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

Advances in modeling transport phenomena in material-extrusion additivemanufacturing: Coupling momentum, heat, and mass transfer

Material-extrusion (MatEx) additive manufacturing involves layer-by-layer assembly ofextruded material onto a printer bed and has found applications in rapid prototyping.Both material and machining limitations lead to poor mechanical properties of printedparts. Such problems may be addressed via an improved understanding of thecomplex transport processes and multiphysics associated with the MatEx process.Thereby, this review paper describes the current (last 5 years) state of the art modelingapproaches based on momentum, heat and mass transfer that are employed in aneffort to achieve this understanding. We describe how specific details regardingpolymer chain orientation, viscoelastic behavior and crystallization are often neglectedand demonstrate that there is a key need to couple the transport phenomena. Such acombined modeling approach can expand MatEx applicability to broader applicationspace, thus we present prospective avenues to provide more comprehensive modelingand therefore new insights into enhancing MatEx performanc

An overview of polymer processing modelling

Polymer processing modelling offers new opportunities for die or mould optimization. We first present a short state of the art of polymer processing technology, followed by a discussion on how to develop reasonable processing models, some illustrations being given. We then deal with the question of constitutive equations in polymer processing modelling, both for classical thermoplastics and for more sophisticated (fibre reinforced) polymer systems. Finally, we revise flow instabilities that limit processability both in confined flows and in free surface extensional flows.(undefined

Dimensions of the deposited strand in the material extrusion process: Experimental and numerical investigations

International audienceThe material extrusion process is investigated by focusing on the geometry of a single strand extruded through a printing nozzle and deposited on a substrate of a 3D printer. An experimental protocol is set to determine the width W , and the height H, of a strand. The geometry depends mainly on the nozzle diameter D, the gap between the substrate and the tip of the nozzle g, the extrusion velocity U and the printing velocity V. The relevant parameter to determine W/D and H/g is reduced to one dimensionless parameter equal to (D/g)(U/V). A computational multiphase flow is described using a level set approach and a finite element method. The heat transfer is also taken into account in the set of governing equations. The polymer is considered as a generalised Newtonian fluid. An accurate description of the interface between the polymer and the surrounding air is developed based on an anisotropic remeshing procedure. Two different situations are numerically solved for which: (i) a first case with a g/D ratio less than one and (ii) a second case with a g/D ratio larger than one. In the first situation, the spreading below the nozzle is more or less radial around the vertical axis of the extruder which is not the case in the second situation. The numerical shape geometry is in good agreement with experimental observations. The thermal cooling underlines that the relevant parameters are the perimeter and the area of the strand cross-section and the Péclet number based on the printing velocity. The numerical predictions of W/D and H/g agree with experimental results

Experimental validation of a tube based constitutive equation for linear polymer melts with inter-chain tube pressure effect

A polydisperse case of an entangled linear polymer melts constitutive equation was studied. This constitutive equation, proposed by S. Dhole et al. [J. Non-Newtonian Fluid Mech. 161 (2009) 10–18], based on the reptation theory and the tube model, was tested on a polystyrene in shear (capillary rheometry) and planar extension in a complex flow (fieldwise measurements in a contraction flow) for different level of strain rates. A good quantitative prediction of all the set of experiments was obtained, using no adjustable nonlinear parameters