The processing characteristics of PVC compounds play a major
role on the ability of the equipment to control the final properties
of the product. Therefore, information on the effect of processing
conditions on such characteristics. and its influence on the final
properties can lead to an optimization of the extrusion process.
In this work. a statistically based experimental design was
used in order to investigate the role of the operating conditions
on the extrusion of a simple lead based PVC formulation. Both a
single and a twin screw extruder were used - they were instrumented,
and data collected by computer. A die was designed for the
formulation used. with both shear and extensional flows being taken
into account. These experiments produced both core samples along
the screw(s) and final products with varying states of fusion.
The fusion mechanism on processing was monitored with the help
of electron and light microscopy techniques. thermal analysis and
density measurements. In both types of extruders the primary
particles were found to fuse well before the grains, but the overall
mechanism differs for each type of machine.
An experimental technique was developed for the study of the
Residence Time (RT) and Residence Time Distribution (RTD) of the
material in the processing equipment. These functions were related
to the operating conditions and compared with the available models
The degree of fusion of the processed products was assessed by
rheology and thermal analysis. A range of mechanical properties,
relevant to the general end - use of rigid PVC formulations. was
analysed: flexural. tensile and impact properties were found to be
directly related with fusion level. Hardness, measured using a
newly developed apparatus. proved to be a potential technique for
the degree of gelation of PVC formulations.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.