Extensional rheological investigation of biodegradable polylactide-nanographite platelet composites via constitutive equation modeling

The focus of this research is on linear and nonlinear melt rheological investigations of polylactide (PLA) and nanographite platelet (NGP) based bionanocomposites. The linear steady and dynamic shear viscoelastic behaviors of the samples is analyzed to study the effects of NGP filler contents on the rheological properties of the composites at terminal and zero-shear viscosity regions whilst the nonlinear shear behaviors are investigated to predict and validate the extensional rheological properties of neat PLA and PLA/NGP composites. Uniaxial extensional measurements are performed to probe the impacts of nanofiller contents along with extensional strain rates on linear viscoelastic envelope (LVE) and nonlinear elongational strain hardening behaviors of the samples. The modeling of strain-hardening behavior of neat PLA and its composites is accomplished by means of analyzing their dynamic moduli, steady shear viscosity, relaxation spectrum and damping function based on Papanastasiou-Scriven-Macosko-Luo-Tanner (PSMLT) form of Kaye-Bernstein-Kearsley-Zapas (K-BKZ) constitutive equation.