Mooney test

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. 

Mooney viscosity is used by many synthetic rubber manufacturers as the single most important measure of their polymer s processing behavior. The Mooney test conditions that must be specified arc as follows ... 

Mooney test temperature. C Mooney running time, min... 

The Mooney test, which is used routinely to assess the processability of both raw stock and compounds,relates to average molecular weight (Mw). However, as the molecular weight distribution has a considerable effect on the processing behaviour of rubbers of the same Mw, it is sometimes inadequate.The Mooney test makes no estimate... 

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. 

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. 

One of the difficulties in the rubber industry is that many of the established and accepted test methods are empirical. An example of this is the Mooney test. As a result there is no such thing as an absolute value of the Mooney of a sample of rubber, in the way that there is an absolute value of its density. Therefore, careful calibration of the instruments, the use of reference, or standard, materials and monitoring the performance of the equipment with control charts, are essential. 

Carboxylated latexes usually are made by hot polymerization processes characterized by high conversion. They tend to have high gel content and very high Mooney viscosities. As a consequence the Mooney test is not often used to characterize them. 

The importance here is to recognise the limitation of the test. In addition to the nonequilibrium temperature of the test and the complex distribution of strain, the curve is measured at 2 rpm, which is an arbitrary time-scale. The material behaviour may be different at other time-scales this situation is exactly like a blind man touching an elephant . In addition, at this time scale the Mooney rheometer is not very sensitive to a small difference between the gum rubbers. Therefore, this method is for the screening and catching only a gross difference among the samples. The Mooney test is performed for the specification in any event, and therefore, it is proposed here to pay attention to the shape of the curves also. 

In TPE, the hard domains can act both as filler and intermolecular tie points thus, the toughness results from the inhibition of catastrophic failure from slow crack growth. Hard domains are effective fillers above a volume fraction of 0.2 and a size <100 nm [200]. The fracture energy of TPE is characteristic of the materials and independent of the test methods as observed for rubbers. It is, however, not a single-valued property and depends on the rate of tearing and test temperature [201]. The stress-strain properties of most TPEs have been described by the empirical Mooney-Rivlin equation... 

In order to test this concept a series of compounds was prepared in a 5 L Shaw Intermix (rubber internal mixer, Mark IV, Kl) with EPDM (Keltan 720 ex-DSM elastomers an amorphous EPDM containing 4.5 wt% of dicyclopentadiene and having a Mooney viscosity ML(1 +4) 125°C of 64 MU 100 phr), N550 carbon black (50 phr), diisododecyl phthalate (10 phr), stearic acid (2 phr), and l,3-bis(tert-butylperoxy-isopropyl)benzene (Perkadox 14/40 MB ex Akzo Nobel 40% active material 6 or 10 phr). A polar co-agent (15 phr) was admixed to the masterbatch on an open mill and compounds were cured for 20 min at 180°C in a rheometer (MDR2000, Alpha Technologies). The maximum torque difference obtained in the rheometer experiments was used as a measure of... 

The B-series of silica samples were also blended with rubber and the compound formulation is shown in Table 17.6. The uncured gums were then tested according to ISO 5794-2 1998. The uncured samples were tested using a Mooney viscometer and an RPA, which measures the dynamic mechanical properties as the samples cure. Figure 17.7 shows the results of these two tests for the Mooney viscosity at 100°C, storage modulus, loss modulus, and tan 8. 

In all of the rheometer testing of the uncured compounds, the commercial silica AZ showed the highest values with the B1 and B3 samples having the highest values among the B-series silica samples. The Mooney viscosity at 100°C increases as the number of particles in the aggregates increases. The same compounds were cured and tested, measuring tensile properties, tear resistance. 

Mooney viscometer is also used to measure the time it takes, from initial exposure of the compound to a particular temperature, to the time of onset of cure at that temperature [2]. This is known as the scorch time. Scorch time is an important parameter to the rubber processor, as a short time may lead to problems of premature vulcanization. As the test is taken past the onset of cure, the rotor tears the cured rubber, and therefore this device cannot be used to investigate rheological properties after the scorch time. 

Over the twentieth century, the mbber industry has developed special rheometers, essentially factory floor instmments either for checking process regularity or for quality control purposes, for instance, the well-known Mooney rheometer (1931), the oscillating disk rheometer (1962), and the rotorless rheometer (1976). All those instmments basically perform simple drag flow measurements but they share a common feature During the test, the sample is maintained in a closed cavity, under pressure, a practice intuitively considered essential for avoiding any wall slip effects. Indeed it has... 

Number-average molecular weights are Mn = 660 and 18,500 g/ mol, respectively (15,). Measurements were carried out on the unswollen networks, in elongation at 25°C. Data plotted as suggested by Mooney-Rivlin representation of reduced stress or modulus (Eq. 2). Short extensions of the linear portions of the isotherms locate the values of a at which upturn in [/ ] first becomes discernible. Linear portions of the isotherms were located by least-squares analysis. Each curve is labelled with mol percent of short chains in network structure. Vertical dotted lines indicate rupture points. Key O, results obtained using a series of increasing values of elongation 0, results obtained out of sequence to test for reversibility. 

The name Mooney is often used in referring to the value obtained on the Mooney viscometer. Mooney Scorch Test... 

A development of plasticity determination by means of the Mooney viscometer. The same instrument is used but the temperature of operation is higher and the test is continued until the sample vulcanises. A curve of Mooney reading against time is drawn, from which the scorch and cure characteristics are estimated (BS 903-A58). 

The determination of the ability of a rubber compound to withstand scorching. See Mooney Scorch Test. 

An early cure instrument which combined in one operation the functions of a Mooney viscometer and of a curometer or vulcameter, i.e., it measures in one quick test the plasticity (viscosity) of the (uncured) mix, its scorch time and cure rate. Now superseded by instruments such as the moving die rheometer. 

Finally, we developed testing procedures that included Brabender studies and the use of high temperature Mooney machines, and our program began to move. We were able to correlate with production sheet extrusion conditions which enabled us to make our numerous product development changes rapidly on a small scale. 

The scorch behaviour of compounds is generally studied with the help of a mooney viscometer. The test is usually conducted at temperatures encountered during processing of the rubber stock. Typically this is in the temperature range of 250°F to 275°F. From a chart of mooney units vs test time, the time required for the... 

In all the above methods, it is necessary to cure specimens of test samples for each of a series of curing times and then perform the desired test on the vulcanizate. However, in the test for continuous measurement of vulcanization complete information could be obtained with saving in time. The mooney viscometer test approaches this objective. However a weakness of the mooney viscometer test is that the test is completed before a measurable modulus value after the scorch point has been obtained. This is because the test sample is destroyed after the induction period is passed due to tearing by continuous rotation of the rotor whether small or large. To overcome this deficiency and to provide a total cure curve for the entire vulcanization cycle, a series of instruments called cure meters was developed. In each of these instruments the stiffness or modulus of the compound was chosen as parameters for vulcanization continuously. The Vulkameter developed by Bayers, Germany was the first of the cure meters developed. 

By weighing the first and last passes, the mill homogenization procedure is also use to measure volatile matter content. Samples are then allocated to such tests as are required in accordance with ISO methods. In particular, it is specified that volatile matter is measured according to the oven method of ISO 24813. Apparently, we have two measures of volatile matter Mooney viscosity and plasticity retention index are measured as discussed later in the chapter. Although the title and the procedure indicate that the method is intended for raw rubber, it is also specified that vulcanization characteristics are measured. 

For synthetic rubbers, the mill homogenization is generally omitted, although it is specified as an alternative where the appropriate evaluation procedure requires it before measuring Mooney viscosity. Different conditions are given for specific polymers. The mill method of ISO 248 for determining volatile matter is specified but the oven method may be substituted if the material sticks to the mill rolls. Regardless of which volatile matter method is used, the mill procedure is required to dry samples for any chemical tests needed - unless this is not possible. To the uninitiated at least, this is not a model of clarity. Vulcanization characteristics are determined for synthetic rubbers, but not plasticity retention index. 

A number of plastimeters of this type have been used for rubbers, often for research purposes, but one instrument, the Mooney viscometer, gained virtually universal acceptance and has been extensively used for routine quality control purposes for several decades. The principle of the Mooney is shown in Figure 6.4 together with several other possible geometries for a rotational instrument. The rotor turns at a constant rate inside a closed cavity containing the test piece so that a shearing action takes place between the flat surfaces of the rotor and the walls of the chamber. The torque required to rotate the rotor is monitored by a suitable transducer. 

Where 50M is the Mooney viscosity, L indicates the use of the large (i.e. standard) rotor, 1 is the preheating time in minutes, 4 is the reading time in minutes and 100°C is the test temperature. 

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