Monsanto processability tester

Rheological and processability behaviors were studied in a Monsanto processability tester (MPT), which is an automatic high-pressure capillary viscometer. The entire barrel and capillary are electrically heated with a microprocessor-based temperature controller [14], The... 

Sadhu et al. [88] reported interesting observations when they processed their nanocomposites through a capillary using the Monsanto Processability Tester. They found that different morphologies were formed and more ordering took place because of the shearing of the nanocomposites through the capillary. 

Most of the results discussed in this paper have been obtained through a suitable use of the Monsanto Processability Tester, and therefore this paper will also consist in an implicit demonstration of the usefullness of this versatile instrument. 

In addition to Mooney viscosities, the rheological properties of raw natural rubber samples were determined at 100 C using the Monsanto Processability Tester (MPT) with a die of 2,01 mm diameter (L/D ratio = 16). Elongational properties were simply estimated at 22°C, using a tensile tester and dumbbell samples die-cut from compression moulded sheets. 

In a capillary rheometer, such as the Monsanto Processability Tester, the extrusion pressure is measured, within the barrel, using a pressure transducer, located just above the die entrance. 

Experimental study. Using short dies of various L/Dq ratios (Dq= 6.35 mm L/Djj 1.088, 2.828 and 5.704 entry angle 90 ), experiments were performed at 121 C with the Monsanto Processability Tester, on a tread band compound ( ). Results are given in Table V, in terms of extrusion pressure and 60 sec. relaxed extrudate swell versus the various shear rates used. 

Correct and imaginative use of suitable rheological equipment, such as the Monsanto Processability Tester, allows pertinent information to be obtained at lower cost than the classical trial-and-error approach. Furthermore, better cost efficiency can be achieved when interpreting capillary rheometer results in terms of processing and selecting the best operating conditions with respect to material flow properties. 

Some capillary rheometers (such as the Monsanto Processability Tester") are equipped to directly measure the die swell of the rubber compound after it exits the die. This is done with special optical die swell detectors. Running die swell is measured at... 

Traditional measurements reported by various investigators have been made on extrudates either with a micrometer or by weight per unit length. The Monsanto Industrial Chemicals Co. (Akron, OH) has introduced an automated capillary rheometer (the Monsanto Processability Tester) which employs an extrudate swell detector based on interaction with a scanning laser beam positioned immediately below the capillary die exit. This enables measurement of the running die swell. 

Figure 2. Schematic diagram of Monsanto Processability Tester (MPT).

The majority of published work on extrusion behaviour deals with compounded stock. Those papers reporting work on raw rubbers have usually been on the use of capillary rheometers to determine extrusion properties at higher shear rates than are possible with Mooney viscometers. Capillary rheometers are, in principle, quite simple to use, and the application of electronic, minicomputer and laser technology has reduced the operation and data analysis to a routine task. There are no standard ASTM or other test procedures, but under a specific set of conditions, once a material is characterized, the data can be used as standard for comparison of all subsequent batches. It is readily possible to characterize a raw rubber by an extrusion experiment to determine the viscosity/shear rate curve, extrudate swell, and stress relaxation.Both Sezna and Karg have shown how the Monsanto Processability Tester (MPT), a modified, computerized extrusion rheometer, can be used in predicting mixing behaviour. The MPT (shown schematically in Fig. 7) is a most versatile instrument. It has a larger than conventional barrel for minimal pressure drop in the barrel, a pressure transducer at the entrance to the orifice, a microprocessor system, and a laser device for... 

Fig. 7. Schematic drawing of Monsanto Processability Tester. Capillary rheometer with die swell detector.

The rheological behaviour of NBR and of NBR compounds loaded with carbon black is discussed by Nakajima and Collins.According to these authors the viscoelastic behaviour of amorphous rubbers can be described by a master curve (temperature/time, pressure/time, stress/time) which permits conclusions as to the processing behaviour of these rubbers on mixing mills. Bittel has reported that the Monsanto processability tester is able to distinguish between NBR grades which are equal in Mooney viscosity, but have different shrinkage tendencies, and also that it is able to indicate the state of mix. 

High shear testing machines such as the Wallace rapid plastimeter, the Monsanto processability tester and extrusion viscometers may better differentiate between natural rubber and polyisoprene, and even between polyisoprenes from different suppliers. None of these machines alone, however, will accurately predict the behaviour of the polymer or batch for all processing operations. Thus Mooney viscosity plus practical experience remain the principal factors in categorising factory processing. 

The only stress relaxation tester commercially available is the Rapra/Monsanto SRPT (Stress Relaxation Processability Tester), although others have been described in the Uterature. The rationale behind this development is that viscosity alone is not able to predict rubber processability some elasticity characteristics must be taken into consideration. Further, since most processing problems are related to memory or relaxation effects, it makes sense to consider using stress relaxation. However, once again, this technique has found most application with compounded stock. It is claimed that the technique is sensitive to small variations in molecular weight distribution. Experience so far indicates that it may not be sensitive enough to differentiate levels of processability within grades. 

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