DEVELOPMENT AND CONTROL OF A BLEND MORPHOLOGY BY IN-SITU CROSS-LINKING OF THE DISPERSED PHASE

The development of the morphology of a reactive blend along a twin-screw extruder has been experimentally studied. A transesterification reaction activated by a catalyst allowed a cross-linking of the dispersed phase during the flow in the extruder. In comparison with the nonreactive system (without catalyst), the resulting morphologies were characterized by larger dimensions. Influence of screw speed and feed rate were similar for both systems, whereas the changes along the screws were more pronounced for the reactive blend. It appeared that the local morphology was strongly dependent on the extent of the reaction. At low extent, the equilibrium between breakup and coalescence was shifted toward coalescence, whereas at high extent, the classical mechanisms were largely modified and replaced by a ''coagulation'' mechanism. It was shown that, for the fully cross-linked dispersed phase, the final morphology remained remarkably stable during successive extrusion steps. For such products, the observation of a low-frequency plateau of the elastic modulus suggested the formation of a copolymer at the interface with the matrix. (C) 1994 John Wiley and Sons, Inc.