Hi Sandan,

Please see the attached article,

This paragraph adapted from it

The actual Mooney viscosity is the value preceding the specified time of reading. The disk-shaped rotor of Mooney viscometer does not induce a viscometric flow field due to significant edge effects, yielding shear stresses significantly higher than expected. It is why the Mooney viscosity is given in the Mooney units (MU).

Hope it helps

Amin

In Mooney Viscometer testing, it is generally torque is being measured. MI indicates the initial torque, while starting the analysis and ML is generally represented as ML(1+4) @ 100 deg C, which indicates the final torque @ 100 deg C after 4 minutes of testing with 1 min preheating time using large rotor.

Thank you. Please tell me whether i should take MI or ML for the viscosity value? My test is to check viscosity of a compound when it is in normal condition(not processing)

You should concentrate on ML value. MI depend on nature of the compound and the temperature it is stored before analysis. MI will not give any suitable information. Now ML at what temperature you will measure that will depend on your project objective. 100 deg C ML value generally indicates the processing behaviour of the compound.

Please consider this situation-

I have a compound which is stored in room conditions. After about 24-36hr compound taken to assemble to another compound by using tackiness property. So im going to check other properties like viscosity of the compound at that time.

ML is taken in elevated temperature to get an idea about processing. But my compound is not processing. Therefore shouldn't i take MI value?

Thank you

Generally No. Initial Torque is due to thixotropic nature of the polymeric compound and it will always show a high value. If all your compounds are kept under same temperature and time, MI can only give difference in thixotropic behaviour of different compounds depending on the Polymer nature, filler dose, and other high volatile ingredients.

If you are measuring the tack at room temperature, you cannot correlate any value of MI or ML with actual tack force.

Thank you for descriptive explanation.

Can please elaborate this logic.

Compound viscosity is correlate with molecular weight of the molecules, Molecular weight depends on molecular length, Molecular length is correlate with tack. 

Therefore ultimately viscosity of the compound has some kind of correlation with tack.

Thanks for your question!

Any polymer, in virgin state and in compound state, behaves differently.

Your explanation about molecular weight, distribution, chain length etc. all are correct when polymer is in raw state.

However, as soon as it is compounded, composite behaviour cannot be explained only by Mooney viscosity. Mooney viscosity is not as simple as we think about.

When polymer is compounded, what is the interaction of the polymer chains with filler (bound rubber, occluded rubber etc), how plasticisers are interacting with polymer chain, how many small chain length fractions are present in the composite are all very complex. So Mooney viscosity is not at all any true characteristics of the compound. It is only a guidelines for compounders, to get an idea about the preliminary processing of the compounds.

So, I doubt, any correlation of viscosity of the compounded rubber with its tack behaviour.

Thank you again. Tack is basically a property which is molecules pass through each other and adhere to each other. So there should be an correlation between viscosity and tack.

Higher the flowbility of molecules, higher the tack. (a logic)

If it's not do you mean that other compounding ingredients interfere with above logic?

Hi,

Mooney viscosity is a property for elastomers and rubbers and defined as the shearing torque resisting rotation of a rotor disk embedded in rubber or elastomer within a cylindrical cavity. it is measured by using Mooney viscometer and calculated from the torque on the rotating disc of the machine. MI is the initial Mooney viscosity whereas ML is the minimum Mooney viscosity value in the last 30 seconds before the rotor stopped. More information about this, you can follow ASTM D 1646 standard.

Hi Sandun,

Please see the attached file.

Thank you very much.

Can you please explain this in attached file? 

"I think that you can correlate the viscous phase S’ at initial

viscosity to tackiness of rubber compound"

@watcharin Sainumsai Please explain. Thank you

ASTM D 1646, determines viscosity of both raw and compounded rubber.Viscosity and scorch characteristics are very important properties of rubber compounds.

Viscosity and its Significance

The key to mixing, whether it is in an open mill or in an internal mixer, is to do it at the

right viscosity to ensure adequate shearing within the rubber matrix. This will help in

the distribution of ingredients into the raw elastomer or force the elastomer into microscopic spaces of each filler particles. Unfortunately, these two requirements are

conflicting. If we keep the rubber viscosity low, incorporation and distribution of ingredients can happen fast, but the dispersion could be poor. Otherwise, if we keep the

viscosity high, the incorporation takes a longer time.

Hi to all

can anyone advise me how to increase Mooney viscosity of SBR rubber compound of hardness 65+/-5 ?i need Mooney viscosity within 70-80 at ML(1+4)100'C. Now i am getting Mooney viscosity 57.

Tack of rubbery systems is not linked directly to rubber viscosity. Fully cured rubber systems can be tacky while having infinite Mm (e.g. Pressure Sensitive Adhesives). In PSA, tack is related to the Dahlquist Criterion so to the ease your rubbery system will deform locally under existing stress to adhere the surface and create VDW bonds. lLw rubber modulus gives you one criteria for tack. The other is obviously related to the surface tension. In rubber adhering to rubber, the adhesion will involve, in addition to the short time tack, the dangling rubbery arms migrating from their initial phase to the other rubber (if miscible).