| Reactive extrusion, a process which combines two or more traditional polymer processes, has been investigated computationally. Flow characteristics of extruders as streamline reactors were first examined by checking the particle trajectories and the residence time distributions. A three dimensional transient tracer flow model was used to compute the residence time distribution of single screw extruder with various geometries. F-curve and the intensity function {dollar}Omega{dollar} were found useful in characterizing stagnancy and channeling.; The problems associated with the convective dominant flow were solved by applying a second order upwinding finite difference method. Parametric studies of reactive extrusion included three groups of variables; geometric factors, operating conditions and material characteristics. Two types of reaction were chosen to demonstrate the reactor performance, irreversible random polymerization and chain addition polymerization with termination.; Coordinate transformation was used to solve the reacting flow in irregular domains. Flows in dish shaped channels and in channels with mixing pins were studied. Free surface flow with arbitrary surface shape arising from starved feed conditions was also investigated.; The three dimensional solution of the velocity profiles in the C-shaped channel of a closely intermeshing counter-rotating twin screw extruder was obtained by vector potential-vorticity formulation method. Good temperature control, a result of good distributive mixing, was found in C-shaped channels when reactor performance was compared with two extreme cases: a batch reactor and a stagnant C-shaped channel.; Proper selection of extruder type for systems with specific reaction requirements is suggested. Experimental verification of the major conclusions is also proposed. This model is used to justify design equations for thermal and compositional homogeneity in reactive extrusion obtained from combining laminar mixing theory and thermal runaway theory. |
