Modeling non-linear rheology of PLLA: comparison of Giesekus and Rolie-Poly constitutive models

ABSTRACT

Rheological models for biobased plastics can assist in predicting optimum processing parameters in industrial forming processes for biobased plastics and their composites such as film blowing, or injection stretch-blow molding in the packaging industry. Mathematical descriptions of polymer behavior during these forming processes are challenging, as they involve highly nonlinear, time-, temperature-, and strain-dependent physical deformation processes in the material, and have not been sufficiently tested against experimental data in those regimes. Therefore, the predictive capability of two polymer models, a classical Giesekus and a physically-based Rolie-Poly, is compared here for extensional and shear rheology data obtained on a poly(L-lactide) (PLLA) across a wide range of strain rates of relevance to those forming processes. Generally, elongational and shear melt flow behavior of PLLA was predicted to a satisfactory degree by both models across a wide range of strain rates (for strain rates 0.05–10.0 s⁻¹), within the strain window up to 1.0. Both models show a better predictive capability for smaller strain rates, and no significant differences between their predictions were found. Hence, as the Giesekus model generally needs a smaller number of parameters, this class of models is more attractive when considering their use in computationally demanding forming simulations of biobased thermoplastics.

KEYWORDS:

• Biobased plastics
• PLLA
• rheology
• constitutive modeling
• Giesekus and Rolie-Poly models

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research has been financially supported by the National Science Centre (Poland) through Grant No. [DEC-2011/01/B/ST8/06492] within the programme OPUS, and Maria Skłodowska- Curie RISE action (691238).

Notes on contributors

Maja Stępień

Maja Stępień is a former PhD student in the Centre of Molecular and Macromolecular Studies of the Polish Academy of Sciences in Łódź.

Gabriel Y.H. Choong

Gabriel Choong is a Research Fellow with the Composites Research Group at the University of Nottingham. His research interests are polymer processing and characterisation of solid-state and melt-state properties of polymeric materials.

Davide S.A. De Focatiis

Davide De Focatiis is an Associate Professor at the University of Nottingham. He is a member of the Composites Research group and of the Department of Mechanical, Materials and Manufacturing Engineering. His main research interests are in rheological and solid-state properties of polymeric materials.

Łukasz Figiel

Łukasz Figiel is an Associate Professor at the University of Warwick – he is a core staff in the International Institute for Nanocomposites Manufacturing (IINM) in WMG Department of the University of Warwick, and in the Warwick Centre for Predictive Modelling (WCPM). His main research interests are in multiscale modelling of multifunctional materials.