Aqueous suspensions of carbon nanotubes (CNTs) containing individual tubes
offer interesting perspectives for a number of new applications which depend
on a high electrical or thermal conductivity, respectively. In particular, this
applies to multifilament yarns coated with such CNT dispersions.
Thanks to the combination of two new dispersion technologies aqueous suspensions of Baytubes carbon nanotubes (CNTs) can be produced which contain single tubes and thus show a high electrical and thermal conductivity. Multifilament yarns coated with such CNT dispersions can be woven to efficient fabric heaters. Such heaters already performed well in preventing the water in water storage tanks of JR Hokkaido's "Ryuhyo-Norokko" train from freezing.
An interesting development using multifilament yarns is a new fabric heater made
by weaving CNTEC® conductive yarns from Kuraray Living Co., Ltd. This fabric
generates heat homogeneously all over the surface because of its outstanding conductivity
and is supposed to be the first commercial use of Baytubes® CNTs from Bayer
MaterialScience in the Japanese market.
The fabric heater is lightweight and thin, compact and shows a long-lasting
bending resistance. It can be used for instance for car seats, household electrical
appliances, for heating of clothes and as an anti-freezing material. Tests revealed
that it may for example be installed in the water storage tank of JR Hokkaido's
"Ryuhyo-Norokko" train. Inside this train the temperature drops
to around -20 °C in wintertime, because so far no heating devices other
than potbelly stoves are available. According to JR Hokkaido railway company
the fabric heater performed well in preventing the water from freezing. A seat
heating application of the fabric heater is still on trial on another JR Hokkaido
train line. It is anticipated that the aqueous dispersions might as well be
suitable for the compounding of various kinds of materials.
In the course of their production CNTs usually form large and stable agglomerates
where the tubes are tightly entangled to each other. Dispersing such agglomerates
into individual tubes which show a maximum of electrical and thermal conductivity
has so far been a challenge. Thanks to a new dispersion technology using a zwitterionic
surfactant developed and patented by Prof. Dr. Bunshi Fugetsu from Hokkaido
University it is now possible to produce stable aqueous suspensions containing
CNTs at a mono-dispersed (tubular) level in industrial quantities. To achieve
this, a unique method for non-destructive dispersion of CNT agglomerates into
individual tubes developed by the Inoac Technical Center Co., Ltd. is applied
as well. The products show a stable and homogeneous conductivity and a durability
that easily covers the service life that is required for industrial products.
Through a combination of both technologies it is possible to disentangle the
agglomerates of Baytubes® in an efficient and stable way.