STRUCTURE AND BEHAVIOR OF MULTICOMPONENT IMMISCIBLE POLYMER BLENDS

The morphology of ternary polypropylene (PP)-polyamine-6 (PA-6) glass (either beads [GB] or fibers [GF]) blends was investigated as a specif ic example of a multicomponent system. The implications of blend struc ture and filler partitioning on several properties, such as viscosity and crystallization behavior, are discussed. The morphology of multico mponent blends is predicted by the spreading coefficient, which is rel ated to the interfacial tension between the various components. In ter nary blends with a PA-6 matrix, the PP domains and glass filler are se parately dispersed within the matrix. In ternary blends with a PP matr ix, most of the PA-6 is found surrounding (encapsulating) the glass fi ller. The spreading coefficient was found to predict correctly the fin al morphology for most ternary blends studied, except for cases of kin etic hindrance, such as a high viscosity for one component. The spread ing coefficient can also be used to predict the structure of four comp onent blends. The different blend structures, encapsulation or separat e dispersion of filler, affect the shear viscosity and its corresponde nce to a rule of mixtures prediction. For PA-6-rich blends (separate d ispersion of filler), the actual viscosity is lower that the viscosity predicted by a proposed modified ''rule of mixtures''. In PP-rich ter nary blends (encapsulation of filler), however, the experimental visco sity data does match a modified rule of mixtures prediction. Dynamic r heological results for PP/PA-6 binary blends indicated that the blend dynamic viscosity increased with PA addition, whereas the shear viscos ity results at high shear rates indicated a reduction in viscosity. Th e difference is a direct consequence of morphological changes during s hear rheometry. Thermal results for the crystallization of PP in terna ry PP/PA-6/GB blends with identical compositions but differing morphol ogies showed that the PP peak crystallization temperature and crystal size distribution were different in blends containing mainly a PP-glas s interface (separately dispersed morphology) and those containing a P P-PA-6 interface (encapsulated morphology). In summary, the structure of multicomponent blends can be correlated with the rheological, mecha nical, and thermal behavior of the blend. Filler segregation within on e polymeric phase is strongly dependent on the surface characteristics of the polymers and the fillers.