Effects of Extruder Die Nozzle Dimensions on Expansion and Micrographic Characterization During Extrusion of Acetylated Starch
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| Online Access: | http://www.viks.sk/chk/star_3_4_04_108_117.doc |
| Abstract: | Conclusions. Die nozzle dimensions determined the extent of pressure buildup behind the die. Due to pressure and temperature drop, blowing agent flashes off and, along with the resulting changes in the material's characteristics, material expands as it exits the die nozzle. Initial expansion of the dough as it exits the die depends upon its shear history and pressure drop. The final stable expansion of extrudate depends upon the elastic properties of the material along with the changes in the states of the material due to the temperature effects as described above. It is critical to involve elastic properties of the material in model development for the prediction of RE. Die nozzle diameter and length together determined the amount of pressure and shear to which the material was subjected before exiting from the die. Die nozzles with 4.0 mm diameter and 16.8 mm length gave maximum radial expansion of 20.6 for the extrusion of acetylated starch in a conical co-rotating twin-screw laboratory extruder. Summary. Starch acetate (DS 2) with ethanol content of 16% (d. b.) was extruded in a twin-screw extruder with nozzle length to diameter (L/D) ratios varying from 2.9 to 13.1, constant screw speed of 140 rpm and barrel temperature of 160°C. Effects of variation in LID ratio and the individual effects of variations in L and D on expansion and micrographic properties were studied. With smallerD and larger/, nozzles, back pressure developed in the die was immense, which resulted in high initial expansion and then collapse of extrudates, after a brief time, leading to smaller diameter extrudates. It was concluded that the pressure drop exerted tensile forces in the cell material in excess of its elastic limits. SEM results of the samples showed the effects. It is important to consider the elastic properties of the material in predicting ultimate radial expansion. The expansion phenomena have been explained in detail. |
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| ISSN: | ISSN 0038-9056 |
