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We have studied the morphology of blends of PS/PMMA, PC/SAN24, and PMMA/EVA and compared the morphologies with and without modified organoclay Cloisite 20A or Cloisite 6A clays. In each case we found a large reduction in domains size and the localization of the clay platelets along the interfaces of the components. The increased miscibility was accompanied in some cases, with the reduction of the system from multiple values of the glass transition temperatures to one. In addition, the modulus of all the systems increased significantly. A model was proposed where it was proposed that in-situ grafts were forming on the clay surfaces during blending and the grafts then had to be localized at the interfaces. This blending mechanism reflects the composition of the blend and is fairly nonspecific. As a result, this may be a promising technology for use in processing recycled blends where the composition is often uncertain and price is of general concern.

Significant enhancement of the mechanical properties in PS/EVA blends is achieved via sc CO2 exposure in the pressure/temperature domain where the amplitude of the density fluctuations is maximal. Before exposure, bulk samples of the blends elongate an average of 134% under uniaxial tension, whereas the average elongation is 682% after exposure. SEM micrographs of the exposed blends indicate that foams with pores roughly 5−15 μm in diameter, separated by splines 1−2 μm wide, are formed at all pressures higher than 800 psi. We attribute the enhancement of the mechanical properties in PS/EVA to an increased degree of miscibilization of the immiscible polymers along the spline surfaces. When foaming occurs, the surface-to-volume ratio is increased, thereby increasing the regions where surface miscibilization can occur. Since tensile stresses in the material are sustained by the splines, reinforcement of the mechanical properties in this specific area results in an overall enhancement of the tensile propertie...

Dynamic secondary ion mass spectrometry (DSIMS) measurements were performed to measure the effects of functionlized organosilicate clay (Cloisite 6A) on the tracer diffusion coefficient, D, in polystyrene (PS) and poly(methyl methacrylate) (PMMA) matrices. The results indicate that D is unaffected by the addition of 5% (by volume) of PS and is reduced by a factor of 3 with the addition of the same volume fraction in a PMMA matrix. The same ratio was also obtained for the extrapolated zero shear rate viscosity of PS and PMMA melt-mixed composites with the same volume fraction of clay. DSIMS was also used to measure the mobility of the clay platelets, which was found to be much lower than the polymer chains in both matrices. Examination of the sample morphology with scanning force and transmission electron microscopy indicated that in contrast to melt mixing, spin casting produced a large degree of exfoliation in both PS and PMMA matrices. Hence the difference in the dynamics in the presence of clay was asc...