4.1 XRD analysis
X-ray diffraction studies were performed on pure PVB and PVB-MWCNTS composite films to study the effect of MWCNTS on polymer structure. Figure-2 illustrates typical X-Ray diffraction patterns for pure PVB and composite films including 1.0 and 2.0 weight percentages of MWCNTS, respectively. The pure PVB has a diffraction peak at 2θ = 19.72O with an interplanar distance of 0.45 nm, which can be attributed to the polymer's amorphous nature. After dispersing MWCNTS into the PVB matrix, the composite film’s diffraction peaks shifted to 19.68O and 19.36O, respectively. At the 2θ position of 42O, the pure PVB and complexed films displayed another broad and low-intensity crystalline peak. Peak locations in the obtained composite films are comparable, confirming MWCNTS dispersion and homogenization inside the PVB. Because of the numerous hydroxyl groups present in its backbone, this may be seen in the successful creation of nanoparticle loaded composite films with slightly changed architectures [18]. This is commonly seen in the purity and success of MWCNTS-loaded composite film creation. The particle size (D) of composite films was calculated to be about 12nm on average.
It could also be observed that the XRD patterns show a relative rise in intensity with a 1.0 wt.% increase in nanotubes concentration while a decrease with a 2.0 wt.% increase in the peak because molecules of polymer pack closely together. This could be owing to the amorphous phase of PVB changing with the addition of MWCNTS. The intensity of the peak and the degree of crystallinity were found to be related by Hodge et al. [14]. The XRD peaks width of the prepared films was broadened by stepwise inclusion of nanoparticles quantity after incorporating MWCNTS [21].
4.2 FTIR analysis:
The FTIR spectra of pure PVB and PVB-MWCNTS composite films are given in Fig-3 and their corresponding peak assignments are listed in Table-3. A typical –O-H stretching band of the PVB functional group was observed at 3436 cm− 1 in pure PVB and 3448 cm− 1in composites which are strong broader peaks deviating from its normal value ~ 3600 cm− 1 to show the presence of intermolecular hydrogen bonding. However, for PVB + 2.0 wt.% MWCNTS a decrease in intensity of this band, characterizing that part of the hydroxyl groups of the PVA was condensed into acetyl and butyral groups [1]. A -C–H asymmetric stretching vibrations of CH2 showed an absorption band at 2,924 cm− 1 in pure PVB and is slightly shifted in the 1.0 and 2.0 wt. % composite films of PVB [4]. The changes in peak troughs were observed in the Nanocomposite spectra, demonstrating the effect of MWCNTS incorporation with PVB bonding. The observed bands at 1630 cm− 1 correspond to the acetyl C = O group and can be explained based on intra/ intermolecular hydrogen bonding with the adjacent O-H group [8]. The C‒H vibrational bands were observed at 1383 cm− 1. A sharp band at 1,058 cm− 1 corresponds to the C-O stretching of the acetyl group present in the PVB backbone. Compared with PVB, the intensity of composites with the range of 1105–980 cm− 1 has weakened owing to the interaction between PVB and CNTS [7]. These results demonstrated that the PVB and MWCNTS had been compounded together excellently because hydrogen bonding was generated between PVB and MWCNTS in composite films. Changes in the FTIR spectra show an increase in hydrogen bonding between the polymer and the nanotubes at higher weight percentage levels. Consequently, loading with MWCNTs enhances the unsaturated conjugated C = C double bonds in the polymer matrix. These observed changes in the FTIR spectra suggest that the addition of MWCNTS forms clustering. This affects the chemical structure of the composite films.
Table-3 FTIR peak assignments of pure PVB and PVB-MWCNTS composite films
S.NO
|
Peak position (cm− 1)
|
Group
|
Compound Class
|
Appearance
|
Comments
|
Pure PVB
|
Composite Films
|
1
|
3436
|
3448
|
O-H Stretching
|
Alcohol
|
Strong/Broad
|
Intermolecular bonded
|
2
|
2924
|
2931
|
CH2 Stretching
|
Alkane
|
Medium
|
CH2Asymmetric stretching
|
3
|
1630
|
1630
|
C = O Stretching
|
Acetyl
|
Medium
|
scissor bending vibrations of
-CH3
|
4
|
1383
|
1382
|
C-H Bending
|
Alkynes
|
Medium
|
CH3– Deformation
|
5
|
1058
|
1057
|
C-O Stretching
|
Carbonyl
|
Strong
|
The out of plane bending H bond
|
4.3 Morphological studies: SEM micrographs of pure PVB and composite films are shown in Figure- 4. The morphologies of these films are of the same kind, with varying degrees of roughness, observed in the films [10]. The smooth surface morphology of the pure PVB film may be seen in SEM images. PVB's semi-crystallinity is therefore expected to be microscopic. MWCNTS is equally distributed throughout the PVB matrix, according to SEM micrographs. In comparison to pure polymers, this determines the flexibility and strength of composites [6]. The presence and random dispersion of 1 wt. per cent and 2 wt. per cent, MWCNTs in the PVB matrix are shown in Figures 4(c) and 4(d). There were no cracks on the films, however, there were many small black patches on the upper surface. On the top surface of the membrane, the surface morphology of the composite film displayed aggregates or particle fragmentation. With increasing MWCNTS content in the composite films, this increase in particle cluster size is seen. On the other hand, the compatibility of MWCNTS and PVB polymer matrices stays isotropic and homogeneous. PVB polymer films mixed with different nanoparticles exhibited similar behaviour [11]. As a result, morphological studies look into phase separation. The colour of the films also changed from obviously transparent (pure PVB) to translucent under normal inspection.
4.4 DSC Analysis DSC is an analytical tool that helps to understand the thermal behaviour of polymer nanocomposites. This helps to determine the glass transition temperature (Tg) and melting point (Tm) of polymers and their composites. PVB is amorphous and exhibits an easily observable transition to the free state. The effect of MWCNTs content on the glass transition temperature of PVB was studied in detail through the observations listed in Table-4 by changing the wt.% of MWCNTs. nanoparticles. The Tg of pure PVB is 63.3°C [1], which is almost 64.8°Cfor films containing 1.0 wt.% MUCNT, whereas it is 84.8°C for PVB containing 2.0 wt.%. It can also be observed that adding only 2.0 wt.% MWCNTS to PVB increases the melting point to 121.6°C (compared to 90.5°C for pure PVB). When the content of MWCNT is 2.0 wt.%, the number of side groups and intermolecular forceincrease, and the glass transition temperature and melting point increase. These results showed that the addition of MWCNTS improved the thermal properties of PVB. A recent study showed a slight change in Tg in polymer nanocomposites regardless of the interaction of the polymer with the surface. This is explained by the fact that the DSC glass transition is only sensitive to the volume of the sample and not the interface [20].
The following factors may increase the glass transition temperature of composite films in this study
(1). The presence of plasticizers in polymers increases the mobility of polymer chains [9]. (2). A significant departure from group addition due to the increased content of hydroxyl groups increases hydrogen bonding. three. Adding nanofillers can affect crystallinity in many ways. In general, the most important effect is the "nucleation effect".
(3). Crosslinking introduces restraint and stiffness in the polymer. It should also be noted that for the composite film, the height of the specific thermal step at Tg was significantly reduced compared to the pure PVB sample. This decrease indicates that the specific heat capacity of the increasing composite film in the glass state is comparable to that of pure PVB. Almost identical results were obtained for other nanocomposites characterized by relatively low loading in a previous study [12].
Table-4 Glass transition temperature and the melting point of pure PVB and PVB-MWCNTS composite films:
S.NO
|
Sample
|
X wt.%
|
Tg (OC)
|
Tm (OC)
|
1
|
PVB
|
0
|
63.3
|
90.5
|
2
|
PVB + X wt. % MWCNTS
|
1.0
|
64.8
|
119.7
|
3
|
PVB + X wt. % MWCNTS
|
2.0
|
84.8
|
121.6
|