Polymer-induced metal diffusion during plastic processing: a reason for deposit formation

Abstract

Abstract In the plastic-processing industry, the formation of unknown deposits at the interface between polymer melt and steel surfaces can pose major challenges, which occurs especially on screws, barrels, and tools. These deposits will detach during production and lead to quality restrictions mostly as spots in the products. We investigated the interactions between tool steel and polymer melt, especially polycarbonate, in the early stages of deposit formation. Steel-polymer-composite samples are prepared close to the realistic conditions in the plastic-processing industry. To get further insight, thin polymer films on tool steel specimens and its alloy elements, representing model systems, are prepared. X-ray-photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are used to characterize the interfaces chemically. Additionally, atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used. We found iron and chromium diffusion into the polycarbonate melt induced by polymer metal interaction. Iron and polymer chains are immobilized at the interface by a chemical interaction, while chromium does not chemically interact with the polymer melt. Basing on these results, we propose a mechanism for deposit formation in plastic-processing machines and tools.