Reactive molding

Composites cured by the polyaddition mechanism are especially interesting for reactive molding, because by-products are not formed and there is no appreciable shrinkage during the reaction. This is the principal difference between polyaddition and polycondensation. 

It is clear that this method cannot be based on the use of similarity parameters since reactive molding in common with other chemical engineering processes, involves nonlinear phenomena that result in the invalidity of similarity conditions as geometric, chemical, and thermal parameters. 

The manufacture of products by reactive molding results in the superposition of interrelated chemical and physical phenomena. These include polymerization, crystallization, vitrification, heat transfer, rheokinetic effects, changes in the physical properties and volume of a material injected into a mold. It is quite natural that special experimental methods are required to study and control the complex processes which take place in molds. 

The FTMS method allows us to follow changes in several parameters that carry information on the role of different mechanisms during formation of an end-product by reactive molding. Specifically, the development of fluctuating entanglements of long-chain macromolecules can be distinguished from the appearance of rubber-like three-dimensional networks of chemical bonds. 

The so-called RIM-process (reactive injection molding) is a current realization of the reactive molding process. The heart of the process is the shock mixing of the reactive ingredients, which is achieved by collision of two jets injected at a pressure of 10 - 20 MPa. The reactive mixture is injected into the mold in a laminar flow regime the pressure at this stage does not exceed 0.1- 0.4 MPa.259 The practical development of this method relies on automatic control systems and modem high quality equipment. 

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