JEC COMPOSITES MAGAZINE - Issue #111 - March 2017 - Special JEC World - o - 27

New epoxies for styrene-free high-performance SMC

Focus
Main features
- Uses same equipment, easy to switch
from traditional unsaturated polyester
and vinylester systems
- Achieves high-volume low-density
parts with superior performance
- Suitable for numerous semi-structural
and structural applications
- Low VOC
- Eliminates styrene monomer exposure
- Cost-effective, reduces labour and
material scrap

Fig. 1: Typical carbon and glass SMC properties as compared to Hexion's new epoxy SMC for both carbon
(CFEP) and glass fibre embedded plastics (GFEP)

Fig. 2 & 3: Epoxy SMC sheet production wherein chopped fibre is deposited onto the resin film, for both glass and
carbon variants

laws and codes. The VDA 278 recommendation governs organic emissions
for moulded components in automobiles. The test measures emission levels
of the ten most common volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs, i.e.
fogging compounds) by thermal desorption. Table 1 shows that the new
Hexion epoxy SMC system results in
substantially lower VOC emissions
than its traditional counterparts and
the emissions stay well below international exposure limits.
Excellent mechanical properties for
structural automotive parts
Epoxy matrices exhibit excellent ad-

hesion to glass and carbon fibre due
to good compatibility with the epoxybased fibre sizing agents. In the case of
epoxy SMC manufacturing, this compatibility results in high mechanical
performance parts suitable for structural automotive applications. Parts made
with carbon fibre, in particular, can
achieve very low densities with significant reductions in mass.
A series of trials evaluated the performance of several commercial carbon
and glass fibres when combined with
Hexion's newly developed epoxy matrix. The results show that most available carbon fibres will achieve good
mechanical properties which vary
with the tow size, impregnation quali-

ty and compression moulding process.
Traditional glass fibres produced lesser results, though the use of the new
Hexion epoxy system did improve
performance more than the traditional
SMC materials. Moreover, several producers have recently begun developing
glass fibre products specifically optimized for epoxy systems.
The current SMC market includes a
wide variety of products, from low-end
UP to moderate-performance VE SMC.
The new Hexion epoxy SMC offers
superior performance as compared to
equivalent competitive systems. Figure
1 represents a property distribution for
competitive SMC in which the fibre
length is 25 mm, the carbon fibre tow
is 12-24 K, and the SMC is unfilled.
Properties are determined from machined samples of isotropic, moulded
material. The improved performance is
a direct result of low-viscosity control
during the critical fibre impregnation
step as the material is compounded.
Hexion's epoxy SMC introduces new
possibilities in tailored SMC manufacturing. Epoxy SMC can be moulded
and co-cured with epoxy-based prepreg
for high-strength performance with increased design freedom. For example,
from a loads perspective SMC alone
might be unsuitable for a seat frame.
A full prepreg solution would also be
challenging due to the geometric complexity of the part. A tailored SMC
solution, on the other hand, utilizing
the moldability of SMC with prepreg

No111 March 2017

/ jec composites magazine

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #111 - March 2017 - Special JEC World - o