JEC COMPOSITES MAGAZINE - Issue #119 - March 2018 - 53

MATERIALS: PUSHING BOUNDARIES
resin

High-performance epoxy/carbon fibre SMC
dr. ian swEntEk
Application Development
Engineer
stEphEn GrEYdanus
Senior Automotive
Applications Manager
dr. alExandEr schmidt
Senior Development Engineer
siGrid tEr hEidE
Global Market Development
Manager Transportation
Hexion

Sheet moulding compound (SMC) is a major, industrially relevant manufacturing process. Epoxy/carbon fibre SMC is a new material that achieves the highest mechanical
performance. To fully impregnate carbon fibre, however, poses a processing challenge
due to its high surface area. This paper describes a systematic approach used to
improve the mechanical performance of epoxy/carbon fibre SMC.

Epoxy: the key ingredient
in high-performance SMC
Epoxy sheet moulding compound
(EP SMC) was manufactured on
Dieffenbacher equipment at the
Fraunhofer Project Centre in London,
Ontario, Canada. This industrial-scale line
is suitable for both standard and direct
SMC processing. In this instance, the
direct process was ignored so as to replicate the standard conditions with which
many SMC producers are already familiar.
A schematic of this equipment is shown
in Figure 1 with some of the heating
components highlighted. Though room

patible sizing, easily spreading during the
compounding and moulding operations.
The quality of the compound is directly
related to the selected processing parameters. From previous work, several key
parameters were selected as the main
optimization targets included the sheet
basis weight, compaction pressure, and
zone temperatures. The target fibre volume content was set to 45%; the baseline
parameters are documented in Table 1.
Panels made from carbon fibre with different filament counts were also fabricated as
previously described: 3K, 12K, 15K, and
50K. While the fibres were of different
manufacturing origin, they were all epoxy
sized at similar concentrations.
Tailored (also called co-cured) epoxy
SMC with epoxy prepreg was created in

Fig. 1: Schematic SMC equipment at the Fraunhofer Project Centre with heating callout

N°119 March 2018

/ jec composites magazine

Materials: pushing boundaries

heet moulding compound (SMC)
has long been used with polyester
and vinyl ester resins to achieve
good overall performance and gain commercial acceptance in a range of applications. Material systems using chemistries
compatible with the SMC processing
technique, such as epoxy, were recently
developed to increase mechanical performance [1]. Epoxy, specifically, is suitable
for numerous structural applications due
to its low-viscosity, which can best wet
carbon fibre. In terms of safety, it is low
in volatile organic compounds and eliminates styrene monomer exposure. To illustrate its range of performance, several
of the process-property relationships of
epoxy/carbon fibre SMC are presented
for semi-structural and structural applications and benchmarked against epoxy/
glass SMC.

temperature processing of epoxy/carbon
fibre is viable, it is common to lightly heat
the paste to further reduce its viscosity.
Since the material is often made in small
batches, a Bowers stand mixer with a lowshear dispersion blade was used instead of
continuous dosing equipment such as a
meter-mix-dispense system or an extruder. The low-viscosity SMC epoxy from
Hexion - EPIKOTE™ resin TRAC 06605
and EPIKURE™ curing agent TRAC
06608 - was provided with an internal
mould release - HELOXY™ additive
06805. The resin was mixed according to
the data sheet, excluding the optionally
recommended BYK A-560 degassing
agent. The epoxy was carefully mixed for
5 minutes to keep the batches consistent.
The selected carbon fibre was the Zoltek
Panex 35 50K-T13. This standard-modulus fibre has a low amount of epoxy-com-

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #119 - March 2018