Morphological Analysis - Project1

4. Morphological Analysis

4.1. Wide angle X-Ray Diffraction (WAXD)

The distance between the silicate galleries in the nanoclays has been studied using WAXD measurement in the range of 2q = 1 to 10°. The X-Ray patterns of Na⁺MMT and organically modified layered silicate C20A, C30B, B109 are depicted in figure 1a.

Figure 1a: WAXD analysis of nanoclays; (a). Na⁺MMT, (b). C20A, (c). C30B,

(d). B109

It is evident that the interlayer distance of d₀₀₁ plane of Na⁺MMT increases with organic modification and varies in the following order: B109>C20A>C30B>Na⁺MMT. The d₀₀₁ spacing was calculated from the peak position using Bragg’s law [23], nl = 2dsinq, where l = 1.54Å is the X-ray wavelength and tabulated in table 4.

Na⁺MMT exhibits a diffraction peak at 2q =8.025° corresponding to d₀₀₁ spacing of 1.1 nm. However modified clays C20A, C30B and B109 reveals a diffraction peak around 4.0⁰, 5.61⁰ and 3.175⁰ with spacing of 2.209, 1.574 and 3.005 nm respectively. This confirms intercalation of clay layers with organic modification.

The bio-nanocomposite structure has also been characterized using WAXD patterns. Direct evidence of intercalation of polymer chains into the silicate clay galleries has been observed within the experimental range of 2q = 1 to 10°. Figure 1b shows the X-ray diffractogram of PBAT/Na⁺MMT nanocomposite with 3wt% of clay loading.

Figure 1b: WAXD analysis for bio-nanocomposites; (a). PBAT/C20A, (b). PBAT/C30B, (c). PBAT/B109, (d). MA-g-PBAT-C30B, (e). MA-g-PBAT-B109

It is observed that the intensity characteristic peak of Na⁺MMT in PBAT/Na⁺MMT nanocomposite shows similar angle of diffraction as that of pristine clay, which clearly indicates the confirmation of formation of a conventional composite, because there is no favorable interactions of PBAT matrix with Na⁺MMT. However, XRD patterns of PBAT/C20A, PBAT/C30B and PBAT/B109 bio-nanocomposite hybrids reveal a characteristic peaks, shifted to smaller diffraction angles at 2.175, 2.145 and 2.03° respectively due to intercalation of PBAT chains into the silicate galleries. The interlamellar d₀₀₁-spacing follows the following order B109 (nm)> C20A (nm)> C30B (nm). This further, shows highly intercalated structure, due to strong interaction between carbonyl groups (>C=O) of PBAT with -OH groups of organoclay.

Further, the average number of clay layers forming tactoids has been calculated using Scherrer equation as

L = Kλ / β₀₀₁ cosq

Where, L is average thickness clay stack, β₀₀₁ (radian) is full width at half maximum for 001 reflection, and k = 0.9.

The number of clay layers per stack (N) was calculated as

N = (L/d₀₀₁) + 1

Test results reported in table 4 indicates that in case of PBAT bio-nanocomposites, N was found to 1.56 – 4.58.This indicates that the clay stacks consisting of 2 – 5 platelets are dispersed in PBAT bio-nanocomposites. In case of MA-g-PBAT/30B and MA-g-PBAT/B109 bio-nanocomposite hybrids, the X-ray diffraction patterns indicate absence of deflection peak within the experimental range, which indicate exfoliation of clay galleries. This is due to the fact that MA acts as a compatibilizing reagent which penetrates into clay galleries forming chemical linkage between the anhydride group of MA and PBAT and layered silicates. The same has been also corroborated using FTIR spectroscopy. This further results in an increase in the gallery spacing allowing the polymer chains to enter and break the galleries during compounding resulting in exfoliated and improved dispersion.