Polymer manufactures

Water is continuously added to the last extraction bath and flows countercurrenfly to filament travel from bath to bath. Maximum solvent concentration of 15—30% is reached in the coagulation bath and maintained constant by continuously removing the solvent—water mixture for solvent recovery. Spinning solvent is generally recovered by a two-stage process in which the excess water is initially removed by distillation followed by transfer of cmde solvent to a second column where it is distilled and transferred for reuse in polymer manufacture. 

Physical Form. Eor compounders, physical form is an important characteristic. They prefer sohd, free-flowing, nondusty materials whereas polymer manufacturers prefer materials that are Hquid and easily emulsified. Undesirable are semicrystalline materials which may stratify during storage. Also, substances to be avoided are highly viscous Hquids and low melting resins which block upon storage. 

Major polymer manufacturers can usually supply creep data on those of their polymers which are likely to be subjected to long-term loads. A typical set of such curves is given in Figure 9.9. Sections through the creep curves at constant... 

Adsorption, which utilizes the ability of a solid adsorbent to adsorb specific components from a gaseous or a liquid solution onto its surface. Examples of adsorption include the use of granular activated carbon for the removal of ben-zene/toluene/xylene mixtures from underground water, the separation of ketones from aqueous wastes of an oil refinery, aad the recovery of organic solvents from the exhaust gases of polymer manufacturing facilities. Other examples include the use of activated alumina to adsorb fluorides and arsenic from metal-finishing emissions. 

Realizing a wide range of selection of composing members including vinyl polymers, polycondensation polymers, and polyaddition polymers, which opens a variety of application areas in the polymer manufacturing and processing industries. 

A feature of polymer solutions which is commonly observed in many polymer manufacturing operations is illustrated in Figure 2. At a given pressure, a two-phase region exists below a concave-downward locus of temperature-composition points. One of the two... 

Another general type of behavior that occurs in polymer manufacture is shown in Figure 3. In many polymer processing operations, it is necessary to remove one or more solvents from the concentrated polymer at moderately low pressures. In such an instance, the phase equilibrium computation can be carried out if the chemical potential of the solvent in the polymer phase can be computed. Conditions of phase equilibrium require that the chemical potential of the solvent in the vapor phase be equal to that of the solvent in the liquid (polymer) phase. Note that the polymer is essentially involatile and is not present in the vapor phase. 

Example 14.7 A polymer manufacturer makes two products in a CSTR. Product I is made by the reaction... 

Step growth polymerization. Important polymers manufactured by step growth are polyamides (nylons), polyesters, and polyurethanes. 

Chain growth polymerization. Important polymers manufactured hy chain growth are polyethylene, polystyrene, polyacrylonitrile, and polymethacrylates. 

To facilitate in-plant compounding, most suppliers have developed systems which efficiently and repro-ducibly deliver a controlled additive package to a compound, using either a specialised concentrate or a masterbatch formulation. Some of the polymer manufacturers have also made available advanced additive delivery systems, which they have often developed originally for their own use (e.g. Eastman, Montell). 

The polymer manufacturing industry monitors extrac-tables in their products for a variety of purposes. These include not only additives but also mineral oils and waxes as well as incompletely polymerised dimers and trimers that have a pronounced effect in the finished product. Myer et al. [390] have compared... 

Many new products tend to be reactive rather than additive, are polymeric, and are more precisely designed to meet the requirements of the polymer manufacturer or formulator. Low-MW additives face two major problems ... 

Carbon steel cannot be used in the production of most polymers because even trace amounts of iron discolor the product. In polymer manufacturing, usually glass-lined or stainless steel equipment must be used. Glass-lined or stainless steel equipment is required for any product that may be ingested by man. This includes all foods, pharmaceuticals, and food additives. 

In practice, there is no such thing as a pure isotactic or syndiotactic polymer. Once again, we find that polymers comprise a statistical distribution of chemical structures. Polymers that contain steric centers inevitably incorporate a certain number of steric defects that prevent us from obtaining 100% isotacticity or syndiotacticity. Polymer manufacturers vary the catalyst type and reaction conditions to control the tacticity level and the resulting properties. 

By using two or more polymerization catalysts simultaneously, polymer chemists can produce copolymers tvith a bimodal composition distribution. This is made possible by the fact that no two catalysts incorporate monomers at exactly the same rate. The net result is that short chain branches may be preferentially incorporated into either the higher or lower molecular weight fractions. Polymer manufacturers can obtain a similar result by operating two polymerization reactors in series. Each reactor produces a resin with a different copolymer distribution, which are combined to form a bimodal product. Copolymers with a bimodal composition distribution provide enhanced toughness when extruded into films. 

Polymers manufactured via single site catalyst technologies, because of the unique chemical catalytic environment, exhibit a more controlled molecular weight distribution and tacticity than seen with Ziegler-Natta catalyst systems. 

In this chapter we have discussed methods of polymerization, the resulting molecular weight distribution, and the interplay between the chemistry of the monomer and the type of polymer that will be produced. We also briefly introduced some of the commercial methods of producing polymers and the role that the type of polymerization has on the choices made in commercial applications. In the following chapters we will build on this framework to explore the role of physical chemical processes, such as the thermodynamic and kinetic processes involved in polymer manufacture. We will also gain an understanding of structural properties of polymers and the means to explore these properties. 

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