Rheoten

One way to characterise thermoplastic melts is by using a Rheotens machine (31) which subjects an extruded strand of melt to tensile elongation at a fixed velocity while measuring the tensile force. The typical response (melt tensile force versus draw velocity) for branched PP extends to twice as high a draw velocity, with six times the force, than that for linear PP. Alternatively a... 

Fig. 9 Melt elongational behavior of PPE/SAN blends at 180°C. (a) Rheotens curves, (b) Apparent elongational viscosity, as calculated by [57] (reprinted from [47])...

Figure 1 (a) Rotary damp rheometer, (b) Rheotens test. For details see Meissner [1]. (Reprinted from Rheol. Acta (1971), by permission of Steinkopff Verlag.)... 

Figure 3 Strength and drawability of PP melts at 200°C (Rheotens apparatus fed by Rheograph 2001 (L/D = 30/2)).

Experimental average Rheotens curves for PEEK-CNF nanocomposites at 360°C. The lines represent a Levenberg-Marquardt fit of the data according to Wagner et... 

Muke, S., Ivanov, I., Kao, N., Bhattacharya, S.N. Extensional rheology of polypropylene melts from the Rheotens test , J. Non-Newton. Fluid Mech. 101(1-3) (2001), 77-93... 

The Rheotens 71.97 is made by Gottfert, Buchen/Odenwald, Germany Rock HiU, SC, USA... 

In the event the devices for measuring are not available, there are two methods for obtaining approximate values of The first method is based on the fiber spinning technique as shown in Figure 3.26. (The device is known as the Rheotens.) Without any discussion of the theory the extension rate is given by... 

FIGURE 3.26 Rheotens apparatus for estimating the uniaxial extensional viscosity. 

The original Doufas-McHugh (1,2) two-phase microstmctural/constitutive model for stress-induced crystallization (SIC) is validated for its predictive capability using on-line Raman crystallinity and spinline tension data of two Dow homopolymer polypropylene resins. The material parameters -inputs to the model - are shown to be obtained from lab scale material characterization data oscillatory shear (DMS), rheotens and DSC. The same set of two SIC material parameters are shown to be able to predict the crystallinity profiles along the spinline and tension very well overall. The model captures quantitatively the effect of take-up speed, throughput and MFR on crystallization rate due to SIC. 

Doufas A.K., Analysis of the rheotens experiment with viscoelastic constitutive equations for probing extensional rheology of polymer melts. J. Rheology, 50 749-769, (2006). 

Table 4. Processing conditions of rheotens experiments used in this work...

Figure 1. Tensile force vs. pull-off speed (data) and fit of the rheotens model for H502-25RG resin... 

The melt strength was determined using the same apparatus in combination with a Goettfert Rheotens device and a die of 25/2 ratio. The melt was extruded at a constant speed of 0.24 mm/min and 210°C. The strand was subsequently pulled between the Rheotens wheels at a constant acceleration rate of 6.2 mm/sec. Two additional reference samples VF3 and VF4 were added for comparison in the melt strength measurements. 

Additional rheological measmements were performed to determine the melt strength and die swell of these resins at 230°C. The melt strength was determined using a Goettfert capillary rheometer with a 25/2 die and a Rheotens device. The extrusion speed was maintained at 0.24 mm/sec while the aceeleration rate of the Rheotens wheel was maintained at 6.2 mm/see. ... 

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