Modeling Flow and Morphology in Extrusion-Based 3D Printing of Semicrystalline Polymers

Fused Granular Fabrication (FGF) is widely used in polymer manufacturing to produce complex geometries directly from digital designs. However, the resulting material properties and dimensional stability of the printed part remain difficult to control, especially for semicrystalline polymers. Delivering consistent, high-performance parts requires models that link molecular structure to rheology and crystallization kinetics and capture their coupling during printing, enabling rational process design.

This work develops a multiscale model that couples rheology with crystallization along the print path to predict semicrystalline morphology from material and process parameters. The framework integrates: (i) a continuum-level model of melt extrusion with a subsequent uniaxial extension of the crystallizing polymer filament between the nozzle and a rotating collector; (ii) a mesoscale constitutive model that captures the two-way coupling between crystallization kinetics and the evolving rheology of the crystallizing melt; and (iii) a spatiotemporal description of the local morphology.

At the mesoscale we employ the crystallizable discrete slip-link model (cDSM) to represent the rheology of semicrystalline polymers during crystallization. The cDSM is updated based on the level of crystallinity, provided by a dedicated kinetics model. To model crystallization kinetics, we adopt the Schneider equations which evolve the number density, characteristic length, area, and volume of growing crystalline domains, as well as total crystallinity, as functions of position and time. Depending on temperature and flow, two morphologies are commonly observed: (i) isotropic spherulites and (ii) anisotropic shish-kebab structures comprising a flow-aligned elongated core (“shish”) decorated with chain-folded lamellae (“kebabs”) that grow normal to the flow.

Finally, the predicted morphology is used to synthesize two-dimensional scattering intensity patterns, which are compared against experimental Small-Angle X-ray Scattering data to validate the model.