Soil contamination impacts feedstock characteristics and drives pyrolysis outcomes in the conversion of polyethylene mulch films to fuel.

Abstract

Recovered plastic mulch films (rMFs) are often burdened with soil contamination, limiting recycling options. While pyrolysis is a promising recycling technology, the effects of soil contamination on rMFs' properties and pyrolytic behavior remain poorly understood. This study investigated the influence of soil contamination on rMFs collected from Washington (WA), Nebraska (NE), Florida (FL), and California (CA). Proximate, elemental, and calorific analyses evaluated the influence of soil texture on rMFs' physicochemical properties, while thermogravimetric analysis (TGA) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) assessed thermal degradation and volatile product composition. Controlled experiments using WA vMFs and WA soil (0-80 wt%) statistically evaluated soil loading effects. Results showed that soil contamination altered rMFs' properties. Clay-rich soils (WA and NE) exhibited the greatest effects, reducing volatile matter (VM) by 31% and 24%, and higher heating values (HHV) by 41% and 33%, respectively. Soil contamination also affected all onset thermal degradation temperatures. However, across all locations, hydrocarbons remained the dominant pyrolysis products (68.63-80.53% peak area), with diesel-range compounds (C13-C20) accounting for 38.51-48.95%. Regression analysis confirmed strong linear relationships contents (R > 0.986 and R2 > 0.971), between soil concentration and proximate/elemental components (VM, ash, carbon, and hydrogen). These findings show how soil texture affects rMFs' physicochemical properties and how presence of soil on rMFs affects thermal degradation behavior and volatile product distribution during pyrolysis. Nevertheless, the hydrocarbon-rich products indicate that soil-contaminated rMFs remain promising feedstocks for pyrolysis and fuel production.