120
5 3D Interphase of PVA Bionanocomposite Films
nanocomposite sample and the variation of elastic moduli from PVA matrices, interphases to NBCs, respectively. According to a typical cut line A 17 B 17 shown in
Fig. 5.2c, elastic modulus has significantly increased from the lowest modulus level
of 14.8 GPa with respect to PVA matrices to the highest of 72.86 GPa for NBCs.
In particular, the interphase exhibits an almost linearly increasing relationship of
its elastic modulus with scan distance except interphase boundary regions around
PVA matrices and NBCs alone, which is in a range from 17.1 GPa near the PVA
region to 64.9 GPa around NBCs with the measured interlayer thickness of 31.8 nm.
Final interphase modulus was obtained from the solid black curve by best fitting
discrete modulus data sets based on 25 representative LSRs in Fig. 5.2d, which
also applied to determine elastic moduli of NBCs and PVA matrices to be 78.4
± 4.9 and 24.25 ± 4.2 GPa, respectively. The same analysis was carried out for
PVA/HNT bionanocomposites and PVA/Cloisite 30B clay bionanocomposites with
associated results presented in Figs. 5.3 and 5.4. It was found that similar fully
and partially embedded Cloisite 30B clays and HNTs were manifested in Figs. 5.3a
and 5.4a, respectively. With respect to PVA/Cloisite 30B clay bionanocomposites,
their interphase modulus was also increased from 20.6 GPa near PVA matrices to
42.2 GPa around Cloisite 30B clays. Such a modulus-gradient phenomenon was
also revealed in PVA/HNT bionanocomposites with the interphase modulus varying
from 19.3 to 40 GPa accordingly. In particular, PVA modulus appeared to be 21.4
± 4.1 and 19.8 ± 3.7 GPa for PVA/Cloisite 30B clay bionanocomposites and
PVA/HNT bionanocomposites, which was equivalent to 13.4 and 22.5% less than
that for PVA/NBC bionanocomposites. It was implied that PVA modulus was the
highest when incorporated with NBCs as opposed to the inclusion of the other two
nanoparticle types, which was in good agreement with higher tensile strength data
of PVA/NBC bionanocomposites previously mentioned in Fig. 4.11b. Such a finding
could be associated with 3D nanofiller shape of NBCs enabling to possibly restrict
more PVA molecular chains as opposed to 2D tubular HNTs and 1D platelet-like
Cloisite 30B clays. The interphase could be considered as transitional zones with
a typical modulus gradient from polymer matrices to reinforcements in order to
achieve effective load transfer for improving the mechanical properties of composite
materials. Our results revealed the existing interphase with excellent elastic properties in PVA/NBC nanocomposites, as shown in Fig. 5.2d. A modulus gradient was
detected ranging from 25.32 ± 3.4 GPa for PVA matrices to 66.3 ± 3.2 GPa for
NBCs, which appeared to be relatively high when compared with those from 22.2
± 2.9 to 43.4 ± 3.1 GPa, as well as from 20.6 ± 3.4 to 41.6 ± 4.6 GPa in case
of PVA/Cloisite 30B clay bionanocomposites and PVA/HNT bionanocomposites,
respectively, according to Figs. 5.3d and 5.4d. Higher interphase modulus identified
in PVA/NBC bionanocomposites may directly benefit from highly porous NBC structures to cover all their 3D structures when compared with 1D platelet-like Cloisite
30B clays and 2D tubular HNTs as reinforcements. This can further facilitate inducing
a highly positive capillary pressure to drive PVA molecular chains into NBC pores
with typical resulting chemical bonding in bionanocomposites [2, 3]. These NBC
pores also possess ‘mechanical anchoring’ mechanism [6] when interacting with
PVA molecular chains, which means that a mechanical interlocking phenomenon
5 3D Interphase of PVA Bionanocomposite Films
nanocomposite sample and the variation of elastic moduli from PVA matrices, interphases to NBCs, respectively. According to a typical cut line A 17 B 17 shown in
Fig. 5.2c, elastic modulus has significantly increased from the lowest modulus level
of 14.8 GPa with respect to PVA matrices to the highest of 72.86 GPa for NBCs.
In particular, the interphase exhibits an almost linearly increasing relationship of
its elastic modulus with scan distance except interphase boundary regions around
PVA matrices and NBCs alone, which is in a range from 17.1 GPa near the PVA
region to 64.9 GPa around NBCs with the measured interlayer thickness of 31.8 nm.
Final interphase modulus was obtained from the solid black curve by best fitting
discrete modulus data sets based on 25 representative LSRs in Fig. 5.2d, which
also applied to determine elastic moduli of NBCs and PVA matrices to be 78.4
± 4.9 and 24.25 ± 4.2 GPa, respectively. The same analysis was carried out for
PVA/HNT bionanocomposites and PVA/Cloisite 30B clay bionanocomposites with
associated results presented in Figs. 5.3 and 5.4. It was found that similar fully
and partially embedded Cloisite 30B clays and HNTs were manifested in Figs. 5.3a
and 5.4a, respectively. With respect to PVA/Cloisite 30B clay bionanocomposites,
their interphase modulus was also increased from 20.6 GPa near PVA matrices to
42.2 GPa around Cloisite 30B clays. Such a modulus-gradient phenomenon was
also revealed in PVA/HNT bionanocomposites with the interphase modulus varying
from 19.3 to 40 GPa accordingly. In particular, PVA modulus appeared to be 21.4
± 4.1 and 19.8 ± 3.7 GPa for PVA/Cloisite 30B clay bionanocomposites and
PVA/HNT bionanocomposites, which was equivalent to 13.4 and 22.5% less than
that for PVA/NBC bionanocomposites. It was implied that PVA modulus was the
highest when incorporated with NBCs as opposed to the inclusion of the other two
nanoparticle types, which was in good agreement with higher tensile strength data
of PVA/NBC bionanocomposites previously mentioned in Fig. 4.11b. Such a finding
could be associated with 3D nanofiller shape of NBCs enabling to possibly restrict
more PVA molecular chains as opposed to 2D tubular HNTs and 1D platelet-like
Cloisite 30B clays. The interphase could be considered as transitional zones with
a typical modulus gradient from polymer matrices to reinforcements in order to
achieve effective load transfer for improving the mechanical properties of composite
materials. Our results revealed the existing interphase with excellent elastic properties in PVA/NBC nanocomposites, as shown in Fig. 5.2d. A modulus gradient was
detected ranging from 25.32 ± 3.4 GPa for PVA matrices to 66.3 ± 3.2 GPa for
NBCs, which appeared to be relatively high when compared with those from 22.2
± 2.9 to 43.4 ± 3.1 GPa, as well as from 20.6 ± 3.4 to 41.6 ± 4.6 GPa in case
of PVA/Cloisite 30B clay bionanocomposites and PVA/HNT bionanocomposites,
respectively, according to Figs. 5.3d and 5.4d. Higher interphase modulus identified
in PVA/NBC bionanocomposites may directly benefit from highly porous NBC structures to cover all their 3D structures when compared with 1D platelet-like Cloisite
30B clays and 2D tubular HNTs as reinforcements. This can further facilitate inducing
a highly positive capillary pressure to drive PVA molecular chains into NBC pores
with typical resulting chemical bonding in bionanocomposites [2, 3]. These NBC
pores also possess ‘mechanical anchoring’ mechanism [6] when interacting with
PVA molecular chains, which means that a mechanical interlocking phenomenon