Reinforcement of Polymer-Based Nanocomposites by Thermally Conductive and Electrically Insulating Boron Nitride Nanotubes
journal contribution
posted on 2019-12-30, 19:39 authored by Weimiao Wang, Zheling Li, Eric Prestat, Teruo Hashimoto, Jingwen Guan, Keun Su Kim, Christopher T. Kingston, Benoit Simard, Robert J. YoungA detailed study has been undertaken of the mechanisms
of stress
transfer in a nanocomposite consisting of hexagonal boron nitride
(hBN) nanotubes (BNNTs) in a poly(vinyl alcohol) (PVA) matrix based
upon the use of non-resonance Raman spectroscopy. The structure of
the BNNTs was characterized by using transmission electron microscopy
(TEM) where it was shown that the majority of the nanotubes had 2–5
walls with some having over 10 walls. The structure and mechanical
properties of nanocomposites containing up to 1 wt % of both pristine
and hydroxyl-functionalized nanotubes (OH-BNNTs) in PVA were investigated.
The dispersion of the BNNTs in the nanocomposites was characterized
by using a combination of transmission electron microscopy and Raman
mapping. The mechanical properties of the nanocomposites were evaluated
by tensile testing, and it was found that the Young’s modulus,
yield strength, and fracture stress all increased on the addition
of the BNNTs. A further improvement in the mechanical properties was
obtained for nanocomposites containing the OH-BNNTs. The variation
of the Young’s modulus of the nanocomposites with volume fraction
of the BNNTs was evaluated by using the rule of mixtures, and it was
shown that the effective Young’s modulus (Eeff) of the BNNTs approached 825 ± 100 GPa at low
volume fractions. The value of Eeff was
found to decrease with increasing BNNT volume fraction as the result
of nanotube bundling. By use of nondestructive Raman spectroscopy,
stress transfer from the PVA matrix to the BNNTs was evaluated from
stress-induced shifts of the hBN Raman G band, enabling the analysis
of interfacial adhesion in the nanocomposites. Larger band shifts
were obtained for the OH-BNNTs indicating a stronger interface between
the BNNTs and the PVA matrix and a better dispersion. A value of 1.34
± 0.72 was determined from the stress-induced Raman band shifts
for the Grüneisen parameter of the BNNTs. In consideration
of their efficient reinforcement of a polymer at very low additions
and unique electrically insulating and thermally conductive properties,
BNNTs are shown to have great potential to be used as nanofillers
for composites in a number of applications.
