Polymer applications devolatilization

The preceding observations on the microscopic features of polymer melt devolatilization are not unique to the PS-styrene system, or to strand devolatilization. Similar, though somewhat less rich, features of blister-covered macrobubbles were observed with low-density polyethylene (PE), high-density PE and polypropylene (PP) systems (40,41). Furthermore, Tukachinsky et al. (11) discovered macrobubbles covered with microblisters in a 50-mm-diameter vented SSE, with PS showing more oblong shapes as a result of shearing. The onset of foaming with the application of vacuum was quicker with increased frequency of screw rotation, and the separation was more efficient. 

It is often of industrial interest to be able to predict the equilibrium sorption of a gas in a molten polymer (e.g., for devolatilization of polyolefins). Unfortunately, the Prigogine-Flory corresponding-states theory is limited to applications involving relatively dense fluids 3,8). An empirical rule of thumb for the range of applicability is that the solvent should be at a temperature less than 0.85 Tp, where Tp is the absolute temperature reduced by the pure solvent critical temperature. 

Biesenberger, J.A., Devolatilization of Polymers Fundamentals, Equipment, Applications. Hanser Publishers, Munich, Vienna, New York, 1983. 

Molten or resinous polymer is then introduced into the integrated process unit and combined with the treated filler. Other stages, including addition of further treatment, devolatilization, pressurization and die-forming may also be required depending on the nature of the composition and its intended application. 

Commercial polystyrenes are normally rather pure polymers. The amount of styrene, ethylbenzene, styrene dimers and trimers, and other hydrocarbons is minimized by effective devolatilization or by the use of chemical initiators (33). Polystyrenes with low overall volatiles content have relatively high heat-deformation temperatures. The very low content of monomer and other solvents, eg, ethylbenzene, in PS is desirable in the packaging of food. The negligible level of extraction of organic materials from PS is of cmcial importance in this application. 

The removal of residual volatile components from polymers is an operation of some importance in the plastics industry. A generalized, although somewhat idealized, model for continuous, wiped-film devolatilization of viscous polymer melts is presented which relates devolatilization capability to important geometry, < perating, and fluid property variables. The applicability and limitations of the model are analyzed experimentally. The data support many aspects of the theory, but also reveal certain deficiencies in the model which should be considered in designing for maximum efficiency. 

Penetrant Concentration-Plasticization Polymer Molecular Structure Relaxation-Controlled Transport Applications of Transport Concepts Barrier Materials Devolatilization Additive Migration Dyeing... 

Equation-of-state approaches are preferred concepts for a quantitative representation of polymer solution properties. They are able to correlate experimental VLE data over wide ranges of pressure and temperature and allow for physically meaningful extrapolation of experimental data into unmeasured regions of interest for application. Based on the experience of the author about the application of the COR equation-of-state model to many polymer-solvent systems, it is possible, for example, to measure some vapor pressures at temperatures between 50 and 100 C and concentrations between 50 and 80 wt% polymer by isopiestic sorption together with some infinite dilution data (limiting activity coefficients, Henry s constants) at temperatures between 100 and 200 C by IGC and then to calculate the complete vapor-liquid equilibrium region between room temperature and about 350 C, pressures between 0.1 mbar and 10 bar, and solvent concentration between the common polymer solution of about 75-95 wt% solvent and the ppm-region where the final solvent and/or monomer devolatilization process takes place. Equivalent results can be obtained with any other comparable equation of state model like PHC, SAFT, PHSC, etc. 

The modular co-rotating twin-screw extruder is the most widely used of all twin-screw extruders. There is probably no application for twin-screw extruders to which it has not been applied. Applications include all aspects of compounding and blending of thermoplastics with particulates, oils, and other polymers. The machine is also widely used for removal of liquids, that is, devolatilization and for reactive extrusion. The modular co-rotating twin-screw extruder has also been used for both polymerization and for grafting reactions. 

Considering the fact that there are already several books on extrusion of polymers, the question can be asked why the need for another book on extrusion. The three most comprehensive books written on extrusion as of the early 1980s were the books by Bernhardt [1], Schenkel [2], and Tadmor [5]. The book by Bernhardt is on polymer processing, but has a very good chapter on extrusion. It is well written and describes extrusion theory and its practical applications to screw and die design. Because of the age of the book, however, the extrusion theory is incomplete in that it does not cover plasticating-this theory was developed later by Tadmor (5]-and devolatilization theory. 

Applications for the diskpack are specialty polymer processing operations, such as polymerization, post-reactor processing (devolatilization), continuous compounding, etc. As such, the diskpack competes mostly with twin screw extruders. Presently, twin screw extruders are usually the first choice when it comes to specialty polymer processing operations. 

Devolatilizing extruder screws are used to extract volatiles from the polymer in a continuous fashion. Such extruders have one or more vent ports along the length of the extruder through which volatiles escape. Some of the applications of vented extruders are ... 

Polymer devolatilization is a separation process in which residual VOCs are removed from the polymer matrix by application of a reduced pressure (lower than the equilibrium partial pressure of the volatile component), and/or heat. Stripping agents are also commonly used. 

Mutual solubility of polymers and volatile organic substances are of importance for many applications in polymer chemistry and polymer engineering. Polymerizations, which should be performed in homogeneous phase, require the complete miscibility of monomer, polymer, solvent (liquid or supercritical) and other additives. Subsequently, the extraction of the polymer product from the reaction mixture requires a phase split (into two liquid phases or into a vapor and a liquid phase) to obtain a polymer product of high purity on one side and the remaining monomer on the other side. In this context, the devolatilization of polymers is of particular interest. Another example is the use of polymer membranes for the separation of two volatile organic compounds. Here, besides the knowledge of diffusivity, the solubility (sorption) of the different components in the polymer membrane is also an important prerequisite for an efficient process. 

Biesenberger, J. A. (1983). Devolatilization of Polymers Fundamentals-Eqnipment-Applications, Hanser, Mnnich. 

There have been many studies of applications of modular co-rotating twin-screw extruders. These investigations include devolatilization [137 to 140], polymerization [141 to 145], and modification of polymer by hydrolysis and grafting [ 146 to 149]. Some of these applications will be discussed in later sections. 

Applications of solubility parameters include selecting compatible solvents for coating resins, predicting the swelling of cured elastomers by solvents, estimating solvent vapor pressure in polymer solutions for devolatilization and reaction systems (16), and predicting phase equihhria for polymer-polymer (107), polymer-binary (93), random copolymer (102), and multicomponent solvents (38, 98,108,109). 

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