| The objective of this research was to synthesize polystyrene (PS)/clay nanocomposites by emulsion polymerization followed by heterocoagulation, characterize the resulting nanocomposites, investigate their rheological behavior, and establish a reliable structure-property-processibility relationship.; A series of cationic polymer latex particles was synthesized by emulsion polymerization with or without surfactants and used for the preparation of polymer layered silicate (PLS) nanocomposites. Both the emulsifier-free emulsion polymerization with the reactive comonomer, ((4-vinylbenzyl) trimethyl ammonium chloride (VTAC)), and that with the cationic initiator, 2,2' -azobis(2-methylpropionamide) dihydrochloride (V-50), form polymers with ammonium groups in the chain. Several types of ammonium- or imidazolium-containing compounds such as cetyltrimethyl-ammonium bromide (CTAB) and 3-hexadecyl-1-methyl imidazolium bromide (HMIB), and pristine silicates such as Gelwhite RTM GP, CloisiteRTM Na, LaponiteRTM XLS, and SOMASIFRTM ME-100 were employed to prepare PLS nanocomposites.; We studied the morphology, coagulation process, oxidative thermal stability, mechanical properties, and melt rheology of the resulting composites, using wide angle X-ray diffraction (WAXD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), tensile measurements and dynamic frequency sweep experiments. TEM analysis displayed that the heterocoagulation process strongly depended on the type and concentration of silicates, and the particle size of the latex. The combination of WAXD and TEM proved that the morphology of the PS nanocomposites could be controlled by the type and amount of surfactant/initiator and the clay content. The thermal stability of the nanocomposites was improved up to 100°C with 5 wt % of silicate incorporated and depended on the interaction between polymer and silicate as well as the presence of free surfactants. However, differential scanning calorimetry and dynamic mechanical thermal analysis measurements indicated that the PS/clay nancomposites showed no significant changes in Tg. The introduction of nonreactive surfactant produced a more stable latex and lowered the degree of crosslinking between polymer chains and the clay, lowering the melt viscosity.; Lowering the degree of crosslinking enhanced the processing. Injection molded dumbbell-shape samples were not significantly discolored and were employed as specimens for the tensile testing. Young's modulus of the sample containing 5 wt silicates was enhanced up to 40%, without sacrificing other properties including toughness. From the investigation of the linear dynamic viscoelastic properties of the PS nanocomposite, we found that the dynamic storage modulus not only increased and showed solid-like behavior as the clay content increased, but also increased as the temperature was increased from 180 to 220°C when a high content of silicate was incorporated. In addition, the viscoelastic behavior strongly depends on the type of the silicate and the molecular weight of PS. |
