Special solvents drying

In principle, the process is quite simple. The input is cut and reduced in size. The key of the process is selective dissolution of the PVC and its additives in a special solvent. The pure PVC is recovered by means of precipitation and dried and is ready for a new life (Figure 2). 

Special solvent — The special solvent shall be equal volumes of anhydrous methanol and benzene thoroughly mixed. If necessary the solvents shall be dried by distillation... 

Dry the sieve and count and examine any particles remaining on the sieve. Brush any particles retained on No 60 sieve onto No 40 sieve. Note if the particles are grit as indicated by their lack of uniformity land a scratching noise when pressing and rubbing the material on a smooth glass slide with.a. smooth steel spatula. Report die number of particles on No 60 sieve and on No 40 sieve 4.4-3.1 Determination of Moisture Use Karl Fischer Method, described in MIL-STD-650 as Method 101.4, with methanol as the special solvent. A detailed description... 

Special attention has been given to the chemical and physical properties of organic solvents commonly used in daily laboratory work. Therefore, all Appendix Tables have been improved some have been completely replaced by new ones. A new well-referenced table on solvent-drying has been added (Table A-3). Chapter 3 has been enlarged, in particular by the inclusion of solvent classifications using multivariate statistical methods (Section 3.5). All these amendments justify the change in the title of the book to Solvents and Solvent Effects in Organic Chemistry. 

Largely lipophyllic molecules of carotenoids are well miscible with lipids (Borel et al, 1996) and like lipids they are well soluble in most organic solvents (some carotenoids require special solvent mixtures to yield efficient solubilization with lipids). This property of both lipids and carotenoids is most frequently applied to prepare carotenoid-pigmented model lipid membranes. It involves the evaporation of a carotenoid lipid mixture followed by the hydration of a thin dry film. There are several different... 

Short oil alkyd resins require special solvent mixtures for each area of use. Principal solvents include aromatic hydrocarbons (e.g., xylene), solvent naphtha fractions, and glycol ethers. Lower alcohols, even in small amounts, have a powerful viscositylowering effect. The choice of solvent depends on the solvent power for the resins and the application method. The last solvent to evaporate during drying must be a true solvent for the binders because otherwise the paint film becomes opaque or inhomogeneous. 

The removal of water from gases may be achieved by passing a stream of the wet gas through special chemical drying agents (such as concentrated sulphuric acid, anhydrous calcium chloride, or silica gel) by rapid cooling or by physical methods. Removal of water from solvents is effected by azeotropic distillation or evaporation, freezing. 

Nonblocking powdered thermoplastic rubber can be made through the use of a special solvent system. In this method, rubber crumb is dispersed in a high solubility parameter solvent which will barely dissolve the endblock domains and which will not dissolve the rubber phase at all. One such single solvent is acetone. Particle size of the crumb is controlled by the amount of shear used in dispersion. Addition of water totally precipitates the small particles. This powder may then be separated from the liquid and dried. The particles do not tend to agglomerate because the hard endblock phase preferentially coats the outside of each particle. 

Benzene. Pure benzene (free in particular from toluene) must be used, otherwise the freezing-point is too low, and crystallisation may not occur with ice-water cooling alone. On the other hand, this benzene should not be specially dried immediately before use, as it then becomes slightly hygroscopic and does not give a steady freezing-point until it has been exposed to the air for 2-3 hours. Many compounds (particularly the carboxylic acids) associate in benzene, and molecular weights determined in this solvent should therefore be otherwise confirmed. 

Solution Casting. The production of unsupported film and sheet by solution casting has generally passed from favor and is used only for special polymers not amenable to melt processes. The use of solvents was generally very hazardous because of their flammabiUty or toxic nature. The cost of recovery and disposal of solvents became prohibitive for many lower price film appHcations. The nature of the drying operations leads to problems with solvent migration and retention that are not problems with melt-processed polymers. 

Web Heat-Set Publication and Commercial Inks. Almost all heat-set inks are now printed on web offset presses, and are based on vehicles containing synthetic resins and/or some natural resins. These are dissolved in hydrocarbon solvent fractions which are specially fractionated for use in the ink industry. They vary in boiling range between 180 and 300 °C. Small percentages of alkyd resins (qv) may be contained in these inks. They dry in less than one second by means of solvent evaporation in a heatset oven. These ovens utilize high velocity hot air to raise the web temperature to 120-150 °C. 

Lamination Inks. This class of ink is a specialized group. In addition to conforming to the constraints described for flexo and gravure inks, these inks must not interfere with the bond formed when two or more films, eg, polypropylene and polyethylene, are joined with the use of an adhesive in order to obtain a stmcture that provides resistance properties not found in a single film. Laminations are commonly used for food applications such as candy and food wrappers. Resins used to make this type of ink caimot, therefore, exhibit any tendency to retain solvent vapor after the print has dried. Residual solvent would contaminate the packaged product making the product unsalable. 

Special drying methods, such as superheated steam, solvent, vacuum, infrared radiation, and high frequency dielectric and microwave heating, are occasionally employed when accelerated drying is desired and the species being dried can withstand severe conditions without damage. None of these methods is of significant commercial importance. 

Several patents describe solvent-free bulk-phase halogenation (67—69). Dry soHd butyl mbber is fed into a specially designed extmder reactor and contacted with chlorine or bromine vapor. The by-product HCl or HBr ate vented directly without a separate neutralization step. Halogenated butyl mbbers produced are essentially comparable in composition and properties to commercial products made by the solution process. 

---