3.3 Characterisation and Properties of PVA/BC Bionanocomposites
67
inclusion of 5 wt% nanodiamonds (NDs), the tensile strength of PVA nanocomposites was enhanced by 30.5%. In comparison, tensile strengths of PVA/NBC
bionanocomposites and PVA/MBC bionanocomposites at the BC content of 3 wt%
have been reported in this study to be increased by 110 and 72%, which appear to be
more desirable than other carbon-based nanocomposites reinforced with GOs and
SWNTs (despite relatively small SWNT contents used) when both nanofiller cost
and enhancement levels in relation to mechanical properties of nanocomposites are
concurrently considered.
3.3.3 Fracture Morphology
As observed in Fig. 3.8, all bionanocomposites have been characterised with rough
fracture surfaces due to embedded BC nanoparticles when compared with neat PVA.
In particular, uniform multi-layered structures are evidently seen for PVA/NBC
bionanocomposites with the inclusion of 3 and 5 wt% NBCs, as illustrated in
Fig. 3.8b, c, along the parallel direction to tensile loading. Such structures are
very similar to nacre structures mentioned elsewhere [3, 27, 28] and are in good
agreement with those observed in PVA-grafted GO (PVA-g-GO) nanocomposites
[28]. The fibrillation effect of fractured materials also takes place particularly in
PVA/NBC bionanocomposites when subjected to the stretching of bionanocomposite films under the unidirectional tension. This phenomenon suggests far higher
ductility of PVA/NBC bionanocomposites when compared with that of PVA/MBC
counterparts, which is also proven by their consistently higher elongation at break
in Fig. 3.7b.
On the other hand, fracture areas of PVA/MBC bionanocomposites demonstrate
less layered structures as opposed to PVA/NBC bionanocomposites at the BC content
of 3 wt%. This phenomenon can be ascribed to smaller surface areas of MBCs
to reduce interfacial interactions between fillers and PVA matrices. As depicted in
Fig. 3.8g, with increasing the MBC content up to 10 wt%, interparticle distance can be
significantly reduced owing to large amounts of particle agglomerates. As a result, the
formation of local networks of MBC particles to act as stress concentration sites prone
to mechanical failure occurs, thus lowering tensile strengths of nanocomposites, as
shown in Fig. 3.7a.
3.3.4 Thermal Properties
From our results mentioned earlier, it is believed that effective load transfer from
PVA matrices to BCs can be affected by the interaction of strong hydrogen bonding
between oxygenated functional groups of BC particles and hydroxyl groups of PVA
molecules in terms of the mobility of polymeric chains. DSC results, shown in
Fig. 3.9a, b and Table 3.3, indicate that the glass transition temperatures T g increase
67
inclusion of 5 wt% nanodiamonds (NDs), the tensile strength of PVA nanocomposites was enhanced by 30.5%. In comparison, tensile strengths of PVA/NBC
bionanocomposites and PVA/MBC bionanocomposites at the BC content of 3 wt%
have been reported in this study to be increased by 110 and 72%, which appear to be
more desirable than other carbon-based nanocomposites reinforced with GOs and
SWNTs (despite relatively small SWNT contents used) when both nanofiller cost
and enhancement levels in relation to mechanical properties of nanocomposites are
concurrently considered.
3.3.3 Fracture Morphology
As observed in Fig. 3.8, all bionanocomposites have been characterised with rough
fracture surfaces due to embedded BC nanoparticles when compared with neat PVA.
In particular, uniform multi-layered structures are evidently seen for PVA/NBC
bionanocomposites with the inclusion of 3 and 5 wt% NBCs, as illustrated in
Fig. 3.8b, c, along the parallel direction to tensile loading. Such structures are
very similar to nacre structures mentioned elsewhere [3, 27, 28] and are in good
agreement with those observed in PVA-grafted GO (PVA-g-GO) nanocomposites
[28]. The fibrillation effect of fractured materials also takes place particularly in
PVA/NBC bionanocomposites when subjected to the stretching of bionanocomposite films under the unidirectional tension. This phenomenon suggests far higher
ductility of PVA/NBC bionanocomposites when compared with that of PVA/MBC
counterparts, which is also proven by their consistently higher elongation at break
in Fig. 3.7b.
On the other hand, fracture areas of PVA/MBC bionanocomposites demonstrate
less layered structures as opposed to PVA/NBC bionanocomposites at the BC content
of 3 wt%. This phenomenon can be ascribed to smaller surface areas of MBCs
to reduce interfacial interactions between fillers and PVA matrices. As depicted in
Fig. 3.8g, with increasing the MBC content up to 10 wt%, interparticle distance can be
significantly reduced owing to large amounts of particle agglomerates. As a result, the
formation of local networks of MBC particles to act as stress concentration sites prone
to mechanical failure occurs, thus lowering tensile strengths of nanocomposites, as
shown in Fig. 3.7a.
3.3.4 Thermal Properties
From our results mentioned earlier, it is believed that effective load transfer from
PVA matrices to BCs can be affected by the interaction of strong hydrogen bonding
between oxygenated functional groups of BC particles and hydroxyl groups of PVA
molecules in terms of the mobility of polymeric chains. DSC results, shown in
Fig. 3.9a, b and Table 3.3, indicate that the glass transition temperatures T g increase