Reaction-injection molding free

A specific attention has been paid to the mechanochemical generation of X in unsaturated elastomers, EPDM, ABS, PVC and polyolefins [243, 252]. This synthetical approach exploits processing operations producing free radicals. In situ chemical reactions can be performed during some important industrial processes like mastication of rubber and extrusion, mixing or reaction injection molding of plastics. 

The extruder can be used for a variety of polymerizations even if no preformed polymer is present.89 These include the continuous anionic polymerization of caprolactam to produce nylon 6,90 anionic polymerization of capro-lactone 91 anionic polymerization of styrene 92 cationic copolymerization of 1,3-dioxolane and methylal 93 free radical polymerization of methyl methacrylate 94 addition of ammonia to maleic anhydride to form poly(succin-imide) 95 and preparation of an acrylated polyurethane from polycaprolactone, 4,4 -methylenebis(phenyl isocyanate), and 2-hydroxyethyl acrylate.96 The technique of reaction injection molding to prepare molded parts is slightly different. Polyurethanes can be made this way by... 

In the reaction injection molding process, the release force also depends on cure time. As cure progresses, less free isocyanate groups are available for reaction with the mold surface and the release stress decreases. Longer cure times also give zinc stearate more time to migrate to the mold surface. 

High performance polyurethane elastomers are used in conformal coating, potting, and in reactive injection molding (or reaction impiugement molding) of IC devices. Furthermore, rigid polyurethane foams, most often in free-foam densities of 128—288 kg/m [8—18 lbs/ft (pc Q] useful for... 

If MDI is initially compounded with starch and 25% water, the dominant interaction would be expected to be between the MDI and water, due to the high free water content. In the current work, not only the gelatinized starch had a lower concentration of water ( 16%), but the water molecules may also have had reduced mobility if they were bound (via hydrogen bonding) to the numerous hydroxyl groups present in the starch. A small amount of bubbles due to NCO/H2O reaction were observed in the compounded pellets however, these were removed in the injection molding process [45]. 

When the mixing head is attached to the mold, it is important that the jet pump effect of the flowing mixture does not suck in air through a leaky joint. Furthermore, the reaction mixture should not be injected as a free jet into the mold cavity (Figure 1.125). The flow should at least keep contact to one cavity wall, preferred is the later visible part surface. 

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