Dissolving solid polymers

There are a number of ways to dissolve the solids, depending upon the quantity to be prepared. For the purpose of this discussion, three orders of magnitude of batch size will be considered. These are a quantity of 100 to 200 ml for laboratory evaluation, 25 to 1001 for small-scale decanter tests, and 1 m or more for plant use. 

For the medium-size sample, the last method may be used with a little up-scaling. This time the mixing vessel is a quarter-filled with water and stirred. The measured quantity of powder is then sprinkled into the remainder of the water as it is squirted, under pressure, into the stirred vessel, which is finally 

Usually, production quantities are made up automatically. The standard automatic make-up plant will consist of a mixing vessel, into which water is admitted at a constant rate. The solid polymer is metered out from a hygroscopically secure hopper, using a screw feeder, into the incoming stream of make-up water. Some automatic systems use an air blower to convey the polymer, entering the air stream via a venturi, to a mixer, where the water enters with a cyclone action to keep the powder away from the mixer walls. From the mixer the product falls into a stirred ageing vessel. 

The physical nature of solid polymer is such that it requires a finite time, at least half an hour, to fully dissolve and for the molecular chain to unwind and become fully functional. Once made up in the mixing vessel, the solution is aged with gentle stirring for the requisite time, usually at least half an hour and up to one hour, before it is transferred to a second tank used for feeding to the decanter. 

An alternative automatic system uses a series of at least four stirred vessels with overflow from one to another. A low-level probe in the final tank triggers the start of make-up in the first. The total volume of the four or more tanks ensures a mean residence time sufficient for the required ageing period. The shortcoming of this system is that ageing time is not uniform. The age of the solution at discharge will vary, from almost zero up to several times the mean. It is possible to calculate this age distribution [3]. The system is simple and offers fully continuous polymer solution make-up. If the size and number of tanks are chosen carefully, the age distribution of the preparation presents no serious problem, apart from the overall size of the system. 

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PL membranes are usually cast from a homogeneous solution of the dissolved solid polymer material (e.g., poly(vinyl chloride)), the liquid extractant (e.g., Aliquat 336 chloride DEHPA) and a plasticizer (e.g., dioctylphtalate n-decanol) in a suitable solvent (e.g., tetrahydrofuran) by the slow evaporation of the solvent. By increasing the concentration of the extractant the permeability of the PL membrane increases while at the same time its mechanical stability deteriorates. For example, the optimal concentration range for Aliquat 336 chloride in a polyvinyl chloride based PL membrane is between 40 and 50%. 

Dissolve 2 ml. of acetaldehyde in 5 ml. of dry ether, cool in a freezing mixture of ice and salt, and pass in dry hydrogen chloride gas for 30-60 seconds. The solid polymer, metaldehyde, may separate in a short time, otherwise cork the tube and allow it to stand for 10-15 minutes. Filter ofiF the crystals. 

Polymers that form from the liqmd phase may remain dissolved in the remaining monomer or solvent, or they may precipitate. Sometimes beads are formed and remain in suspension sometimes emulsions form. In some processes solid polymers precipitate from a fluidized gas phase. 

These formulations may be modified to further reduce the impact of adding dissolved solids to the program by substituting the SHMP for an organic polymer calcium carbonate control agent, such as PMA. 

Blanks, left to right, starting upper left water, liquids or dissolved solids, size exclusion, porous polymer beads, any liquid type, polymer beads with ionic sites ions, gas, thin liquid film, thin layer, liquids or dissolved solids. 

Solid polymer and gel polymer electrolytes could be viewed as the special variation of the solution-type electrolyte. In the former, the solvents are polar macromolecules that dissolve salts, while, in the latter, only a small portion of high polymer is employed as the mechanical matrix, which is either soaked with or swollen by essentially the same liquid electrolytes. One exception exists molten salt (ionic liquid) electrolytes where no solvent is present and the dissociation of opposite ions is solely achieved by the thermal disintegration of the salt lattice (melting). Polymer electrolyte will be reviewed in section 8 ( Novel Electrolyte Systems ), although lithium ion technology based on gel polymer electrolytes has in fact entered the market and accounted for 4% of lithium ion cells manufactured in 2000. On the other hand, ionic liquid electrolytes will be omitted, due to both the limited literature concerning this topic and the fact that the application of ionic liquid electrolytes in lithium ion devices remains dubious. Since most of the ionic liquid systems are still in a supercooled state at ambient temperature, it is unlikely that the metastable liquid state could be maintained in an actual electrochemical device, wherein electrode materials would serve as effective nucleation sites for crystallization. 

Geometric effects coupled with diffusion and nucleation usually control the rates of all solids deposition phenomena. Such effects can be put to good use in the production of special products such as cellulose yarn (rayon), by the precipitation of cellulose in filament form as it emerges as sodium cellulose xanthate liquid from the spinnerets into a bath containing sulphuric acid, which extracts the sodium as sodium sulphate, and the carbon disulphide. In a similar manner, the fabrication of aromatic polyimide fibres is performed by dissolving the polymer in concentrated sulphuric acid and forcing the solution through spinnerets into water. 

Thus, the separation of this polymer can easily be done by scratching off with a spatu-lum. After isolation, the solid polymer is purified by dissolving it in 50 ml water at 80 °C. After cooling down to room temperature, the poly(ethyleneimine) is isolated by filtration and washed with water and dried under vacuum at 80-90 °C for 3-5 h. Linear po-ly(ethyleneimine) is obtained quantitatively as a colorless solid, which has to be stored under dry conditions. 

The orthoacetate above polymerizes by heating alone Or in the presence of benzoyl peroxide to give a dark, viscous liquid. A solid polymer, of unknown structure, may be isolated by dissolving the latter in acetone and precipitating in cold water. 

Lyophilic sols are true solutions of large molecules in a solvent, Solutions of starch, proteins, or polyvinyl alcohol in water are representative of numerous examples. Properties of these solutions at equilibrium (for example, density and viscosity) are regular functions of concentration and temperature, independent of the method of preparation. The solvent-macromolecule compound system may consist uf more than one phase, each phase in general containing both components. Thus, if a solid polymer is added to a solvent in an amount exceeding the solubility limit, the system will consist of a liquid phase (solvent with dissolved polymer) and a solid phase (polymer swollen with solvent, i.e., a polymer with dissolved solvent). 

For two-photon memories, a number of media types and reading mechanisms have been used (165). Generally, media comprise two photon-absorbing chromophores dissolved within a solid polymer matrix. Suitable reversible photochromic dyes are, for example, spiropyrans. Although photochromic materials often suffer from photobleaching, as well as from instability leading to self-erasure, new materials and host environments are under development (172). Bacteriorhodopsin (BR) also has been proposed as a two-photon memory material. 

Slurry processes in which dissolved ethylene is polymerised to form solid polymer particles suspended in a hydrocarbon diluent... 

Figure 11.21 Long-term performance of a composite solid polymer electrolyte membrane consisting of 80 wt% AgBF4 dissolved in a propylene oxide copolymer matrix. Feed gas, 70 vol% ethylene/30 vol% ethane at 50 psig permeate pressure, atmospheric [33,61]...

The slurry process is the oldest and still widely used method for manufacturing polymers of ethylene, propylene and higher a-olefins. In this process, the monomer dissolves in the polymerisation medium (hydrocarbon diluent) and forms a solid polymer as a suspension containing ca 40 wt-% of the polymer the polymerisation occurs below the melting point of the polymer. In slurry polymerisation, the temperature ranges from 70 to 90 °C, with the ethylene pressure varying between 7 and 30 atm. The polymerisation time is 1-4 h and the polymer yield is 95-98 %. The polymer is obtained in the form of fine particles in the diluent and can be separated by filtration. Removal of the catalyst residues from the polymer can be achieved by the addition of alcohol (isopropanol, methanol), followed by recovery and extraction of the catalyst residues. The polymer is freed from diluent by centrifuging and then dried. In the case of polypropylene manufacture, the atactic fraction remains in the diluent [28,37]. 

Calculations using the UNIFAC-FV model are carried out as follows for a binary mixture of solute (a = 1) dissolved in a solid polymer (P = 2) (Goydan et al., 1989) The activity of the solute, aj, is separated into the three components the combinatorial contribution, a, the residual contribution, a, and the free-volume contribution,... 

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