Boron nitride nanotubes (BNNTs) are structurally similar to carbon nanotubes but are electrically insulating. When added to polymer matrices as nanocomposites, BNNTs can improve the mechanical, thermal, and dielectric properties of polymers. BNNTs enhance stiffness, thermal conductivity, and breakdown voltage while maintaining the electrical insulation of polymers. They disperse well due to strong interfacial interactions and do not negatively impact polymer properties. BNNTs show promise as nanofillers for high performance polymer composites.

1. Polymer/Boron Nitride Nanotube
(BNNTs) Nanocomposites
METE 560
Ümit TAYFUN
Middle East Technical University
Polymer Science & Technology

2. Boron nitride nanotubes
Boron nitride nanotubes, firstly synthesized in
1995, are structural analogues of carbon
nanotubes with boron and nitrogen atoms
instead of carbon atoms.
BNNTs can be imagined as a rolled up
hexagonal BN layer or as a carbon nanotube
(CNTs) in which alternating B and N atoms
entirely substitute for C atoms
Similar to CNTs, BNNTs have chiralities, an
important geometrical parameter, but for them,
the chiralities do not play an important role in
determining electrical properties
Atomic models of BNNT;
 (a)arm-chair
 (b)zig-zag
 (c)chiral

3. Properties of BNNTs
BNNTs are chemically inert, oxidation resistant, and
structurally stable.
BNNTs are electrically isolating materials with uniform
electronic properties independent of their size and
chirality.
Therefore, they are evaluated as suitable fillers for the
fabrication of mechanically and thermally enhanced
polymer composites, while preserving the electrical TEM images of single to multi-wall BNNTs with six walls
isolation of the polymer matrix
Excellent mechanical and thermal properties
Unusually efficient electrical insulators
Structurally stable and inert to most chemicals
Uniform band gap (5.5 eV)
High sensitivity for sensor materials
High resistance to oxidation
TGA showed that the oxidation of BNNTs starts
approximately at 800 °C, which is much higher
than the oxidation temperature of CNTs, which is
about 400 °C. High oxidation resistance of BNNTs
allows their applications in high temperature
environments.

4. BNNT vs CNT
Besides their structure, mechanical and thermal properties of BNNTs are very similar to CNTs.
Both BNNTs and CNTs have superb mechanical properties: the Young’s modulus of them has
been predicted to reach a TPa level.
However, BNNTs have better resistance to thermal oxidation than CNTs.
The electronic properties of BNNTs are also different from CNTs. BNNTs have a constant and
wide band-gap of 5.5 eV. Therefore, they are electrically isolating independent of their size or
chirality‟s. The electronic properties of BNNTs make them suitable nanofillers for the
production of isolating polymeric materials.
The obvious and most appealing difference between BNNTs and CNTs is their visible
appearance:
BNNTs are pure white (sometimes slightly yellowish due to N vacancies) while CNTs are totally
black
Comparison of properties of carbon nanotubes and boron nitride nanotubes Images of (a) CNTs and (b) BNNTs

5. Synthesis Methods of BNNTs
There are several methods used for synthesizing boron nitride nanotubes.
Mainly used methods are:
arc-discharge,
laser ablation,
ball milling,
chemical vapor deposition

6. Polymer/BNNT composites
The studies on the polymeric composites of BNNTs have been flourished
only over the last years.
The exciting properties of BNNTs, such as high elastic modulus and high
thermal conductivity make them advantageous for novel nanofillers in
composite materials to obtain mechanical reinforcement, high thermal
conductivity and a low coefficient of thermal expansion in a matrix.
Polymer/BNNT composites that have been studied to date were prepared as
thin films via solution–mixing, evaporation and melt-mixing techniques

7. Mechanical Properties
C. Zhi et al. fabricated PS/BNNT composites using a solution method
The mechanical properties of a polymer were improved
It was found that the results were solvent-
dependent, that is, when chloroform
was used to disperse BNNTs, the elastic
modulus of the composite film was decreased.
However, improvements can be obtained by
using DMF as a solvent. This is attributed to
different BNNT dispersions in different organic
solvents
Benefiting from the pure white appearance of BNNTs,
the composite films retained good transparency
(a) a blank PS film (b) BNNT/PS film (c) BNNT/PmPV/PS film
C. Zhi, Y. Bando, C. Tang, S. Honda and H. Kuwahara, J. Mater. Res., 2006, 21, 2794.

8. Mechanical Properties
Zhou et al. used isophorone diisocyanate (IPDI) activated BNNTs to
synthesize BNNT/polyvinyl alcohol (PVA) and hydroxypropyl methylcellulose
(HPMC) composites
Addition of a small fraction of activated
3 wt%IPDI–BNNTs IPDI–BNNTs leads to a considerable
1 wt%IPDI–BNNTs 3 wt%IPDI–BNNTs increase in both Young’s modulus and
Pure PVA
1 wt%IPDI–BNNTs
1 wt% BNNTs tensile strength.
3 wt% BNNTs Pure HPMC
1 wt% BNNTs
3 wt% BNNTs
When the amount of ap-BNNTs was
added, both tensile strength and Young’s
BNNT/PVA BNNT/HPMC
modulus were decreased
Activated IPDI–BNNTs exhibit good
dispersibility and chemical activity.
Adding IPDI–BNNTs into the solution of
PVA or HPMC, the strong interfacial
interactions between BNNTs and polymers
were achieved
In contrast, due to the well-crystallized
BNNT/PVA BNNT/HPMC
surface, pristine BNNTs exhibit limited
dispersibility and poor interfacial
S-J Zhou et al, Nanotechnology 23 (2012) 055708 interactions with PVA and HPMC.

9. Mechanical Properties
PMMA/BNNTs composites were fabricated using a solution method by C. Y. Zhi et
al.
The elastic modulus of PMMA was improved up to 19% while using only a 1wt.%
BNNTs loading fraction. These results show that the external force can be
transferred to BNNTs in some degree
Tensile strength decreased
The elongation also decreased, indicates that the interaction between
BNNTs and polymer chains exists.
C. Y. Zhi et al., Journal of Nanomaterials, 2008, 642036

10. Mechanical Properties
Four kinds of polymeric composites with BNNTs were fabricated by Chunyi
Zhi et al.
Vickers hardness of polymethyl methacrylate (PMMA), polystyrene (PS),
polyvinyl butyral (PVB), and polyethylene vinyl alcohol (PEVA) was only
slightly affected when they were loaded with the BN nanotubes.
This indicates that there is no obvious negative effect on the mechanical
properties of the composites.
With the exception of PVB, the Vickers hardness did not notably
decrease after adding BNNTs
Chunyi Zhi et al., Adv. Funct. Mater. 2009, 19, 1857–1862

11. Mechanical Properties
NASA have developed new materials with greater anti-penetration characteristics.
By using BNNT polymer composites, researchers have successfully fabricated the
new materials to demonstrate enhanced material toughness and hardness.
Nonwoven mats of BNNTs are used as toughening layers to maximize energy
absorption and/or high hardness layers to rebound or deform penetrators.
They can also be used as reinforcing inclusions, combining with other polymer
matrices to create reinforcing composite layers to maximize anti-penetrator
protection
Microindentation test of BNNT composite
NASA Langley, Jefferson Lab, www.nianet.org

12. Thermal Properties
After adding BNNTs, the coefficient of thermal
expansion (CTE) of PMMA dramatically decreases,
 This indicates that BNNTs significantly restrict the
mobility of polymer chains
Tg of a PMMA/BNNT composite becomes 85.2 °C
In case of organic-inorganic nanocomposites, the mobility
of polymer chains is significantly affected by the
confinement and strength of polymer-surface interactions.
This applies to the interactions between BNNTs and
PMMA chains.
C. Y. Zhi et al., Journal of Nanomaterials, 2008, 642036

13. Thermal Properties
Low CTE is a thermal parameter in polymeric composites used in packaging materials.
Chunyi Zhi et al. fabricated polymethyl methacrylate
(PMMA), polystyrene (PS), polyvinyl butyral (PVB), and
polyethylene vinyl alcohol (PEVA) composites filled with
BNNTs by solution mixing.
All composites exhibit much lower CTE compared
with the corresponding neat polymers. This implies the
appearance of constraints to the polymer chain
movements due to their interactions with BNNTs.
Due to the different affinity of BNNTs for various
polymers, the BNNT absorb different fractions of
polymer.
The weight fractions of BNNTs in the composites
range from 18 to 37 wt%. It was found that the weight
fraction of BNNTs in a composite can be controlled by
the concentration of the polymer solution.
Chunyi Zhi et al., Adv. Funct. Mater. 2009, 19, 1857–1862

14. Thermal Conductivity
Chunyi Zhi et al. also performed Thermal conductivity measurements;
Neat polymers possess low thermal conductivity.
After embedding BNNTs, this property was improved.
Thermal conductivity of PMMA sample drastically increases up to a
21-fold gain after adding BNNT.
 The thermal conductivity improvements of the composites are
roughly related to the BNNTs fractions in them.
In the case of a PVB composite loaded with BNNTs, a 7-fold increase
was documented.
It is also assumed that an interfacial (BNNT–polymer) thermal transfer
varies from one polymer to another, inducing the observed discrepancy
in thermal conductivity values for almost the same BNNT loading
fractions in different matrices.
Chunyi Zhi et al., Adv. Funct. Mater. 2009, 19, 1857–1862

15. Thermal Conductivity
Composite films with 5wt.% and 10wt.%
BNNTs fractions of PMMA nanocomposites
were chosen by Zhi et al. for the thermal
conductivity measurements.
Thermal conductivity of PMMA loaded with
a 10wt.% BNNT fraction was improved 3
times
compared to blank PMMA
It should be emphasized that this gain is
likely to display the lower estimate for the
observed improvement since the BNNT
texture within the film is generally misaligned
with the direction used for the heat flow
measurements
C. Y. Zhi et al., Journal of Nanomaterials, 2008, 642036

16. Thermal Conductivity
Huang et al. demonstrated that POSS modified
BNNTs are very effective nanofillers for making
dielectric epoxy composites with high thermal
conductivity.
The room temperature thermal conductivity of
the pure epoxy is about 0.2. The highest
measured room-temperature thermal
conductivity is 2.77 at 30.0 wt% BNNT fraction,
which is 13.6 times higher than that of the pure
epoxy resin.
Improvement of thermal conductivity in
the present epoxy/BNNT nanocomposites
is nonlinear: at a high fraction of BNNTs, a
more effective improvement was observed.
This implies that efficient thermal transfer
pathways start to form at a high fraction of
BNNTs due to tube-to-tube connections
Xingyi Huang et al., Adv. Funct. Mater. 2012, 201201824

17. Dielectric Properties
The dielectric loss tangent is closely
associated with the electrical conductivity in
the epoxy composites, which is determined
by a charge carrier density at the certain
temperature.
Therefore, the decreased dielectric loss
tangent of epoxy/BNNT nanocomposites
should be attributed to a reduction of the
electrical conductivity, which is confirmed by
the conductivity spectra of the composites
One of the possible reasons for lower
dielectric constant obtained in the
epoxy/BNNT composites is the relatively low
intrinsic dielectric constant of hexagonal
BNNTs
 Besides this factor, the other contribution
may come from the restriction of bulk
polarization in epoxy resin due to the
immobility of polymer chains hindered
by BNNTs.
Xingyi Huang et al., Adv. Funct. Mater. 2012, 201201824

18. Dielectric Properties
Chunyi Zhi et al. examined the breakdown electric fields of neat polymers
with that of their BNNTs composites.
Only in the case of PS does the breakdown electric field decrease, while in
the other three cases, it marginally increases.
 In any case, all the materials remain insulating and possess a high
breakdown electric field, which is fully suitable for dielectric packages.
Chunyi Zhi et al., Adv. Funct. Mater. 2009, 19, 1857–1862

19. Dielectric Properties
The appealing point of BNNT usage in polymeric composites is that the original
dielectric nature of a polymer is kept in the resultant composite. This fact is crucial in
many cases, such as packing materials for electrical circuits and power modules.
The electrical breakover voltages of a
blank PMMA and its composites
are compared.
This reveals that both blank PMMA
and its BNNTs composites have a
similar breakover electric field
Therefore, the presently developed
BNNTs/polymer composites are surely
suitable materials for heat-releasing
parts due to unique combination of
decent thermal conductivity and perfect
electrical insulation.
C. Y. Zhi et al., Journal of Nanomaterials, 2008, 642036

20. Radiation Shielding Properties
NASA have developed a neutron shielding material using boron-containing
polymer nanocomposites, which include boron nanoparticles (BNPs) (0D),
boron nitride nanotubes (BNNTs) (1D), and boron nitride nano-platelets (2D).
The large neutron absorption cross section, along with the light weight and
large surface area of BNNT, enable effective shielding with much less volume
and weight.
NASA Langley, Jefferson Lab, www.nianet.org

21. Morphology
10 wt% BNNT-POSS 10 wt% BNNT-POSS
Huang et al. performed the SEM
observations of the fractured surface of the
BNNT-POSS based epoxy composites
It is seen that BNNTs are uniformly
dispersed in the epoxy matrix.
In addition, interface-debonding between
20 wt% BNNT-POSS 30 wt% BNNT-POSS BNNTs and the epoxy resin is not
observed, suggesting the strong interfacial
adhesion.
Such uniform dispersion of BNNTs and
strong interface are beneficial to the
thermal conductivity enhancement
Xingyi Huang et al., Adv. Funct. Mater. 2012, 201201824

22. Morphology
D. Lahiri et al reinforced biodegradable
b
polylactide–polycaprolactone copolymer
(PLC) with 0, 2 and 5 wt.% BNNTs
Figures show the BNNTs bridges
within PLC matrix.
Dangling BNNTs with the other end fully
embedded in the polymer matrix are also
observed.
BNNTs behave as rigid reinforcements and
provide benefits of short fiber strengthening.
D. Lahiri et al., Acta Biomaterialia, 2010

23. Conclusion
Mechanical properties of CNTs and BNNTs are similar. They are both ideal for
mechanical applications.
High oxidation resistance of BNNTs allows their applications in high temperature
environments.
The electronic properties of BNNTs are different from CNTs. BNNTs have a constant
and wide band-gap of 5.5 eV. The electronic properties of BNNTs make them suitable
nanofillers for the production of isolating polymeric materials
The exciting properties of BNNTs, such as high elastic modulus and high thermal
conductivity make them advantageous for novel nanofillers in polymer composites to
obtain mechanical reinforcement, high thermal conductivity and a low coefficient of
thermal expansion in a matrix.
Chemical modification of inert BNNTs results dispersibility improvement in polymeric
matrices.
Future research efforts are needed to demonstrate the performance of functionalized
BNNTs in mechanical, electronic, chemical, and biological applications.

24. References
Sheng-Jun Zhou et al., 2012 Nanotechnology, 23, 055708
C. Zhi, Y. Bando, C. Tang, S. Honda and H. Kuwahara, J. Mater. Res., 2006, 21,
2794.
C. Y. Zhi, Y. Bando, C. Tang, H. Kuwahara, and D. Golberg, Journal of
Nanomaterials, 2008, 642036
Chunyi Zhi, Yoshio Bando, Takeshi Terao, Chengchun Tang, Hiroaki Kuwahara, and
Dimitri Golberg, Adv. Funct. Mater. 2009, 19, 1857–1862
Xingyi Huang , Chunyi Zhi , Pingkai Jiang , Dmitri Golberg , Yoshio Bando,
Toshikatsu Tanaka, Adv. Funct. Mater. 2012, 201201824
NASA Langley, Jefferson Lab, www.nianet.org
D. Lahiri et al., Acta Biomaterialia, 2010