INFLUENCE OF INTERFACE MODIFICATION ON COALESCENCE IN POLYMER BLENDS

Interfacial modifiers (compatibilizers), such as block and graft copolymers have been found to yield a pronounced influence on the morphology development in blends. In the reviewed work the influence of A-B copolymers on coalescence (agglomeration) in A:B blends have been revealed by electron microscopy and rheo-optical measurements. Divergent criteria and experimental evidence appear in literature on the copolymer molecular weight if the requirement is the copolymer to effectively modify the interfacial properties. Branch lengths, composition and volume fraction of copolymer do influence the ''steric stabilization'' effect. Graft copolymers have been generally found to be somewhat more effective in inhibiting coalescence and, thus minimizing the particle size and its distribution. Rheo-optical measurements on a blend containing a block copolymer (BC) revealed that the stabilization effect of the BC is not unconditional during the flow: coalescence is prevented for a time which decreases with increasing shear rate due to a removal of the BC away from the interface. The origin of the observed behavior is outlined based on various mechanisms.