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 specific example of a multicomponent system. The implications of blend structure and filler partitioning on several properties, such as viscosity and crystallization behavior, are discussed. The morphology of multicomponent blends is predicted by the spreading coefficient, which is related to the interfacial tension between the various components. In ternary blends with a PA-6 matrix, the PP domains and glass filler are separately dispersed within the matrix. In ternary blends with a PP matrix, most of the PA-6 is found surrounding (encapsulating) the glass filler. The spreading coefficient was found to predict correctly the final morphology for most ternary blends studied, except for cases of kinetic hindrance, such as a high viscosity for one component. The spreading coefficient can also be used to predict the structure of four component blends. The different blend structures, encapsulation or separate dispersion of filler, affect the shear viscosity and its correspondence to a rule of mixtures prediction. For PA-6-rich blends (separate dispersion of filler), the actual viscosity is lower that the viscosity predicted by a proposed modified "rule of mixtures". In PP-rich ternary blends (encapsulation of filler), however, the experimental viscosity data does match a modified rule of mixtures prediction. Dynamic rheological results for PP/PA-6 binary blends indicated that the blend dynamic viscosity increased with PA addition, whereas the shear viscosity results at high shear rates indicated a reduction in viscosity. The difference is a direct consequence of morphological changes during shear rheometry. Thermal results for the crystallization of PP in ternary PP/PA-6/GB blends with identical compositions but differing morphologies showed that the PP peak crystallization temperature and crystal size distribution were different in blends containing mainly a PP-glass interface (separately dispersed morphology) and those containing a PP-PA-6 interface (encapsulated morphology). In summary, the structure of multicomponent blends can be correlated with the rheological, mechanical, and thermal behavior of the blend. Filler segregation within one polymeric phase is strongly dependent on the surface characteristics of the polymers and the fillers.