4.9 Thermal Properties
109
compared to that of PVA, which is evidently noted from consistently high T 5% , T 80%
and T d values shown in Fig. 4.14b. For instance, T 80% of PVA increases from 363.5
to 407 °C with the inclusion of 5 wt% Cloisite 30B clays. Such a result is in good
agreement with previous studies of PVA/MMT nanocomposites [16, 56]. Moreover,
the shift in the decomposition temperatures T d for PVA/Cloisite 30B bionanocomposites depicted in Fig. 4.15b suggested the hindrance of a dehydration process. Such
a finding in thermal stability is associated with the presence of nanolayers acting as
the barriers to maximise the heat insulation and minimise the permeability of volatile
degradation products in the materials. This increase is also attributed to the decrease
in oxygen permeability related to good clay dispersion in PVA matrices.
On the other hand, the thermal stabilities of PVA/NBC bionanocomposites are
improved significantly with reference to that of PVA, as evidenced by consistently
higher T 5% , T 80% and T d values, Fig. 4.14c. The degree of thermal stability of
nanocomposites 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 in Fig. 4.15c
means that the dehydration process is hindered, which can result from the interaction between hydroxyl groups of PVA and hydroxyl groups on NBCs, as confirmed
from previous FTIR results. Furthermore, the mass loss process occurring in the
third DTG peaks means that the thermal decomposition of PVA bionanocomposites requires more reaction activation energy with a higher reaction order [55]. This
finding may be attributed to the existence of NBCs working as effective barrier materials to limit the exothermicity of pyrolysis reaction with better thermal resistance
of PVA bionanocomposites. The wider DTG peaks of PVA/NBC bionanocomposites beyond 3 wt% NBCs at the second decomposition step demonstrate a similar
trend to those of corresponding PVA/HNT bionanocomposites along with the same
dual-peak effect, as mentioned elsewhere [55].
According to the above-mentioned results, the incorporation of HNTs, Cloisite
30B clays and NBCs consistently enhances thermal properties of PVA bionanocomposites according to Table 4.1. However, the increasing rate for thermal properties
has been strongly relevant to nanofiller types. It is clearly seen that the T g of PVA
bionanocomposite films with the incorporation of NBCs and Cloisite 30B clays are
much higher than that of PVA/HNT bionanocomposites. Such results indicate that
NBCs and Cloisite 30B clays can restrict PVA molecular chains more efficiently, as
evidenced by increased mechanical properties of corresponding bionanocomposite
films. According to previous studies [57, 58], the phenomenon of increasing T g
is primarily correlated to the reduction in polymeric chain mobility by incorporating inorganic nanofillers. The addition of nanoparticles into polymer matrices can
change the distribution of chain segments, which is most likely due to a change
in chain packing density in the vicinity of nanofiller surfaces. It should be noted
that filler geometry may play a critical role in the effect of T g . NBCs and Cloisite
30B clays have different nanofiller shapes to render the absorption of polymeric
chains with the entangled structures on their surfaces when nanofiller diameters are
comparable to gyration radii of polymeric chains. As such, it leads to increasing the
packing density for polymeric chains and restricting their chain mobility as a result
of higher T g values. However, the incorporation of HNTs into PVA matrices has
109
compared to that of PVA, which is evidently noted from consistently high T 5% , T 80%
and T d values shown in Fig. 4.14b. For instance, T 80% of PVA increases from 363.5
to 407 °C with the inclusion of 5 wt% Cloisite 30B clays. Such a result is in good
agreement with previous studies of PVA/MMT nanocomposites [16, 56]. Moreover,
the shift in the decomposition temperatures T d for PVA/Cloisite 30B bionanocomposites depicted in Fig. 4.15b suggested the hindrance of a dehydration process. Such
a finding in thermal stability is associated with the presence of nanolayers acting as
the barriers to maximise the heat insulation and minimise the permeability of volatile
degradation products in the materials. This increase is also attributed to the decrease
in oxygen permeability related to good clay dispersion in PVA matrices.
On the other hand, the thermal stabilities of PVA/NBC bionanocomposites are
improved significantly with reference to that of PVA, as evidenced by consistently
higher T 5% , T 80% and T d values, Fig. 4.14c. The degree of thermal stability of
nanocomposites 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 in Fig. 4.15c
means that the dehydration process is hindered, which can result from the interaction between hydroxyl groups of PVA and hydroxyl groups on NBCs, as confirmed
from previous FTIR results. Furthermore, the mass loss process occurring in the
third DTG peaks means that the thermal decomposition of PVA bionanocomposites requires more reaction activation energy with a higher reaction order [55]. This
finding may be attributed to the existence of NBCs working as effective barrier materials to limit the exothermicity of pyrolysis reaction with better thermal resistance
of PVA bionanocomposites. The wider DTG peaks of PVA/NBC bionanocomposites beyond 3 wt% NBCs at the second decomposition step demonstrate a similar
trend to those of corresponding PVA/HNT bionanocomposites along with the same
dual-peak effect, as mentioned elsewhere [55].
According to the above-mentioned results, the incorporation of HNTs, Cloisite
30B clays and NBCs consistently enhances thermal properties of PVA bionanocomposites according to Table 4.1. However, the increasing rate for thermal properties
has been strongly relevant to nanofiller types. It is clearly seen that the T g of PVA
bionanocomposite films with the incorporation of NBCs and Cloisite 30B clays are
much higher than that of PVA/HNT bionanocomposites. Such results indicate that
NBCs and Cloisite 30B clays can restrict PVA molecular chains more efficiently, as
evidenced by increased mechanical properties of corresponding bionanocomposite
films. According to previous studies [57, 58], the phenomenon of increasing T g
is primarily correlated to the reduction in polymeric chain mobility by incorporating inorganic nanofillers. The addition of nanoparticles into polymer matrices can
change the distribution of chain segments, which is most likely due to a change
in chain packing density in the vicinity of nanofiller surfaces. It should be noted
that filler geometry may play a critical role in the effect of T g . NBCs and Cloisite
30B clays have different nanofiller shapes to render the absorption of polymeric
chains with the entangled structures on their surfaces when nanofiller diameters are
comparable to gyration radii of polymeric chains. As such, it leads to increasing the
packing density for polymeric chains and restricting their chain mobility as a result
of higher T g values. However, the incorporation of HNTs into PVA matrices has