Development of an advanced extrusion process for the reduction of volatile and semi-volatile organic compounds of recycled HDPE from fuel tanks

Plastic fuel tanks of vehicles are typically made by high density polyethylene (HDPE). The easiness of the dismantling procedure from end-of-life vehicles and the intrinsic recyclability of HDPE allows them to be accounted in principle in the “white list” of recyclable components. However, the strong contamination and odor produced by the volatile (VOCs) and semi-volatile (SVOCs) organic compounds which have been absorbed during the service life, drastically hinders the use of this end-of-life material. This aspect reduces its actual recyclability, especially in higher-value applications. In this paper, we report a study on an innovative extrusion process specifically designed for the stripping out of these organic contaminants. We also report an in-depth analytic approach to identify their nature and fraction, as a way for ranking the effect of the different processing conditions, which have been tested. The developed extrusion process uses a co-rotating twin-screw extruder with degassing points and the injection of water as medium for desorbing the organic contaminants. The analytic approach is based on headspace (HS) sampling associated to gas chromatography coupled to a mass spectrometric detection (GC–MS). The multivariate approach of the Principal Components Analysis (PCA) was applied on the entire dataset collected in the experiments, comprising the HS GC–MS data, the different process parameters, and the mechanical and thermal data. As a result, the effect of the processing conditions and all the organic contaminants present in the material were identified. The developed extrusion process allows one to obtain a material with higher opportunity to be used in applications which require enhanced performance, therefore, to be considered effectively recyclable, further reducing the environmental impact of the end-of-life vehicles.