On Flow Layer Uniformity in the Co-Extrusion of Polymer Multilayer Film

Abstract

In the multilayer co-extrusion process, two or more materials are simultaneously brought together and layered in a single extrusion process. When co-extruding two polymers with different rheological properties, uniformity control of the flow layer at and downstream of the confluence is vital for the quality of multilayered film products. This work aimed to investigate the effects of viscosity and elasticity of the co-extruding polymers on the layer uniformity at the confluence. We conducted a PC/PMMA/PC three-layer film co-extrusion experiment to observe the flow of polymer melts at the confluence in the die. The thickness variation of each layer along the flow was recorded through a viewing window structured on the die wall using a camera. In addition, the flow and stress field analyses of PC/PMMA/PC co-extrusion were performed using POLYFLOW software. The research results demonstrated that oscillation of flow velocity in machine direction along the PC/PMMA interface accompanying a wavy distribution of layer thickness along the flow may occur due to the differences of viscosity and elasticity between the PC and PMMA. Although slipping may occur at the PC/PMMA interface, which reduces the shear stress between the PC and the PMMA layer boundaries, the shear stress distribution crossing the PC/PMMA interface is not continuous. The imbalance of the shear stresses along the adjacent PC and PMMA boundaries expands with the extrusion rate, which can cause the interface to distort. To avoid the occurrence of interfacial instability, the length of die channel downstream the confluence must be shortened as much as possible, and the extrusion rate must be lowered.

Understanding the mechanical and interfacial properties of core–shell structured bamboo–plastic composites

“…The extrusion speed was maintained by a speed‐controlled puller. The details can also be found in the literature …”

“…For example, to produce optimum performance and structures, necessary steps, such as coloring, covering of UV, moisture barrier addition, and the mixing of additives, can be realized by the simple design addition of one or more layers. In addition, coextrusion is suitable for the use of certain waste materials and, thereby, significantly reduces production costs …”

Comparative Analysis of the Effect of Organoclay, Boron Nitride, and Fluoropolymer on the Rheology and Instabilities in the Extrusion of High Density Polyethylene

“…The major challenge during extrusion is the onset of melt instabilities that hinder high productivity [1][2][3][4]. Processing aids are often added to polyolefins during their extrusion to make the processes economically viable.…”