamination in a production
environment.
In addition to using portable devices to
evaluate production tools, each inspection step
consisted of utilizing laboratory instruments to
analyze small-scale test coupons. Coupons were
initially prepared to mimic each surface condition
on both production tools, then underwent RA
reapplications and autoclave processing cycles in
a parallel manner. One-half of the coupons were
analyzed using FTIR, and the others were used
for contact angle testing. The portability of the
coupons allowed for high-precision laboratory
analysis of each surface condition, which would
later be used as a reference to enhance the lowfidelity
portable measurements through ML
techniques. Data analysis and ML methods were
conducted using various libraries within Python
and MATLAB.
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JANUARY FEBRUARY 2023
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SAMPE Journal - January/February 2023

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