SAMPE Journal - May/June 2017 - 7

Feature Article
K. C. Chuang
NASA Glenn Research Center, Cleveland, OH
T. A. Yip, R. B. Kollmansberger and T. K. Tsotsis
Boeing Research & Technology, Huntington Beach, CA

Evaluation of RTM370 Polyimide Composites
by Resin Film Infusion (RFI)
Abstract
RTM370 imide oligomer based on 2,3,3',4'-biphenyl dianhydride (a-BPDA), 3,4'-oxydianiline (3,4'-ODA) and terminated
with the 4-phenylethynylphthalic (PEPA) endcap has been shown to exhibit a low melt viscosity (10-30 poise) at 280°C with a
pot-life of 1-2 h and a high cured glass-transition temperature (Tg) of 370°C. RTM370 resin has been successfully infused into
fiberglass-stitched T650-35 carbon-fabric preforms (ranged from 3- to 6-mm thick) by resin film infusion (RFI). The resulting
composite panels were inspected by ultrasonic C-scan and by photomicrographs before and after post-curing as a quality control.
Mechanical tests such as un-notched compression (UNC), open-hole compression (OHC), and short-beam shear strength (SBS)
at ambient and elevated temperatures were performed before and after isothermal aging at 288°C for 1000 h to assess hightemperature performance. Thermal cycling of RTM370 stitched composites was also conducted from -54°C to 288°C for up to
1600 cycles to evaluate the microcrack resistance of RTM370 polyimide composites fabricated by RFI.
Introduction
Resin film infusion (RFI), developed
initially by Boeing1, is a relative new
technique to fabricate polymermatrix composites without the use of
carbon-fiber prepregs impregnated
with resins and, often, with solvents.
A resin as a film is placed on top
or underneath a fibrous preform,
tooling is located, and the assembly is
enclosed with a vacuum bag through
which the vacuum is applied. As the
temperature rises in the autoclave,
the resin film melts and infuses into
the laminates beneath under the
combined pressure gradient of the
vacuum and autoclave pressure.
The assembly is then cured into
composites at elevated temperature.
The advantages of RFI include: 1)
Ability to produce composites with
high fiber-to-resin ratio and low void
content. 2) Environmental friendly
without volatiles. 3) Capability to
fabricate large components with
minimum workforce. Numerous
epoxies2 and bismaleimides (BMI)
resins3 have been fabricated by

Figure 1. Solvent-free preparation of RTM370 imide oligomers.

RFI into high-quality composites
and aircraft parts4 in the aerospace
field. However, the performance
of epoxy and BMI are limited to
177°C and 232°C use temperatures5,
respectively. Boeing has conducted
RFI using newly developed lowmelt-viscosity, imidized oligomers,
such as PETI-3306 or RTM3707, in
order raise the higher temperature
capability of composites for aircraft
applications.
This paper presents an evaluation

of RTM370 polyimide composites,
fabricated with fiberglass stitched
T650-35 fabric preforms (ranged
from 3- to 6-mm thick) by resin
film infusion (RFI), for potential
airframe application. Mechanical
properties were conducted from
room temperature to 288°C (550°F).
Additionally, mechanical properties
after isothermal aging at 288°C for
1000 h and microcrack resistance
after thermal cycling from -53°C to
288°C will be discussed.

RTM370 imide oligomers (Figure 1) based on 2,3,3',4'-biphenyl dianhydride (a-BPDA), 3,4'-oxydianiline (3,4'-ODA) and
terminated with the 4-phenylethynylphthalic (PEPA) endcap has been shown to exhibit a low melt viscosity (10-30 Poise) at 280°C
with a pot-life of 1-2 h and a high cured glass-transition temperature (Tg) of 370°C8. RTM370 polyimide/T650-35 carbon-fiber
composites fabricated by resin transfer molding (RTM) have been shown to display outstanding mechanical-property retention
after isothermal aging at 288°C (550 °F) in an air-circulating oven9. RTM370 infused into triaxially braided T650-35 carbon-fiber
preform afforded composites that exhibited 28-30% better impact resistance at 288°C (550°F) than at ambient temperature10.
SAMPE Journal, Volume 53, No. 3, May/June 2017

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