High-pressure shear mixing

The BMC materials are fed from a hopper into the plasticization section of a relatively low-temperature (to minimize cure) single-screw extruder, where the material is mixed, metered and sheared into a homogenous mixture and collected in an injection cavity is the end of the screw. Once this cavity has been filled the entire screw is hydraulically plunged forwards and the material in the extruder cavity is injected into the mould under high pressures (typically 15 000-30 000 psi). The mould is at high temperature to facilitate curing of the part in the mould. 

The conductivity and high-frequency dielectric constant of an emulsion are both indicators of which phase (water or CO2) is the continuous one. If CO2 is the continuous phase in an emulsion, the emulsion conductivity will be extremely low. In contrast, if water is the continuous phase, substantial conductivity will be observed, provided that ionic solutes are present. Likewise, the dielectric of a CO2-continuous emulsion should be similar to that of CO2 (ca. 1.2), whereas the dielectric of a water-continuous emulsion should approach that of water (ca. 80). Emulsions were created by using a high-pressure emulsifier (Emulsiflex, Avestin) to provide high-shear mixing for systems containing CO2, water, and Mn(PFPE)2 surfactant as shown in Figure 2.4-8. 

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