Rheology of wood plastics melt, part 3: NonLinear nature of the flow

The nonlinear rheology of HDPE/maple melt in both shear and extensional flow was studied using a rotational parallel plate rheometer and the hyperbolic die technique, respectively. Nonlinear features were found in oscillatory shear tests at strain levels far below the values for neat polymer melt. The shear stress relaxation tests revealed the time-strain factorizability, and the damping function was found to follow the sigmoidal-type relation. The nonlinear nature of the shear flow was further observed as the shear stress growth function from step rate tests as compared to the prediction based on linear viscoelasticity. Extensional stress growth functions of the filled HDPE was build through the viscosity data based on hyperbolic dies with different Hencky strain. The comparison with prediction based on linear viscoelasticity and the Trouton's law further indicated significant damping owing to the particulate suspension nature of the wood plastics melts.