Optimization of HDPE direct fluorination conditions by XPS studies

A fluorination reactor was designed and built in the laboratory. The optimal conditions of fluorination within the reactor were selected by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis of fluorinated surfaces of a film and a plaque of pure high-density polyethylene (HDPE). This reactor was used to post-mould fluorinate plaques and films of a range of mixtures of virgin and recycled HDPE with and without (re)introduction of additives. The ability to be fluorinated has shown no dependence on the composition virgin/recycled HDPE. Comparison of in-line and post-mould fluorinated samples showed that fluorine concentration profile in depth is thinner in the in-line fluorinated sample when compared with the post-mould fluorinated sample, though the fluorination degree in the extreme surface is larger in the in-line fluorinated sample. This is attributed to a migration of lower surface energy chain blocks towards the surface in the material at high temperatures, which is the case in the in-line fluorination, hindered in the post-mould fluorination where maximum temperature is below the melting point to keep the macroscopic shape. The additives played a minor role in the ability of the surface to be fluorinated. (C) 2004 Elsevier B.V. All rights reserved.