There are usually three methods for determining the plasticity of raw rubber and mixed rubber: compression method, rotational torque method and extrusion method. They all need to be carried out at a constant temperature because plasticity changes with temperature.
Compression method
This type of determination method is commonly used in three methods: Williams method, Wallace rapid plasticity method and Dever plasticity method.
1. Williams method
Under constant temperature and constant load, the plasticity is evaluated based on the change in sample height after a certain period of time. Preheat the cylindrical sample of Φ=16mm, h0=10mm at T=70±1℃ or 100±1℃ for 3min, compress for 3min, remove the load and take out the sample to recover for 3min at room temperature, measure the compression deformation of the sample height and the deformation after removing the load, and calculate the plasticity P.
h0 — original height of the sample, mm; h1 — height of the sample after compression for 3 minutes, mm; h2 — height after recovery for 3 minutes, mm
If the sample is an absolute fluid, that is, h1=h2=0. P=1;
If the sample is an absolute elastic body, that is, h2=h0. P=0;
Raw rubber and mixed rubber are viscoelastic bodies, and their plasticity is between 0 and 1. The larger the value, the greater the plasticity.
2. Wallace rapid plasticity method
The principle is the same as the Williams method, and the change in film thickness under constant temperature, constant load and constant time is used to represent plasticity.
This method is easy to operate and is often used for rapid inspection in industrial production.
3. Defer method
It is represented by the load value required when the sample is compressed to a specified height at a constant temperature and a constant time.
Rotational Torque Method - Mooney Viscosity Method
The principle is: under certain temperature, time and pressure, the plasticity of the rubber compound is determined according to the torque applied to the sample when it is deformed between the active surface (rotor) and the fixed surface (mold cavity).
During the test, the sample is placed in the mold cavity as required, preheated at 100°C for 1 minute, and the rotor is rotated at 2r/min for 4 minutes. The measured torque value is the Mooney viscosity, which is generally expressed as , and L indicates the use of a large rotor (diameter of 38.1±0.03mm).
The Mooney viscosity method is faster and simpler than the compression method, and the dynamic fluidity it represents is closer to the actual process conditions.
Extrusion method
Use a capillary rheometer for determination.
Under certain temperature, pressure and die shape, the extrusion speed of the rubber compound is measured with a capillary rheometer within a certain period of time, and the plasticity is expressed in milligrams extruded per minute.
Advantages: This method is similar to the working conditions of the extruder die, and can provide a more specific understanding of the effect of the plasticity of the mixed rubber on the extrusion performance.
Disadvantages: The extrusion method requires more rubber material, and the sample must be preheated for a longer time.
