Reaction injection molding discussion

Polyurethane in the rubber industry can be used in (1) the thermoplastic elastomer form (TPE), discussed earlier, (2) a two-part liquid system in reaction injection molding (RIM), (3) the cast molding of rubber parts, or (4) as a millable gum that can be processed on a two-roll mill and cured with agents such as peroxides or sulfur, just as with conventional rubber. Although different versions of polyurethane elastomers must be tailor-made for each of these four common applications, the basic chemistry used is very similar in all. 

The materials presented in this chapter will be used in the discussions on the processing of thermosets in Chapters 11-13 of Volume 2, which cover reaction injection molding, pultrusion of thermoset/fiber composites and compression molding of thermoset/fiber composites, respectively. 

The values obtained above are used to calculate "Pc for a range of values for "N Produce a plot for reaction injection molding and compare and discuss. 

As mentioned in the introduction, the synthesis of telechelics is important to preparative polymer chemistry because of their use as macromonomer precursors (and therefore graft copolymer and network precursors), as precursors to block copolymers, and as the basis of reaction injection molding. Some general reviews on telechelics include those of A they and Heitz. In addition, the synthesis, reactions and properties of acetylene-terminated oligomers were recently reviewed.An extensive discussion of this class of reactive polymers is the subject of a recent book. ... 

Macosko, C. W., RIM Fundamentals of Reaction Injection Molding , Hanser, New York, 1989. The book emphasizes fundamentals and discusses the operations of material delivery, mixing, mold filling, curing, for urethanes and nonurethanes, and reinforced RIM. Additional references are provided with each chapter. 

The crosslinking reaction may be catalyzed by a small amount of suitable organometalUc catalysts. The blends typically contain ca. 5-20% silicone. Injection molded or extruded parts are further heat-treated to complete the curing reactions. There is, of course, a significant level of phase separation. In the thermoplastic molding compounds such as glass-filled PA and PBT, addition of the silicone semi-IPN in small amounts (ca. 5-10%) is reported to reduce the mold shrinkage, improve mold release, and increase wear and friction resistance. Polyamide-silicone blends have already been discussed under PA blends section. 

Bulky, complex shapes and thin-walled articles can be produced in this way. Reaction times of a few seconds are possible, and mold residence times of one or two minutes have been achieved. RIM consumes less energy and uses less expensive equipment than conventional injection-molding processes. The process is used to make fascias, bumpers, and other flexible automotive parts. Fillers may be incorporated in the components to lower cost and increase rigidity. This fabrication technique is discussed further in the section on Fabrication of Plastics under Injection Molding. ... 

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