SYNOPSISComposites of styrene-butadiene rubber were prepared with three different types of lead oxide, namely, monolead oxide ( PbO) , lead dioxide ( PbOz), and red lead oxide ( Pb304).Concentrations of PbsO, ranging between 17 and 88 wt % were utilized, whereas 87 wt 7% was used for PbO and Pb02. The prepared composites were investigated for their gamma radiation shielding properties. Moreover, physical and mechanical properties, and electrical conductivity were measured for both the unirradiated and irradiated composites. The highest value obtained for the linear absorption coefficient was 0.424 cm-' for 88% Pb304.
The kinetics of emulsion polymerization of vinyl acetate using the redox system potassium persulfate – acetone sodium bisulfite as initiator is studied. The effect of the reaction conditions on the rate of polymerization and on the number and size of the formed particles is established. The polymerization proceeded smoothly till high conversion and yielded stable emulsions. The apparent activation energy for the polymerization system has been calculated.
Summary: Na‐montmorillonite (MMT) with a cation exchange capacity (CEC) of 90 meq/100 g was converted to MMT‐CTAB and MMT‐CPC by the intercalation of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC), respectively. The intercalation of CPC onto the basal space of the montmorillonite expanded the basal space from 12.19 to 21.47 Å, whereas in the case of CTAB, the spacing was only expanded to 19.35 Å. The MMT‐CPC and MMT‐CTAB forms were subsequently used as hosts for the preparation of polystyrene nanocomposites via intercalative free‐radical polymerization of styrene. Different structures were obtained by varying the preparation conditions; the exfoliated and intercalated nanocomposites were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and differential scanning calorimeter (DSC). The produced nanocomposites exhibited improved thermal stability in comparison with that of pure polystyrene above 400 °C especially in the case of the nanocomposites based on the MMT‐CPC, in which intercalation exists. A glass transition temperature (Tg) could not be detected for the prepared nanocomposites using DSC; this was assumed to result from the restricted molecular motion of the polymer chains.XRD pattern of PS nanocomposites prepared by intercalative polymerization.magnified imageXRD pattern of PS nanocomposites prepared by intercalative polymerization.
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