The research evaluated the means in which mild variations in the
polymer properties could be modified during the mixing process so
that the final mixed compound met the desired rheological parameters.
The initial work developed a model to measure the viscosity of the
material in the internal mixer during the mixing process. The model
assumed the mixer could be treated as two concentric rotary viscometers.
The model had a rotor speed dependence which was caused by
the assumption not being valid.
However, this led to the work continuing in a modified form. It was
felt that at a given rotor speed and temperature the torque measured
on the rotors would be proportional to the viscosity of the material.
This was found to be correct and therefore work continued using this
principle. Programs were developed for internal mixers with variable
speed rotors and fixed speed rotors. The programs were evaluated using
natural rubber with different viscosities and were found to be capable
of modifying the polymers to obtain a final mixed compound to a target
viscosity. The control program was also used to mix a series of batches
at different processing conditions. The rheological properties
of these batches were compared to a similar group mixed to a specification
based on unit work. The result was the control system gave more
rheologically uniform material.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy at Loughborough University.