Encapsulation during melt processing of ternary immiscible polymer blends

Filled immiscible polymer blends may exhibit several typical morphologies: filler particles and minor polymer particles separately dispersed in the matrix, filler particles located at interfaces between the continuous matrix and the dispersed polymer particles, and filler particles encapsulated by the minor polymer phase. The actual morphology developed during a melt blending process is determined by thermodynamic parameters, e.g., polymer/filler interfacial tensions, or spreading coefficients, and by kinetic factors, e.g., polymer viscosity, The main objective of this study was to investigate the dominant parameters that have led to a preferred morphology and to relate the mechanical and thermal behavior of some multicomponent blends to their morphology. A series of ternary blends with varying compositions was chosen, comprising polar EVOH as the minor phase, a semi-crystalline matrix of varying polarity (PP and EVA) and mica as the filler. The morphology of the blends studied has revealed the existence of two dispersed phases: EVOH encapsulating mica particles and some separately dispersed EVOH particles in the polymer matrix. The size and amount of the separately dispersed EVOH particles and the shape of the encapsulated particles varied according to differences in interfacial tension between the polymer matrix and the EVOH. The structure of the multicomponent blends studied has a significant effect on their behavior as depicted by their thermal, rheological, static and dynamic mechanical properties. The structure itself can be controlled by careful selection of the blend's components, its composition and processing details.