Suspensions bulk properties

Polymethacrylates. Poly(methyl methacrylate) [9011-14-7] is a thermoplastic. Itis the acryUc resin most used in building products, frequendy as a blend or copolymer with other materials to improve its properties. The monomer is polymerized either by bulk or suspension processes. Eor glazing material, its greatest use, only the bulk process is used. Sheets are prepared either by casting between glass plates or by extmsion of pellets through a sHt die. This second method is less expensive and more commonly used. Peroxide or azo initiators are used for the polymerization (see Methacrylic polymers). 

Manufacture Peroxide initiation Suspension or bulk Properties... 

Bulk properties of the suspension. This is particularly important for concentrated systems, and requires measurement of the rate of sedimentation and equilibrium sediment height. More quantitative techniques are based on assessing the rheological properties of the suspension (without disturbing the system that is, without its dilution and measurement under conditions of low deformation) and how these are affected by long-term storage. This subject is discussed in detail in Chapter 20. 

Bulk Properties of Suspensions Equilibrium Sediment Volume (or Height) and Redispersion... 

To discuss the macroscopic (or bulk ) properties of a suspension, it is necessary to specify the connection between local variables at the particle scale andmacroscopic variables at the scale L. One plausible choice, in view of the relationship between continuum and molecular variables in Chap. 2, is to assume that the macroscopic variables are just volume averages of the local variables. In particular, we assume in the discussion that follows that the macroscopic (or bulk) stress can be defined as a volume average of the local stress in the suspension, namely,... 

PARTICLES AND suspensions of many kinds play an important role in our interaction with the physical environment. They abound in earth, soil, water, and air. They are also present in chemicals and many other industrial products. If particles were spherical or cubical, characterization would be easy. Unfortunately, most of the particles present in the environment are of irregular size and shape. In many industrial processes, size characterization is a critical aspect of understanding particle behavior in suspension, the bulk properties of suspensions, and their bulk behavior. Therefore, it is important to understand the strengths and limitations of techniques used to characterize particles and suspensions. 

Among the most difficult systems to characterize from the electrical standpoint are aqueous suspensions. It is clear from experiment that the ionic double layers as well as the bulk-bulk properties play roles. The effective dielectric constant of about 10,000 can be obtained from what might at first seem to be a simple system of water (dielectric constant 80) containing suspended polymer particles of dielectric constant about 2 Similar results have been obtained with glass spheres or with living cells suspended in aqueous media. 

When solid polymer precipitates fiom bulk, solution, suspension, or emulsion polymerizations by a chain mechanism, the kinetics of the reaction and properties of the product may change sharply. If the solid phase is not swollen by the reaction mixture, the active site of the polymerization is isolated from possible termination reactions and may produce pronounced auto acceleration and increases in molecular weight of polymer formed. This behavior was quantified for one chain reaction polymer, polyvinyl chloride, covered in this book. Micldey (9) showed that polyvinyl chloride synthesis in bulk followed a two term kinetics equation with the second term representing incremental increases in polymerization rate due to accelerated polymerization in precipitated particles of polymer. 

Styrene-Acrylonitrile Copolymers (SAN). Styrene-acrylonitrile polymers are copolymers prepared from styrene and acrylonitrile monomers. The polymerization can be done under emulsion, bulk, or suspension conditions. The polymers generally contain between 20 to 30 percent acrylonitrile. The acrylonitrile content of the polymer influences the final properties with tensile strength, elongation, and heat distortion temperature increasing as the amount of acrylonitrile in the copolymer increases. 

Apart from the fluoro monomers vinyl fluoride (VF), vinylidene fluoride (VF2), and tetrafluoroethylene (TFE), only chlorofluoroethylene has found commercial use as homopolymer. It is applied as thermoplastic resin based on its vapor-barrier properties, superior thermal stability (Tdec > 350 °C), and resistance to strong oxidizing agents [601]. Chlorofluoroethylene is homo- and copolymerized by free-radical-initiated polymerization in bulk [602], suspension, or aqueous emulsion using organic and water-soluble initiators [603,604] or ionizing radiation [605], and in solution [606]. For bulk polymerization, trichloroacetyl peroxide [607] and other fluorochloro peroxides [608,609] have been used as initiators. Redox initiator systems are described for the aqueous suspension polymerization [603,604]. The emulsion polymerization needs fluorocarbon and chlorofluorocarbon emulsifiers [610]. 

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