100
4 PVA Bionanocomposite Films with Different Particle …
those of PVA. The former finding can be explained by good particle–matrix interactions with more uniform particle dispersion at low HNT contents. Whereas, the latter
result can be associated with typical particle agglomeration at high HNT contents up
to 10 wt% with the disappearance of ‘nanoeffect’ of HNTs since most HNT aggregates become less favourable microfillers with poor particle dispersion. As such,
those HNT aggregates could act as typical defects with high stress concentration
prone to crack initiation towards mechanical failure, thus leading to poor material
toughness [31].
In this study, the incorporation of three different nanofillers (i.e. HNTs, Cloisite
30B clays and NBCs) successfully enhanced mechanical properties of PVA
bionanocomposite films. According to our results, the highest increasing level among
PVA/HNT nanocomposites and PVA/NBC nanocomposites could be achieved at the
filler content of 3 wt%, as opposed to the optimum content of 5 wt% for PVA/Cloisite
30B clay bionanocomposites. Nonetheless, the increasing rate achieved in PVA
bionanocomposites using three nanofillers appeared to be quite different, which could
be associated with a variety of nanofiller features in terms of their structures and
geometries, as well as the degree of compatibility between nanofillers and polymer
matrices. With respect to nanofiller shape, it is well known that NBCs are regarded as
3D nanofillers as opposed to 2D nanofillers for HNTs and 1D nanofillers for Cloisite
30B clays. Different nanofiller shapes thereby influence the overall interfacial areas
between fillers and polymer matrices, which plays a key role in the improvement
of tensile strengths of nanocomposites with different filler–matrix interactions. The
second aspect is related to the structures, particularly for the location of hydroxyl
groups with respect to nanofiller structures and the amounts of hydroxyl groups within
nanofillers. In case of NBCs, hydroxyl groups are located inside their pores, which
tend to more closely interact with PVA in a 3D view. As for HNTs, the majority of
hydroxyl groups is constrained in inner tubes between layers, which make the matrixHNT interaction limited to inner tubes of HNTs only. Moreover, in case of Cloisite
30B clays, hydroxyl groups are located between layered structures, which means
that the interactions between polymer matrices and platelet-like clays are limited
to small constrained interlayer areas. Highest tensile moduli and tensile strength of
bionanocomposite films have been achieved with the incorporation of NBCs relative to those of PVA. Several reasons could explain the above-mentioned results in
relation to mechanical properties of bionanocomposites. First, 3D nanofiller shape
of NBCs can be generated at low nanofiller contents and in small particle sizes with
relatively large interfacial areas as compared with 2D HNTs and 1D Cloisite 30B
clays. Liu and Brinson [2] investigated the effect of nanofiller geometry on the reinforcing efficiency of nanocomposites, which showed that at a low nanofiller content
with the random nanofiller orientation, the transverse modulus of nanoparticle-based
nanocomposites significantly exceeded those of nanotube-based nanocomposites, as
well as nanoplatelet-based nanocomposites. Schadler et al. [45] reported that in case
of a nanocomposite system with the incorporation of nanoparticles and nanotubes
having a nanofiller diameter of 10 nm at the volume fraction of 10 vol%, the volume
4 PVA Bionanocomposite Films with Different Particle …
those of PVA. The former finding can be explained by good particle–matrix interactions with more uniform particle dispersion at low HNT contents. Whereas, the latter
result can be associated with typical particle agglomeration at high HNT contents up
to 10 wt% with the disappearance of ‘nanoeffect’ of HNTs since most HNT aggregates become less favourable microfillers with poor particle dispersion. As such,
those HNT aggregates could act as typical defects with high stress concentration
prone to crack initiation towards mechanical failure, thus leading to poor material
toughness [31].
In this study, the incorporation of three different nanofillers (i.e. HNTs, Cloisite
30B clays and NBCs) successfully enhanced mechanical properties of PVA
bionanocomposite films. According to our results, the highest increasing level among
PVA/HNT nanocomposites and PVA/NBC nanocomposites could be achieved at the
filler content of 3 wt%, as opposed to the optimum content of 5 wt% for PVA/Cloisite
30B clay bionanocomposites. Nonetheless, the increasing rate achieved in PVA
bionanocomposites using three nanofillers appeared to be quite different, which could
be associated with a variety of nanofiller features in terms of their structures and
geometries, as well as the degree of compatibility between nanofillers and polymer
matrices. With respect to nanofiller shape, it is well known that NBCs are regarded as
3D nanofillers as opposed to 2D nanofillers for HNTs and 1D nanofillers for Cloisite
30B clays. Different nanofiller shapes thereby influence the overall interfacial areas
between fillers and polymer matrices, which plays a key role in the improvement
of tensile strengths of nanocomposites with different filler–matrix interactions. The
second aspect is related to the structures, particularly for the location of hydroxyl
groups with respect to nanofiller structures and the amounts of hydroxyl groups within
nanofillers. In case of NBCs, hydroxyl groups are located inside their pores, which
tend to more closely interact with PVA in a 3D view. As for HNTs, the majority of
hydroxyl groups is constrained in inner tubes between layers, which make the matrixHNT interaction limited to inner tubes of HNTs only. Moreover, in case of Cloisite
30B clays, hydroxyl groups are located between layered structures, which means
that the interactions between polymer matrices and platelet-like clays are limited
to small constrained interlayer areas. Highest tensile moduli and tensile strength of
bionanocomposite films have been achieved with the incorporation of NBCs relative to those of PVA. Several reasons could explain the above-mentioned results in
relation to mechanical properties of bionanocomposites. First, 3D nanofiller shape
of NBCs can be generated at low nanofiller contents and in small particle sizes with
relatively large interfacial areas as compared with 2D HNTs and 1D Cloisite 30B
clays. Liu and Brinson [2] investigated the effect of nanofiller geometry on the reinforcing efficiency of nanocomposites, which showed that at a low nanofiller content
with the random nanofiller orientation, the transverse modulus of nanoparticle-based
nanocomposites significantly exceeded those of nanotube-based nanocomposites, as
well as nanoplatelet-based nanocomposites. Schadler et al. [45] reported that in case
of a nanocomposite system with the incorporation of nanoparticles and nanotubes
having a nanofiller diameter of 10 nm at the volume fraction of 10 vol%, the volume