The physical properties of rigid PVC products can be related
to formulation, preblending and processing characteristics. A fuller
understanding between these interrelations involves investigation of a
complete processing system from powder additives to end product. A
knowledge of these relationships can lead to a optimisation of
formulation aspects and processing conditions.
Fillers and lubricants have often been incorporated into PVC
compounds on a empirical basis, however in this investigation a wide
range of compositions were carefully chosen and included a calcium
carbonate filler at levels up to 40 phr. These were dry blended and then
characterised by bulk density and filler content. The premix was
processed using an instrumented twin screw extruder, a wide processing
'window' being chosen to provide a product range with large variations
in fusion level. Further compounds were extruded, incorporating two
different impact modifiers.
The extrudates was assessed for degree of fusion by
differential thermal analysis, solvent immersion and microscopy. The
filler distribution, surface appearance and residual grain structure was
observed using a range of microscopy techniques and the results related
to operating conditions. A measure of fusion level was obtained from
mast er curves of heat of fusion versus processing temperature'. The
filler level did not influence the degree of fusion.
Various mechanical properties of the pipe were assessed.
Impact performance was measured using an instrumented falling weight
impact tester and the subsequent fracture behaviour depended on the
composition and fusion level. Impact properties were dramatically
reduced at a critical filler content and ductile-brittle transition
temperatures were obtained for the extrudates by testing at low and high
temperatures. Tensile properties did not follow the trends observed
during impact testing but indicated a progressive reduction in tensile properties with increasing filler content.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.