Clay, compositions melting point

Reddy and Das made a silica-supported zirconocene catalyst in situ, by subliming ZrCl4 onto a high surface area silica, then adding NaCp. This catalyst was combined with an organically modified montmorillonite (Cloisite 20A), mixed with additional MAO (Al/Zr = 500). Propylene polymerization was conducted in the gas phase, at 8 bar and 70°C. Despite the absence of an obvious mechanism for interaction between the catalyst with the clay, or the presence of a solvent to swell the clay, the composite material was claimed to contain delaminated clay on the basis of decreased basal peak intensity in the XRD. The polypropylenes showed low melting points (132°C-134°C) consistent with large amorphous fractions. 

The melting point of neat PP-g-MA was fotmd to be 145.5° C, its composites with I.30P clay and Cloisite 15 A had melting temperatures of 146.6° C and 146.1° C, respectively. The temperature for processing and compression molding was chosen on the basis of these melting points. 

The composition of talc is situated close to the eutectic, so that the amount of liquid phase suddenly formed would deform the product. However, in a talc-day mixture, one may choose a proportion of components providing an amount of meJt just suitable for satisfactory sintering (about 30%) and for inhibition of the proto-enstatite-clinoenstatite inversion. This amount corresponds to approximately 10% clay. The composition of such a mix which roughly corresponds to commercial steatite compositions is indicated in Fig. 189 by point A. The diagram then allows equilibrium amounts of the melt to be evaluated for various temperatures, as shown in the diagram in Fig. 190. The shape of curve A indicates that about 30 % of melt is formed rapidly at 1345 °C. This is the temperature of the tridymite-enstatite-cordierite eutectic. The amount of melt increases with temperature, so that the sintering interval is comparatively narrow. 

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