4.3 Chemical Bonding Effect
87
peaks detected at 2417.5 and 1567.4 cm
−1 reveal the existence of C≡H stretching [17]
and C=C vibration in an aromatic system [18], respectively. On the other hand, the
peak spectrum at 1696 cm
−1 is assigned to C=O band primarily for ionisable carboxyl
groups as an indicator of surface hydrophilicity [19]. In case of bionanocomposite
systems, the FTIR spectra of PVA/HNT bionanocomposites and PVA/Cloisite 30B
clay bionanocomposites are also illustrated in Fig. 4.2a, b, respectively. The FTIR
peak located at 3271.5 cm
−1 is associated with O–H stretching, which shifts to higher
wavenumbers at 3280 and 3289 cm
−1 , as well as 3279 and 3283 cm
−1 with the inclusion of HNTs and Cloisite 30B clays at the nanoparticle contents of 3 and 5 wt%,
respectively. Such a finding is attributed to the strengthening effect of hydrogen
bonds between –OH groups obtained from PVA molecules and those located on
Cloisite 30B clay surfaces such as silanol groups (–SiOH), which is in good agreement with previous investigations on PVA/organomodified Cloisite Na
+ (OMMT)
nanocomposites [16], poly (ε-caprolactone) (PCL)/Cloisite 30B clay nanocomposites [20], as well as PVA/chitosan (CS)/HNT nanocomposites [21]. However, when
the HNT content increases up to 10 wt%, two Al 2 OH stretchings appear with respect
to embedded HNTs in bionanocomposite films, which can be ascribed to typical
HNT agglomeration [22]. As for PVA/NBC bionanocomposite films, increasing the
NBC content from 0 to 10 wt% yields the band-peak shift to lower wavenumbers at
3240.6 and 3245.5 cm
−1 , respectively, due to large amounts of hydroxyl groups in
PVA molecules [4], as well as strong filler–matrix interactions. As a result, hydrogen
bonds are generated to be intertwined at PVA/NBC interfaces with a broad O-H band.
Such a variation associated with –OH stretching vibration proves the formation of
hydrogen bonds, which is in good accordance in PVA/graphene nanocomposites
[23] and PVA/BC nanocomposites [5]. The aforementioned results failed to show
existing new bands in PVA films with the inclusion of both HNTs and Cloisite 30B
clays. On the contrary, the inclusion of 3 and 5 wt% NBCs within PVA matrices in
bionanocomposite films gives rise to a new band in relation to –CH 2 – asymmetric
and symmetric stretchings [4]. Such a finding can arise from typical porous structures
of NBCs, enabling to absorb molecular chains of hydrophilic polymers such as PVA
with combined mechanical and chemical bondings. More consistently, the inclusion
of HNTs and Cloisite 30B clays in PVA bionanocomposites shift the hydroxyl peaks
of PVA to relatively high wavenumbers as opposed to the addition of NBCs [4].
Such results indicate that the numbers of hydrogen bonding generated in PVA/HNT
bionanocomposites and PVA/Cloisite 30B clay bionanocomposites are higher when
compared with those detected in PVA/NBC bionanocomposites owing to different
chemical structures of nanofillers. Since NBCs do not possess –OH peaks, most
hydrogen bonding formed in bionanocomposites can be associated with hydroxyl
groups of PVA molecules. Whereas, the existing –OH peaks detected in HNTs and
Cloisite 30B clays in PVA bionanocomposites are believed to further facilitate the
formation of more hydrogen bonds within PVA matrices.
87
peaks detected at 2417.5 and 1567.4 cm
−1 reveal the existence of C≡H stretching [17]
and C=C vibration in an aromatic system [18], respectively. On the other hand, the
peak spectrum at 1696 cm
−1 is assigned to C=O band primarily for ionisable carboxyl
groups as an indicator of surface hydrophilicity [19]. In case of bionanocomposite
systems, the FTIR spectra of PVA/HNT bionanocomposites and PVA/Cloisite 30B
clay bionanocomposites are also illustrated in Fig. 4.2a, b, respectively. The FTIR
peak located at 3271.5 cm
−1 is associated with O–H stretching, which shifts to higher
wavenumbers at 3280 and 3289 cm
−1 , as well as 3279 and 3283 cm
−1 with the inclusion of HNTs and Cloisite 30B clays at the nanoparticle contents of 3 and 5 wt%,
respectively. Such a finding is attributed to the strengthening effect of hydrogen
bonds between –OH groups obtained from PVA molecules and those located on
Cloisite 30B clay surfaces such as silanol groups (–SiOH), which is in good agreement with previous investigations on PVA/organomodified Cloisite Na
+ (OMMT)
nanocomposites [16], poly (ε-caprolactone) (PCL)/Cloisite 30B clay nanocomposites [20], as well as PVA/chitosan (CS)/HNT nanocomposites [21]. However, when
the HNT content increases up to 10 wt%, two Al 2 OH stretchings appear with respect
to embedded HNTs in bionanocomposite films, which can be ascribed to typical
HNT agglomeration [22]. As for PVA/NBC bionanocomposite films, increasing the
NBC content from 0 to 10 wt% yields the band-peak shift to lower wavenumbers at
3240.6 and 3245.5 cm
−1 , respectively, due to large amounts of hydroxyl groups in
PVA molecules [4], as well as strong filler–matrix interactions. As a result, hydrogen
bonds are generated to be intertwined at PVA/NBC interfaces with a broad O-H band.
Such a variation associated with –OH stretching vibration proves the formation of
hydrogen bonds, which is in good accordance in PVA/graphene nanocomposites
[23] and PVA/BC nanocomposites [5]. The aforementioned results failed to show
existing new bands in PVA films with the inclusion of both HNTs and Cloisite 30B
clays. On the contrary, the inclusion of 3 and 5 wt% NBCs within PVA matrices in
bionanocomposite films gives rise to a new band in relation to –CH 2 – asymmetric
and symmetric stretchings [4]. Such a finding can arise from typical porous structures
of NBCs, enabling to absorb molecular chains of hydrophilic polymers such as PVA
with combined mechanical and chemical bondings. More consistently, the inclusion
of HNTs and Cloisite 30B clays in PVA bionanocomposites shift the hydroxyl peaks
of PVA to relatively high wavenumbers as opposed to the addition of NBCs [4].
Such results indicate that the numbers of hydrogen bonding generated in PVA/HNT
bionanocomposites and PVA/Cloisite 30B clay bionanocomposites are higher when
compared with those detected in PVA/NBC bionanocomposites owing to different
chemical structures of nanofillers. Since NBCs do not possess –OH peaks, most
hydrogen bonding formed in bionanocomposites can be associated with hydroxyl
groups of PVA molecules. Whereas, the existing –OH peaks detected in HNTs and
Cloisite 30B clays in PVA bionanocomposites are believed to further facilitate the
formation of more hydrogen bonds within PVA matrices.