MORPHOLOGY DEVELOPMENT DURING THE INITIAL-STAGES OF POLYMER-POLYMER BLENDING

The development of morphology from pellet-sized particles to submicrometre droplets during the polymer blending process is investigated for several polymer blends. In order to determine the morphology at short mixing times, a model experiment is developed that allows the matrix to be dissolved away so that the dispersed phase may be observed directly using scanning electron microscopy. The dispersed phase for the model experiments is an amorphous nylon. The matrix phases investigated include polystyrene, an oxazoline functional polystyrene, a styrene-maleic anhydride copolymer, an amorphous polyester and a polycarbonate. These model experiments dramatically reveal the primary modes of particle deformation and the nature of the morphologies at short mixing times. The major reduction in phase domain size occurs in conjunction with the melting or softening of the components. The initial mechanism of morphology development involves the formation of sheets or ribbons of the dispersed phase. These sheets or ribbons become unstable due to the effects of flow and interfacial tension. Holes develop in the ribbons, which grow in size and concentration until a fragile lace structure is formed. The lace structure breaks into irregularly shaped particles, which are then broken up into nearly spherical particles. This mechanism results in very fast formation of small dispersed-phase particles, which are nearly the same size as those observed at long mixing times. Continued mixing action primarily reduces the size of the largest particles in the size distribution.