Abstract
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.
Highlights
Polymer nanofibers (NFs) have been developed for a variety of applications due to their high surface volume ratios, flexible functionalities, and outstanding mechanical properties[1]
The thermal conductivity of an electrospun composite NF is expected to increase because the addition of high k fillers is one of the representative methods to improve the thermal conductivities of polymers[24]
Peresin et al reported that enhancement of the elastic modulus in electrospun poly(vinyl alcohol) (PVA)/cellulose nanocrystal (CNC) NFs was observed, which was attributed to CNC reinforcement[12]
Summary
To measure the thermal conductivity of PVA and PVA/CNC NFs, nine NFs with different CNC contents of 0, 2, and 5% (w/w) were assembled on suspended microdevices as shown in Fig. 1 (for details see Methods). The Young’s modulus values of the PVA/CNC-2 and PVA/CNC-5 films are higher than that of the neat PVA film by 13% and 83%, respectively; the stiffness of the PVA/CNC composite films increased with increasing content of CNCs in the range of 0 to 5% Considering that they are made of the same solutions, we assumed that NFs had mechanical properties similar to those of the films. While the k values monotonously increased with increasing temperature, it is expected that further reduction of diameter may yield a peak (originating from higher crystallinity and Umklapp scattering) in k as a function of temperature as was observed in previous reports[17,19] This study demonstrated k enhancement in electrospun composite NFs for the first time and elucidated the mechanisms of the k increase
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