Modem Extrusion Processes

FIGURE 13.14 Extruder system designed to produce flavorings. (From Fulger, C., L.M. Popplewell, Flavor encapsulation, U.S. Patent 5601865, Assigned to McCormick Company, Inc., (Sparks, MD) 1997. With permission.) 

In the example above, the authors set the system up to extrude under pressure (08 — potentially cold temperatures) so that highly volatile substances (such as acetaldehyde) would not volatilize and be lost thereby producing a porous capsule. Alternatively, the product discharge could be air cooled or injected into a cold isopropanol bath (T2). This process required particle size reduction as a final step. Size reduction by grinding potentially could damage the particle structure, reducing volatile retention and shelf life. 

Benczedi and Bouquerand [111] approached the problem of particle formation by working both with formulation and processing conditions. By using the formulation and process conditions noted in the patent example below, they were able to form very uniform particles directly from the extruder. 

It appears that process development has progressed to the point where continuous exuusion processes can be used to produce encapsulated flavorings without the need for cooling, drying, or size reduction steps. These innovations all have contributed to reduced manufacturing costs for this product. 

The advent of continuous extrusion has also provided the opportunity to use a wider variety of matrix materials. In the past, viscosity has been a limiting factor, but this is no longer as critical when twin screw extruders are used. The wider range of matrix materials has provided the opportunity to use materials that can offer some controlled release properties, e.g., proteins or less soluble carbohydrates. This offers further advantage to this encapsulation process. 

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As with other processes, fully automated process control is applied. Surface quality and thickness variation of blown extrusion geomembranes may cause problems. Besides, properties within the area of the two creases may potentially deviate from those of the base material. Modem equipment however is capable of mastering all these problems. 

Goldsworthy, W. B. (1979), New technology for continuous reinforced plastics processing It s called Pulforming , and it permits extrusion of variable cross-section parts, curves, or both . Modem Plastics, 56, 82-83. 

An early description of the cast film process was published in Modem Plastics in 1952 [26] which was very similar to the cast-film scheme shown in Figure 6.19 which represents the process used today. The cast film process involves the extrusion of polyethylene through a die to form a thin molten layer of material that is drawn down to a thinner gauge based on the difference between the rate the molten polymer exits the extruder and the rate that the molten polymer is cooled onto a chill roll. The film cools very rapidly on the chill roll and film orientation is only in the machine direction. Optical properties are usually better with cast film as compared to blown film and line rates may be higher with the cast film process. A cast film line may also involve coextrusion of several layers of different types of thermoplastics to fabricate specialty films with improved properties. A... 

Fugitive emissions such as those around pipe flanges and pump seais Process operations, in modem chemical operations, automation and computer control have greatly reduced contact with feedstock, intermediates, and products Extrusion of solid products such as a solid polymer that normally is hot when released through an extruder head and may give off vapors of residual monomers, oligomers, and additives that may be inhaled... 

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