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

The development of morphology from pellet-sized particles to submicrom etre 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 t o be dissolved away so that the dispersed phase may be observed direct ly using scanning electron microscopy. The dispersed phase for the mod el experiments is an amorphous nylon. The matrix phases investigated i nclude polystyrene, an oxazoline functional polystyrene, a styrene-mal eic anhydride copolymer, an amorphous polyester and a polycarbonate. T hese model experiments dramatically reveal the primary modes of partic le deformation and the nature of the morphologies at short mixing time s. 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 th e effects of flow and interfacial tension. Holes develop in the ribbon s, which grow in size and concentration until a fragile lace structure is formed. The lace structure breaks into irregularly shaped particle s, which are then broken up into nearly spherical particles. This mech anism results in very fast formation of small dispersed-phase particle s, which are nearly the same size as those observed at long mixing tim es. Continued mixing action primarily reduces the size of the largest particles in the size distribution.