3.3 Characterisation and Properties of PVA/BC Bionanocomposites
71
water. Then the second peak at the temperature of 274 °C is attributed to the decomposition of PVA due to the dehydration reaction on polymeric chains, as well as
degradation of main backbones. Finally, the third peak in relation to the degradation
of polyene residues appears at the temperature below 429 °C. With increasing NBC
and MBC contents, the thermal stabilities of both PVA/BC bionanocomposites are
improved significantly with reference to that of PVA, as evidenced by consistently
higher T 5% , T 80% and T d values. Thermal stability level of bionanocomposites is even
more pronounced when incorporated with NBCs in relation to T 5% and T 80% . The
shift of decomposition temperatures T d and T
d means that the dehydration process
can be potentially hindered, arising from the interaction between hydroxyl groups of
PVA and hydroxyl groups on NBC and MBC surfaces, as confirmed from previous
FTIR results. Furthermore, the mass loss process occurring in the third DTG peaks
suggests that the thermal decomposition of PVA bionanocomposites requires more
reaction activation energy with the higher reaction order [46]. This finding may be
attributed to the existence of NBC and MBC particles acting as barrier materials to
limit the exothermicity of pyrolysis reaction with better thermal resistance of PVA
bionanocomposites. On the other hand, DTG peaks of PVA bionanocomposites at the
second decomposition step become much wider than that of neat PVA, consisting of
main and side peaks, as opposed to single DTG peak for PVA at the same step. Such
a single peak for PVA can be associated with the elimination reaction, while side and
main peaks for PVA/BC bionanocomposites correspond to elimination reaction, as
well as the overlap of continual eliminations and chain-scission reactions that require
more energy to accrue at high temperatures [46].
3.3.5 Topography and Nanomechanical Properties
Nanomechanical properties of PVA films are presented in Fig. 3.10. As seen in
Fig. 3.10a, there are two typical distinct phases known as crystalline phase (in bright
white colour) and amorphous phase (in dark colour), which are generally detected
in semicrystalline polymers [47, 48] like PVA. Elastic modulus mapping image of
PVA has been analysed in its middle section (A 1 -B 1 ) with associated results being
depicted in Fig. 3.10c. The regions with a high modulus level of 24 ± 4.2 GPa and
a phase width of 20–76 nm are related to the bundles of semicrystalline stacks in
crystalline phase. This value appears to be far higher than the elastic modulus of 9.9
GPa for local PVA/poly (acrylic acid) (PAA) nanophase, as previously reported by
Pakzad et al. [49]. Nonetheless, it is very similar to corresponding elastic modulus of
23.69 GPa obtained from PVA/chitosan composite film coating [50]. In comparison,
the regions assigned to amorphous phase have a relatively low modulus of 11.4
± 3.1 GPa along with the amorphus phase width of 18–65 nm. The variation of
crystalline phase width is attributed to different orientation of semicrystalline bundles
for the designated section [47]. Elastic modulus of bulk PVA films is about 2.08
GPa at a macroscopic level, which is far less than that of local PVA nanoscaled
regions based on AFM. Such a phenomenon is manifested when nanomechanical
71
water. Then the second peak at the temperature of 274 °C is attributed to the decomposition of PVA due to the dehydration reaction on polymeric chains, as well as
degradation of main backbones. Finally, the third peak in relation to the degradation
of polyene residues appears at the temperature below 429 °C. With increasing NBC
and MBC contents, the thermal stabilities of both PVA/BC bionanocomposites are
improved significantly with reference to that of PVA, as evidenced by consistently
higher T 5% , T 80% and T d values. Thermal stability level of bionanocomposites is even
more pronounced when incorporated with NBCs in relation to T 5% and T 80% . The
shift of decomposition temperatures T d and T
d means that the dehydration process
can be potentially hindered, arising from the interaction between hydroxyl groups of
PVA and hydroxyl groups on NBC and MBC surfaces, as confirmed from previous
FTIR results. Furthermore, the mass loss process occurring in the third DTG peaks
suggests that the thermal decomposition of PVA bionanocomposites requires more
reaction activation energy with the higher reaction order [46]. This finding may be
attributed to the existence of NBC and MBC particles acting as barrier materials to
limit the exothermicity of pyrolysis reaction with better thermal resistance of PVA
bionanocomposites. On the other hand, DTG peaks of PVA bionanocomposites at the
second decomposition step become much wider than that of neat PVA, consisting of
main and side peaks, as opposed to single DTG peak for PVA at the same step. Such
a single peak for PVA can be associated with the elimination reaction, while side and
main peaks for PVA/BC bionanocomposites correspond to elimination reaction, as
well as the overlap of continual eliminations and chain-scission reactions that require
more energy to accrue at high temperatures [46].
3.3.5 Topography and Nanomechanical Properties
Nanomechanical properties of PVA films are presented in Fig. 3.10. As seen in
Fig. 3.10a, there are two typical distinct phases known as crystalline phase (in bright
white colour) and amorphous phase (in dark colour), which are generally detected
in semicrystalline polymers [47, 48] like PVA. Elastic modulus mapping image of
PVA has been analysed in its middle section (A 1 -B 1 ) with associated results being
depicted in Fig. 3.10c. The regions with a high modulus level of 24 ± 4.2 GPa and
a phase width of 20–76 nm are related to the bundles of semicrystalline stacks in
crystalline phase. This value appears to be far higher than the elastic modulus of 9.9
GPa for local PVA/poly (acrylic acid) (PAA) nanophase, as previously reported by
Pakzad et al. [49]. Nonetheless, it is very similar to corresponding elastic modulus of
23.69 GPa obtained from PVA/chitosan composite film coating [50]. In comparison,
the regions assigned to amorphous phase have a relatively low modulus of 11.4
± 3.1 GPa along with the amorphus phase width of 18–65 nm. The variation of
crystalline phase width is attributed to different orientation of semicrystalline bundles
for the designated section [47]. Elastic modulus of bulk PVA films is about 2.08
GPa at a macroscopic level, which is far less than that of local PVA nanoscaled
regions based on AFM. Such a phenomenon is manifested when nanomechanical