Anisotropic electrical and thermal characteristics of carbon nanotube-embedded wood

Wood has a long history as a traditional material which has been widely recognized to be hardly conductive electrically and thermally. Making wood conductive electrically and thermally is technically a new challenge to think outside the box. Here, we demonstrate that wood can be electrically and thermally conductive by dipping wood in the solution where multi-walled carbon nanotube (MWCNT) is dispersed evenly. Our idea is based on the fact that wood usually absorbs water or moisture due to its hygroscopic properties. When walnut wood was dipped in the MWCNT solution, the wood started to absorb water containing MWCNT. As a result, well-networked MWCNTs were homogeneously formed in the structure of wood with natural porosity. Interestingly, superior electrical and thermal conductivity were observed along the cellulose fiber direction of the walnut wood, compared with the tangential direction perpendicular to the fiber. We found that wood has electrically and thermally anisotropic characteristics due to the grain boundary by wood fibers. Furthermore, the degree of conductivity was controllable by varying dipping times. We think that this discovery will open a new avenue to utilize wood as a nanocomposite material having electrical and thermal properties.