The thermal conductivity enhancement of neat poly(vinyl alcohol) and poly(vinyl alcohol) (PVA)/cellulose nanocrystal (CNC) composite was attempted via electrospinning. The suspended microdevice technique was applied to measure the thermal conductivity of electrospun nanofibers (NFs). Neat PVA NFs and PVA/CNC NFs with a diameter of approximately 200 nm showed thermal conductivities of 1.23 and 0.74 W/m-K, respectively, at room temperature, which are higher than that of bulk PVA by factors of 6 and 3.5, respectively. Material characterization by Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis confirmed that the thermal conductivity of the PVA/CNC NFs was enhanced by the reinforcement of their backbone rigidity, while that of the neat PVA NFs was attributed to the increase in their crystallinity that occurred during the electrospinning.
The interfacial effect between an organic matrix and inorganic nanofillers on the thermal conductivity of a polymer composite was systematically explored by assembling amine-functionalized boron nitride nanotubes (BNNTs) onto an electrospun polyacrylic acid/polyvinyl alcohol nanofibrous web through either physical electrostatic interactions or chemical coupling reactions. The amine functionalization of BNNTs and their integration onto the electrospun nanofiber webs were confirmed by various analytical techniques. No distinctive change in thermal stability and conductivity could be observed between the pristine-and physically assembled polymeric nanofiber films; however, the chemically assembled nanofiber film produced via the chemical coupling reaction showed large improvements in both thermal stability and thermal conductivity. Our study demonstrated that it is possible to produce a highly thermally conductive polymer nanofiber film through interfacial engineering, even if the incorporation of inorganic filler is below 1 wt%.
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