Delta Mooney

The Delta Mooney (A Mooney) test is an extension of the Mooney used on empirical grounds as a general indication of processibility for non-pigmented oil extended emulsion styrene/butadiene rubber. It quantifies the changes that occur in Mooney viscosity with time, either as the difference between viscosities recorded at two specified times or as the difference between the minimum viscosity recorded immediately after the commencement of the test and the subsequent maximum viscosity. Several alternative Delta Mooney values are defined depending on the times, whether minimum/maximum viscosity difference is used and whether or not the sample has been massed on a mill. Procedures for Delta Mooney are standardised in ISO 289-341, BS 903 Part A58-142 and in ASTM D334643. 

ISO 289-3, 1999, Determination of the delta Mooney value for non-pigmented, oil extended, emulsion polymerized SBR. 

ASTM D3346, 2003. Processibility of emulsion SBR (styrene-butadiene Rubber) with the Mooney viscometer (Delta Mooney). 

Figure 3 shows that the delta Mooney indexes show an abrupt change from negative to positive values in the same region. Thus, there is a clear relationship between the onset of dominant crosslinking and processability. The deterioration in physical characteristics is not coincidental with the formation of gel since, in both of these examples, the gel point occurs at conversions greater than 60%. 

Figure 3. Delta Mooney indexes (no oil) as a function of conversion for series A (a) and series B (O) (3)...

There have been a number of developments of the Mooney test. The generally useful and accepted one has been the Delta Mooney test, which has achieved the status of an ASTM test, and is well recognized within the industry. Other techniques which have been reported are Mooney recoil, initial Mooney torque peak (PMT), and variable-speed Mooney tests. 

The Delta Mooney is defined as the difference between two Mooney viscosity readings, either at two fixed times or between the early trough (b) and the subsequent maximum (c), as shown in Fig. 6. 

By 1976, a variety of tests had therefore become available, many developed in Australia, and these were subjected to what might be considered a definitive comparison by Mills and Giurco, also working in Australia. They compared Delta Mooney, BIT tests, die swell peak times and t points. Table 1, taken from Mills and Giurco s paper, gives the correlation coefficients, not only between some of the processability tests but also with a number of molecular parameters. (A value of 1 indicates a perfect positive correlation, a value of 0, zero correlation and a value of —1, perfect negative correlation.)... 

The mixing of acrylate elastomer compounds was investigated with the aim of reducing mixing time. Compounds were mixed upside down or right side up at low rpm or high rpm in a Farrell BR1600 (1.6 litres) Internal Mixer. The Mooney viscosity and tan delta were used to determine the processability of the compounds. 

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