110
4 PVA Bionanocomposite Films with Different Particle …
minor impact on increasing the T g instead, which is consistent with the previous
work [50]. Although the diameter of HNTs is on the nanometre scale, their length
turns to be microsized, which becomes considerably higher than typical gyration
radii of polymeric chains. As a consequence, it is very difficult for polymeric chains
to cover entire HNT structures. Moreover, the presence of microvoids along HNT
lengths could offer free sites for the segments of polymeric chains resulting in a
significant increase in T g [50].
The crystallinity of PVA bionanocomposite films reinforced with HNTs, Cloisite
30B clays and NBCs is relatively similar. Moreover, the T m values in case of PVA/3
wt% NBC bionanocomposites and PVA/5 wt% Cloisite 30B clay bionanocomposites
are nearly the same despite being slightly less than that of neat PVA at 222.91 °C. The
occurrence of lower melting temperature and melting-peak broadening effects could
be associated with the recrystallisation phenomenon of PVA matrices in nanocomposites [23] in that the decrease in T m is more likely to be correlated to the changes
in crystal lamellar thickness and its distribution (i.e. the formation of less perfect
crystal structures).
TGA results reveal that the T 5% of PVA/3 wt% NBC bionanocomposites is determined to be 256.3 °C, and increases up to 262.95 °C with the incorporation of 5 wt%
NBCs, which is relatively similar to that of PVA/5 wt% Cloisite 30B bionanocomposites at 261.1 °C. On the other hand, the T 5% of PVA/3 wt% HNT bionanocomposites
appears to be determined at 265.29 °C, which is significantly higher, as compared
with PVA bionanocomposites reinforced with NBCs and Cloisite 30B clays. On the
contrary, the T 80% of PVA/3 wt% NBC bionanocomposites has been found to be
390.67 °C, and reaches 440.28 °C with the inclusion of 5 wt% NBCs, which is
significantly higher than those of PVA bionanocomposites reinforced with HNTs
and Cloisite 30B clays. This result suggests that the maximum thermal stability is
achieved in the presence of NBCs, as opposed to HNTs and Cloisite 30B clays. In
contrast to other nanofillers, the better NBC dispersion within PVA matrices takes
place along with the higher barrier towards the thermal degradation. Therefore,
such barrier effect can counterbalance the degradation drawback with the further
improvement of thermal stability [5].
4.10 Summary
PVA bionanocomposites reinforced with different nanoparticles of Cloisite 30B
clays, HNTs and NBCs were successfully prepared and characterised. The following
conclusions can be drawn:
• When HNTs are embedded within PVA matrices, the properties of PVA/HNT
bionanocomposites are remarkably affected and strongly depend on the HNT
content. The morphological structures reveal that nanofiller dispersion can lead to
various structures resulting in different enhancement levels of mechanical properties for such bionanocomposites. The incorporation of 3 wt% HNTs has improved
4 PVA Bionanocomposite Films with Different Particle …
minor impact on increasing the T g instead, which is consistent with the previous
work [50]. Although the diameter of HNTs is on the nanometre scale, their length
turns to be microsized, which becomes considerably higher than typical gyration
radii of polymeric chains. As a consequence, it is very difficult for polymeric chains
to cover entire HNT structures. Moreover, the presence of microvoids along HNT
lengths could offer free sites for the segments of polymeric chains resulting in a
significant increase in T g [50].
The crystallinity of PVA bionanocomposite films reinforced with HNTs, Cloisite
30B clays and NBCs is relatively similar. Moreover, the T m values in case of PVA/3
wt% NBC bionanocomposites and PVA/5 wt% Cloisite 30B clay bionanocomposites
are nearly the same despite being slightly less than that of neat PVA at 222.91 °C. The
occurrence of lower melting temperature and melting-peak broadening effects could
be associated with the recrystallisation phenomenon of PVA matrices in nanocomposites [23] in that the decrease in T m is more likely to be correlated to the changes
in crystal lamellar thickness and its distribution (i.e. the formation of less perfect
crystal structures).
TGA results reveal that the T 5% of PVA/3 wt% NBC bionanocomposites is determined to be 256.3 °C, and increases up to 262.95 °C with the incorporation of 5 wt%
NBCs, which is relatively similar to that of PVA/5 wt% Cloisite 30B bionanocomposites at 261.1 °C. On the other hand, the T 5% of PVA/3 wt% HNT bionanocomposites
appears to be determined at 265.29 °C, which is significantly higher, as compared
with PVA bionanocomposites reinforced with NBCs and Cloisite 30B clays. On the
contrary, the T 80% of PVA/3 wt% NBC bionanocomposites has been found to be
390.67 °C, and reaches 440.28 °C with the inclusion of 5 wt% NBCs, which is
significantly higher than those of PVA bionanocomposites reinforced with HNTs
and Cloisite 30B clays. This result suggests that the maximum thermal stability is
achieved in the presence of NBCs, as opposed to HNTs and Cloisite 30B clays. In
contrast to other nanofillers, the better NBC dispersion within PVA matrices takes
place along with the higher barrier towards the thermal degradation. Therefore,
such barrier effect can counterbalance the degradation drawback with the further
improvement of thermal stability [5].
4.10 Summary
PVA bionanocomposites reinforced with different nanoparticles of Cloisite 30B
clays, HNTs and NBCs were successfully prepared and characterised. The following
conclusions can be drawn:
• When HNTs are embedded within PVA matrices, the properties of PVA/HNT
bionanocomposites are remarkably affected and strongly depend on the HNT
content. The morphological structures reveal that nanofiller dispersion can lead to
various structures resulting in different enhancement levels of mechanical properties for such bionanocomposites. The incorporation of 3 wt% HNTs has improved