Processing of polyurethane/polyester interpenetrating polymer networks by reaction injection molding. Part II: Mixing at high reynolds numbers and impingement pressures

The impingement mixing process is analyzed considering the characteristic times of all the mechanisms involved. Two models of the mixing phenomenon are postulated; one takes into consideration the energetic nature of the shearing and stretching mechanisms during impingement while the other calls for the statistical variations in the kinetic energy dissipation process. Experimental data are presented to document the mixing scale obtained at high stream Reynolds numbers and impingement pressure. Model fluids are used on several occasions to characterize this scale. The best technique, however, involves mixing polyurethane with an inert component, dissolving the latter after gelation of the polyurethane network, and observing stereologically the ensuing morphology. Results indicate that high Reynolds numbers and impingeme it pressures reduce the scale of mixing to submicron dimensions. Autocorrelation coefficients are derived from the morphologies obtained after gelation. The initial slopes and oscillations in the correlograms are found to be good descriptive features of the degree of mixing in reaction injection molding (RIM).