Extrudate Swell Behavior in Polymer Processing
Summary
Extrudate swell refers to the tendency of a polymer melt to expand in cross‐section on emerging from a die, a phenomenon driven by the recovery of elastic stresses accumulated during flow through the confined geometry. The magnitude of swell is influenced by the viscoelastic character of the polymer, the temperature profile at the die wall, the rate of deformation within the channel and the die exit geometry. Accurate prediction and control of swell are vital in applications ranging from film and fibre extrusion to additive manufacturing and medical tubing, where dimensional precision and surface quality are paramount. Modelling strategies combine constitutive equations that capture non-Newtonian rheology with numerical methods for free-surface evolution, while experimental techniques employ high-speed imaging and in situ measurement of strand dimensions. Advances in die design, real-time feedback control and multi-scale simulation have converged to offer pathways for minimising geometric error and optimising productivity. Understanding extrudate swell thus underpins both fundamental rheology and the practical realisation of complex polymer products on an industrial scale.
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Extrudate Swell Behavior in Polymer Processing publication trend
The graph below shows the total number of articles in extrudate swell behavior in polymer processing across all publications each year (not limited to Nature Index journals).
Technical terms
Extrudate swell: Expansion of a polymer strand’s cross-section upon exiting a die due to elastic stress recovery.
Viscoelasticity: Material behaviour exhibiting both viscous flow and elastic deformation under applied stress.
Constitutive model: Mathematical description of material stress–strain relations, such as Giesekus or Phan-Thien Tanner models.
Weissenberg number: Dimensionless ratio of elastic to viscous forces in flow, defined by deformation rate and relaxation time.
Shear-thinning: Reduction in viscosity with increasing shear rate, common in polymer melts.
Swell ratio: Dimensionless measure of extrudate expansion, calculated as post-die diameter divided by die exit diameter.
References
- Improved Optimization of a Coextrusion Die with a Complex Geometry Using the Coupling Inverse Design Method. Polymers (2023).
- Experimental and Numerical Investigation of the Die Swell in 3D Printing Processes. Micromachines (2023).
- Transient 3D finite element method for predicting extrudate swell of domains containing sharp edges. Journal of Non-Newtonian Fluid Mechanics (2019).
- Die shape optimization for extrudate swell using feedback control. Journal of Non-Newtonian Fluid Mechanics (2021).
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