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MIT World Peace University

School of Polymer Engineering

The mechanical properties viz.impact strength and tensile modulus of polypropylene (PP) containing two different types of calcium sulphate (prepared by in situ method under controlled conditions in a polymer matrix i.e. polyethylene oxide in the composition range 0-25 wt% of filler were studied. Increase of impact strength together with high crystallinity and improved tensile modulus was observed in one of the grades of CaSO4 filled composite as compared to pure PP. This could be associated with the long needle shaped CaSO4 crystals and the change in the structure and morphology induced by the same in the PP matrix.

World University root node

Engineering and Technology

Journal of Materials Science

Structure and properties of PP/CaSO4 composite. Part III: Effect of the filler grade on properties

The I-V characteristics of multilayer structures having vacuum deposited copper phthalocyanine on conducting polypyrrole films have been studied. Tunneling type characteristics were observed in some cases which followed the Fowler-Nordheim relationship whereas the Schottky effect was obtained in others depending on the crystalline nature/morphology of the phthalocyanine films which was affected by the substrate preconditioning prior to film deposition.

Thin Solid Films

Effect of substrate preconditioning on charge transport at the phthalocyanine-conducting polymer film interface

Current-voltage characteristics were studied for polypyrrole films contacted with different electrolytes in aqueous form and complex polymer solid electrolytes. Cyclic voltammograms for the conducting polymer in aqueous medium exhibited the typical oxidation and reduction peaks, whereas for solid polymer electrolytes, there was large asymmetry in curves; with the anodic current being much higher than that in the cathodic region. A rapid switching-type response was noted in the case of polyethylene oxide-cupric chloride complex as solid electrolyte. This effect was pronounced when the same complex contained the polypyrrole deposited within it as a composite. These various results have been discussed in the light of different energy levels in the conducting polymer and the contacting medium, as well as the formation of a microdispersed system with higher charge transport. © 1999 John Wiley & Sons, Inc.

Journal of Applied Polymer Science

Current-Voltage Characteristics of Conducting Polypyrrole in Solid Polyethylene Oxide Electrolytes

The structure, growth, and morphology of composite films made by dispersing para nitroaniline (PNA) in poly(methyl methacrylate) (PMMA) was investigated with respect to different crystallization methods, composition, and application of electric field. The wide-angle X-ray diffraction scans showed large variations in intensity of different reflections, especially the Okl with composition and in the presence of an electric field. In addition, it also showed the occurrence of a new crystalline structure, possibly due to complex formation between PNA and PMMA. The presence of this complex was further confirmed by infrared spectroscopy and thermal analysis. In a certain range of composition (30 to 40% PNA), spherulitic morphology was observed, which otherwise consisted of needle-shaped crystals dispersed in amorphous matrix. The transparency of these films also depended strongly on the crystallization conditions, and highly transparent films could be obtained, even at high PNA content by application of electric field. These various results could be explained on the basis of the intermolecular interaction between PNA and PMMA, as well as preferential growth direction and orientation of the PNA crystals.

Structure, growth, and morphology in para nitroaniline dispersed polymethyl methacrylate guest-host NLO composites

The effect of small concentration of methylene blue on the photocurrents were studied in solid-state photoelectrochemical cells fabricated using conducting polypyrrole (PPy) coated electrodes sandwiched with solid polymer electrolyte viz. polyvinyl alcohol (PVA) with phosphoric acid. These exhibit excellent photo-response to visible light: photocurrent being 3 to 4 orders of magnitude greater than dark current depending on the concentration of the sensitizer. The current-voltage characteristics in such cells reveal that the charge transport is mainly governed by the space charge effects and the sensitization effects are due to lowering of potential barrier formed at the PPy/PVA interface under photoexcitation. © 1998 Elsevier Science B.V. All rights reserved.

Materials Letters

Sensitization of photocurrents in solid-state electrochemical cells using conducting polypyrrole

The structure, growth and morphology of calcium sulphate prepared in situ of a polymer has been investigated using polyethylene oxide as the growth medium. The structure was predominantly the dihydrate type with monoclinic configuration for these samples as compared to the anhydrite type with orthorhombic structure obtained in commercial samples. The crystal morphology consisted of sharp needle shape, having aspect ratio of more than 10. The concentration of the polymer used had a profound effect on the crystal size and its distribution. The size distribution became narrow and the average crystal size reduced with the increase of polymer concentration. Highly oriented crystals could be obtained with application of a small shearing force on the samples. These results have been explained on the basis of polymer mediated crystallization and large interaction between the filler and the matrix. © 1998 Chapman & Hall.

Structure development in PP/CaSO4 composites: Part I Preparation of the filler by an in situ technique

The structure development in melt crystallized polypropylene (PP) containing different types and concentration of calcium sulphate has been studied by X-ray diffraction and optical polarizing microscopy. The commercial CaSO4 containing mostly the anhydrite form gives the α form of PP while the CaSO4 prepared by in situ method yields the β form of PP. This takes place first by conversion of the dihydrate form of CaSO4 to the τ form which preferentially nucleates the β form of PP. The crystallization behaviour in the latter case clearly reveals two processes. The presence of PEO which is used for the in situ preparation of CaSO4, however, is found to hinder the rate of crystallization and nucleation of the β form of PP but it gives a high degree of orientation of the CaSO4 needle-like crystals during extrusion of the PP-CaSO4 composites. © 1998 Chapman &amp; Hall.

Structure development in PP/CaSO4 composites: Part II Effect of filler on crystallization and morphology

The electrochromic response of polypyrrole (PPy)/Prussian blue (PB) composite films has been studied in different electrolytes such as KCl, LiClO4, K2SO4, KNO3, KI/I2, etc., by depositing the Prussian blue films on top of the conducting polypyrrole films, both being prepared by an electrochemical method. The results show that the use of PB on PPy not only yields high contrast but also extends the electrochromic response to a wider region of the visible spectrum, thus working as a sensitizer for improving the electrochromic contrast of the conducting polypyrrole.

Chemical Physics Letters

Electrochromic response in polypyrrole sensitized by Prussian blue

The structure development and mechanical properties of blow extruded polypropylene containing β-phase nucleating additives was studied. Quinacridone red and cadmium red were both found to nucleate the β phase in polypropylene, the former being a much more efficient nucleator than the latter. The β-phase spherulites formed in the presence of these nucleating agents were small and extensively volume filled, yielding high crystallinity. The modulus increased 2-3 times, elongation at break decreased, and there was a sharp break point without much yield when the β-phase nucleating agents were added as compared to the pure α-phase polypropylene. © 1997 John Wiley of Sons, Inc.

School of Civil Engineering

Effect of β-phase nucleating additives on structure and properties of blow extruded polypropylene

The crystallization behavior of polyethylene oxide (PEO) containing microdispersed nonlinear optical chromophores such as para-nitroaniline (PNA) has been investigated with respect to comopsition and different methods of film preparation techniques viz. solvent casting, melt casting, and powder molding. Large variations in the intensities of major reflections, 012 and 101, from PNA crystallites were observed depending on the composition as well as the method of preparation. The morphology of the samples examined under cross-polarizing conditions revealed highly birefringent crystallites dispersed in the spherulitic morphology of the PEO matrix in contrast to weakly birefrindgent crystals of the additive by itself. At high concentrations exceeding 45 wt % the PNA crystals act as substrates for the growth of polymer crystals. These results have been explained on the basis of intermolecular interaction as well as good lattice match between the crystalizing components, leading to preferential growth of the crystals along a certain direction. © 1997 John Wiley & Sons, Inc.