Influence of carbon nanotubes on the characteristics of polymer melt flow during extrusion of two-layer pipes

This paper presents the results of numerical simulation of the extrusion process of two-layer polymer pipes in a two-dimensional axisymmetric formulation using the ANSYS Polyflow software package. The influence of the introduction of multi-walled carbon nanotubes (MWCNTs) into polypropylene (PP) on the rheological properties of the melt and the flow characteristics in the extrusion head was investigated. The Bird-Carreau model was used to describe the viscosity of the PP/MWCNT composite, taking into account the concentrations of MWCNTs (0, 1, 2, 4, and 8 wt%). The second layer of the pipe was made of polyvinyl chloride (PVC). An analysis of the distributions of pressure, melt flow velocity, and layer thicknesses of the extruded pipe was conducted. It was found that with increasing MWCNT content, the viscosity of the PP/MWCNT composite significantly increases, leading to an increase in pressure in the extrusion head (from 91.3 kPa at 0 wt% to 28.5 MPa at 8 wt%) and affecting the layer thickness distribution: the thickness of the PP/MWCNT layer decreases from 2.49 mm to 1.70 mm, while the thickness of the PVC layer increases from 2.50 mm to 3.45 mm. The optimal concentration of MWCNTs was determined to be 2 wt%, which provides balanced rheological characteristics and stable pipe geometry (total thickness of 5.23 mm). At a concentration of 8 wt%, the PP/MWCNT layer remains intact, but its thickness becomes insufficient for practical use. The obtained data allow optimizing the composition of the polymer nanocomposite and the parameters of the extrusion process for the production of two-layer pipes with specified properties.