Plateout is an extrusion defect that has caused formulators and processors major
problems throughout the history of poly(vinyl chloride) (PVC) processing. It is an
unwanted deposit that forms on the die, calibration and degassing sections of extrusion
equipment that can cause unacceptable streaking and scoring on the final product through
continued deposition. Extrusion companies must therefore periodically strip their
equipment to stop excessive formation, but the downtime associated with this cleaning
procedure is obviously costly.
The purpose of this thesis is to develop an understanding of the lubrication mechanisms
within lead stabilised rigid PVC compounds using polyethylene (PE) wax as a source for
external lubrication, in order to make formulation recommendations to minimise
Plateout samples supplied by commercial processors were analysed to identify deposit
prone additives. Of the techniques investigated, laser ionisation mass analysis (LIMA),
gas chromatography/mass spectrometry and infra-red spectroscopy by the diffuse
reflectance infra-red Fourier transform (DRIFT) method identified calcium carbonate,
titanium dioxide and dibasic lead phosphite as the bulk of die plateout.
Additive interactions were investigated by differential scanning calorimetry (DSC) and
hot-stage microscopy. Majority of the additives in a lead stabilised window profile
formulation did not interact, but molten calcium stearate and normal lead stearate did not
recrystallise when mixed together.
To simulate commercial processes, a laboratory-scale twin-screw extruder equipped with
a plateout sensitive die was used to analyse window profile formulations containing
various homopolymer grades of PE wax and oxidised PE or high-density PE lubricants.
Structural properties that influence physical properties such as melting point and
viscosity were related to their tendency to plateout. The influence of calcium stearate and
normal lead stearate dosage on lubrication and plateout performance was also
investigated using experimental design.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
Honeywell Speciality Wax & Additives and Chemson Polymer-Additive AG