CRIS -Creative Research Institution- Hokkaido University

【Past Projects】Research on practical application of nanomaterials/technologies

Research on practical application of nanomaterials/technologies
Creating future industries through carbon nanotube (CNT) applications: contributions to environmental protection by manufacturing products with businesses
Dr. Bunshi FUGETSU

Professor, Graduate School of Environmental Science
and Creative Research Institution, Hokkaido University

Carbon nanotubes (CNTs) have been increasingly popular owing to their curious structure and peculiar characteristics. The latter comprise high strength and flexibility, chemical stability, and relatively high surface area with respect to the mass among others. In addition, the unique geometry/morphology of each tube characterized by an exceptionally small nanometer-scale diameter but a length of several centimeters holds enormous potentialities. Furthermore, CNTs have shown potential to transform from a highly conductive body to a semiconductor when subjected to structural changes and this has been a matter of great concern from the standpoint of their applicability as electrode material.

    In the course of their production CNTs usually form large and stable agglomerates, i.e., lumps of mass, where the tubes are tightly entangled to each other. This high degree of agglomeration of CNTs has been a major hurdle in their physical and chemical manipulation as well as industrial applications. Dispersing such agglomerates into individual tubes which show a maximum of electrical and thermal conductivity has so far been a challenge. In other words, the first urgent task for easy handling of the CNT assemblies is splitting them up into individual tubes through an appropriate dispersion technology.

    Thanks to a new dispersion technology using a zwitterionic surfactant (a special type of dispersant solution in which a single molecule can have both positive and negative electrical charges simultaneously) developed and patented by us at Hokkaido University, it is now possible to achieve non-destructive dispersion of CNT agglomerates into individual tubes(Fig. 1). CNT-dispersion tests conducted using various zwitterionic materials, ranging from the low-molecular weight double-ion boundary activators to high-molecular weight double-ion polymers, as dispersants have yielded good results. Development of novel method to prepare CNT-dispersant has made it possible to produce stable aqueous suspensions containing CNTs at a mono-dispersed (tubular) level in industrial quantities without the need of any specialized equipment. This in turn has led to the recent rapid surge in the development of novel applications of CNTs.


  

   Let us briefly describe some CNT-based product development and their industrial applications. Our laboratory has been involved in joint R&D, already for several years, with a number of business enterprises targeted at production of soft yarn capable of generating heat and also a sheet/surface heating element utilizing it. Joint work with Kurarayliving, Co., Ltd, Chakyu Dyeing Co., Ltd., and Matsubun Sangyo Co., Ltd has resulted in the development of application of aqueous dispersion technologies into individual nanotubes, namely, the development of CNT-coated electro-conductive (CNTEC) fibers. Considering the ease to handle, flexibility and applicability, as widely as possible, of the products produced using electrically conductive yarns, we adapted the polyester multifilament yarns as a base material. For coating the multifilament yarns, we have developed a yarn-printing method as one of the variants of the conventional yarn-based dyeing technology (Fig. 2).


  

   It is known that CNTEC itself is capable of producing heat upon applying electrical current. However, by arranging the CNT-based conductive yarn into a mesh pattern and then weaving it into a fabric using the regularly polyester-treated yarns, we succeeded in developing a surface/sheet heating element that entirely serves as a heater when supplied with power. The fabric heater produced in this way is lightweight, compact and shows a long-lasting bending resistance (Fig. 3).


  

   During January to middle of March in 2009, the conductive fabric/heater system was installed in the water storage tank of JR Hokkaido's "Ryuhyo-Norokko" train that runs between Shiretoko-Shari and Awashiri. According to JR Hokkaido railway company, the fabric heater shows good performance in preventing the water from freezing in wintertime, when the temperature inside this train drops to around -20°C (Fig. 4)


  

  Here is one more example. A CNTs-based road heating system has been in use in Sapporo Campus at the sidewalk near the main entrance of Hokkaido University. A CNT-coated heat-generating yarn tucked, with the help of a rubber mat, under the interlocked base material serves as the source of heat for snow-melting (Fig. 5).


   
  Both above-mentioned examples represent trailblazing CNT-based technologies, that utilize efficient sheet heating elements, developed in Hokkaido.