Differential Scanning Calorimetry (DSC)

DSC traces of pure Phenoxy and polymer nanocomposite materials are shown in Fig.30. Ph exhibited a shallow endotherm at 61oC corresponding to the glass transition temperature (Tg) of Ph. All the nanocomposite materials with different critical loading percentage of modified red mud were found to have a high Tg as compared to the pristine Phe. This could be attributed to the confinement of the intercalated polymer chains within the red mud galleries that prevents the segmental motions of the polymer chains, thereby enhancing the glass transition temperature of the polymer matrix. The PNC3 nanocomposite membrane showed maximum Tg and melting temperature (Tm) of 66 oC and 220 oC respectively. This depicted that PNC3 is thermally more stable than PRC3 nanocomposite membrane on account of better dispersion and adhesion of the ORM within the polymer matrix. The glass transition temperature (Tg) and melting temperature (Tm) of pure phenoxy and Ph nanocomposite membranes have been tabulated in table 17.

Sample

Tg (o C)

H

3

0

n

Pure Phe

61

206

PNC3

64

211

PRC3

66

220

Differential Scanning Calorimetry (DSC)

Fig. 30. DSC thermograms of (a) Ph (b) PRC3 (c) PNC3

1.6 Conclusion

– Red mud was successfully modified with the inorganic acids and organic moiety (aniline formaldehyde). The modification ameliorates both the dispersion level and the material properties of the polymer nanocomposites.

– The PVA – boric acid modified red mud nanocomposite films showed better glass transition temperature Tg and thermal stability at a filler concentration of 3.0wt percentage.

– In PVA/ORM nanocomposite systems, 2.0wt% modified red mud (CP4) based nanocomposite film exhibited relatively good dispersion with increase in the thermal stability, glass transition temperature.

– In PVA/PRM nanocomposite systems, 2.5wt% modified red mud (PRM4) based nanocomposite film exhibited relatively good dispersion with increase in the material properties as compared to the pristine poly (vinyl alcohol).

– PVA based nanocomposites showed an increase in the roughness values with the increase in the filler content but the 3.0wt% of boric acid modified red mud nanocomposite membrane showed lower roughness values as compared to the critical loading percentage of ORM and PRM based nanocomposites.

– On comparing the material properties of all the three nanocomposite systems, it was found that the critical loading percentage of BRM based nanocomposite system (i. e., SP5) showed better enhancement as compared to the critical loading percentage of ORM and PRM based nanocomposite systems.

– The TEM images of the PVA-modified red mud nanocomposite membranes showed homogeneous nano phase dispersion of the modified red mud in the PVA polymer matrices at a scale of 8- 23 nm particle size.

– In the poly(hydroxy ether of bisphenol A) (Phe) based nanocomposites as reported in this work, mostly intercalated structures were produced in the acid modified red mud modifications, but modification by organic moiety (ORM) resulted in a mixed intercalated-exfoliated structure.

– Thermal stability of polymer also increases after nanocomposites preparation, because red mud acts as a heat barrier, which enhances the overall thermal stability of the system, as well as assist in the formation of char after thermal decomposition.

– Phe based nanocomposites showed an increase in the roughness values with the increase in the filler content but the 3.0wt% of organically modified red mud nanocomposite membrane showed lower roughness values as compared to the critical loading percentage of PRM based nanocomposites. Thus, PNC3 showed homogenous and non-porous morphology as compared to the coarse morphology of PRC3 type of nanocomposites.

– The average particle size in case of PNC3 is 14 nm while the particle size of PRC3 is 19 nm as revealed by TEM studies.

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