Shearing Device

Many methods for the conversion of acid copolymers to ionomers have been described by Du Pont (27,28). The chemistry involved is simple when cations such as sodium or potassium are involved, but conditions must be controlled to obtain uniform products. Solutions of sodium hydroxide or methoxide can be fed to the acid copolymer melt, using a high shear device such as a two-roU mill to achieve uniformity. AH volatile by-products are easily removed during the conversion, which is mn at about 150°C. A continuous process has been described, using two extmders, the first designed to plasticate the feed polymer and mix it rapidly with the metal compound, eg, zinc oxide, at 160°C (28). Acetic acid is pumped into the melt to function as an activator. Volatiles are removed in an extraction-extmder which follows the reactor-extmder, and the anhydrous melt emerges through a die-plate as strands which are cut into pellets. 

Fig. 12. Molecular weight falloff with time for various rotating-hlade shearing devices [32]...

Jiang, Q., and Logan, B. E., Fractal dimensions of aggregates from shear devices. J. AWWA, February, pp. 100-113 (1996). 

Figure 28. Deformation and breakup of green granules in a constant shear device.

The techniques that have been used to characterise the mechanical properties of microparticles may be classified as indirect and direct. The former includes measurement of breakage in a "shear" device, for example, a stirred vessel (Poncelet and Neufeld, 1989) or bubble column (Lu et ah, 1992). However, the results from these indirect techniques are rather difficult to use since the mechanical breakage depends not only on the mechanical properties but also the hydrodynamics of the processing equipment, and the latter are still not well understood. To overcome this problem, a cone and plate viscometer that can apply well-defined shear stresses has been used to study breakage of hybridomas (Born et ah, 1992), but this is not a widely applied or applicable technique because the forces are too small to break most cells. 

To measure the adhesion strength of bacteria, it is necessary to remove them from the surface. Weiss (1961) measured bacterial adhesion by allowing cells to settle onto a glass surface of a sealed chamber, and then counting them with the aid of a microscope. After a period of incubation the chamber was turned upside down, the unattached cells fell from the surface and the remaining attached cells were recounted. This adhesion number method is purely observational, as it does not measure adhesion directly. Weiss also described a disc-shearing device,... 

The volume is closed with a contribution by J. Bibette who describes and illustrates a simplified process of making monodisperse emulsions and emulsion based particles with predictable size and size distribution by a simple shearing device. I regard this very flexible route as important for the conception of many future particle-based systems, devices and procedures, and it is rather the rule than the exception that colloid chemistry nicely integrates mechanical and engineering procedures to access the nanoscale in a rational way. 

The effect of the type of impact modifier on the melt flow of a PVC window profile formulation as a function of shear rates encountered during extrusion was investigated and the relationship between the melt flow and mechanical properties of the profiles evaluated. A Rheoplast Capillary Rheometer with a pre-shearing device was employed to investigate the melt viscoelastic properties of the formulations and the performance of the formulations in terms of post-extrusion shrinkage, surface gloss and enthalpy relaxation discussed. 2 refs. 

For laboratory investigations of miniemulsions, a variety of high-shear devices have been used, although sonication has been the most popular. Soni-cation, however, may not be very practical for the large-scale production of commercial miniemulsion polymers. An effective alternative to sonication is also driven by the need to design an efficient miniemulsion polymerization process. A continuous process places greater demand on the shear device in terms of energy consumption and dissipation. 

The performance of a membrane process is a function of the intrinsic properties of the membrane, the imposed operating and hydrodynamic conditions, and the namre of the feed. This chapter describes methods available to enhance performance by various techniques, mainly hydrodynamic but also chemical and physical. The focus is on the liquid-based membrane processes where performance is characterized by attainable flux, fouling control, and separation capabilities. The techniques discussed include secondary flows, flow channel spacers, pulsed flow, two-phase flow, high shear devices, electromagnetic effects, and ultrasound. 

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