SAMPE Journal - March/April 2024 - 9

II. NOVEL OXIDIZED PAN FIBERS
Carbon fiber is generally made from three
feedstocks - 1) Polyacrylanitrile (PAN), 2) Rayon,
and 3) Pitch. There are efforts on other feedstocks,
such as lignin, for carbon fiber but these are still
in development. Today, most of the carbon fiber
is produced with PAN feedstocks. We will focus
this paper on PAN-based carbon fibers. Relevant
publications on oxidized PAN fibers are listed in the
References.[1-3]
Oxidized polyacrylonitrile fiber (OPF) is a
synthetic fiber derived from polyacrylonitrile
(PAN), a polymer resin with the formula
(CH2CHCN)n. OPF is produced by heating PAN
in air at temperatures above 200°C, which causes
the polymer chains to crosslink and stabilize. This
process is called oxidation.
The key properties of OPF includes:
* Higher flame resistance:
OPF has a
limiting oxygen index (LOI) of 45% to
55%, which means it requires a high
concentration of oxygen to burn. This
makes it a very flame-resistant material,
and it is often used in applications where
fire protection is important, such as
protective clothing, welding drapes, and
insulation blankets.
* Lower thermal conductivity: OPF has a
lower thermal conductivity than PAN,
which means it is a better insulator.
This makes it a desirable choice for
applications where heat insulation is
important, such as automotive parts and
industrial textiles.
* Better chemical resistance: OPF is more
chemically resistant than PAN, which
means it can withstand exposure to a
wider range of chemicals. This makes it
an excellent choice for applications where
chemical resistance is important, such as
aerospace and marine applications.
* Lower toxicity: OPF emits extremely low
levels of toxic gases and halogens when
burned, making it a more environmentally
friendly and safer material than other
synthetic fibers.
*
OPF has a target carbonization percentage
of 58-62%.
OPF can be processed into different forms,
such as tow, staple, yarn, woven, knit, or nonwoven
fabrics. It can also be blended with other fibers,
such as polyester, cotton, or wool, to improve its
properties and appearance. OPF is a cost-effective
alternative to other heat and flame-resistant fibers,
such as aramid or modacrylic.
OPF fibers have been used for decades
thermal
for
protection
applications.
Typical
applications are brake systems, thermal insulation,
fire-resistant applications, welding blankets, and
www. sampe.org
Figure 1. Spool of HexTow® 85 24k carbon fiber.
friction linings. OPF requires less processing versus
carbon fiber which results in lower costs.
There are several aerospace applications
where OPF is of interest. Typically, carbon-carbon
materials are ablative which is acceptable in
applications, such as rocket nozzles or TPS on nonflight
control surfaces. For hypersonic weapon
applications, the need is for TPS that are not
ablative as they will be needed on control surfaces.
OPF materials may be a satisfactory solution
but today, OPF materials on the market are not
aerospace qualified. An aerospace grade OPF is
needed to support future offensive and defensive
weapon systems. Hexcel is currently exploring
the process to produce a US-domestic aerospacegrade
Oxidized PAN Fiber (OPF).
III. HEXTOW® 85
Dating back to the 1950's, Rayon-based carbon
fiber has been used to produce ablative carboncarbon.
Rayon-based carbon fiber has excellent
thermal conductivity which makes it good for
ablative carbon-carbon materials. The rayon-based
supply chain has been notoriously complicated
since its inception; leaving end-users to deal with
the frustrations of high and variable prices, lead
times best measured in years, and most notably,
an extremely limited selection of US-based (or
US-ally based) industry players to help process the
materials. For these reasons, all of which are still
true today, roughly 30 years ago the industry began
MARCH APRIL 2024
|
SAMPE JOURNAL |
9
http://www.sampe.org
SAMPE Journal - March/April 2024

Table of Contents for the Digital Edition of SAMPE Journal - March/April 2024
