106
4 PVA Bionanocomposite Films with Different Particle …
unchanged with the addition of HNTs in bionanocomposite films, indicating that
HNTs do not play an important role in inhibiting the chain mobility of PVA molecules.
Qiu and Netravali [41] also reported a similar result in T g with the incorporation of
HNTs into PVA. Such a finding might be related to the reduction in the entanglements and interactions of PLA polymeric chains with HNT inclusions. The relatively
unchanged T g in PVA/HNT bionanocomposites, as compared to that of neat PVA,
may arise from different nanofiller geometries. The diameters of HNTs are at a
nanoscaled level as opposed to microsized tubular lengths that considerably exceed
typical gyration radii of polymeric chains [4]. As a result, HNTs cannot be completely
wrapped by PVA molecular chains leading to many voids surrounding HNT particles.
On the contrary, high T g values for all PVA/Cloisite 30B clay bionanocomposites are
evidently shown as opposed to that of neat PVA. With the incorporation of 3, 5 and 10
wt% Cloisite 30B clays, T g values of such PVA bionanocomposites are moderately
enhanced up to 67.5, 70.2 and 71.8 °C, respectively, when compared with that of neat
PVA at 65.19 °C. This phenomenon can be attributed to the confinement of polymeric chains by intercalated clay structures to prevent their segmental motions [1],
which has also been reported in PVA/MMT nanocomposites [51, 52], PVA/bentonite
nanocomposites [53], as well as PVA/starch/MMT nanocomposites [54]. In case of
PVA/NBC bionanocomposites, the T g increased monotonically up to 75.06 °C with
increasing the NBC content from 0 to 10 wt% accordingly. The incorporation of
rigid NBC particles can restrict the chain mobility of PVA matrices so that higher
T g values are required for the phase change of nanocomposites from a glassy state
to a rubbery state. This finding is well known for many types of nanofillers such as
nanoclays, GOs, CNTs and HNTs [1].
The degree of crystallinity (χ c ) of PVA slightly increased from 36.65% for neat
PVA to 38.2, 37.2 and 40% for corresponding bionanocomposites with the incorporation of 5 wt% of HNTs and Cloisite 30B clays and 10 wt% of NBCs, respectively.
This suggests that such nanofillers have minor effect on crystalline phases of PVA
matrices in bionanocomposites. On the other hand, the melting temperature T m of
PVA bionanocomposites virtually has no change with the addition of Cloisite 30B
clays and NBCs, as evidenced by the given T m ranges of 220.44–221.62 °C and 221–
225 °C, respectively, when compared with that of neat PVA at 222.91 °C. However,
PVA/HNT bionanocomposites possess a moderate increase in T m up to 226.67 °C
with the inclusion of 10 wt% HNTs. A similar phenomenon was also noticed in
PHBV/HNT nanocomposites [23] with their T m values being increased from 169 to
173 °C when incorporated with 5 wt% HNTs. It is believed that based on XRD results
in which HNTs were embedded within PHBV matrices, thicker and more oriented
HNT/PHBV structures could be formed leading to higher melting temperatures.
Thermal decomposition behaviour of PVA/HNT bionanocomposites,
PVA/Cloisite 30B clay bionanocomposites and PVA/NBC bionanocomposites
was evaluated using a thermogravimetric analysis (TGA) with results being
presented in Figs. 4.14 and 4.15, as well as Table 4.1. Relevant results for both
systems reveal the existence of three major degradation steps according to previous
studies [16]. Initially, the first degradation takes place at 107 °C owing to the
breakage of hydrogen bonds, impurities and monomers of vinyl alcohol. Then the
4 PVA Bionanocomposite Films with Different Particle …
unchanged with the addition of HNTs in bionanocomposite films, indicating that
HNTs do not play an important role in inhibiting the chain mobility of PVA molecules.
Qiu and Netravali [41] also reported a similar result in T g with the incorporation of
HNTs into PVA. Such a finding might be related to the reduction in the entanglements and interactions of PLA polymeric chains with HNT inclusions. The relatively
unchanged T g in PVA/HNT bionanocomposites, as compared to that of neat PVA,
may arise from different nanofiller geometries. The diameters of HNTs are at a
nanoscaled level as opposed to microsized tubular lengths that considerably exceed
typical gyration radii of polymeric chains [4]. As a result, HNTs cannot be completely
wrapped by PVA molecular chains leading to many voids surrounding HNT particles.
On the contrary, high T g values for all PVA/Cloisite 30B clay bionanocomposites are
evidently shown as opposed to that of neat PVA. With the incorporation of 3, 5 and 10
wt% Cloisite 30B clays, T g values of such PVA bionanocomposites are moderately
enhanced up to 67.5, 70.2 and 71.8 °C, respectively, when compared with that of neat
PVA at 65.19 °C. This phenomenon can be attributed to the confinement of polymeric chains by intercalated clay structures to prevent their segmental motions [1],
which has also been reported in PVA/MMT nanocomposites [51, 52], PVA/bentonite
nanocomposites [53], as well as PVA/starch/MMT nanocomposites [54]. In case of
PVA/NBC bionanocomposites, the T g increased monotonically up to 75.06 °C with
increasing the NBC content from 0 to 10 wt% accordingly. The incorporation of
rigid NBC particles can restrict the chain mobility of PVA matrices so that higher
T g values are required for the phase change of nanocomposites from a glassy state
to a rubbery state. This finding is well known for many types of nanofillers such as
nanoclays, GOs, CNTs and HNTs [1].
The degree of crystallinity (χ c ) of PVA slightly increased from 36.65% for neat
PVA to 38.2, 37.2 and 40% for corresponding bionanocomposites with the incorporation of 5 wt% of HNTs and Cloisite 30B clays and 10 wt% of NBCs, respectively.
This suggests that such nanofillers have minor effect on crystalline phases of PVA
matrices in bionanocomposites. On the other hand, the melting temperature T m of
PVA bionanocomposites virtually has no change with the addition of Cloisite 30B
clays and NBCs, as evidenced by the given T m ranges of 220.44–221.62 °C and 221–
225 °C, respectively, when compared with that of neat PVA at 222.91 °C. However,
PVA/HNT bionanocomposites possess a moderate increase in T m up to 226.67 °C
with the inclusion of 10 wt% HNTs. A similar phenomenon was also noticed in
PHBV/HNT nanocomposites [23] with their T m values being increased from 169 to
173 °C when incorporated with 5 wt% HNTs. It is believed that based on XRD results
in which HNTs were embedded within PHBV matrices, thicker and more oriented
HNT/PHBV structures could be formed leading to higher melting temperatures.
Thermal decomposition behaviour of PVA/HNT bionanocomposites,
PVA/Cloisite 30B clay bionanocomposites and PVA/NBC bionanocomposites
was evaluated using a thermogravimetric analysis (TGA) with results being
presented in Figs. 4.14 and 4.15, as well as Table 4.1. Relevant results for both
systems reveal the existence of three major degradation steps according to previous
studies [16]. Initially, the first degradation takes place at 107 °C owing to the
breakage of hydrogen bonds, impurities and monomers of vinyl alcohol. Then the