KINETIC AND THERMODYNAMIC CONTROL OF THE SELECTIVE LOCALIZATION OF CARBON-BLACK AT THE INTERFACE OF IMMISCIBLE POLYMER BLENDS

Several strategies are reported that allow carbon black (CB) particles to be selectively localized at the interface of polyethylene/polystyr ene (PE/PS) blends used as models of two-phase polyblends. A first gen eral approach relies upon a kinetic control, i.e., the choice of such processing conditions that the CB particles are ''immobilized'' at the polyblend interface at least for a workable period of time. The dry p remixing of the two powdery polymers and CB particles followed by comp ression molding is the first valuable kinetic control. A second one ca n be implemented during the melt blending of the immiscible polymers, which makes this strategy more attractive. Actually, CB is first dispe rsed in the melted polymer with which it less strongly interacts. Upon the addition and melting of the second polymer, CB particles are ther modynamically driven to this second polymer phase. The conducting part icles are observed to accumulate at the polyblend interface at a rate and for a period of time that depend on the rheology of the polyblend under the processing conditions. The thermodynamically controlled loca lization of the CB particles at the two-phase polyblend interface is c ertainly the most efficient strategy, even though it:is not the most g eneral one. In this respect, CB particles have been oxidized in such a way that they cover a large range of pH. Depending on this surface pr operty, the CB particles are spontaneously localized either in one pol ymer phase or at the interface. Actually, the selective localization o f the CB particles changes from the PS phase to the interface and fina lly to the PE phase, when the pH of these particles is increased from 2.4 to 7.0. The selective localization of the CB particles at the poly blend interface is most interesting when the polymer phases are co-con tinuous, since then the conducting particles can percolate at a volume fraction as small as 0.002-0.003. Furthermore, this selective modific ation of the polyblend interface improves the stability of the phase m orphology against coalescence when the Material is annealed.