3.3 Characterisation and Properties of PVA/BC Bionanocomposites
73
and bulk materials [51, 53]. Finally, despite the robust data and good repeatability
of calculated elastic moduli, PFQNM method via AFM is inevitably different from
conventional tensile testing to determine the tensile modulus for bulk properties due
to distinct measurement mechanisms [54]. The difference in PVA phases can also
be characterised by the adhesion force mapping image exhibited in Fig. 3.10d, in
which adhesion forces for crystalline and amorphous phases have been determined
to be 19.7 ± 0.6 and 33 ± 2.8 nN, respectively. The higher adhesion of amorphous
phase arises from prevalent viscoelastic material behaviour of amorphous polymers
in a non-glassy state. This finding indicates that amorphus phase has less density and
surface tension as compared to corresponding crystalline phase [48].
The elastic modulus mapping image of PVA/3 wt% NBC bionanocomposites is
assessed on the A 2 -B 2 section, as depicted in Fig. 3.11b. The circled peaks with high
modulus values can be associated with the presence of NBCs within PVA matrices. In
addition, a cyclic pattern of low and high modulus domains depicted in Fig. 3.11b is
correlated with the alternating sequence of amorphous and crystalline phases of PVA
accordingly, which is considered as a very common characteristic in semicrystalline
polymers [47, 48]. Furthermore, the modulus trend of PVA matrices with the addition
of 3 wt% NBCs, as shown in Fig. 3.11b, is totally different from that of neat PVA along
with the change to the degree of structural orderness, Fig. 3.11c. Such a difference
may be attributed to reinforcing effect of NBCs on both crystalline and amorphous
phases of PVA matrices. The morphological structures of bionanocomposites in term
of elastic modulus have been further investigated at a high magnification in Fig. 3.11c.
Furthermore, a data analysis in the middle of the mapping image (A 3 -B 3 ) is depicted
in Fig. 3.10d. It is worth noting that both crystalline and amorphous phase widths are
in a range of 5–53 and 4–35 nm, respectively, which, however, are lower than that
of corresponding PVA (Fig. 3.10c). Decreasing the phase width means that the stack
size decreases accordingly from neat polymer to bionanocomposite films. In other
words, the number of lamellae stacks per unit volume, on the other hand, increases
from neat polymer to bionanocomposites illustrated in Fig. 3.11e, thus resulting in
the improvement of tensile strengths of PVA bionanocomposites. This phenomenon
can be interpreted by the Hall–Petch relation [55, 56] where yield stress and tensile
stress depend on the grain size. As a consequence, much higher tensile strength of
PVA/NBC nanocomposites at 147.94 MPa can be achieved as opposed to that of
PVA at 70.32 MPa. These findings offer the insight to establish a more accurate
theoretical modelling framework by combining both nanomechanical properties of
bionanocomposites and their bulk properties at the macroscopic level.
In case of PVA/3 wt% MBC bionanocomposites, the mapping image
of elastic modulus is shown in Fig. 3.12a, and the data analysis in the mapping
image (A 4 -B 4 ) is depicted in Fig. 3.12b. The crystalline phase width is in a range
of 14–60 nm when compared with the amorphous width of 15–59 nm, which is still
lower than that of PVA. This finding suggests that the number of lamellae stacks per
unit volume increases with the inclusion of MBCs as compared with that of pure
PVA. Such a result also explains why higher tensile strength of PVA/3 wt% MBC
bionanocomposites can be achieved as opposed to that of pure PVA.
73
and bulk materials [51, 53]. Finally, despite the robust data and good repeatability
of calculated elastic moduli, PFQNM method via AFM is inevitably different from
conventional tensile testing to determine the tensile modulus for bulk properties due
to distinct measurement mechanisms [54]. The difference in PVA phases can also
be characterised by the adhesion force mapping image exhibited in Fig. 3.10d, in
which adhesion forces for crystalline and amorphous phases have been determined
to be 19.7 ± 0.6 and 33 ± 2.8 nN, respectively. The higher adhesion of amorphous
phase arises from prevalent viscoelastic material behaviour of amorphous polymers
in a non-glassy state. This finding indicates that amorphus phase has less density and
surface tension as compared to corresponding crystalline phase [48].
The elastic modulus mapping image of PVA/3 wt% NBC bionanocomposites is
assessed on the A 2 -B 2 section, as depicted in Fig. 3.11b. The circled peaks with high
modulus values can be associated with the presence of NBCs within PVA matrices. In
addition, a cyclic pattern of low and high modulus domains depicted in Fig. 3.11b is
correlated with the alternating sequence of amorphous and crystalline phases of PVA
accordingly, which is considered as a very common characteristic in semicrystalline
polymers [47, 48]. Furthermore, the modulus trend of PVA matrices with the addition
of 3 wt% NBCs, as shown in Fig. 3.11b, is totally different from that of neat PVA along
with the change to the degree of structural orderness, Fig. 3.11c. Such a difference
may be attributed to reinforcing effect of NBCs on both crystalline and amorphous
phases of PVA matrices. The morphological structures of bionanocomposites in term
of elastic modulus have been further investigated at a high magnification in Fig. 3.11c.
Furthermore, a data analysis in the middle of the mapping image (A 3 -B 3 ) is depicted
in Fig. 3.10d. It is worth noting that both crystalline and amorphous phase widths are
in a range of 5–53 and 4–35 nm, respectively, which, however, are lower than that
of corresponding PVA (Fig. 3.10c). Decreasing the phase width means that the stack
size decreases accordingly from neat polymer to bionanocomposite films. In other
words, the number of lamellae stacks per unit volume, on the other hand, increases
from neat polymer to bionanocomposites illustrated in Fig. 3.11e, thus resulting in
the improvement of tensile strengths of PVA bionanocomposites. This phenomenon
can be interpreted by the Hall–Petch relation [55, 56] where yield stress and tensile
stress depend on the grain size. As a consequence, much higher tensile strength of
PVA/NBC nanocomposites at 147.94 MPa can be achieved as opposed to that of
PVA at 70.32 MPa. These findings offer the insight to establish a more accurate
theoretical modelling framework by combining both nanomechanical properties of
bionanocomposites and their bulk properties at the macroscopic level.
In case of PVA/3 wt% MBC bionanocomposites, the mapping image
of elastic modulus is shown in Fig. 3.12a, and the data analysis in the mapping
image (A 4 -B 4 ) is depicted in Fig. 3.12b. The crystalline phase width is in a range
of 14–60 nm when compared with the amorphous width of 15–59 nm, which is still
lower than that of PVA. This finding suggests that the number of lamellae stacks per
unit volume increases with the inclusion of MBCs as compared with that of pure
PVA. Such a result also explains why higher tensile strength of PVA/3 wt% MBC
bionanocomposites can be achieved as opposed to that of pure PVA.