Non-isothermal viscoelastic polymer film casting process

Although polymer films are widely used in chemical applications, their flow and tensile hardening behaviors are still not well understood due to the complex non-isothermal process rheology. In this paper, we investigate the effects of die structures, process conditions, and physical parameters on non-isothermal viscoelastic polymer film processing through numerical simulations, aiming at optimizing the final film products. The viscoelastic Phan-Thien-Tanner constitutive equation is utilized to describe the rheological properties of polymers. Focusing on the effects of polymer strain hardening on the neck-in phenomenon and edge bead effect, the thickness profile of polymer films and viscoelastic stress distributions have been studied. Our results demonstrate that increasing the air gap or reducing the die width can effectively mitigate the edge bead effect and neck-in phenomenon. Decreasing chill roll speed and increasing axial velocity at the die lead to a higher level of tensile hardening, thus mitigating neck-in. Additionally, lower heat transfer coefficients and higher Deborah numbers decrease the tensile hardening level. Higher viscosity films are more susceptible to flow instability due to localized stress concentrations. This work provides a deep understanding of flow instability and tensile hardening behavior with film processing and contributes to the optimization of polymer films for chemical applications.