Dependence of the rheological properties of polymers on their molecular structure
An applicability of polymeric materials in industrial processing is given by their rheological properties. Based on the type of the process (extrusion, injection moulding, thermoforming, blow moulding), the relevant rheological properties play a significant role (e.g. shear viscosity, uniaxial and planar extensional viscosities, etc.). All the rheological properties are determined by the molecular structure of the material [the linear polymer (e.g. linear low density polyethylene – LLDPE) exhibits thinning behaviour in extensional viscosity (extensional viscosity decreases with increasing extensional strain rate) in contrast to the branched polymer (e.g. low density polyethylene – LDPE), which exhibits strain hardening in extensional viscosity (an overshoot in extensional viscosity occurs at low extensional strain rates followed by decreasing of extensional viscosity with increasing extensional strain rate)]. In the case of polymeric materials, the rheological properties are determined by the molecular weight, polydispersity, and topology of the molecule [linear, branched (type of branching), cross-linked]. Hence, the connection between the molecular structure and rheological properties of the polymers plays an important role.
The objective is to study the impact of molecular structure of polymers on the rheological properties, which strongly influence their processing and quality of the final product. Especially, we focus on the measurement of elongational viscosity and large amplitude oscillatory shear measurements which seems to be promising way to quantify the non-linear rheological phenomena given by the different molecular structure.