synopsisCriteria for rheological compatibility of polymer blends are suggested. The criteria suggested make use of plots of first normal stress difference (Nl) against shear stress ((rl&, and of storage modulus (G') against loss modulus (Gff). Compatible blend systems considered are (1) blends of two different grades of lowdensity polyethylene, (2) blends of poly(viny1idene fluoride) and poly(methy1 methacrylate), (3) blends of poly(2,6dimethyl-l,4-phenylene oxide) and polystyrene, and (4) blends of poly(styrene-co-acrylonitrile) and poly(styreneco-maleic anhyride). And incompatible blend systems considered are (1) blends of nylon 6 and poly(ethy1ene-m-vinyl acetate) and (2) blends of nylon 6 and an ethylene-based multifunctional polymer. It has been found that plots of Nl vs. uI2 and G ' vs. G" give (a) temperature-independent correlations for both compatible and incompatible blend systems; (b) composition-independent correlations for compatible blends, (c) compositiondependent correlations for incompatible blends.

SynopsisSteady and oscillatory shearing flow properties of compatible and incompatible polymer blend systems were measured, using a cone-and-plate rheometer. The compatible blend systems investigated are blends of two low-density polyethylenes (LDPE) having different values of molecular weight and blends of poly(methy1 methacrylate) (PMMA) with poly(viny1idene fluoride) (PVDF). The incompatible blend system investigated is a blend of poly(methy1 methacrylate) (PMMA) with polystyrene (PS). It was found that (1) plots of first normal stress difference (711 -722) vs. shear stress (712) and plots of storage modulus (G') vs. loss modulus (G") for the LDPE blends become independent of temperature and blend composition; (2) plots of 711 -7 2 2 vs. 712, and G' vs. G " for the PMMA/PVDF blends become independent of temperature but dependent upon blend composition. It was found further that, for the incompatible PMMA/PS blends, the dependence of 711 -722 on blend composition, when plotted against 712, is different from the dependence of G' on blend composition, when plotted against G". However, in both compatible and incompatible blend systems, plots of 711 -7 2 2 vs. 712 and plots of G' versus G" are independent of temperature. The seemingly complicated composition-dependent rheological behavior of the incompatible blend system is explained with the aid of photomicrographs describing the state of dispersion.

synopsisThe interfacial structure and diffusion kinetics of two compatible polymers, poly (methyl methacrylate) and poly (vinylidene fluoride) are studied in the melt. The interdiffusion rates of the two components are found to be unequal, giving unequal diffusion coefficients, a net mass flow across the interface, and an asymmetric interfacial composition profile. The structure and kinetics confirm the predictions of the reptation theory. The interfacial thickness d grows with P Z , and the interdiffusion coefficient is proportional to M-2, where t is the time and M is the molecular weight. The scaling law for the interfacial thickness is therefore d a M-1t1'2. The number of chains per unit area crossing the original interface reaches a constant value independent of diffusion time after a short induction time on the order of the tube disengagement time (about 0.1-10 s in the present cases depending on the molecular weights). The adhesive bond strength (T is scaled by (T p: t"M-5 and (T/(T, a t"M-* [l -(MJkO1-1, where (T, is the (T at infinite molecular weight and M, is the entanglement molecular weight.