A novel on-line capillary rheometer (OLR) was used to examine the shear and extensional characteristics of polyolefin melts during twin screw extrusion (TSE). Comparisons with off-line rheometry were made using a twin-bore capillary rheometer and a modular in-line slit die rheometer (ILR) provided in-line rheometry comparisons. Both capillary rheometers were controlled via PCs running dedicated software, and the extrusion line and ELR were fully instrumented allowing real-time process monitoring to be carried out by IBM compatible PCs via data acquisition hardware and software. The prototype OLR was developed by the re-design of several key features including an instrumented transfer section and capillary die block which facilitated the use of various die geometries. Shear and extensional on-line rheometry of three polyethylenes (linear and branched), and four molecular weight grades of polypropylene were examined, and a direct comparison with off-line capillary rheometry showed a good correlation. The effect of a high loading of filler on two of the polyethylenes was investigated. In-line shear stress and entry pressure measurements showed a reasonable correlation with on-line rheometry. A study of entry flows in the OLR using capillary dies approaching orifice showed non-linearities occurred at very low capillary length to diameter(L:D) ratios, and this was repeatable using off-line rheometry. Predicted zero length entry pressures (Po) were used to estimate apparent extensional viscosity using a number of standard models. Melt instability and capillary wall slip were also investigated using on-line rheometry. Melt pressure and temperature in the twin screw extruder and OLR were monitored at various process conditions to examine the ability of the OLR to condition melt during testing, and the effect of OLR testing on extrusion conditions. Pressure variation in the extruder, OLR and off-line rheometer were compared in order to quantify process noise. The effect of OLR testing on melt rheology and polymer molecular weight were examined using off-line rheometry and gel permeation chromatography(GPC).

A novel on-line capillary rheometer (OLR) was used to examine the shear and extensional characteristics of polyolefin melts during twin screw extrusion (TSE). Comparisons with off-line rheometry were made using a twin-bore capillary rheometer and a modular in-line slit die rheometer (ILR) provided in-line rheometry comparisons. Both capillary rheometers were controlled via PCs running dedicated software, and the extrusion line and ELR were fully instrumented allowing real-time process monitoring to be carried out by IBM compatible PCs via data acquisition hardware and software. The prototype OLR was developed by the re-design of several key features including an instrumented transfer section and capillary die block which facilitated the use of various die geometries. Shear and extensional on-line rheometry of three polyethylenes (linear and branched), and four molecular weight grades of polypropylene were examined, and a direct comparison with off-line capillary rheometry showed a good correlation. The effect of a high loading of filler on two of the polyethylenes was investigated. In-line shear stress and entry pressure measurements showed a reasonable correlation with on-line rheometry. A study of entry flows in the OLR using capillary dies approaching orifice showed non-linearities occurred at very low capillary length to diameter(L:D) ratios, and this was repeatable using off-line rheometry. Predicted zero length entry pressures (Po) were used to estimate apparent extensional viscosity using a number of standard models. Melt instability and capillary wall slip were also investigated using on-line rheometry. Melt pressure and temperature in the twin screw extruder and OLR were monitored at various process conditions to examine the ability of the OLR to condition melt during testing, and the effect of OLR testing on extrusion conditions. Pressure variation in the extruder, OLR and off-line rheometer were compared in order to quantify process noise. The effect of OLR testing on melt rheology and polymer molecular weight were examined using off-line rheometry and gel permeation chromatography(GPC). / Rosand Precision Ltd. and Raychem Ltd.

Depuis quelques années, la microplasturgie est un secteur en plein développement. Cependant, le comportement rhéologique des matériaux polymères dans des géométries très minces (dimension inférieure à 100 µm) n’est pas bien caractérisé. Peu de travaux ont été entrepris à ce sujet, en particulier en ce qui concerne les écoulements de Poiseuille qui sont pourtant les plus représentatifs des conditions de mise en œuvre usuelles. Ainsi, ce travail a pour but la mise au point d’une méthode expérimentale permettant d’obtenir des données pertinentes afin de caractériser de façon approfondie le comportement des matériaux polymères en écoulement de Poiseuille dans des géométries micrométriques. Afin de décrire au mieux la physique de tels écoulements, nous avons également cherché à les simuler numériquement, soit en utilisant des lois de comportement classiques, soit à l’aide de modèles se référant à la dynamique moléculaire. Pour atteindre ces objectifs, une filière à fente plate instrumentée avec des capteurs de pression et température, d’entrefer variant entre 50 et 200µm, a été conçue afin d’effectuer des mesures à l’aide d’un rhéomètre capillaire. Ce dispositif a été validé en confrontant les mesures à celles obtenues par d’autres méthodes (rhéométrie capillaire en filière classique et rhéométrie dynamique). Le glissement à la paroi a également été étudié, selon la méthode de Mooney. La simulation numérique de l’écoulement a d’abord été réalisée à l’aide de POLYFLOW®. L’effet de la pression sur la géométrie ainsi que sur le matériau polymère a été étudié. Puis, l’écoulement a également été simulé sous MATLAB® en utilisant des lois constitutives de type moléculaire basées sur le modèle du tube de Doï-Edwards ainsi que sur le concept de « Molecular Stress Function » introduit par Wagner pour rendre compte des effets d’orientation des molécules (variation du diamètre du tube) dans le champ de contraintes. L’écart constaté entre ces calculs et les résultats expérimentaux est expliqué et discuté à la lumière des simulations sous POLYFLOW®. Il modifie les perspectives d’étude de ce type d’écoulements. / The rheological behavior of polymer melts in microscale geometries is not really understood yet. In such processes which involve gaps thinner than 100µm (e.g. micro-injection molding), the material behaves differently compared to macroscopic flows. Besides, most polymer processing techniques involve pressure flows and only very few studies can be found about pressure flows in such thin geometries. The aim of this study was, first, to develop an experimental method which can provide relevant data about the rheological behavior of polymer melts in pressure flow taking place in microscale geometries. In order to get better descriptions of the physics involved in such flows, numerical simulation with commercial and home-made softwares was also implemented, especially with molecular dynamics constitutive models. Thus, a modular rheometrical slit die equipped with pressure and temperature transducers was designed to be adapted to a capillary rheometer, with different gap dimensions available, between 50µm and 200µm. The device was assessed by comparing to usual rheological ones, and wall slip was investigated according to Mooney’s method. Then, simulation of the flow was performed with POLYFLOW®. The pressure effect on the geometry and on the polymer material was investigated. Besides, simulation was also conducted with MATLAB® by implementing the Doi-Edwards’ tube model (reptation theory) and the Molecular Stress Function concept of Wagner to take into account the enhanced orientation of the molecules due to the very close vicinity of the die walls. Experimental results were compared to calculations, and the discussion of the discrepancies was supported by POLYFLOW® simulations. The conclusions somewhat modify the prospects for future studies of such flows.

In-line rheological and process measurements are studied, during the primary injection phase, as a potential aid to closed loop process control for injection moulding. The feasibilities of attaining rheological and process measurements of sufficient accuracy and precision for use in process control are investigated. The influence of rheological and process measurements on product quality are investigated for semi-crystalline thermoplastic materials. A computer based process and machine parameter monitoring system is utilised to provide accurate and precise process data for analysis