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 of high-density polyethylene (HDPE). The easiness of the dismantling procedure from end-of-life vehicles and the intrinsic recyclability of HDPE allow them to be accounted in principle in the “white list” of recyclable components. However, the strong contamination and the odor produced by the volatile (VOCs) and semi-volatile (SVOCs) organic compounds, which have been absorbed during the service life, drastically hinder the use of this end-of-life material. This aspect reduces its actual recyclability, especially in higher-value applications. The aim of this scientific work is the achievement of an innovative extrusion process, specifically designed for the stripping out of these organic contaminants. An in-depth analytic approach is also reported 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 with gas chromatography coupled to a mass spectrometric detection (GC-MS). The multivariate approach of the Principal Components Analysis (PCA) is applied on the entire dataset collected in the experiments, including the HS-GC-MS data, the different process parameters and the mechanical and thermal data. As a result, the effect of the process conditions and all the organic contaminants present in the material are identified. The developed extrusion process allows to obtain a material with higher opportunity to be used in applications which require enhanced performance and, therefore, to be considered effectively recyclable, further reducing the environmental impact of the end-of-life vehicles.