Plastics News Europe - October 2019 - 14

additives & masterbatch

➡ Continued from page 12
and they are 100 times stronger than
steel, yet up to six times lighter.
The working dosage for graphene
nanotubes starts from just 0.01%.
Along with imparting conductivity to
silicones, these nanotubes improve
the physical and mechanical properties. Such remarkably low effective
concentrations also enable the production of transparent and coloured
products without the greying effect
that is usually associated with carbon-based additives.
Despite the obvious advantages of
graphene nanotubes compared with
other widely used additives, their utilisation was long confined to research
laboratories. The reason for this was
their high price and the lack of technologies for effectively dispersing nanotubes homogeneously in various media. However, the situation has changed
significantly over the last few years - in
2014, graphene nanotubes transitioned from being a potentially attractive material into an economically and
technologically viable product for the
industry. This was thanks to the launch
of the world's only facility for industrial-scale production of high-quality
graphene nanotubes by a Luxembourg
company called OCSiAl, whose products are marketed under the brand
name Tuball at an economically viable
price. The company has moreover developed a line of Tuball Matrix concentrates containing pre-dispersed nanotubes. These concentrates are suitable
for all types of industry-standard formulations of silicones. They provide
homogeneous dispersion and significantly simplify nanomaterial handling,
allowing a standard and clean manufacturing process without the powder
or dust usually associated with carbon-based additives.

Graphene nanotubes
outperform carbon black
Apart from their conductive properties, the ability of graphene nanotubes also to improve the physical
and mechanical characteristics of silicones has been proven by numerous

Figure 3. Grace Continental's line of coloured masterbatches based on
OCSiAl's graphene nanotubes

studies. Testing was recently carried
out on two-component room temperature vulcanised (RTV) silicone,
where component A was Neukasil
RTV 230 and component B was Neukasil crosslinker A 149, from Altropol
Kunststoff. For the nanotube-formulated compounds, OCSiAl's Tuball
Matrix 601 concentrate was dispersed in component A using an
overhead stirrer (at a linear speed of
40 m/min for 30 minutes). Component B was then added and stirred
with an overhead stirrer (at 20 m/
min). The resulting compounds were
vacuum treated for several minutes
and then cured at room temperature.
For comparison, conductive carbon black Vulcan XC72R from Cabot
was used. Half of the amount of carbon black was dispersed in component A with an overhead stirrer (at a
linear speed of 10 m/min for 20 minutes). The second half of the amount
of carbon black was dispersed in
component B using the same method. The resulting compound was
then mixed with an overhead stirrer
(at 10 m/min for 20 minutes), vacuumed for 1-2 minutes and then
placed in a form for curing. The vulcanisation was carried out at room
temperature for the standard time.
The volume resistivity level of the
final compounds was measured by a
four-point method in accordance with
ASTM D991 - "Standard Test Method
for Rubber Property-Volume Resistivity Of Electrically Conductive and Anti-

Table 1. Comparison of plain, nanotube-formulated and carbon black-based silicone compounds
Filler

Concentration
Tensile
Elongation
%
strength MPa at break
None (base)
-
5.34
510.3
Nanotube-based
0.5
5.62
468.0
concentrate
0.7
5.52
441.0
0.9
5.62
477.0
1.1
4.77
422.0
3.0
4.38
420.0
5.0
4.64
402.0
Carbon black
10.0
1.845
260.0
15.0
0.90
100.0

M50,
MPa
0.314
0.33
0.39
0.35
0.37
0.42
0.57
0.253
0.38

M100,
MPa
0.53
0.58
0.68
0.60
0.64
0.69
0.87
0.61
0.82

M200, M300,
MPa
MPa
1.27
2.39
1.44
2.80
1.62
3.08
1.43
2.74
1.49
2.82
1.45
2.63
1.72
3.03
1.43
-
-
-

static Products". As shown in Figure 1,
just 3% of the nanotube-based concentrate resulted in a volume resistivity
of 120 Ω·cm, while the same level of
resistivity could only be achieved with
15% of carbon black.
To assess the effect of these conductive additives on the material's mechanical properties, the compounds
were tested in accordance with ASTM
D412 - "Standard Test Methods for
Vulcanised Rubber and Thermoplastic
Elastomers - Tension" (Figure 2).
Tensile strength, elongation at
break and modulus parameters were
measured to compare compounds incorporating 3% of the graphene nanotube concentrate and 15% of carbon black. The nanotube-containing
compound demonstrated minimal
impact on the tensile strength and
elongation at break, whereas carbon
black reduced both by 80% or more.
Similarly, modulus and elongation of
the silicone were also only minimally
affected by the low loading of
graphene nanotubes, whereas the
high loadings of carbon black significantly adversely impacted both. Additional properties at various concentrations of additives can be seen in
Table 1.

From laboratory to industry
The recent emergence of graphene
nanotubes as a cost-effective additive
solution promises to be a game-changer in the global industry.
Graphene nanotube-formulated
high-performance liquid silicones for
electromagnetic interference (EMI)
shielding, gaskets, sealants, conductive coatings, adhesion-promoting
primers, cable accessories, conductive
textiles and pressure-sensitive adhesive (PSA) films have recently been
launched onto the market and are
already experiencing rapidly growing
demand from producers.
In the application cases described
below, OCSiAl's Tuball Matrix pre-dispersed concentrates have been used
to facilitate the introduction of the
graphene nanotubes.
The Korean chemicals manufacturer

october 2019

Plastics News Europe - October 2019

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