Plastics News Europe - October 2019 - 12

additives & masterbatch

Graphene nanotubes
are a game-changer
Graphene nanotubes are among the
world's most advanced materials. When
applied as a conductive additive in
silicones, they demonstrate amazing
results. Even at concentrations as low
as hundredths of a percent of the
total weight of the material, graphene
nanotubes make silicone conductive,
while improving its mechanical
properties. Such a low working dosage
means that it is now possible to obtain
conductive polymers in various colours,
or even ones that are transparent

ilicones are widely used in a multitude of industries; however, in
some areas such as the aerospace, automotive and electronics industries, they need to have electrically
conductive properties. Examples of
conductive silicone products include
cables and cable accessories, power
supply components, PSA films, printing rollers and keyboards, EMI shielding products, static protection textiles,
and many others. The market volume
for conductive silicones is projected to
grow to USD 2.6 billion by 2022.
To provide silicones with conductive properties, conductive additives
need to be incorporated during the
compounding process. Depending on
the requirements of the specific manufacturer and on the end application
of the silicone, additives such as carbon black, carbon fibre, copper powder, and silver- and nickel-coated
graphite, copper and aluminium can
be used for reaching the desired level
of conductivity. However, these additives all negatively affect the physical

+30% +55%
0.82
0.69

2.39

105
TUBALL™ MATRIX
10% carbon black
15% carbon black

Volume resistivity, Ω.cm

104

103

102

101

0.5

1
1.5
2
2.5
3 10
Content of conductive filler, wt.%
Measurements conducted according to the ASTM D991 standard

Figure 1. Comparison of the volume resistivity of RTV compounds
containing various concentrations of graphene nanotubes with those
containing 10% and 15% of carbon black

and mechanical properties of silicone,
decreasing the performance characteristics of the end products.
Moreover, the most widely used
additives need to be added in concentrations that are a significant proportion of the total weight of the
material. Such high loadings not only
degrade the mechanical properties,
they also lead to a greying effect on
the colour. For consumer goods, the
colour is often of great importance,
so this greatly limits the wider application of silicone products.
Obtaining conductive and coloured silicones that also have good mechanical properties is an important
focus for the industry.

Conductivity without
compromise
According to manufacturers, at least
70% of existing solutions for impart-

-18% -83%

+10%
2.63

5.34

-18%

-80%

510
4.38

420

0.53

RTV base

M300, MPa

100

0.9

N/A
M100, MPa

Tensile strength, MPa

3% Nanotube-based concentrate

Elongation at break, %

15% Carbon black

Figure 2. Comparison of the mechanical properties of plain, nanotube-formulated and
carbon black-based silicone compounds

ing permanent conductivity properties to silicones are based on carbon
black. The use of other additives has
been significantly limited by the complexity of the technological process,
by the fact that these yield only temporary conductivity, by high prices or
limited production volumes.
Typical concentrations of carbon
black, depending on the formulation,
range from 10% to 40% of the total
weight of the compound. High working dosages have a destructive impact
on the physical and mechanical properties of silicone and result in a compound that is black in colour.
Multi wall carbon nanotubes are
an alternative additive that have recently entered the market of conductive additives and which partially
solve the problem of degradation of
mechanical characteristics. However,
they still negatively affect the colour:
typical working dosages of rigid and
short multi wall carbon nanotubes,
which can also be described as a
rolled up sheet of graphite, are in the
range of 1-6%.
Graphene nanotubes - also
known as single wall carbon nanotubes - are the most advanced and
effective conductive additive solution
available. These nanotubes can be
described as a graphene sheet rolled
into a tube with an extremely high
length-to-diameter ratio. Their conductivity is similar to that of copper

➡ Continued on page 14
october 2019

Plastics News Europe - October 2019

Table of Contents for the Digital Edition of Plastics News Europe - October 2019