Alternative to the Extruder

The extruder is substituted by a deep flash vessel (which operates at 150 mbar), a gear pump, and a static mixer. The only exergy input is the energy requirement of the pump and the compressor, which removes the gas. The pump only needs to increase the pressure of the polymer such that it can 

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The extruder is used since it mixes, melts, and degases the polymer. However, as said in the previous paragraph, from an exergetic point of view, it is not an efficient apparatus, since it dissipates mechanical work into heat by frictional forces. A possible alternative to the extruder could therefore be a separate degasser, a static mixer, or a gear pump to push the polymer melt through the mixer and perforated plate (Figure 11.6). 

Fig. 8.75b depicts an optional execution of the discharge end whereby two different, hinged discharge configurations can be attached alternatively to the extruder. 

The eccentric rotation of filler in virtue of the variant shear rates along the extrudate cross-section has been proposed as an alternative to the plug flow mechanism to explain this orientation pattern [355]. In [357] it was noted that the cross-wise orientation of fibers at the core of molded specimens was established only after the entire mold had been filled the authors assumed this orientation to be due to the quasi-static stresses arising in the material under pressure. 

The catalyst is normally contained on a ceramic substrate. These ceramics are extruded in a malleable state and then fired in ovens. The process consists of starting with a ceramic and depositing an aluminum oxide coating. The aluminum oxide makes the ceramic, which is fairly smooth, have a number of bumps. On those bumps a noble metal catalyst, such as platinum, palladium, or rubidium, is deposited. The active site, wherever the noble metal is deposited, is where the conversion will actually take place. An alternate to the ceramic substrate is a metallic substrate. In this process, the aluminum oxide is deposited on the metallic substrate to give the wavy contour. The precious metal is then deposited onto the aluminum oxide. Both forms of catalyst are called monoliths. 

A dramatic improvement in the performance of PMDA in chain extension of PET is possible if the PMDA is added to the extruder in a concentrate using a polycarbonate (PC) carrier [10]. The reason being that if PMDA is compounded in a PET carrier resin then a premature reaction results leading to ultra-high MW PET and gel problems. Alternatively, if PMDA is compounded in a polyolefin carrier then degradation of the polyolefin occurs whereas, when PMDA is compounded in a polycarbonate carrier there is no premature reaction because PC contains no acid end groups (rather, -OH end groups instead). Furthermore, PC is quite miscible with PET. 

An alternative to the thermolysis of sulfolenes is reaction with excess LAH (77TL947). Under mild conditions, SO2 is extruded and dienes are formed from sulfolenes as well as their adducts (Scheme 228). This method is thus useful in those cases where thermolysis is detrimental to the stability of the product. It is believed that even here the reaction proceeds only by thermal cleavage, the transition state being lowered by LAH acting as a catalyst. 

Copolymerizations are powerful ways to produce polymers with speeifie properties with well defined strueture. However, they involve the costly modification of existing production facilities of polystyrenes. To satisfy small market niches, modified polystyrenes ean be obtained through grafting reactions by chemical reactions on a polymer melt in an extruder (reactive extrusion) to achieve functionalities on the polymeric chains. Thus, grafting reactions are the preferred methods to achieve functionality commercially because they are low cost alternatives to the eopolymerization processes despite low grafting efficieney. For example, polystyrenes have been grafted with brominated styrene to enhanee the flame resistance of polystyrenes, as shown in Reaction 13. 

Film is usually extruded down onto a chill-roll assembly (Fig. 5 44103) gjjjj ig cooled and drawn by two or more water-cooled rolls while the surface of the chill roll imparts a finish to the film. Alternately, the film can be extruded down into a trough of water (Fig. 5.45 ). In the water bath, the film passes under a guide shoe before it is raised out of the water. Since chill rolls cool more efficiently than the water bath, they increase transparency and gloss, decrease haze, and provide a better surface finish to the extruded film. Consequently, chill rolls are preferred even though they are more expensive than a water bath. Water cooling is limited to films, such as tarps, where good surface finishes are not required. Chill rolls (Fig. 5.46 ) are also used in sheet extrusion. However, the sheet is typically extruded horizontally into nip between two chill rolls and then wrapped around another roll. 

Copolymers of vinyl silane VTMO can also be bonded to polymer chains by copolymerization, to produce vinyl silane thylene or vinyl silane ethylene butyl acrylate. These can be processed in granular form together with the appropriate catalyst master batch in conventional extruders. They can thus be regarded as alternatives to the grafted versions above but, due to their production process, they are only available as high pressure polyethylene grades. 

One alternative approach to the two-stage steam moulding process is that in which impregnated beads are fed directly to an injection moulding machine or extruder so that expansion and consolidation occur simultaneously. This approach has been used to produce expanded polystyrene sheet and paper by a tubular process reminiscent of that used with polyethylene. Bubble nucleating... 

Base Metal Catalyst - An alternate to a noble metal catalyst is a base metal catalyst. A base metal catalyst can be deposited on a monolithic substrate or is available as a pellet. These pellets are normally extruded and hence are 100% catalyst rather than deposition on a substrate. A benefit of base metal extruded catalyst is that if any poisons are present in the process stream, a deposition of the poisons on the surface of the catalyst occurs. Depending on the type of contaminant, it can frequently be washed away with water. When it is washed, abraded, or atritted, the outer surface is removed and subsequently a new catalyst surface is exposed. Hence, the catalyst can be regenerated. Noble metal catalyst can also be regenerated but the process is more expensive. A noble metal catalyst, depending on the operation, will typically last 30,000 hours. As a rule of thumb, a single shift operation of 40 hours a week, 50 weeks a year results in a total of 2,000 hours per year. Hence, the catalyst might have a 15 year life expectancy. From a cost factor, a typical rule of thumb is that a catalyst might be 10%-15% of the overall capital cost of the equipment. 

The convention extrusion blow moulding process may be continuous or intermittent. In the former method the extruder continuously supplies molten polymer through the annular die. In most cases the mould assembly moves relative to the die. When the mould has closed around the parison, a hot knife separates the latter from the extruder and the mould moves away for inflation, cooling and ejection of the moulding. Meanwhile the next parison will have been produced and this mould may move back to collect it or, in multi-mould systems, this would have been picked up by another mould. Alternatively in some machines the mould assembly is fixed and the required length of parison is cut off and transported to the mould by a robot arm. 

Extrusion press processing (express processing) was developed for the production of flax fiber-reinforced PP at the research center of Daimler Benz (Ulm, Germany) [62]. In this processing, natural fiber nonwovens and thermoplastic melt-films are alternatively deposited in a tempered molding tool and molded afterwards. The thermoplastic melt-films are laid on by a mobile extruder. If thi.s process is optimally adapted to the element, a single passage by the extruder suffices. The structural order consists of three layers two layers of... 

The mechanism of ATP synthesis discussed here assumes that protons extruded during electron transport are in the bulk phase surrounding the inner mitochondrial membrane (intermembrane and extramitochondrial spaces). An alternative view is that there are local proton circuits within or close to the respiratory chain and complex V, and that these protons may not be in free equilibrium with the bulk phase (Williams, 1978), although this has not been supported experimentally (for references see Nicholls and Ferguson, 1992). The chemiosmotic mechanism is both elegant and simple and explains all the known facts about ATP synthesis and its dependence on the structural integrity of the mitochondria, although the details may appear complex. This mechanism will now be discussed in more detail. 

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