Reagglomeration

Sediment Volume. If the dispersion is unstable, the sediment bed will be quite deep and sedimenting particles will stick together where they first strike the sediment bed, thus forming an open stmcture with considerable occluded Hquid. If the dispersion is stable to reagglomeration, the particles will move freely past one another to avoid contact as long as possible. The result is a thin sediment bed with maximum soHds packing and minimum occluded hquid (12). Since dispersed particles setde more slowly than docs, centrifugation maybe needed to force sedimentation of small particles within a reasonable analysis time. 

Another technique to reduce the problems caused by stickies is to use additives to reduce the tackiness of these particles. This prevents their later reagglomeration and attachment to paper machine surfaces. These additives are usually added to the pulper. The most common is talc (17) usually added to the pulper in repulpable bags. Emulsified talc is also sometimes added to the pulp just before the pulp encounters high shear. Organic polymers (18) such as a polyvinylpyrrohdinone (PVP) copolymer (19) have also been reported to reduce the tackiness of stickies. 

The particle size of the dispersed phase depends upon the viscosity of the elastomer-monomer solution. Preferably the molecular weight of the polybutadiene elastomer should be around 2 x 10 and should have reasonable branching to reduce cold flow. Furthermore, the microstructure of the elastomer provides an important contribution toward the low-temperature impact behavior of the final product. It should also be emphasized that the use of EPDM rubber [136] or acrylate rubber [137] may provide improved weatherability. It has been observed that with an increase in agitator speed the mean diameter of the dispersed phase (D) decreases, which subsequently levels out at high shear [138-141]. However, reagglomeration may occur in the case of bulk... 

Even a routine operation, such as applying the pigment suspension to a microscope slide by ultrasound vaporization, may be a source of complications. Pigment particles, previously completely dispersed in suspension and even in a vaporized droplet, may reagglomerate in the suspension whose volume is reduced as the carrier (organic solvent or water) evaporates. 

The pigmented system that is comprised of dispersed particles is stabilized to preclude reagglomeration and/or flocculation Stabilization. 

The particle size of a pigment, however, has an impact not only on those steps within the dispersion process in which pigment agglomerates are broken down. It also affects retroactive processes, such as reagglomeration, flocculation, and rubout effects [19]. Reagglomeration (Sec. 1.5) occurs if the pigment particles are not covered adequately by the binder. Flocculates (Sec. 1.5) are loose associations... 

Maiti et al. [64] took typical fluorocarbon-based exfoliated nanocomposites and observed that they reagglomerate while they are processed in a hydraulic press during the curing operation. Their XRD studies revealed that the level of exfoliation was, however, not disturbed if oven curing was performed, instead of press curing. 

The consequence is an inhomogeneous distribution of additives in the individual polymer phases and thermodynamic nonequilibrium after mixing. The latter effect may cause demixing and re agglomeration of additives. A well-known example in this regard is the flocculation or reagglomeration of silica in S-SBR compounds [3]. 

The particle size distribution suggests that nonirradiated PTFE powder has a broad particle size distribution compared to 500 kGy-irradiated PTFE powder. The nonirradiated PTFE powder shows a characteristic bimodal distribution compared to the unimodal distribution of 500 kGy-irradiated PTFE powder (Fig. 14). This specific bimodal distribution clearly signifies that nonirradiated PTFE powder is mainly composed of bigger agglomerates that tend to reagglomerate. By contrast,... 

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