Abstract
This study presents an overview of viscoelastic characteristics of biocomposites derived of natural-fibre-reinforced thermoplastic polymers and predictive models has been presented in order to understand their rheological behavior. Various constitutive equations are reviewed for a better understanding of their applicability to polymer melt in determining the viscosity. The models to be investigated are the Giesekus-Leonov model, the Upper Convected Maxwell (UCM) model, the White-Metzner model, K-BKZ model, the Oldroyd-B model, and the Phan-Thien-Tanner models. The aforementioned models are the most powerful for predicting the rheological behavior of hybrid and green viscoelastic materials in the presence of high shear rate and in all dimensions. The Phan-Thien Tanner model, the Oldroyd-B model, and the Giesekus model can be used in various modes to fit the relaxation modulus accurately and to predict the shear thinning as well as shear thickening characteristics. The Phan-Thien Tanner, K-BKZ, Upper convected Maxwell, Oldroyd-B, and Giesekus models predicted the steady shear viscosity and the transient first normal stress co-efficient better than the White-Metzner model for green-fibre-reinforced thermoplastic composites.
Highlights
The rheological properties and extrudate behavior of polymer melts are of central importance in the processing and fabrication of polymer products
The melt-rheological behavior of short sisal, coir, and pineapple fibre-reinforced polymer systems has been studied in various works [1] [2]
From a mathematical point of view, the integral representation of a viscoelastic constitutive equation is more difficult to perform than the differential form
Summary
The rheological properties and extrudate behavior of polymer melts are of central importance in the processing and fabrication of polymer products. For a viscoelastic liquid this relationship is nonlinear and it has no standard form universally valid for each fluid in every flow situation. The constitutive equation should describe the rheological characteristic of the polymer melt and give the final fibre orientation of the composite. For this reason it is fundamental to evaluate the role of the biocomposite’s rheology and the natural fibre-polymer interaction. A review of nonlinear rheological models for viscoelastic materials from natural-fibre-reinforced thermoplastic polymers will be presented by a special review of the Upper convected Maxwell, Phan-ThienTanner (PTT), K-BKZ, Oldroyd-B, Giesekus and Whhite-Metzner constitutive models
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