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ABSTRACT: The rheological behavior of nanocomposites based on multiwalled carbon nanotube (MWNT) with three commercial grades of ethylene methyl acrylate (EMA) copolymers containing 9, 24, and 30 wt% methyl acrylate (MA) was investigated under dynamic and steady shear flow (in a capillary) conditions. Storage modulus (in dynamic shear) value increases especially at higher frequency levels due to increased polymer-filler interactions. Both the unfilled and filled composites exhibit rheological behavior of non-Newtonian fluids. In both steady shear and capillary flow, the nanocomposites register a slightly higher viscosity than neat EMAs, with dependence on the MWNTs content. All systems with various loading of MWNTs represent an increase in elastic response with increasing frequency. The die swell decreases with the MWNTs loading. Dynamic and steady shear rheological properties register a good correlation in regard to the viscous versus elastic response of such systems inline with the Cox–Merz concept. Increased MA content leads to inferior dispersion of MWNTs in EMA matrix. Morphological studies exhibit that MWNTs become more aligned along longitudinal direction after extrusion leading to improved dispersion. Copyright © 2010 John Wiley & Sons, Ltd.
Polymers for Advanced Technologies 11/2010; 23(1):65 - 76. · 2.01 Impact Factor
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ABSTRACT: In this study, nanocomposites based on multi walled carbon nanotube (MWNT) with three commercial grades of ethylene methyl acrylate copolymers (EMA) with 9, 24 and 30 wt% methyl acrylate (MA) contents, respectively have been prepared by solution mixing followed by melt blending technique. The state of dispersion of the MWNTs found to be inferior with increasing MA content in the EMA matrix as observed by HRTEM. Higher state of dispersion of MWNTs in EMA matrix lead to decreased crystallinity, increased crystallite size and increased crystallization temperature. The storage moduli of the composites drop very sharply with increasing% strain for EMA with 30% MA content and it reflects the typical Payne effect. The storage modulus of the composite is significantly increased by the incorporation of MWNTs particularly at higher temperatures. A unique crossover of tan versus frequency plots of composites with that of the pristine polymers is noticed for EMA with 24 and 30% MA contents based composites, respectively, where the degree of aggregation are higher. The frequency corresponding to the crossover depends on the degree and length scale of aggregation. The MWNTs provide better thermal stability especially for the composites based on EMA with 9% MA, where the highest state of dispersion is observed by morphological analysis. Thus, in EMA with 9% MA, pristine MWNTs can be homogeneously dispersed by solution mixing followed by melt processing technique.
Journal of Computational and Theoretical Nanoscience 02/2010; 3(1):10-19. · 0.91 Impact Factor
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ABSTRACT: The ethylene methyl acrylate copolymer (EMA) and multiwalled carbon nanotube (MWNT) based composites were prepared by solution mixing as well as by melt processing of the films obtained after solution mixing. Field emission scanning electron microscopy, transmission electron microscopy, and XRD were used to characterize morphologies of various composites. MWNTs were found to be more dispersed in the composites prepared by melt process after solution process. There was no obvious agglomeration of MWNTs at lower % loading (up to 2.5%) in the polymer matrices especially the composites are prepared solution plus melt mixing and consequently better interaction between MWNTs and EMA matrix was anticipated. XRD and differential scanning calorimetry studied showed that the nanotubes affect the crystallization process and subsequently their role as a nucleating agent was established. These are reflected in the mechanical properties of the composites. Dynamic mechanical analysis showed that the storage modulus of the composites drop very sharply beyond 2.5 wt% of MWNT content with increasing % strain and it reflects the Payne effect (a substantial decrease in the storage modulus of a particle-reinforced polymer with an increase in the amplitude of dynamic oscillations). The influence of concentration of filler was also realized by frequency sweep experiment. The incorporation of MWNTs in EMA offered a stabilizing effect since onset of degradation occurs at higher temperatures for composites. POLYM. COMPOS., 31:1168–1178, 2010. © 2009 Society of Plastics Engineers
Polymer Composites 09/2009; 31(7):1168 - 1178. · 1.23 Impact Factor
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ABSTRACT: Carbon black (N-330), organically modified nanoclay (NC) based ternary, particulate nanocomposites comprising of epoxidized natural rubber matrix having 25 mol% of epoxy group (ENR-25) were prepared in an open two-roll mill. Investigations of cure characteristics, dynamic mechanical, tensile, thermal, and morphological characteristics were conducted using Rheometric analysis, Dynamic Mechanical Analysis (DMA), mechanical property evaluation, Thermo-gravimetric analysis (TGA), High Resolution Transmission Electron Microscopy (HR-TEM), respectively, to derive the interrelation among the developed nanostructures inside the composite, crosslinking density, performance properties obtained there from. A satisfactory level of correlation was obtained among various results, which indicated the formation of “nanounit” comprising of N-330 and NC inside ENR-25 matrix. To optimize the nanostructures, ENR based compounds containing various combinations of NC and N-330 was prepared. Thorough and systematic structure-property analyses were performed on those composites. Optimum stoichiometric combination of N-330 and NC inside the ENR-25 matrix was derived (ratio of N-330 and nanoclay in wt% = 20:15), which showed synergistic effect of one filler upon another that was ultimately reflected in their dynamic mechanical and tensile properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Polymer Composites 04/2009; 31(5):835 - 846. · 1.23 Impact Factor
