Dynamic modeling of the reactive twin-screw co-rotating extrusion process: experimental validation by using inlet glass fibers injection response and application to polymers degassing

International audienceIn this paper is described an original dynamic model of a reactive co-rotating twinscrew extrusion (TSE) process operated by the Rhodia company for the Nylon-66 degassing finishing step. In order to validate the model, dynamic experiments have been performed on a small-scale pilot plant. These experiments consist in a temporary injection of glass fibers at the inlet of the extruder after it has reached a given operating point. The outlet glass fibers mass fraction time variation is then measured. This experiment does not lead to the RTD measurement. As a matter of fact, due to the high quantity of glass fibers that is introduced, the behavior of the flow through the extruder is perturbed so that the glass fibers cannot be considered as an inert tracer. The dynamic model that we have published elsewhere (Choulak et al., Ind. Eng. Chem. Res., 2004, 43(23), 7373-7382) is adapted to take into account this nonlinear behavior of the extruder with respect to the glass fibers injection and is favorably compared to experimental results. The description of the degassing operation is also included in the model. The model allows simulations of the complete dynamic behavior of the process. When the steady state is reached, the good position of the degassing vent with respect to the partially and fully filled zones positions can also be checked, thus illustrating the way the model can be used for design purposes

Entgasen von Polymeren

After the polymerisation reaction different low molecular solvents remain in the polymer. They are separated from the polymer during a degassing step. Because of the high viscosity of the polymers machines with rotating devices like extruders are used for the degassing step. For the design and the economic instigation of these machines it is necessary to calculate the flow field and the mass transfer in the degassing section. In the experimental part of the work the mass transfer is investigated. A bench-scale unit and a corotating twin-screw extruder are used. The barrel walls of the machines are transparent in order to observe the flow field. The mass transfer takes place out of polymer films which are permanently renewed. In the rotating screw channel of the extruder a melt pool is formed in front of the screw, at the barrel wall thin films are formed. In the polymer melt bubble can be nucleated, the polymer can foam. The influence of different parameters on the efficiency of the degassing is investigated. The parameters are in detail the rotational speed of the screws, the vacuum pressure in the degassing section, the degree of fill, the viscosity, the concentration of the evaporating solvent, the thickness of the films and the length of the degassing section. Also the influence of the position and size of the degassing vent is discussed. A better design of the degassing section is proposed. (orig.)SIGLEAvailable from: http://edok01.tib.uni-hannover.de/edoks/e01dh01/357611063.pdf / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Canals as Vectors for Fish Movement: Potential Southward Range Expansion of Lepisosteus osseus L. (Longnose Gar) in South Florida

Lepisosteus osseus (Longnose Gar) is a large-bodied predator, whose Florida distribution remains unclear at the southern edge of its range. We reviewed available literature and museum voucher specimens to provide a more accurate range description, and we discuss recent collections in south Florida. Longnose Gar has not been previously reported in natural habitats south of Lake Okeechobee. Instead, records south of the lake are from canals, and most are recent (since 2000), including our own southernmost 2011 record. No records from Everglades natural habitats have been collected. Previous studies have shown native range expansions in anthropogenically disturbed landscapes. We suggest that the Longnose Gar is expanding its range southward in Florida using canals as dispersal vectors and/or suitable habitat