Dry extrusion

Both wet and dry extrusion techniques are available, and both are strongly influenced by the friclional properties of the particulate phase and wall. In the case of wet extrusion, rheological properties of the liquid phase are equally important. See Pietsch [Size Enlargement by Agglomeration, John Wiley Sons Ltd., Chichester, 346 (1992)] and Benbow et al. [Chem. Eng. Sci., 422,2151 (1987)] for a review of design procedures for dry and wet extrusion, respectively. 

Ref Cal Tech Lab Program 209, Investigation of the Dry Extrusion of Solvent Prepared H4 Propellant , Status Rept 1-6 (12 Jan 1945 -16 June 1945)... 

Effects of Encapsulation by Spray-Drying, Extrusion, and Molecular Inclusion... 

Spray drying, extrusion, coacervation and adsorption techniques are among the more widely used (1 ), A relatively new method is the molecular inclusion of flavor in beta-cyclodextrin (2, 3). 

Little work has been published comparing the shelf life of flavors encapsulated by different processes. The purpose of this investigation was to determine the shelf life of cold pressed orange oil encapsulated by spray drying, extrusion, and molecular inclusion. Limonene-1,2-epoxide concentration was used to monitor oxidation. 

Cellulose Acetate and Triacetate Fibers. Polymer solutions arc convened into fibers by extrusion. The dry-extrusion process, also called dry spinning, is primarily used lor acelate and triacetate. 

The dry-extrusion process consists of four operations dissolution of the polymer in a volatile solvent filtration of the solution to remove insoluble matter extrusion of the solution to form libers and lubrication, yam formuliun. and packaging. 

Polymers may be induced to encapsulate other molecules by a variety of means (Risch and Reineccius, 1995) as diverse as dipping, spray-drying, extrusion, evaporation, and coacervation each technique has its special applications, strengths, and weaknesses. Advantages in common are the protection and slow release of the encapsulate. In any of the mechanisms, a coagulable polymer precipitates around a core of labile material. Polysaccharides are regular encapsulating polymers (Risch and Reineccius, 1995) acacia gum is particularly efficacious because of its protein content. 

Extrusion cooking of the bran was pioneered by the Western Regional Research Laboratory (28, 29, 29a). Dry extrusion was found more suitable for stabilizing bran to be used as a food ingredient (38). Stabilization within 1 hour after milhng is considered ideal for bran quality. 

M-J Kiang, Dry Extrusion of Whole Soybeans, Insta-Pro International, Des Moines, Iowa, 1993. 

The principle advantage of dry extruder preparation is that no expensive stacked-tray cookers or steam boiler are required, and the total capital investment for facilities under 100 tons per day in size is significantly less than for traditional full-press or solvent extraction processes. Therefore, this means of preparation is commonly applied in very small-scale plants commonly referred to as mini-mills. The primary disadvantage of dry extruder preparation is that the meal produced is higher in fat content than many poultry producers desire, and lower in bypass protein than many cattle producers desire. Thus, meal produced from a full-press mill using dry extrusion preparation generally obtains a lower price than meal produced from a traditional full-press operation. 

Heat generated by the dry extrusion method does not adversely effect fat quality. Temperatures of the magnitude of 350-400°F are needed to produce off-odor development, whereas temperature for extrusion is generally in the 250-300°F range. 

The term dry extrusion, as opposed to wet extmsion, refers to the fact that this type of extruder does not require an external source of heat or steam (29). Dry extruders generate heat and pressure mechanically as a result of the frictional and shear forces produced within the extruder barrel. Provided that adequate operating temperatures are achieved (138°-150°C), this combination of heat and pressure is sufficient to substantially denature the important antinutritive factors in soybeans and render... 

Some of the more obvious areas definitely requiring test work are filtration, sedimentation, spray, or fluidized bed or any other kind of solids drying, extrusion pelleting, pneumatic and slurry conveying, adsorption, and others. Even in such thoroughly researched areas as vapor-liquid and liquid-liquid separations, rates, equilibria, and efficiencies may need to be tested, particularly of complex mixtures. A great deal can be found out, for instance, by a batch distillation of a complex mixture. 

Both wet and dry extrusion techniques are available, and both are strongly influenced by the frictional properties of the particulate phase and wall. In the case of wet extrusion, rheological properties... 

Depending on capital investment limitations, extruders may be heated by passing steam through the barrel jacket and/or by direct steam injection. Low-cost autogenous machines, which create heat by friction between the feed material and the surfaces of the barrel, screw and steam locks, and do not require steam-generating equipment, are also used (Wiejratne et al., 2004). This process is referred to as dry extrusion, and the extruder can be powered by a farm tractor and was originally developed to cook whole soybeans on-farm to prepare feeds. 

Patil, R.T. D.S. Singh R.E. Tribelhorn. Effect of processing conditions on extrusion cooking of soy-rice blend with a dry extrusion cooker. /. Food Sci. Technol. India 1990, 27, 376—378. 

CD may be used in combination with carbohydrates (spray-drying, extrusion) to ensure both encapsulation and further protection (Qi and Xu, 1999). 

FIGURE 11.2 Dry extrusion-dry-spinning of cellulose acetate fibers. (From C.E. Schildknecht, ed., Polymer Processes, Interscience, New York, 1956, p. 841.)... 

FIGURE 11.3 Dry extrusion filaments emerging from spinner. (From G.M. Moelter and R. Steele, In J. McKetta, ed., Encyclopedia of Chemical Processing and Design, vol. 1, Marcel Dekker, New York, 1976, p. 171.)... 

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