Thermochemical degradation of agricultural mulch films for potential organic fertilizer precursors: Low-temperature pyrolysis in nitric acid

Abstract

Polyethylene mulch films (PEMFs) are widely used in agriculture to boost crop yields but pose significant environmental challenges due to their non-degradable nature. This study investigated the pyrolysis of PEMFs in nitric acid (HNO3) using micro-glass reactors under mild conditions for the production of thermochemical degradation products (TDP) as potential organic fertilizer precursors. The effects of HNO3 concentration (10–60 %), HNO3:PEMF ratio (0.5–2), pyrolysis temperature (150–250 °C), and reaction time (1 – 45 min) on the yield of TDP, tetrahydrofuran-soluble fraction (THF-S), tetrahydrofuran-insoluble fraction (THF-IS), and HNO3 consumption were studied. SEM, elemental analysis, GPC, and FTIR were employed to assess product characteristics and degradability potential. Optimal conditions were HNO3 concentration of 36 %, HNO3:PEMF ratio of 0.5, pyrolysis temperature of 200 °C, and reaction time of 10 min. Higher temperatures or longer time would lead to TDP condensation to carbonaceous residues. The introduction of N and O-containing functional groups in TDP suggested its potential as an organic soil fertilizer. This study presents a novel, eco-friendly, and cost-effective solution to address the waste PEMF disposal problem.