Rheometry of polymer melts using processing machines

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1 Korea-Australia Rheology Journal, 28(3), (August 2016) DOI: /s Rheometry of polymer melts using processing machines Walter Friesenbichler 1, *, Andreas Neunhäuserer 1 and Ivica Duretek 2 1 Department Polymer Engineering and Science - Institute of Injection Molding of Polymers, Montanuniversitaet Leoben, Leoben A-8700, Austria 2 Department Polymer Engineering and Science - Institute of Polymer Processing, Montanuniversitaet Leoben, Leoben A-8700, Austria (Received July 10, 2016; final revision received July 28, 2016; accepted July 29, 2016) The technology of slit-die rheometry came into practice in the early 1960s. This technique enables engineers to measure the pressure drop very precisely along the slit die. Furthermore, slit-die rheometry widens up the measurable shear rate range and it is possible to characterize rheological properties of complicated materials such as wall slipping PVCs and high-filled compounds like long fiber reinforced thermoplastics and PIM-Feedstocks. With the use of slit-die systems in polymer processing machines e.g., Rauwendaal extrusion rheometer, by-pass extrusion rheometer, injection molding machine rheometers, new possibilities regarding rheological characterization of thermoplastics and elastomers at processing conditions near to practice opened up. Special slit-die systems allow the examination of the pressure-dependent viscosity and the characterization of cross-linking elastomers because of melt preparation and reachable shear rates comparable to typical processing conditions. As a result of the viscous dissipation in shear and elongational flows, when performing rheological measurements for high-viscous elastomers, temperature-correction of the apparent values has to be made. This technique was refined over the last years at Montanuniversitaet. Nowadays it is possible to characterize all sorts of rheological complicated polymeric materials under process-relevant conditions with viscosity values fully temperature corrected. Keywords: applied rheometry, slit-die, temperature correction, pressure dependency, rubber compound 1. Introduction In conventional rheology for thermoplastics and elastomers round dies are used. Measurements are usually performed for 3 different capillary diameters and 3 different die lengths. In order to perform a correct measurement, the material has to be filled and compressed into a cylindrical chamber. In this chamber, the material gets melted and heated to a defined measurement temperature, ideally to future processing temperatures. Once the material is heated it gets pressed through the capillary at 10 to 15 different piston speeds. Afterwards, the inlet pressure drop has to be corrected according to Bagley (1957). This provides the true wall shear stress. The apparent flow-curve provides the true shear rate after the Weissenberg/Rabinowitsch-correction (Eisenschitz et al., 1929). Problems are encountered if polymer melts with flow-anomalies (slip-stick or wall slipping) are measured. The main weaknesses of the capillary rheometry with round dies are the non-flush mount pressure sensors. In this case, the pressure is determined via a pressure hole, a small hole filled with molten polymer. When working with high-filled # This paper is based on an invited lecture presented by the corresponding author at the 16th International Symposium on Applied Rheology (ISAR), held on May 19, 2016, Seoul. *Corresponding author; Walter.Friesenbichler@unileoben.ac.at polymers, this method is highly inaccurate since the Bagley correction for this type of polymers provides non-linear or even negative values. More problems that come along with measuring high-filled polymers is the impractical melt-preparation in the cylindrical preparation chamber (no material-shearing) and the impossibility of measuring the melt temperature directly. The use of slit-die systems allows measuring the pressure drops and temperatures very precisely and directly during the measurement process. Friesenbichler (1992) and Knappe and Krumböck (1986) showed that it is possible to control the linearity of the pressure profile and to detect wall-slipping with the help of multiple pressure sensors along the slit. 2. Historical Background 2.1. Slit-die systems In the year 1963 Eswaran et al. (1963) developed the first slit-die system with a width/height ratio of 10/1 and direct pressure measurement and, for the first time ever it was possible to determine the inlet pressure loss without the Bagley correction. Wales et al. (1965) showed that the experimental values for different PE-types where nearly the same for round-die and slit die systems. In 1972 Offermann (1972) performed rheological tests on wall-slipping rigid-pvc with slit-dies. During his work he developed an 2016 The Korean Society of Rheology and Springer pissn X eissn

2 Walter Friesenbichler, Andreas Neunhäuserer and Ivica Duretek iterative calculation model regarding dissipative shear heating under non-isothermal flowing conditions. This model showed the significance of wall-slip effects on the viscosity function. Laun (1983) published a model and a detailed mathematical analysis of the pressure dependency of viscosity for the slit-die rheology. The non-linear pressure curve along the length l of the slit die, measured with 3 pressure sensors is approximated with a quadratic polynomial (Eq. (1)). With the coefficients of the quadratic polynomial a, b, and c the pressure coefficient β p is calculated according to Eq. (2), but using only 3 measurement points. In Eq. (2), η ap is the apparent viscosity and the apparent shear rate. γ ap p(l)=a + bl + cl 2, (1) β p = ln ( η ap( γ ap) ) = 2c (2) p b 2 The pressure coefficient allows calculating the viscosity at various pressure levels. It is important to eliminate possible negative influences such as inaccurate pressure measurements and non-isothermal flow conditions due to viscous dissipation as these lead to severe errors and bad results. When using this model, it is recommended to operate with shear rates < 5,000 s 1 and to use 4 to 5 pressure sensors along the slit die Temperature correction of viscosity due to viscous dissipation Further achievements were made by Daryanani et al. (1973). In this work the authors experimentally verified viscous dissipation in non-isothermal flow and suggested a calorimetric method for correcting the viscosity due to viscous dissipation. Fig. 1 shows the measurement system that was used in these experiments. In the first step, the melt was heated up to measurement temperature. Afterwards the hot melt was pressed through a thin steel tube. During the experiment the temperature rise, as a result of viscous dissipation, was measured with thermocouples in 2 sections along the flow path. Afterwards, the power of the heating system for the tube was reduced in order to regain isothermal conditions in the capillary. This experimentally found frictional heat was used for the temperature correction and the shifting of the viscosity curve to lower temperatures. One year later, Cox and Macosko (1974) investigated viscous dissipation in round- and slit-dies and developed a model for the calculation of the temperature profile in the flow channel. This model was experimentally verified with the use of infrared radiation pyrometers. They investigated isothermal and adiabatic boundary conditions as well as non-isothermal flows with viscous heating in flow direction. The onset of non-isothermal flow was found for shear rates higher than 3,000 s 1. Other notable works on viscous dissipation and its calculation were issued by Brinkmann (1951), Laun (2003), and Winter (1977). Agassant et al. (1991) came up with a simplified mathematical method for the viscous heating of Newtonian fluids in round- and slit-dies. This method was further developed by Schuschnigg (2004) for the calculation of viscous heating of pseudo-plastic fluids and experimentally verified on highly non-isothermal rheological experiments on an injection molding machine (Duretek et al., 2006; Friesenbichler et al., 2005; Friesenbichler et al., 2010). For the evaluation of apparent viscosity data viscous dissipation is taken into account in case of non-isothermal capillary flow. For each measurement the degree of nonisothermal condition is estimated by calculating the Cameron number Ca (Eq. (3)) which is equal to the inverse Graetz-Number Gz. Ca represents the ratio between heat conduction in direction of flow and convective heat transport in flow direction. If Ca is higher than 1 the flow is isothermal and no viscosity correction is needed. λl Ca = = (3) ρc p vh 2 Gz In Eq. (3), λ is the thermal conductivity, L the length of the slit, ρ the density at melt temperature, c p the specific heat at melt temperature, v the average velocity in the slit, Fig. 1. (Color online) Measurement system for the determination of friction heat (left) and temperature shifted viscosity curve (right) (Daryanani et al., 1973). 168 Korea-Australia Rheology J., 28(3), 2016

3 Rheometry of polymer melts using processing machines and H the slit height. In case of very high shear rates adiabatic flow conditions will prevail (Ca < 10 2 ). In this case, Eq. (4) is used for calculating the temperature rise, Tx ( ) = T w Δp x (4) ρc p L -- where T(x) is the average melt temperature of the cross section as a function of flow length, T W is the wall temperature of the slit-die, Δp is the pressure drop, and x the flow coordinate in flow direction. For calculating the temperature development in the transition regime (0.01 < Ca < 1), Eq. (5) is used (Friesenbichler et al., 2005; Schuschnigg, 2004) where k is the consistency and n the exponent of the power law. 1+ n 1 n n kv H 1+ 2n 2 n(1+ 3 n) T( x) = Tw + λ 2 n (1+ 4 n)(2+ 5 n). (5) 4 x 1 exp Ca n n 1+ 2n 2 n(1+ 3 n) n L n (1 + 4 n)(2 + 5 n) 1 + 2n For the polypropylene PP ExxonMobil 1095E1 (Figs. 2 and 3) below shear rates of 5,000 s 1 isothermal flow was found. Within the shear rate range of 5,000 s 1 to 500,000 s 1 a rise in average melt temperature over the whole slit volume up to 23 C was found und taken into account for temperature correction of the viscosity. At shear rates higher than 500,000 s 1 adiabatic boundary conditions were found. At a shear rate of 1,200,000 s 1 a temperature increase of 40 C was calculated. Fig. 2 shows the temperature corrected viscosity curve at 190 C for PP Exxon-Mobil 1095E1 while Fig. 3 displays the viscosity curve that is formed out of measurements on the cone-plate-, high pressure capillary-, and injection molding rheometer over more than 8 decades of shear rates with temperature correction of viscosity for Fig. 2. (Color online) Viscosity curve of PP ExxonMobil 1095E1 at 190 C and temperature correction according to Schuschnigg (2004). Fig. 3. (Color online) Temperature corrected viscosity curve formed out of 5 different experiments. shear rates higher than 5,000 s 1. The shifting direction of the viscosity due to temperature increase (see Fig. 2) fits perfectly to the results that were achieved by Daryanani et al. (1973). Hay et al. (1999) developed a method how to calculate the temperature increase in non-isothermal melt flow due to dissipation and compression. These methods were further developed by Friesenbichler et al. (2005) and Friesenbichler et al. (2011) for correcting the measured viscosity values due to viscous dissipation. Perko et al. (2014) found a way to successfully combine these methods for measuring and calculating shear and elongational viscosities for elastomers and was able to determine the heating caused by shear and elongational flows for rubber compounds. 3. Slit-die Rheometry Using Processing Machines When working with viscoelastic materials, the material prehistory is from utter importance. In order to be as close to processing conditions regarding the melt treatment, the first rheological measurements under processing conditions were performed during the 1980s Extrusion rheometer Rauwendaal and Fernandez (1984) developed a slit-die rheometer for an extrusion line. The shear rate was regulated by the screw speed. The problem with using the screw speed for setting the shear rate is that viscous dissipation increases with rise of the screw speed and influences the pressure drop measured. As a result, the measured viscosity values on the extrusion rheometer developed by Rauwendaal and Fernandez were significantly lower compared to those on the capillary rheometer. These above mentioned problems were avoided by Duretek and Friesenbichler (1994) with a by-pass extrusion rheometer (BP-EXR), displayed in Fig. 4. The measurements of the BP-EXR match very well with the ones Korea-Australia Rheology J., 28(3),

4 Walter Friesenbichler, Andreas Neunhäuserer and Ivica Duretek Fig. 4. (Color online) By-pass extrusion rheometer (left) and comparison of viscosity measurements of cone-plate, capillary and bypass extrusion rheometer (right); HPCR High pressure capillary rheometer, BP-EXR By-pass extrusion rheometer; CPR cone/plate rheometer. performed on the capillary rheometer. With continuously variable slit-heights, 4 pressure sensors, 2 temperature sensors, a throttle unit, and a parting knife, it is possible to characterize unfilled as well as high-filled extrusion-type polymers. This system works for single- and twin-screw extruders (PVC, wood plastic composites (WPC) etc.). When working with plasticized PVC or rigid PVC it is possible to control the pressure at the screw top with the help of the throttle unit. Therefore, in terms of melt preparation processing conditions like in PVC extrusion processes can be reproduced for rheological measurements of different PVC-types Injection molding rheometers Knappe and Krumböck (1986) firstly adapted an injection molding machine with slit-dies for rheological characterization of rigid PVC (Fig. 5). This system consists of a continuous adjustable slit-height, direct pressure measurement, and a flow-rate measurement system with a backwards running opposed piston. With this rheometer it was possible to investigate the wall-slipping behavior of rigid PVC and the relevant material laws. In order to avoid wall-slipping the slit surfaces were saw-tooth profiled. Friesenbichler (1992) and Krumböck (1984) performed systematic experiments for rigid PVC as a function of shear stress and showed onset of wall-slip (Fig. 6) for different PVC types at particular yield stresses. The yield stresses were found to be a function of melt temperature and K-value which is an indication for the molecular weight. Out of these measurements material laws for pure shear-flow, pure wall-slipping, superimposed shear, and slip-flow were compiled dependent on the viscosity (Kvalue) and the wall shear stress. These were worked out with the method of Mooney (1931). Based on the work done by Friesenbichler (1992) and Krumböck (1984), a vertical rubber injection molding rheometer was developed by Holzer (1996) and Holzer and Langecker (1997). As displayed in Fig. 7 the rheometer is Fig. 5. Injection molding machine rheometer opened (left) and sectional illustration (right); A mold platen, B machine platen, C slit entrance (change from round to rectangular geometry) and slit-die, D wedge for slit height adjustment from 0.3 mm to 3.5 mm, E injection unit, F cylinder, outlet valve, and piston for flow rate measurement, G tempering channels, T1, T2 temperature measurement, P pressure measurement (entrance E and positions 1 to 4). 170 Korea-Australia Rheology J., 28(3), 2016

5 Rheometry of polymer melts using processing machines Fig. 6. (Color online) Onset of wall-slip for unplasticized PVC with a K-value of equipped with 4 pressure sensors, 4 temperature sensors (2 infrareds, 2 thermocouples), a flow-rate measurement piston and a patented shear and heating-unit to reach higher mass temperatures in the slit compared to the plasticizing unit. The rheometer itself is designed as split mold and opens the measuring gap as wide so that the crosslinked rubber specimen can be taken out of the mold. In 2005 a Micro Rheology Technique (Fig. 8) was developed by Friesenbichler et al. (2005) and Schuschnigg (2004). It consists of a slit-die system which can be used on a conventional capillary rheometer as well as on the injection molding machine instead of the injection nozzle. The system has micro-slits ranged from 0.1 mm to 0.15 mm height and 5 mm width. Due to these low slit heights it is possible to measure in the very high shear rate range e.g., for low-viscous packaging materials. The measurable shear rates range from 10 3 to 10 6 s 1. With help of the thermocouples T 1 and T 3 placed 1 mm below the surface the wall temperature increase along the slit could be estimated. The thermocouples T 2 and T 3 Fig. 8. (Color online) Micro rheology measurement system for capillary rheometer (above left) and injection molding machine (above right); temperature profile in the steel body and extrapolated wall temperature (below, left), cross-sectional illustration of the slit-die system (below, right), 1 die housing, 2,3 conically shaped slit-die inserts, 4 thermal insulation, p v pressure sensor at the inlet, T 1, T 2, T 3 temperature sensors. placed 3 mm and 1 mm below the surface allow for estimating the wall temperature of the slit applying a linear approximation. Measured viscosities using this system are shown in Fig. 3 up to shear rates of 1,200,000 s 1. At the same time Gornik (2005) developed an injection molding machine rheometer dedicated to characterizing thermoplastic melts and powder injection molding (PIM) feedstocks. Again the injection molding machine was used to prepare the material under shear conditions related to the injection molding process which particularly is of crucial importance for PIM feedstocks. The slit-die insert was exchangeable and shows a height of 3 mm and a width of Fig. 7. (Color online) Rubber injection molding machine rheometer with shear and heating unit (left) and measured viscosity curve for EPDM at a reference temperature of 93 C (right); E 0 activation energy. Korea-Australia Rheology J., 28(3),

6 Walter Friesenbichler, Andreas Neunhäuserer and Ivica Duretek Fig. 9. (Color online) Measurement system with rheological mold (left) and the mold in cross-sectional illustration (right). 15 mm. The pressure measurement was realized with 4 flush-mounted pressure sensors. With those settings shear rates ranging from s 1 were possible. In 2009 a rheological injection molding machine rheometer based on an injection mold and slit-dies was developed by Friesenbichler et al. (2011). The new concept of an injection mold with implemented conically shaped slitdies (Fig. 9) allowed for easily changing the slit inserts while the mold is open and for performing rheological measurements without time consuming change of the machine nozzle. As well the melt preparation is close to practical conditions. The rheometer mold mounted in the clamping unit of the injection molding machine is shown in Fig. 9. The wall temperature of the slit-die is controlled by selfdeveloped heat-flow-sensors. For the measurement of low or high viscous melts various inserts (different width/height ratios) are available. The shear rates that can be achieved reach from 10 2 to 10 6 s 1. The piston for the determination of the volume flow rate can be servo-hydraulically regulated to a certain back pressure. With this technique, it is possible to measure the pressure dependence of viscosity very precisely. Fig. 10 shows results of the measurements for polystyrene PS 454C (left) and for polypropylene PP HG313MO measured under back pressures up to 600 bars (Fig. 10, on the right). After measurement the reciprocating piston injects the melt into the open air while the mold is open. A stripper blade cleans the parting area. Based on the Barus equation (Eq. (6)) the pressure coefficient β p was determined for polystyrene PS 454C with MPa 1, and for polypropylene PP HG313MO with MPa 1. In further measurements the pressure coefficient β p was measured for polystyrene PS 495F with MPa 1, and for PP ExxonMobil 1095E1 with MPa 1. ( ) η p = η p0 e β p p p 0. (6) Additionally, this setup allows measuring non-cross linking rubber compounds e.g., NBR, EPDM, SBR, etc. Additional experiments verified that results of the measurements with the injection molding machine rheometer and the ones of a capillary rheometer match perfectly if the measured viscosity values are temperature corrected for viscous dissipation. In order to understand the dissipation even better and to be able to perform measurements under non-isothermal conditions a further development of the concept was made at Montanuniversitaet (Fig. 11). The new rubber injection molding machine rheometer allows for measuring non-crosslinking rubbers as well as crosslinking rubbers over a wide range of shear rates. The movable mold half is as well equipped with a reciprocating Fig. 10. (Color online) Pressure dependent viscosity of PS 454C (left) and of Polypropylene PP HG313MO with a calculated pressure coefficient βp of MPa Korea-Australia Rheology J., 28(3), 2016

7 Rheometry of polymer melts using processing machines Fig. 11. (Color online) Sectional view of a rheological split-mold with slit-die, operated on a horizontal rubber injection molding machine; a: heat flux sensors, b: pressure sensors, c: piston for applying the counter pressure. piston to measure the volume flow rate and to apply back pressure. A split-mold system allows demolding the crosslinked specimen. A double flat-centering and sealing unit in the split mold allows to apply back pressures to up to 600 bars with nearly no leakage flow. As can be seen in Fig. 11, the mold is equipped with 2 heat flux (position a) and 4 pressure sensors along the measuring slit (position b). In an ongoing research, the pressure dependent viscosity of rubbers compounds will be measured. Because of the high injection pressure in rubber injection molding (2,500 to 3,000 bar) for the prediction of the pressure demand necessary for filling multi-cavity molds pressure dependent viscosity is of crucial importance. 4. Summary The first developments of slit-dies go back to In a sequence of scientific works, the advantages of using such measuring systems compared to conventional capillary rheometers became very clear. Most of all, the direct pressure measurement along the slit-die and the possibility to measure the melt temperature in the slit allows fast detection of viscous dissipation and non-isothermal conditions. Flow anomalies like wall-slipping and stick-slip effects are visible very fast. First works regarding the temperature correction of the viscosity curves relate to the years 1972 and As a result of the complexity of this phenomenon it doesn t come as a surprise that the first usable mathematical models in rheological evaluation software were achieved in 1999/2000. The works performed by Agassant et al. (1991), Hay et al. (1999), Schuschnigg (2004), and Friesenbichler et al. (2005) were crucial in order to reach this goal. Another field where slit-dies have a huge impact is rheology on processing machines like single- or twin-screw extruders and injection molding machines. With processing machines it is possible to perform measurements near to processing conditions in the industry (especially regarding pre-shearing and preparation of the melt). In this field developments at Montanuniversitaet for machine rheometers are highlighted, measuring materials like unfilled thermoplastics, rigid PVC (PVC injection molding machine rheometer, by-pass extrusion rheometer), crosslinking and non-crosslinking rubbers (rubber injection molding machine rheometers), high-filled compounds (e.g., PIM-feedstocks) and wood plastic composites. The reachable shear rates range from 100 s 1 up to 1,000,000 s 1, if micro-slits with heights of 0.1 mm are used in the rheological systems, which are placed as a nozzle at the injection unit. For most of the materials characterized at shear rates higher than 5,000 s 1 viscous dissipation has to be taken into account by means of temperature correction of the viscosity values evaluated. Within the last years slit-die systems were implemented into injection molds and equipped with servo-hydraulically controlled back pressure units for measuring the pressure dependence of viscosity. The developed injection molding machine rheometers allow for characterizing thermoplastics and rubber compounds regarding their temperature-, shear- and pressure-dependent viscosity near to processing conditions. The pressure coefficients of the viscosity values measured for polystyrene and polypropylene are in good agreement with literature. A new setup for cross-linking rubber compounds will be used in future research to characterize different rubber types. Acknowledgments The authors want to thank the EU, the Austrian Research promotion Agency FFG and the Polymer Competence Center Leoben (PCCL) for the financial support of the research projects. Additionally, the authors want to thank the industry partners Engel Austria GmbH, Semperit Technische Produkte GmbH, Rosendahl Nextrom GmbH, and Greiner Extrusionstechnik GmbH for their financial support and providing processing machines. Furthermore, we have to thank the companies Solvay Vienna GmbH and Borealis A/S in Linz/Austria for providing thermoplastic materials. Further thanks go to Eduard Leitner for Korea-Australia Rheology J., 28(3),

8 Walter Friesenbichler, Andreas Neunhäuserer and Ivica Duretek the outstanding construction work done for the rubber injection molding rheometer and Leonhard Perko, Michael Fasching, and Bernhard Lechner for carrying out the rheological experiments for rubber compounds. References Agassant, J.F., P. Avenas, J.P. Sergent, and P.J. Carreau, 1991, Polymer Processing: Principles and Modelling, Hanser Gardner Publications, Cincinnati. Bagley, E.B., 1957, End correction in the capillary flow of polyethylene, J. Appl. Phys. 28, Brinkman, H.C., 1951, Heat effects in capillary flow, Appl. Sci. Res. A2, Cox, H.W. and C.W. Macosko, 1974, Viscous dissipation in die flows, AIChE J. 20, Daryanani, R., H. Janeschitz-Kriegl, R. van Donselaar, and J. van Dam, 1973, A calorimetric measurement of frictional heat in capillary rheometry of polymer melts, Rheol. Acta 12, Duretek, I. and W. Friesenbichler, 1994, Rheologische Messungen mit einem neuentwickelten Extrusionsrheometer, 13. Leobener Kunststoff Kolloquium - Aktuelle Forschungsarbeiten in den Bereichen Spritzgießen, Extrusion, Rheologie und Messtechnik, Duretek, I., W. Friesenbichler, S. Schuschnigg, and J. Rajganesh, 2006, Viskositätsmessungen bei extrem hohen Schergeschwindigkeiten unter Berücksichtigung von Schererwärmung und Druckeinfluss, 19. Leobener Kunststoff Kolloquium - Spritzgieß- und Extrusionstechnik-Innovationen aus Industrie und Forschung, Eisenschitz, R., B. Rabinowitsch, and K. Weissenberg, 1929, Zur Analyse des Formänderungswiderstandes, Mitteilungen der deutschen Materialprüfungsanstalten, Springer, Berlin, Eswaran, R., H. Janeschitz-Kriegl, and J. Schijf, 1963, A slit viscometer for polymer melts, Rheol. Acta 3, Friesenbichler, W., 1992, Ermittlung von rheologischen Kenndaten für wandgleitende PVC-U Mischungen und ihre Anwendung für Düsenberechnungen beim Extrudieren, Dissertation Thesis, Montanuniversitaet Leoben. Friesenbichler, W., G.R. Langecker, I. Duretek, and S. Schuschnigg, 2005, Polymer melt rheology at high shear rates using a new micro-rheology technique, 21 th Polymer Processing Society Annual Meeting, Leipzig, Germany. Friesenbichler, W., I. Duretek, J. Rajganesh, and S. R. Kumar, 2011, Measuring the pressure dependent viscosity at high shear rates using a new rheological injection mold, Polimery 56, Friesenbichler, W., J. Rajganesh, T. Lucyshyn, P. Filz, and K. Webelhaus, 2010, Measurement of pressure dependent viscosity and its influence on injection molding simulation, 4 th International PMI Conference, Ghent, Belgium, Gornik, C., 2005, Viscosity measurement: Determining rheological data directly at the machine, Kunststoffe Int. 95, Hay, G., M.E. Mackay, K.M. Awati, and Y. Park, 1999, Pressure and temperature effects in slit rheometry, J. Rheol. 43, Holzer, C., 1996, Messverfahren zur praxisnahen rheologischen Charakterisierung von Kautschuken, Dissertation Thesis, Montanuniversitaet Leoben. Holzer, C. and G.R. Langecker, 1997, Praxisnahe rheologische Untersuchungen an einer EPDM-Mischung, KGK-Kautsch. Gummi Kunstst. 50, Knappe, W. and E. Krumböck, 1986, Slip flow of non-plasticized PVC compounds, Rheol. Acta 25, Krumböck, E., 1984, Zum Wandgleiten von PVC-hart Mischungen im fließfähigen Zustand, Dissertation, Montanuniversitaet Leoben. Laun, H.M., 1983, Polymer melt rheology with a slit die, Rheol. Acta 22, Laun, H.M., 2003, Pressure dependent viscosity and dissipative heating in capillary rheometry of polymer melts, Rheol. Acta 42, Mitsoulis, E., L. Perko, and W. Friesenbichler, 2014, Capillary flow behavior of a rubber compound, Polymer Processing Society Regional Conference Europe-Africa, Tel Aviv, Israel. Mooney, M., 1931, Explicit formulas for slip and fluidity, J. Rheol. 2, Offermann, H., 1972, Die Rheometrie wandgleitender Kunststoffschmelzen, untersucht am Beispiel von Hart-PVC, Dissertation Thesis, RWTH Aachen University. Perko, L., M. Fasching, and W. Friesenbichler, 2014, Model for the prediction of bulk temperature changes and pressure losses in rubber compounds flowing through conical dies: an engineering approach, Pol. Eng. Sci. 55, Rauwendaal, C. and F. Fernandez, 1984, Experimental study and analysis of a slit-die viscometer, Pol. Eng. Sci. 25, Schuschnigg, S., 2004, Rheologische Untersuchungen bei hohen Schergeschwindigkeiten mit Hilfe eines Mikrorheologie-Schlitzdüsen Messsystems, Master Thesis, Montanuniversitaet Leoben. Wales, J.L.S., J.L. den Otter, and H. Janeschitz-Kriegl, 1965, Comparison between slit viscometry and cylindrical capillary viscometry, Rheol. Acta 4, Winter, H.H., 1977, Viscous dissipation in shear flow of molten polymers, Adv. Heat Transf. 13, Korea-Australia Rheology J., 28(3), 2016