Sticky-stage

The hazard of agglomeration is greatest when acrylates are polymerized. The products tend to be elastomers and, in the course of the polymerization of these monomers, they tend to go through a sticky stage. However, the proper selection of the suspending agent frequently prevents agglomeration. 

In semibatch emulsion polymerizations the polymer particles are kept monomer-starved to obtain higher rates of polymerization and to permit easier control of the rate and particle size distribution. There are two aspects to the control of PSD. The controlled addition of emulsifier during particle growth stabilizes the particles without further particle nucleation. The second aspect is related to the particle sticky stage which often occurs... 

Anotlier type of trough-and-screw mixer is the AP Conti paste mixer, shown in Fig. 18-60. These self-cleaning mixers are particularly appropriate when the product being handled goes through a sticky stage, which could plug the mixer or foul the heat-transfer surfaces. 

In the case of a polymer that is miscible in all proportions with its monomer (e.g., styrene and methyl methacrylate), a very large variation of the range of the dispersed-phase viscosity is observed during the course of polymerization. The initially low viscosity liquid monomer is transformed gradually into an increasingly viscous polymer in monomer solution and, as conversion increases, the dispersed phase acquires the characteristics of a solid particle. Rapid polymerization during the sticky stage minimizes the... 

Another close analogy is the precipitation mass polymerization system for polyvinyl chloride (PVC). In that case, the polymer does precipitate from the monomer, but it does not go through a self-adhering sticky stage. This allows... 

Bubble columns in series have been used to establish the same effective mix of plug-flow and back-mixing behavior required for Hquid-phase oxidation of cyclohexane, as obtained with staged reactors in series. WeU-mixed behavior has been established with both Hquid and air recycle. The choice of one bubble column reactor was motivated by the need to minimize sticky by-products that accumulated on the walls (93). Here, high air rate also increased conversion by eliminating reaction water from the reactor, thus illustrating that the choice of a reactor system need not always be based on compromise, and solutions to production and maintenance problems are complementary. Unlike the Hquid in most bubble columns, Hquid in this reactor was intentionally weU mixed. 

An alternative approach to solving the exotherm problem is to polymerise in suspension. In this case the monomer is vigorously stirred in water to form tiny droplets. To prevent these droplets from cohering at the stage when the droplet is a sticky mixture of polymer and monomer, suspension or dispersion agents... 

Fig. 2. Pathophysiological sequence of events in periodontal disease. Bacteria produce byproducts (e.g. toxins or enzymes) which, along with mucus, constantly form a sticky, colorless plaque on teeth. If not removed, plaque can harden and form bacteria-harboring tartar around teeth. Tissue that attaches the gums to the teeth can be destroyed by the irritants of plaque. If this is the case, gums pull away from the teeth and small pockets arise between the teeth and gums. The pockets then become filled with more plaque, deepen, and it becomes impossible to clean plaque out. At this stage the bone structure supporting teeth can actually be destroyed (courtesy of Drs J. Chavez and S.E. Zaragoza, El Paso Community College, Texas, USA).

This formula can promote free flow of Qi and eliminate damp-heat. It is used to treat dampness which is mingled with mild heat that obstructs the Qi in the Middle-Jiao. This occurs at the initial stage of damp-febrile disease or in humid summer conditions. The manifestations are headache with a heavy sensation, heaviness of the body, a wan complexion, fullness in the chest and epigastria, no appetite, afternoon fever, an absence of thirst, a white, sticky, thick tongue coating and a wiry, thready pulse, which is soft in the deep position. 

The limits to the areal density of deposit for filters are set by clogging of the filter that sets in at typically 100 xg/cm2. The limit of areal density for impactors is set by the problem of particle bounce. This is a serious problem for coarse, dry aerosols but less so for fine, wet, secondary aerosols. Nevertheless, sticky substrates are universally used (19), and deposits are generally limited to a few monolayers of particles for a 2.5- xm particle. This limit amounts to no more than 7 xm of deposit, or, for 1.5- xg/m3 aerosols (per stage), about 1000 xg/cm2 of deposit. 

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