Processing of polyurethane/polyester interpenetrating polymer networks by reaction injection molding. Part III: Flow reorientation through multiple impingement

Abstract This is the third of a three‐part paper investigating the feasibility of processing polyurethane/polyester Interpenetrating Polymer Networks (IPN) by Reaction Injection Molding (RIM). Part of this paper was presented at the Third International Conference on Reactive Processing. Bischenberg Congress Center, Alsace, France, September 4– (1984) Two basic issues are addressed concerning the improvement of the mixing scale in impingement mixing, namely, the influence of multiple impingement on the microscale and the number of flow dividing elements needed to achieve a certain degree of mixing. It was found that the incorporation of cascading stages does improve mixing further. The extent of improvement depends on the secondary stream Reynolds number and the local impingement pressure. A transition zone generally demarcates the beginning of marginal improvement on the number of elements used. Since the cascading configuration operates in a manner analogous to “motionless mixers,” there is a practical limit to the number of stages that can be used. At a primary impingement pressure of 18,000 psi, for instance, an overall improvement of 53 percent is recorded for a flow through a total of 80 stages. A noticeable 23 percent is noted within the first ten stages while the next 70 stages enhance mixing by only 30 percent. Thermal and dynamic mechanical analysis revealed some degree of interpenetration between the two networks.