4.4 XRD Patterns
89
decreasing the HNT content significantly reduces the intensity of XRD peaks for all
PVA/HNT bionanocomposites, which may result from uniform HNT dispersion at
the low HNT content levels. Such a phenomenon suggests that homogeneous HNT
dispersion in a more randomly-oriented manner may contribute to the disappearance
or intensity reduction of XRD peaks at low HNT contents. On the other hand, the
reappearance of XRD peaks at higher HNT contents is indicative of possible HNT
agglomeration.
The XRD patterns of Cloisite 30B clays reveal the diffraction peak at 2θ = 4.72°
corresponding to the d-spacing value of 1.87 nm as shown in Fig. 4.3b, c. The (001)
diffraction peak shifts to lower angles, as evidenced by d-spacing values of 2.5, 2.6
and 2 nm for PVA/Cloisite 30B clay bionanocomposites at the clay contents of 3,
5 and 10 wt%, respectively. It clearly arises from the diffusion of polymeric chains
inside clay interlayers to create clay intercalation. Such a result is in good agreement
with PVA/Na
+ MMT nanocomposite [16] and PLA/Cloisite 30B nanocomposites
[26]. The XRD peak for PVA alone appears at 2θ = 19.7°, which is associated with
total (101) crystalline atactic formation of PVA molecular chains [27] to slightly shift
to lower diffraction angles when increasing the clay content in PVA bionanocomposites. The occurrence of PVA molecular chains at (101) crystalline plane suggests that
PVA matrices evolve towards crystalline structures under more constraints. A similar
behaviour has also been reported by Strawhecker and Manias [27] as well as Gaume
et al. [28] in PVA/clay nanocomposites, which is ascribed to strong chemical interactions between nanofillers and polymer matrices. The aforementioned results indicate that Cloisite 30B clays are successfully intercalated and/or exfoliated into PVA
molecular chains, and HNTs are homogenously dispersed at their low contents within
continuous PVA matrices. This is attributed to close interactions of PVA matrices with
clay nanoparticles due to strong hydrogen bonding taking place between carboxyl
groups of PVA molecules and hydroxyl groups in the interlayer areas of Cloisite 30B
clays or at the surface edges of HNTs [23].
In comparison, the XRD patterns of NBCs demonstrate two broad XRD peaks, as
depicted in Fig. 4.3d. The broad peaks located at 2θ = 22.9° are associated with sharp
peaks of graphite assigned to (002) diffraction plane [29]. Besides, the second broad
peak detected at 2θ = 43.6
◦ characterises 2D in-plane symmetry (101) along with
graphene layers. Moreover, XRD patterns of PVA/NBC bionanocomposites only
show the diffraction angles from PVA, as illustrated in Fig. 4.3(d). This phenomenon
is consistent with previous finding in PVA/5 wt% graphene oxide (GO) nanocomposites [30] with clear disappearance of GO diffraction peaks in regular and periodic
structures leading to individually exfoliated GOs within PVA matrices.
89
decreasing the HNT content significantly reduces the intensity of XRD peaks for all
PVA/HNT bionanocomposites, which may result from uniform HNT dispersion at
the low HNT content levels. Such a phenomenon suggests that homogeneous HNT
dispersion in a more randomly-oriented manner may contribute to the disappearance
or intensity reduction of XRD peaks at low HNT contents. On the other hand, the
reappearance of XRD peaks at higher HNT contents is indicative of possible HNT
agglomeration.
The XRD patterns of Cloisite 30B clays reveal the diffraction peak at 2θ = 4.72°
corresponding to the d-spacing value of 1.87 nm as shown in Fig. 4.3b, c. The (001)
diffraction peak shifts to lower angles, as evidenced by d-spacing values of 2.5, 2.6
and 2 nm for PVA/Cloisite 30B clay bionanocomposites at the clay contents of 3,
5 and 10 wt%, respectively. It clearly arises from the diffusion of polymeric chains
inside clay interlayers to create clay intercalation. Such a result is in good agreement
with PVA/Na
+ MMT nanocomposite [16] and PLA/Cloisite 30B nanocomposites
[26]. The XRD peak for PVA alone appears at 2θ = 19.7°, which is associated with
total (101) crystalline atactic formation of PVA molecular chains [27] to slightly shift
to lower diffraction angles when increasing the clay content in PVA bionanocomposites. The occurrence of PVA molecular chains at (101) crystalline plane suggests that
PVA matrices evolve towards crystalline structures under more constraints. A similar
behaviour has also been reported by Strawhecker and Manias [27] as well as Gaume
et al. [28] in PVA/clay nanocomposites, which is ascribed to strong chemical interactions between nanofillers and polymer matrices. The aforementioned results indicate that Cloisite 30B clays are successfully intercalated and/or exfoliated into PVA
molecular chains, and HNTs are homogenously dispersed at their low contents within
continuous PVA matrices. This is attributed to close interactions of PVA matrices with
clay nanoparticles due to strong hydrogen bonding taking place between carboxyl
groups of PVA molecules and hydroxyl groups in the interlayer areas of Cloisite 30B
clays or at the surface edges of HNTs [23].
In comparison, the XRD patterns of NBCs demonstrate two broad XRD peaks, as
depicted in Fig. 4.3d. The broad peaks located at 2θ = 22.9° are associated with sharp
peaks of graphite assigned to (002) diffraction plane [29]. Besides, the second broad
peak detected at 2θ = 43.6
◦ characterises 2D in-plane symmetry (101) along with
graphene layers. Moreover, XRD patterns of PVA/NBC bionanocomposites only
show the diffraction angles from PVA, as illustrated in Fig. 4.3(d). This phenomenon
is consistent with previous finding in PVA/5 wt% graphene oxide (GO) nanocomposites [30] with clear disappearance of GO diffraction peaks in regular and periodic
structures leading to individually exfoliated GOs within PVA matrices.