Coalescence in the process of melt blending of incompatible polymers

Previously abstracted from original as item 9112-A1-P-0630. The formation of dispersed phase structure in ternary blends of incompatible polymers during melt blending has been investigated. Transmission electron microscopy and a semi-computerized technique for particle size analysis were used to evaluate the influence of addition of small portions of the third polymer on diameters and polydispersities of domains of the primary dispersed phase of blends. The systems studied are represented by a poly(methylmethacrylate) (PMMA)--polystyrene (PS) basic blend to which small amounts (1-5 wt.%) of polypropylene (PP) of different molecular weight were added during the mixing process on the two-roll mill at 180. It was shown that the addition of only 1 wt.% of PP to the binary blend 45/55 PMMA/PS resulted in more than two-fold decrease of PMMA primary dispersed phase particle diameters and their polydispersity, as compared to those of the binary blend. Further increase of PP concentration up to 5 wt.% produced much less, if any, effect. Similar phenomena concerning dispersive effect of small additives of the third incompatible polymer were also evaluated in ternary blends of incompatible elastomers. The proposed mechanism of the dispersive action of small portions of the third polymer, added to a binary blend during mixing, is based on an assumption about the depression of coalescence of the primary dispersed phase droplets, in presence of the droplets of the third incompatible phase. The depression of coalescence rate shifts the dynamic equilibrium breakage /coalescence towards formation of smaller particles.