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Resin Particles as Flow Units in Poly(vinyl Chloride) Melts
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1967
Year
EngineeringMechanical EngineeringVinyl ChlorideResinsPolymersEntanglement DistributionPolymer ProcessingPolymer PhysicRheologyPolymer ChemistryMaterials SciencePolymer BlendMelt FlowPolymer MeltMechanical PropertiesResin ParticlesPolymer SciencePolymer CharacterizationPolymer PropertyPolymer Modeling
Flow behavior of PVC may be influenced by particle structure and the presence of particle boundaries acting as discontinuities in the entanglement network, whose elimination extends the network via diffusion. The authors measured PVC melt flow at shear rates of 10–5000 s⁻¹ using a constant-load capillary rheometer. The study found that apparent viscosity, swelling, and extrudate roughness varied with sample history, not molecular weight, and that intact resin particles persist during melt flow, causing particle slippage; when particle identity is lost, flow becomes more viscous and elastic, highlighting the role of entanglement distribution in PVC rheology.
The melt flow of a variety of poly(vinyl chloride) (PVC) samples was studied at shear rates of 10–5000 sec−1 in a constant-load capillary rheometer. Pronounced differences were observed in apparent viscosity, post-extrusion swelling, and extrudate roughness, depending upon sample preparation and previous history. These differences could not be correlated with molecular weight, molecular weight distribution, or other parameters of molecular structure. A possible explanation was suggested by certain correlations between flow behavior and particle structure or state of fusion. Fracture-surface electron photomicrographs of molded or extruded PVC samples provided clear evidence that resin particles, as formed during polymerization, can maintain their identity and shape during melt flow processes. The melt flow of PVC under some conditions thus must involve the slippage of resin particles past one another, rather than a homogeneous deformation of the melt. Thermal and mechanical history severe enough to obliterate particle identity in fracture-surface photos also shifts melt flow behavior toward higher apparent viscosity and greater melt elasticity, due to a reduction of particle slippage and a more homogeneous flow process. Particle boundaries may be viewed as discontinuities in an entanglement network, and elimination of boundaries as an extension of the network by molecular diffusion. On this basis, our results demonstrate the important contribution of entanglement distribution to polymer melt rheology.