Rubber processability is largely dependent on its viscosity parameter. Viscosity of elastomeric material can be defined as inverse of its plasticity or simply resistance to flow. Viscosity is dependent on temperature and its molecular weight and its distribution. The most commonly used method is Mooney viscosity determination. Tests are carried out on Mooney rotating disc viscometer. Torque is measured on axis of the shearing disc.
In addition to Mooney viscosity, the measurement may also indicate Delta Mooney, scorching and stress relaxation. Delta Mooney (rubber processability characteristics) is the difference between two Mooney viscosity values measured in two time intervals at preset temperature. Delta Mooney (ΔM) is defined as between the viscosities measured in minute 15 and in minute 1.5 from the rotor start. Stress relaxation test may determine elastic and structural-viscosity properties of rubber. Relaxation is determined as following: after viscosity measurement has been completed, residual torque (viscosity) is measured on switched-off rotor in second 30 and 60.
Another important parameter for prediction of processability is its Rheo characteristics. It enables a compounder to select correct curing package for a compound.
Mooney & MS: ASTM D1646, ISO289
Delta Mooney: ASTM D3346
Rheometric Properties: ASTM D5289, ISO6502