Polypropylene/calcium carbonate nanocomposites

Polypropylene/Calcium Carbonate Nanocomposites

Printed Paper Photovoltaic Cells

Dielectric properties of Al- epoxy compos- ites were characterized as a function of composition, fre- quency, and temperature. The dielectric constant increased smoothly with an increase in the concentration of alumi- num. An increase in dielectric constant was also observed with an increase in temperature as well as with a decrease in frequency. In general, dissipation factor values for compos- ites with higher concentrations of aluminum were greater than those with lower volume content of aluminum. Also, the dissipation factor showed an increase both with a de- crease in frequency and an increase in temperature. The increase in values of dielectric constant and dissipation fac- tor with an increase in concentration of aluminum was attributed to interfacial polarization. The absence of any discontinuity in the plot of dielectric constant versus com- position was ascribed to the absence of continuous alumi- num chains in the composition range investigated. The in- crease in dielectric constant with a rise in temperature was attributed to the segmental mobility of the polymer mole- cules. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3602-3608, 2003

Dielectric Properties of Aluminum-Epoxy Composites

Ordered poly(ethylene)-poly(vinylcyclohexane) (PE-PVCH) block copolymers are employed to study the crystallization of tethered PE in confined geometries. The high Tg of the PVCH component of these materials forces PE chains to crystallize in well-defined geometries dictated by the mesophase structure of the block copolymer. Effects of chain tethering on crystallization are examined through comparison of singly-tethered PE chains in PE-PVCH (EV) diblocks and doubly-tethered PE in PVCH-PE-PVCH (VEV) triblocks. Crystallinity is independent of the block copolymer mesophase structure in both the EV and VEV systems, although crystallinity in VEV depends on the molecular weight of the PE block of the copolymer. Melting temperature data indicate that spatial confinement reduces crystallite size in EV and VEV, and that the double tethering of PE chains in VEV reduces crystallite size further through topological constraints. Crystal nucleation and growth depend strongly on the type of microstructure in both EV and VEV block copolymers. Differences in the overall rate of crystallization are correlated with the dimensional continuity of the PE microdomains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37:2053–2068, 1999

Crystallization of tethered polyethylene in confined geometries

The effect of CaCO3 on the crystallization behaviour and the modification of structure in polypropylene (PP) has been investigated using X-ray diffraction and optical microscopy. The crystallization half time deduced from spherulitic growth rate was found to vary sharply and decreased considerably from 5–6 min for pure polymer to less than 2 min in the presence of CaCO3. The ultimate spherulite size also decreased considerably for PP containing CaCO3. Its dependance on composition however, showed a plateau region at about 10–15 wt % of additive. The intensities of certain reflections especially the 130 and 040 of the α phase were greatly affected by the presence of CaCO3 and large variations in the crystallinity (Ci) values were observed with composition. The ratio of intensities of 130 and 040 reflections and theCi revealed a maximum at a certain concentration of CaCO3. The above results can be explained on the basis of nucleation and preferential growth of the α phase of PP crystallites.

Effect of CaCO3 on the crystallization behaviour of polypropylene

The electrical properties, namely d.c. and a.c. conductivity, of polyester elastomer filled with various metallic and ferrite fillers have been investigated as a function of temperature, frequency and filler concentration. The temperature dependence of resistivity exhibited two regions of low and high activation energy (ΔE). The value of ΔE the lower temperature region (I) decreased while in the higher temperature region (II) it increased with the increase of work function of the metal used. Only in the case of ferrite-filled composites could a positive temperature coefficient of resistance be observed. The frequency dependence of conductivity revealed that there is a very large intergranular capacitance which was even more in the case of ferrite-filled samples than in metal-filled ones. The various results have been explained on the basis of Schottky barrier formation and the depletion regions formed near the polymer-metal interface.

S. Radhakrishnan

Papers

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