Prepolymer agitation

Thermocouple probe pockets also need to be fitted. Their location needs to be in conjunction with the design of the agitator and the need to obtain, as accurately as possible, the true temperature of the prepolymer as it is... 

Figure 4.18. Schematic sketching the experimental procedure used in 3D mesoscale self-assembly. Molding of a polyurethane prepolymer in a PDMS master generated polyhedra. Lubricant was added to the polyhedra in a water-filled Morton flask the use of liquid solder as a lubricant required the covering of selected faces with solder-coated copper tape. Axial rotation of the flask provided the agitation needed to cause collisions between liquid-coated pieces. The schematic depicts the formation and self-...

A level of agitation above the minimum shear can be used to reduce the rubber particle size. However, agitation is not always effective in reducing the rubber particle size (see section 5.2) and there is also an upper limit based on hardware limitations (torque). Another aspect that plays a role related to shear is the feed rate. Increasing the feed rate means that the residence time in the reactor(s) is shorter. A lower amount of shear is transferred to the prepolymer, giving in general larger rubber particles in the end product. 

Related to particle sizing, Molau and Kesskula described the concept of type I and II occlusion [5]. The prepolymer is viscous and has a retarding effect on the phase inversion. In most cases multiple emulsions are formed after the phase inversion point. If the agitation is not extremely high these multiple emulsions survive the further copolymerization and give SAN occlusions in the rubber particles. These occlusions are called type I. Type II occlusions are formed when monomer dissolved in the rubber phase is copolymerized. Because SAN is not compatible with the rubber, separation occurs within the rubber particle, giving type II occlusions. 

When the temperature of the prepolymer has dropped to 80 + 2 C, It Is stirred together with 1R)CA, which Is at 122-124 C. After agitating for about two minutes, the resultant solution at a tenqierature of 87-88 C Is poured Into the mold which was preheated to the same temperature and then cured.at that temperature for 6 hours. 

Heat the prepolymer amine salt to 60 to 80 °C and slowly pour into a resin kettle charged with a known amount deionised water at 25 to 50 °C with strong agitation. Add the prepolymer to give the desired solids content. 

Paste adhesives. Paste adhesive formulations are produced by mixing the base resin with low-molecular weight diluents or solvents, if necessary, to reduce viscosity. Other prepolymer resins may be added and agitated until dissolved. Viscosity and temperature are continuously monitored and more diluents or resin added as required. Finally, one or more types of fillers are added and mixed and the viscosity of the mixture is adjusted. In incorporating the filler into the resin, best results are obtained when the filler is preheated... 

The tower reactors similar to the ethylene polymerization reactors are used in other free-radical vinyl polymerization processes. Figure 4a shows a schematic of the tower reactor for bulk styrene polymerization developed by Farben in the 1930s [4]. The prepolymers prepared in batch prepolymerization reactors to about 33-35% conversion are transferred to a tower reactor whose temperature profile is controlled from 100°C to 200°C by jackets and internal cooling coils. There is no agitation device in the tower reactor. The product is then discharged from the bottom of the tower by an extruder, cooled, and pelletized. 

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