Moldability studies in reactive polymer processing

Reactive polymer processing is the combined polymerization and processing of reactive prepolymers in a single operation. It encompasses a wide variety of processing methods including Reaction Injection Molding (RIM), a relatively new and growing fabrication method. Reaction Injection Molding utilizes impingement mixing of low viscosity fluids, injection of the reactive mixture into a mold, and polymerization therein to enable the molding of large plastic items. Polyurethane is currently the most commercially utilized RIM material although a number of other systems such as epoxy, nylon, and polyester are also suitable. Non‐urethane systems such as epoxy are often not as amenable to the process, however, since they are slower reactions and have a potentially damaging exotherm. A comprehensive analysis was developed to determine if a molding system is processable by RIM. Criteria for processability were established and include the ability to mix on impingement, fill large molds characteristic of the process, and provide a short cycle time without promoting a damaging exotherm. The treatment, consisting of both experimental and numerical techniques, was applied to identify potential epoxy molding systems, establish their processing window, and conduct an optimization of the process parameters to evaluate productivity. The analysis and its conclusions are applicable to most reactive polymer processing operations that employ a rapid, exothermic, polymerization reaction.