Polymer bead, material balance

The behavior of a bead-spring chain immersed in a flowing solvent could be envisioned as the following under the influence of hydrodynamic drag forces (fH), each bead tends to move differently and to distort the equilibrium distance. It is pulled back, however, by the entropic need of the molecule to retain its coiled shape, represented by the restoring forces (fs) and materialized by the spring in the model. The random bombardment of the solvent molecules on the polymer beads is taken into account by time smoothed Brownian forces (fB). Finally inertial forces (f1) are introduced into the forces balance equation by the bead mass (m) times the acceleration ( ) of one bead relative to the others ... 

The material balance equation for radial transport and reaction within a polymer bead is... 

The rate In a batch reactor must be based on the total amount of substrate In the system. There Is no way to measure the concentration (or moles) of substrate inside the polymer beads It must be computed. Substrate Is depleted from the bulk phase for two reasons Initially the polymer phase contained no substrate, and substrate reacts Inside the polymer beads. Total moles of substrate are easily determined In systems which Involve addition of a gas phase reactant at constant pressure. The reaction rate Is developed using the conversion of substrate. Equation 2 uses the total moles of substrate In the system. A material balance Is performed over the batch reactor at any time t to give the moles of substrate in the bulk and polymer phases. The derivative of this balance may be used to calculate reaction rates by making use of Equation 3. The derivative of the total mole balance with respect to dimensionless time is... 

As described earlier in the section on bead or suspension polymers (Section 3.3.1.2), a solution of monomer(s) is prepared in water and then mixed into a low to medium viscosity non-volatile oil phase. In this process, which is often referred to as an inverse emulsion polymerisation technique, surfactants which promote the formation of water-in-oil emulsions are commonly used. These would usually be materials with an HLB (hydrophihc-lipophilic balance) value in the range 4—7, an example of which is sorbitan mono-oleate. In order to achieve the desired droplet particle size of a maximum around 1 pim prior to polymerisation, high shear homogenisers are used to assist the formation of such very small... 

Suspension copolymers of acrylic acids with many comonomers have been prepared. In some cases the acids are present in only small amounts to modify the bulk of the resin beads in other cases a major fraction of the resin may be an acrylic acid. By the proper balancing of the copolymer composition, materials have been prepared that may permit sustained releases of pharmaceuticals. Chloamphenicol or chlorothiazide have been incorporated in bead polymers as possible delayed-action or sustained-release preparations [35]. 

The ease with which materials can be identified and separated varies with the source of supply. Most automobile (lead-acid) batteries are made with PP casings. Since the metal in the batteries is reclaimed (97% reeovery in 1999), the casings represent a centralized and relatively homogeneous source of one polymer. In 1990 it was reported that almost 150 million pounds of PP were recovered annually in the United States, representing as much as 95% of all discarded batteries. About 40% of the recovered PP went into the next generation of batteries, with the balance going into other automotive products and miscellaneous consumer products [50]. Automobile tires, however, contain several different polymers in addition to the metal bead and fabric reinforcement. The reuse of tires by separating all the components is economically unsound. 

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