Vacuum extrusion

Empty space in which there are no atoms or molecules. A perfect vacuum cannot be attained in practice and the term denotes a space containing air or other gas at a very low pressure. In industry vacuum is measured in inches of mercury (in Hg) ranging from 0 in at atmospheric pressure to around 30 in at zero absolute pressure. Vacuum Extrusion... 

In this process, a vacuum extrusion step (melt treatment) is followed by a continuous SSP (solid treatment). The process starts with PET flakes which are introduced without pre-drying into a ring extruder. The flakes are dried, melted and degassed inside the extruder. A gear pump builds the necessary pressure for melt filtration, where solid particles are removed. After granulation the pellets are fed to a continuous three-step SSP unit [10]. 

The raw materials are blended with water to form a slip from which most of the water is removed by filter-pressing. The body is then homogenized and de-aired in a vacuum extrusion pug-mill . The extruded blanks may be further... 

The solvent-containing polymer phases are separated by evaporation (steps VI, VII, IX and X in Figure 4) and traces of solvent can be removed by vacuum extrusion. 

Fredette, L. Tanguy, P.A. Hurez, P. Blouin, D. On the determination of heat transfer coefficient between PVC and steel in vacuum extrusion calibrators. Int. J. Num. Methods Heat Fluid Flow 1996, 6, 3-12. 

Vacuum extrusion. All ceramic materials contain a certain percentage of gas, for the most part in the form of the finest air bubbles embedded between the individual body components. The aim of de-airing, degasification, or evacuation of the body, is to remove the embedded air, which has a grogging effect and creates bubbles, in order to achieve an increase in plasticity and reduce the risk of laminations. 

Numerous variations of the interfacial process have been published. The reactions can be carried out in batch in stirred tank reactors or continuously in series of CSTRs and tubular reactors. Intensive mixing with dispersion and redispersion is required throughout the reaction stages. After the reaction is complete, the brine phase is separated and the polymer solution washed to remove residual amine and base. Several processes for devolatilization are in use, including solventless precipitation, steam precipitation, spray drying, falling-strand devolatilization, and vacuum extrusion in devolatilizing extruders. 

In the industrial recycling practice, SSP is usually applied in combination with other decontamination techniques, such as vacuum extmsion, superaitical extraction, and vacuum melt polymerization. An example is the Buhler s bottle-to-bottle recycling, which involves in-house or market PET flakes, melt decontamination via vacuum extrusion, pellet crystallization and then their SSP. Another example is the Komes process, which involves bottle sorting by mass spearoscopy, washing, and SSP of the flakes. ... 

The addition of phthalimidylnitrene (374) to simple alkynes affords 1-azirines in yields of 1-15% (Scheme 10). In this reaction, which is of no real preparative value, the symmetrical 2-azirines (375) were suggested as the most plausible intermediates and unequivocal proof of the existence of such species was demonstrated from a series of 1,2,3-triazole pyrolysis reactions <71CC1518). Extrusion of nitrogen from the regioisomeric 4,5-disubstituted 1,2,3-triazoles (376) during flash vacuum pyrolysis furnished identical product mixtures which included both regioisomeric 1-azirines (377). 

In vacuum and blow forming, sheets produced by extrusion are shaped by vacuum or pressure forming. Heat-softened sheet is pressed into a mould by atmospheric pressure when a vacuum is created between the mould and the sheet. Fig. 24.4(a). Plastic bottles are made by blowing instead heated tube is clamped in a split mould and expanded with compressed air to take up its shape (Fig. 24.4b). Both methods are cheap and quick, and can be fairly accurate. 

Silicone greases do, however, have uses in extrusion for coating dies etc., to facilitate stripping down. Greases have also found uses in the laboratory for lubricating stop cocks and for high-vacuum work. 

The venting works because at a typical extrusion temperature of 250°C the water in the plastic exists as a vapour at a pressure of about 4 MN/m. At this pressure it will easily pass out of the melt and through the exit orifice. Note that since atmospheric pressure is about 0.1 MN/m the application of a vacuum to the exit orifice will have little effect on the removal of volatiles. 

Polyolefins (Polyethylene, Polypropylene) Powder, pellets Tough and chemical resistant. Weak in creep and thermal resistance. Polyethylene maximum use temperature 210 F, polypropylene 260 F. May be injection and extrusion molded, vacuum formed. Low cost. Antistatic sheet and tiles, heat-shrinkable tubing, deicer boots. 

PVC, PVA, PVAC, Copolymers) organosols forms available including hard and flexible types. Properties are highly dependent on plasticizer used. May be injection, extrusion, compression molded, vacuum formed. Low cost. antistatic sheet and hose, RF gaskets, heat-shrinkable tubing. 

Extrusion with the aid of a vacuum applied to the screw. The process is applied particularly in the preparation of extrudates to be vulcanised by either the liquid curing medium or fluid bed techniques. It assists in removing the volatiles from the compound and thus improves the quality of the extrudate. 

The Diels-Alder adduct of sulpholene and cyclopentadiene is a useful starting material for substituted diene synthesis121. The diene moiety is unmasked by retro-Diels-Alder reaction and sulphur dioxide extrusion under flash vacuum pyrolysis conditions (equations 74 and 75)122,123. 

The appearance of air bubbles in the polymer melt may occur under certain circumstances during processing. This phenomenon is rarely related to obvious faults in the polymer, but sometimes gas bubbles can be observed in cases of decreased thermal stability. Gas bubbles appear due to a certain amount of dispersed gas in the polymer matrix. Insufficient removal of gas from the extruder, particularly from the compression zone, can also cause the problem of air bubbles in the melt. An influence of the extruder screw could be established, because gas bubbles can be removed to some extent by using special screws or changing the extrusion conditions, along with the application of a vacuum. 

The strain of cycloproparenes is the principal obstacle that must be overcome in their synthesis. Cycloproparenes decompose usually at moderate temperatures, and they undergo ring-opening in the presence of electrophilic or metallic reagents. In contrast, they support even strongly basic conditions quite well. Accordingly, most successful cycloproparene syntheses use some base-induced elimination in the last step. Alternatively, flash vacuum pyrolytic or photochemical extrusion of a neutral fragment, followed by biradical closure or flash vacuum pyrolysis may be used. In these latter approaches the reaction conditions are neutral, and reactive products may be trapped at low temperatures. 

By analogy, benzocyclopropene (1) is formed in low yield via biradical cycliza-tion upon irradiation of benzocyclobutenone (79), upon its flash vacuum pyrolysis, or upon pyrolysis of indan-2,3-dione (80). Reaction of phthalide 81 in a RF plasma leads also to However, these latter extrusion methods are of no preparative interest. 

Other approaches to alkylidenecycloproparenes have been attempted without success. Aromatization of appropriate alkylidenecyclopropanes or their precursors could not be realized, and flash vacuum pyrolysis of methylene phthalide and 3-methylene-2-coumaranone afforded rearrangement products rather than alkylidenecycloproparenes via extrusion of 002. The photochemical or thermal decomposition of the sodium salt of benzocyclobutenone p-toluenesulfonyl hydrazone led to products derived from dimerization of the intermediate benzocy-clobutenylidene, or from its reaction with the solvent, but no ring-contracted products were observed. When the adduct of methylene-l,6-methano[10]annulene to dicyanoacetylene (249) was subjected to Alder-Rickert cleavage, phenylacety-lene (250) was formed, which derives reasonably from the parent 234. ... 

Another method of functionalizing 72 was initiated by catalytically hydrogenating 78 to 79. Thermolysis of 79 at 220 °C under vacuum resulted in an ethylene extrusion to generate furan 80. Diels-Alder reaction of 80 with dimethyl acetyle-nedicarboxylate (DMAD) provided endoxide 81, which on subsequent deoxygenation with low-valent titanium gave ester 82 (Scheme 17). ... 

Fig. 7 Extruder and extrusion. 1 Drive unit, 2 barrel inlet, 3 temperature control, 4 feed hopper and dosing unit, 5 vacuum vent, 6 barrel, 7 screw. (Reproduced with permission from Reifenhauser)...

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