Mooney tester

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. 

Despite these acknowledged limitations it is still regarded, by the industry as a whole, as a most useful processability tester. The value of the Mooney test for assessing raw rubbers is as a benchmark. It is the basis for current specifications and is the major parameter for empirical control of polymerization reactions. 

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... 

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. 

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