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Copyright: 2014 Wiley. Abstract only.The definitive version is published in Macromolecular Materials and Engineering, vol.299(8), pp 939-952

Copyright: 2019 Wiley. Due to copyright restrictions, the attached PDF file contains the abstract version of the full-text item. For access to the full-text item, please consult the publisher's website. The definitive version of the work is published in the Journal of applied polymer science, vol. 137(9), pp. 1-11

The effect of OMLS incorporation on the thermal properties of PET/LCP blends is studied. Pure and OMLS-modified PET/LCP blends were prepared by melt-extrusion using twin-screw extruder. The morphological analyses of PET/LCP blends show that OMLS addition enhances the phase-separated structure of the pure blend. A detailed study on the thermal properties of the pure and OMLS-modified PET/LCP blends were carried out by means of DSC in both conventional and modulation modes. Results show a complex melting behaviour comprises of successive melting and re-crystallisation. Finally, non-isothermal crystal-growth kinetics of pure and OMLS-modified blends were investigated.

The main theme of this work is to support the unusual melt-state rheological properties of the clay-containing nanocomposites of thermotropic liquid crystal polymers by small- and wide-angle X-ray scattering. The changes of dispersion of silicate particles in the LCP matrix as well as change in crystal growth of LCP were extensively studied by X-ray scattering in both small- and wide-angle regions. The generalised indirect Fourier transformation technique developed by Glatter was used to study the structural changes in nanocomposites with temperature. This is a new approach recently proposed by us for the quantitative analysis of the nanoparticles dispersion in the polymer matrix.

The nanocomposites of liquid-crystal polymer (LCP) with two different weight per cents of clay were prepared via the melt extrusion method. To investigate the properties of the materials in the linear and non-linear viscoelastic regions, both oscillatory and rotational tests were carried out. The results showed that the nanocomposite with higher clay content exhibited an almost defectless partially cross-linked structure compared to the nanocomposite with lower clay content or the pure LCP. The linear stress relaxation measurements revealed that the pure LCP relaxed faster than nanocomposites after imposition of a constant strain for a specific time. During the step rate relaxation test, high shear rate modified the defects in the pure LCP very quickly and probably attained almost an equilibrium position while the nanocomposite samples showed strong shear thinning behaviour.

The preparation and thermal and thermo-mechanical properties of nanocomposites based on liquid-crystalline polymers (LCP) and organically-modified layered silicate (OMLS) is described. From XRD patterns, very little smectic ordering is present in the pure LCP; in the nanocomposites, the polymer chains tended to orient in the direction of the dispersed clay layers. According to the DSC results, during first heating, the first melting peak represents the crystalline to nematic transition and, after that, a broader isotropization takes place. Although TGA of the samples showed a single-step decomposition through chain scission under an inert atmosphere, in air the nanocomposites underwent a two-step process, with onset of degradation at a higher temperature. The first step is mainly due to chain scission and the second is due to oxidative reactions.

The effect of organically modified clay on the morphology and properties of poly(propylene) (PP) and poly[(butylene succinate)-co-adipate] (PBSA) blends is studied. Virgin and organoclay modified blends were prepared by melt-mixing of PP, PBSA and organoclay in a batch-mixer at 190 °C. Scanning electron microscopy studies revealed a significant change in morphology of PP/PBSA blend in the presence of organoclay. The state of dispersion of silicate layers in the blend matrix was characterized by X-ray diffraction and transmission electron microscopic observations. Dynamic mechanical analysis showed substantial improvement in flexural storage modulus of organoclay-modified blends with respect to the neat polymer matrices or unmodified blends. Tensile properties of virgin blends also improved in the presence of organoclay. Thermal stability of virgin blends in air atmosphere dramatically improved after modification with organoclay. The effect of organoclay on the melt-state liner viscoelastic properties of virgin blends was also studied. The non-isothermal crystallization behavior of homopolymers, virgin, and organoclay-modified blends were studied by differential scanning calorimeter. The effect of incorporation of organoclay on the cold crystallization behavior of PP/PBSA blends is also reported.