EoW July 2010

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EuroWire – July 2010 52
technical article
Conversely, the anhydride functionality
containing analogues both provided
higher tensile strength and, in the case
of LPBD-3, better elongation. It seems
evident that the anhydride functionality
rendered the LPBD more compatible with
the EVA phase, and that the lower Mw
of LPBD-3 over LPBD-4 created smaller
droplet dispersion.
Introducing ATH into the system yielded
the results presented in Figures 3 and 4.
Figure 3 demonstrates that the LPBDs
all reduce the tensile strength at yield
of the ATH filled EVA. The functionalised
LPBD-3 and LPBD-4 outperformed their
unfunctionalised counterparts, which in
part suggests an improvement in interfacial
adhesion between phases. In Figure 4 all
but LPBD-3 improved the elongation at
break. In the case of LPBD-3, the cause of a
further reduction in elongation is possibly
two-fold.
First, the highly functional small chains
(Mn 2,500) may have had multiple sites
of interaction with the ATH surface and
enveloped the mineral. Consequently,
there would be no free chain segments
to entangle with EVA to serve as a
compatibiliser. Secondly, LPBD-3 was 70%
vinyl, which could have crosslinked during
compounding. An analysis of the elastic
modulus indicated that LPBD-3 had induced
a significant increase over the base material
indicative of a crosslinked material.
The unfunctionalised LPBDs served to
better wet-out the mineral filler, so aiding
in its dispersion. The LPBD-4 improved the
elongation of the filled system by 450%.
The LPBD-4 is likely to have had fewer
interactions between the ATH surface
hydroxyl functionality and the anhydride
functionality, while maintaining a tail to
compatibilise/entangle with the EVA.
In addition to molecular weight and vinyl
content, alternate functionalised LPBDs
were evaluated. Figures 5 and 6 illustrate
the results of these additives, in addition to
the SR-732.
Figures 5 and 6 demonstrate that reducing
the anhydride loading on the LPBD
(LPBD-5) will increase both the tensile
strength and elongation. As mentioned
previously, it is imperative to have an
association between the additive and the
filler surface, but also to ensure that there is
sufficient chain entanglement between the
additive and EVA. Reducing the MA content
on the additive decreased the probability
of multiple bonds being formed with the
ATH surface, thus increasing the average
chain length remaining to entangle in
the EVA. LPBD-6 and LPBD-7 demonstrate
that alternate functionalities can replace
maleic anhydride in the form of epoxy and
amine. Both functional groups performed
analogously to equal loadings of anhydride
in terms of tensile strength and elongation.
Figures 5 and 6 also demonstrate the
influence of the ionic monomer, SR-732,
on the ATH/EVA system. Unlike the LPBD
additives the SR-732 increased the tensile
strength of the system and also statistically,
if modestly, improved the elongation. It
is believed that introduction of the ATH
induced high shear environments within
the melt during compounding that reacted
with the acrylic functionality.
Previous work indicates that these
monomers have a tendency to cluster
within a polymeric compound, which
creates an ionic bridge, or crosslink,
between adjacent chains. At ambient
temperature the cluster will serve to
increase the mechanical properties of
the system. Unlike the LPBDs, the SR-732
altered the bulk properties of the EVA as
opposed to the interface.
4 Conclusions
Significant improvements in the elongation
of highly filled ATH/EVA compounds were
achieved by introduction of low molecular
weight, functional polybutadienes.
The functionality of the additive served
to compatibilise at the organic/inorganic
interface by reaction with the ATH surface,
and chain entanglements with the EVA.
Molecular weight, or chain length, was
an important attribute in improving
the elongation properties. Alternate
functionalities to maleic anhydride, such
as epoxy and amine groups, proved to
be equally valuable at improving the
elongation.
Increasing the tensile strength of the
system was equally part of the objective.
Introduction of a di-acrylic ionic monomer
yielded improvement in tensile strength
that the liquid polybutadienes could not
obtain. Formation of an ionic network
within the EVA is probably the mechanism
by which the tensile strength was
improved.
Future experiments will further examine
the influence of molecular weight on low
functional LPBD. Increasing the length
of the free chain should further increase
the elongation phenomenon. Examining
mixed additives systems to include both a
LPBD and the SR-732 to increase both the
tensile strength and elongation will also
be considered. n
5 Acknowledgments
The authors would like to thank DuPont
USA and Almatis, for supplying material
for this investigation; the team at Boy
Machines, for moulding the tensile
specimens on an XS microinjection
moulder; and Brett Robb for careful
preparation and characterisation of the
EVA-ATH materials.
6 References
1 Plentz, RS, Miotto, M, Schneider, EE, Forte, MSM,
Mauler, RS, and Nachtigal, SMB: Journal App.
Polym. Sci., 101, 1799 (2006)
2 Jancar, J, and Kacera, J: Journal App. Polym. Sci.,
30, 714 (1990)
3 Duval, J, Sellitti, C, Myers, C, Hiltner, A, and Baer, E:
Journal App. Polym. Sci., 52, 591 (1994)
4 Sun, Y, Hu, G, Lambla, M: Polym. 37, 4119 (1996)
5 Mai, K, Li, Z, Qiu, Y, and Zeng, H: Journal App.
Polym. Sci., 84, 110 (2002)
6 Wang, J, Tung, JF, Fuad, MYA, and Hornsby, PR:
Journal App. Polym. Sci., 60, 1425 (1996)
This paper was first presented at the
58th International Wire & Cable and
Connectivity Symposium, held in Charlotte,
NC 8th – 11th November 2009, and is
reproduced with the generous permission of
the organisers.
Figure 6 ▼ ▼ : Elongation results using alternate
functionalities demonstrating significant improve-
ments in ductility over the neat EVA-ATH system
Figure 5 ▼ ▼ : Tensile strength results for alternate
functionalities indicating that LPBD with 5%
functionality (anhydride included) impact the tensile
strength less
Jeremy R Austin
Sartomer Company, Exton PA
Email:
Herbert S.-I Chao
Sartomer Company, Exton PA
Email:
Tensile strength (MPa)
Elongation (%)
Tensile stre
i ( )