SYNOPSISIn this article we studied the potential of ethylene vinyl acetate copolymer (EVA) as an impact modifier for isotactic polypropylene (PP). PP/EVA blend in the range 0-40 wt % EVA content is studied by using three grades of EVA containing 9, 12, and 19 wt % VA.Izod impact strength measurements were made at temperatures ranging from liquid nitrogen temperature to 60°C to explore the impact-toughening effect as a function of blending ratio both at low and above ambient temperatures. The results are compared with various reported blends of PP with other elastomers. Morphological studies through scanning electron microscopy on etched impact-fractured surfaces are carried out and a correlation of morphology and impact properties at various blending ratios is presented. Finally, a mathematical analysis of the data is performed in terms of second-degree polynomial to express impact strength as a simultaneous function of two variables, and an equation is proposed that shows the best fit with the experimental data. Relevant contour diagrams, based on the proposed equation, for optimization of properties are also presented.
Several modified clays have been designed and created for selective removal and recovery of
heavy metals such as Cd, Cu, Cr, etc. These surfactant−clay complexes were prepared using
hectorite or montmorillonite as the base clay. A simple two-step approach has been developed
to synthesize these modified-clay complexes through ion exchange and hydrophobic anchoring
of several surfactants such as long-chain alkyldiamines, long-chain dialkylamines, and long-chain carboxylic acids onto the clay matrices. The adsorption capacities and affinity constants
of the modified clays can be found to approach those of commercial chelating resin (Chelex 100,
Bio-Rad). Using cadmium as a model metal and montmorillonite−cetylbenzyldimethylammonium−palmitic acid (M−CBDA−PA) as a model modified-clay complex, the maximum adsorption
capacity of the modified clay is found to be 42 ± 0.8 mg/g of clay and the affinity constant is 3.0
± 0.1 mg/L. The metal adsorption has been shown to be mainly through chemical complexation
rather than ion exchange. The immobilization of the metal ions is pH dependent, and thus, pH
can act as a molecular switch to regenerate the modified-clay complexes.
SYNOPSISMelt rheological properties of the ternary blend of isotactic polypropylene (PP) , styreneethylene-butylene-styrene terpolymer (SEBS) , and polycarbonate ( P C ) , PP/SEBS/PC, are studied in a wide range of composition, such that PP is the matrix and SEBS and PC are the minor components, with the proportion of one varying from 0 to 30% at various fixed compositions of the other. The respective binary blends, P P / S E B S and P P / P C , studied as the reference systems for interpretation of results on the ternary blends yielded interesting new information about the morphology development and its correlation with melt rheological properties of these binary blends. The studies include the measurement of melt rheological properties on a capillary rheometer in the shear rate range 10'-104 s-l at a fixed temperature of 240°C. The data presented as conventional flow curves are analyzed for the effect of blend composition and shear rate on pseudoplasticity, melt viscosity, and melt elasticity, and role of each individual component is identified. Morphology of dispersed phases of these blends is studied through scanning electron microscopy of the cryogenically fractured and suitably etched surfaces. Variations of morphology with blend composition and shear rate showed interesting correlation with melt rheological properties, which are discussed in detail. An important finding of the morphological studies is that in the PP/ SEBS/PC ternary blend the SEBS phase forms two types of morphologies depending on the blend composition and shear rate: ( i ) simple droplets and (ii) boundary layer at the surface of the PC droplets.
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