Mixing Considerations in Multicomponent Miscible Reactive Polymer Processing Systems

3 MIXING CONSIDERATIONS IN MULTICOMPONENT MISCIBLE REACTIVE POLYMER PROCESSING SYSTEMS 

Following the preceding discussions on the various types of reactors for reactive processing, we now discuss the requirements for attaining completed reactions, uniform reactor environment, and uniform reaction product. 

First and foremost, the laminar mixing flow created in the reactive processing equipment, must reduce the striation thickness to a level where the diffusion characteristic time, tD = r2/ )AB, is small compared to the reaction characteristic time. Since the molecular diffusivities of low molecular weight components in polymeric melts (see Section 8.3) are very small and of the order of 10 6 cm2/s, the striation thickness must be reduced to the micron level in order to get a characteristic time t of the order of 1 s. Shear flow can accomplish this in reasonable mixing times because the striation thickness is inversely proportional to the total shear (see Section 7.3) 

The second requirement, for reactions that are not diffusion controlled to reach completion, is that the Damkohler number be larger than 10. The previous discussion and Fig. 11.12 strongly indicate that for SSEs, where at t 0.757 there is an almost vertical ascent of F(t), we use Da = 0.75 t/tr 10 as the requirement for completion. 

Example 11.1 Chain Modification (Branching and Partial Cross-linking) of PET with Triglycidyl Isocyannrate (TGIC) Dhavalkikar (39) conducted the reaction cited in the Example title on samples placed between the rheometrics mechanical spectrometer (RMS) parallel disks in the temperature-controlled chamber under nitrogen. He followed the reaction dynamics chemorheologically by measuring, in-line, the in- and out-of-phase dynamic moduli G (t) and G (t) they are indicative of the elastic and viscous nature of the molten reactive samples. 

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