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Development of the CNT Composite Conductive Resin Using Nano-Dispersion Process
1. Introduction
CNTs are very good to thermal conductivity, electrical conductivity, and molecular adsorption. It is expected when composite resin and CNTs, to become new functional composite materials. However, The CNTs would form aggregates with intermolecular forces of each other. Aggregated CNTs is not be able to exert the original characteristics. CNTs dispersion technology for acid treatment or the use of surfactants has been reported. However, suppression of re-aggregation is difficult in this technique. Serious problems of cost for manufacture of CNTs remain.
We found an effective technique of dispersing nano-scale CNTs [1]. By mixing and stirring the CNTs and an aromatic compound having a specific structure (dispersion medium), CNTs to form a gel having a three-dimensionall network structure. This gel can maintain long time nano-dispersion of CNTs. This effective technique is very simple. We expect a decrease in production costs using this technique.
In this study, we tried to prepare conductive composite resins using the CNTs dispersion techniques. A water-soluble resin and a polyester resin were examined. We used an aromatic and polyester resin. And, we used the polyvinyl alcohol (PVA) as a water-soluble resin, and water soluble dispersion medium. Prepared composites were studied by transmission electron microscopy (TEM). Volume resistivity was measured by using four-point probe method.
2. Experiment
Benzoyl peroxide was used as curing agent of multi-walled carbon nanotubes (MWNTs). After addition of benzoyl peroxide and MWNTs (1.0-5.0 wt%) in the polyester resin, we repeated the ultrasonic irradiation and mixed with a centrifugal stirrer. In case of water-soluble resin, After addition of water-soluble dispersion medium and MWNTs (1.0-5.0 wt%) in the PVA resin, we repeated the ultrasonic irradiation and mixed with a stirrer. In either case, the resin became a black gel with fluidity. These gels were on the substrate, and dried or cured at room temperature.
3. Result and Discussed
TEM images of the composite resin spread were shown in Fig.1. In either case, MWNTs formed network structures in three dimensions. It was succeeded in forming the persistent nano-dispersion of the MWNTs in the resin.
Measurement of the volume resistivity of the composite films using four-point probe method is shown in Table I. In the case of polyester, was shown maximum conductivity (MWNTs content 5.0 wt%) 8.15×10-1 [Ω・cm]. In the case of PVA, was shown maximum conductivity (MWNTs content 2.5 wt%) 9.9 [Ω・cm]. It was found that MWNTs formed three-dimensional conductive network structures. For PVA, the addition of 3.0 wt% or more, CNTs brings poor workability so poor.
4. References
1. KONISHI Toshifumi, MOCHIZUKI Takayuki, MATSUI Koichiro, PCT/JP2010/069666
Fig.1. Microscope(TEM) observation of (a) PVA/ MWNTs composite resin, (b) polyester/ MWNTs composite resin.
Table I. Volume resistivity of the conductive composite resin |
||
MWNTs content [wt %] |
Polyester [Ω・cm] |
PVA [Ω・cm] |
1.0 |
1.15×102 |
1.14×102 |
1.5 |
7.89×101 |
8.65×101 |
2.0 |
3.43×101 |
1.78×101 |
2.5 |
2.00×101 |
9.99 |
3.0 |
1.48×101 |
－ |
3.5 |
5.85 |
－ |
4.0 |
3.36 |
－ |
4.5 |
1.98 |
－ |
5.0 |
8.15×10-1 |
－ |
