ENGINEERED POLYMER SOLUTIONS

Rodriguez C L Weathers J Corujo B Peterson P Lyondell Chemical Co. Engineered Polymer Solutions Avecia... 

Why have so many different models been developed for polymer systems The simation could be easily considered confusing for the practicing engineer. Polymer solutions and blends are complicated systems the frequent occurrence of LLE in many forms (UCST, LCST, closed loop), the significant effect of temperature and polymer molecular weight in phase equilibria, the FV effects, and other factors cause these difficulties. The choice of a suitable model depends on the actual problem and demands, especially the following ... 

Many further developments can be expected in the use of corresponding-states polymer solution theory in engineering practice. However, the reliability and versatility of this method is now well demonstrated for engineering use. 

The proposed mechanisms of models to explain the drag reduction phenomenon are based on either a molecular approach or fluid dynamical continuum considerations, but these models are mainly empirical or semi-empirical in nature. Models constructed from the equations of motion (or energy) and from the constitutive equations of the dilute polymer solutions are generally not suitable for use in engineering applications due to the difficulty of placing numerical values on all the parameters. In the absence of a more generally accurate model, semi-empirical ones remain the most useful for applications. 

It is worth noting at this point that the various scientific theories that quantitatively and mathematically formulate natural phenomena are in fact mathematical models of nature. Such, for example, are the kinetic theory of gases and rubber elasticity, Bohr s atomic model, molecular theories of polymer solutions, and even the equations of transport phenomena cited earlier in this chapter. Not unlike the engineering mathematical models, they contain simplifying assumptions. For example, the transport equations involve the assumption that matter can be viewed as a continuum and that even in fast, irreversible processes, local equilibrium can be achieved. The paramount difference between a mathematical model of a natural process and that of an engineering system is the required level of accuracy and, of course, the generality of the phenomena involved. 

In fact, one reason we use polymer solutions is because of their viscosity. Examples include engine oil, paint, glues, shampoo, and hair conditioner. Say you were painting the walls in your bedroom. If the paint had the viscosity of water, it would be very difficult to apply and keep from running right down the wall—or down your arm. If your shampoo or hair conditioner had too little viscosity, it would feel watery and just rim out of your hair before it was able to do its job. Many personal care products contain polymers to control viscosity and texture. 

The design engineer dealing with polymer solutions must determine if a multicomponent mixture will separate into two or more phases and what the equilibrium compositions of these phases will be. Prausnitz et al. (1986) provides an excellent introduction to the field of phase equilibrium thermodynamics. 

In 1988 the Design Institute for Physical Property Data of the American Institute of Chemical Engineers established Project 881 to develop a Handbook of Polymer Solution Thermodynamics. In the area of polymer solutions, the stated purposes were (1) provide an evaluated depository of data, (2) evaluate and extend current models for polymers in both organic and aqueous, solvents, (3) develop improved models, and (4) provide a standard source of these results in a computer data bank and a how-to handbook with accompanying computer software. During the four years of this project most of these objectives have been met and the results are presented in this Handbook. 

In several industrial processes the engineer has to deal with non-Newtonian fluids of which food processing and production processes involving glues, colors, polymer solutions, and pure polymers are well-known examples. 

We also have an interest in solution processing, that is in ternary phase diagrams of the type PLC + engineering polymer + solvent. A statistical mechanical theory of rigid-rod systems has been developed by Flory he started the work in 1956 (44.) when most of the present applications of PLCs were unknown and continued it more than two decades later (45). The Flory configurational partition function is... 

Gampert, L Rensch, A. Polymer concentration and near wall turbulence structure of chemical flow of polymer solutions. In Turbulence Modification and Drag Reduction, Proceedings of the 1996 ASME Fluids Engineering Division Summer Meeting, San Diego, CA, Jul 7-11, 1996 Coleman, H., et al., Eds. ASME New York, 1996 FED-Vol. 237-242, 129-136. 

Harismiadis, V.I. et al.. Miscibility of polymer blends with engineering models, AIChE J., 42,3170,1996. Pappa, G.D., Voutsas, E.C., and Tassios, D.P., Prediction of solvent activities in polymer solutions with simple group-contribution models, Ind. Eng. Chem. Res., 38, 4975, 1999. 

The practical solution of these protection tasks are connected to specific chemical agents, well engineered polymer additives, elaborated mainly for the stabilization of general purpose polymers [8], The radiation stabilizers, called antirads represent only a modest, but flourishing fraction of that thermo-oxidative- and UV stabilizers. 

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