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 Entgasen:
Effiziente Lösungen für die Aufbereitung von Polymeren.
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Devolatilization is a common process task in many polymer producing and compounding operations. Depending on the process small (< 0.2 %) to large amounts (ca. 50 %) of volatiles have to be removed from the polymer melt rsp. solution or the solid polymer pellet. Required residual volatile levels depend on type and application of polymer. Volatiles could be monomers, moisture, gases e.g. air or solvents.
The type of volatile depends on polymer and way of polimerization. The table below shows initial and final (in pellet) volatile levels of different polymers. It also shows where there is the possibility to devolatilize both in extruder and silo.
Different types of volatiles to be extracted
from polymers by devolatilization. |
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| Basics of devolatilization of polymer melts, powders and pellets |  | |
Polymers are polymerized in different processes from monomeric components.
All processes have in common that not all monomers can be completely polymerized to the requested chain length. A certain amount of monomers and oligomers will remain in the end product. Depending on the chain length of these short-chain molecules and the application conditions (e.g. temperature) the volatiles will, by diffusion, come to the melt or particulate surface after a certain time.
Therefore these volatiles have to be removed to meet legal requirements of the final product or, during plant operation, could cause local accumulations of the lightly volatile substances and thus lead to an explosive mixture. Such explosions could result in local fires (causing agglomerates in silos) or even damage a complete silo with considerable potential for damage to operating personnel.
The devolatilization process can be simulated using diffusion coefficients of the critical volatiles, operating conditions and extruder / plant layout data. Thus a forecast for the commercial plant can be made.
Devolatilization of volatiles from polymers
| Polymer |
Type |
Initial content |
Final content; Extruder
devolatilization |
Final content; Silo
devolatilization |
| LDPE |
Ethylene |
< 3,000 ppm |
< 1,000 ppm |
< 50 ppm |
| LLDPE |
Hexane, Cyclohexane |
10 - 15 % |
< 500 ppm |
n.a. |
| 3 % |
< 250 ppm |
< 250 ppm |
| EVA |
Vinylacetate |
5,000 ppm |
< 50 ppm |
< 50 ppm |
| PS |
Styrene |
3,000 - 5,000 ppm |
< 300 ppm |
n.a. |
| ABS |
Acrylonitrile (AN ) |
20 ppm |
< 4 ppm |
n.a. |
| PC |
Methylenchloride |
20 % |
< 50 ppm |
n.a. |
| PA 6 |
Caprolactame |
8 % |
< 0.8 % |
n.a. |
| SBR, SBS |
Hexane, Cyclohexane |
15 - 70 % |
< 1,000 ppm |
n.a. |
| Acrylic adhesive |
Acetone |
50 % |
< 1,000 ppm |
n.a. |
| Polyimid |
Chlorobenzene |
70 % |
< 500 ppm |
n.a. |
| PP |
various |
approx. 1,000 ppm |
< 50 ppm |
< 100 ppm |
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